Diagnosing the dyno issues - Porsche 911 2.8 RSR Build Season 3.12
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Hi from the UK Jef, Twin Plugs in Aro engines have the same effect when one is isolated, also I have twin plus on my race bikes, and when one is isolated on tick over, the engine loses revs... Especially if the ignition is adjusted to compensate for the extra plugs, I.e. Reduce advance,
I believe this can be typical on large diameter bores couples with high dome Pistons, shielding the flame front ... Just a thought. J
totally agree - when I used to fly light aircraft which have strikingly similar engines to this, you would check each magneto seperately for the permitted RPM drop, by disconnecting them in turn as part of the preflight checklist
th-cam.com/video/YUO29lTTInM/w-d-xo.html
Even with those few issues, that motor sound is sweet as.
jeff, a resistor in series will only drop the signal level to the tacho, you need both a series resistor then a capacitor between signal active and earth to filter noise, this is called an RC ( Resistor + Capacitor ) filter. These need to be as close as possible to the tacho to eliminate noise-induced in the signal cable. Plenty of calculators online to work out the RC values so you block high-frequency noise but pass clean low-frequency pulses, or, you can buy pre-made automotive RC filters. Keep the value of R small as it causes a reduction in overall signal peak voltage. Get a mate with an oscilloscope to look at the signal quality at the tacho terminals, if it's clean then the problem is likely mechanical bounce.
OK, here is some rough maths. let's assume the pulses to the tacho are 0v-12v, the impedance of the tacho needs to be such that it draws enough current to not get swamped by noise but be able to detect the transition of the pulses cleanly and also does not draw so much current as to waste battery/alternator energy, this could be around 4-20mA ( guess 10mA ) So given V=I*R this makes impedance of tacho 12=0.01*R. Thus R= 1200ohm or 1.2Kohm impedance ( again big guess ). So if we don't want voltage drop to be more than 5% we must use a series resistor of 300ohm or less. Now you have R you need to know the max frequency of the pulses. The filter should kick in just above the max frequency of pulses. Once you have R and the cutoff frequency use an online calculator to generate the value of C. I'm an Australian living in New-York, like to watch your channel and similar to remind me of home
Hey Jeff
To diagnose try a few things to determine if you have any issue.
1 - Replace the plugs
2 - what’s the voltage at the coil packs? Can you monitor voltage at the packs to determine drop in volts to the packs are at higher revs
3 - with a volt meter check the voltage at the packs, disconnect one bank and then the other to see any change in volts?
This is to determine if you are having a voltage drop to the coil packs
4 - check all your plug leads and connections
5 - if you have a newer or better alternator try it
Just some ideas.
I was researching some info on early twin plug 911s, and I read something from a long-time Porsche tech, stating that there is a 12 degree delay in ignition timing, from when the lower plug fires, & the upper plug. This is to optimize the flame propagation, & ensure that the mixture completely burns, which of course translates to maximizing the engine’s power & efficiency. At any rate, I thought I’d share, in hopes that you’re able to wring every last pony out of that glorious flat six. Good luck, I think what you’ve done with your car, & created with this channel are fantastic. Thanks for sharing!
Hey Jeff, I'd also go with what your now thinking, Voltage drop in the supply circuit feeding the coils, being coil packs, pity its not single coil, I found a great 80's diag test on my last 914 video with measuring RPM drop on carbs! Still amazes me! Supplying extra voltage confirms loss in the circuit, gauge of wire maybe, or more likely voltage drop between the battery to fuse output, looking for less than 0.5V. Multimeter either end of the Positive '12v' wire and then in sections. Most likely a connection or relay if the Amps/draw of packs is lower than the combined total of the packs. Digital thermometer on the connections will also flag up resistance surprisingly - Good Luck 👍
Check your dwell times, spark gaps and that you have a capacitor on the coil positive. Also make sure your coil ground is close to the heads (on the heads ).
Dwell varies, especially with voltage, but a common value would be around 3ms @ 15V. Too low and you will get a weak spark, too high and there is a chance you will fry the coils. Have a feel of the coils after a run and see how hot they get.
It sounds like the gauge of the cable you have used. Too small in other words. Voltage drop in 12vdc systems can be a major concern in these areas.
That's what I was thinking as well. Same reason why it's a good idea to increase the thickness of the wires when you upgrade your fuel pumps.
try doubling up on the supply wiring
th-cam.com/video/YUO29lTTInM/w-d-xo.html
The number one cause of strange electrical issues is bad grounding.
Often just cleaning the connections and adding an extra earth will cure the weirdest problems.
th-cam.com/video/YUO29lTTInM/w-d-xo.html
On the plus side, you did not break anything ;)
The joys of classics, sometimes you just don't win. Glad you show the rough with the smooth. Hope ya get it sorted soon.
In airplanes, we got also 2 sets of spark pluga per cylinder, and for testing is needed to disconect the two sets separetly as you did. You got a limit on RPM drop for each coil pack. So I think that the RPM loss when running on a single spark plug is a normal thing.
my 2,7 mfi with 2 sparkplugs does the same, a small drop in rpm's when I disable top or bottom plugs
Check voltage of each circuit, coil pack, check the value from the coil to the spark plug. Check for pinched wires.
Also look at the temperature of each header. If one cylinder is cooler it might be your problem.
Could not agree more. Jeff Make sure to check the coil voltage on load with the engine running. If necessary make up an in-line test loom so you can measure voltage on each in coil pack individually. The header temp is one of my favourites in diagnosing this sort of fault use a laser marker on your temp gun and check the diagram on the side of the (IR) temp gun to understand the size of the sample spot you are taking.
Header temps! Yes, of course!
I'm glad you've got a handle on this, and I'm sure the answer will appear very obvious in a dream, or taking an epiphany piss. I hope the twin spark hunch is on track.
Jeff when it comes to checking electrolytic capacitors (like the ones you want to change on the clock). A quick visual inspection may help, look for obvious signs of leakage. The Silver cap on top of the can may have a stamped indentation but generally should be flat. I often find caps with bulging tops - they always need changing. A decent DVM will have a capacitance range which will display Uf (micro Farads, pF Pico Farads or nF Nano Farads) which should be close to the stated value, but the capacitors need to be removed to be checked. There are other meters that do the same thing and some work in-circuit but that's getting a bit specialised. When you do finish soldering spray some brake cleaner or IPA in to a jar then use a stiff cut down 1/2" paint brush to remove all traces of flux from the PCB. It will avoid problems latter on. Good luck. If you have access to a scope you could look at the signal going to the tacho on load (with the resistor removed) engine running as it is generated by your engine management I guess it should be a clean sine or square wave without lots of noise. Just in case you have not picked up on it the capacitors you want to change are polarity conscious, look at the black negative marking on the can and just make sure the new ones go in the same way or it could get very messy.
Download speed logic app. Similar to dragy by the free version is better. U can do any speed interval acceleration timing. Very accurate and consistent to compare times if done in 3rd gear 2000rpm to redline on the same stretch of road, same weight and same weather conditions.
Please recheck the cam timing. I know you are confident its correct but you have been wrong before 😀
The sharp drop off in torque at higher revs suggest lack of air. You have confirmed that filters, throttle are all in good shape. Check the cam timing again
You are presuming two plugs won't make a diff at idle, but maybe they do. Better burning of the fuel. You adjusted the valve clearances between tests, maybe a thing, I dunno. The tuner must have some suggestions, surely. Good luck in your fault finding venture
Hello Jeff, Suggestions: The heat range of the spark plugs used in this updated twin spark engine. And yes the exhaust.
G'day Jeff,
Kevin here I've been following you since day 1 and you have really done some amazing things.
Anyhoo your exhaust.
I have a 63 vw beetle with about 130hp at the wheels. Recently i got onto Vintage speed in Taiwan they are doing some amazing work in exhaust systems and gear shifters and im extremely happy with what i purchased. They are certainly not cheap but they are well worth the money.
Keep up the good work Jeff.
✌ peace.
I'm a little late catching up on your videos, but this might help someone.
I have a scan tool, the kind used to reset the check engine light and read codes through the OBDII port and it has a Dyno feature. I love it and use it all of the time. I've never used a stand-alone fuel injection system though, so I don't know if it would work for you. The guy at the company that wrote the software says it was calibrated to a Mustang Dyno, which apparently has a reputation for conservative numbers. You should love it.
To use it, you have to do some homework first. You measure your car and calculate the frontal area, then you look up it's coefficient of drag and a bunch of weather related things on the net. Enter the weight of the car with driver, gas, etc. Enter the gear ratio, which it can calculate for you using another feature of the software. Then when you've created the file, you take your car onto a lonely stretch of road and it gives you audible commands so you don't have to take your eyes off the road. Then you floor it. The higher the gear, the more accurate the measurement, but of course you accelerate until redline so the faster you will be going. When you complete the run, you can save the file and it will display horsepower and torque. I usually do three runs and then average them in a spreadsheet program.
I've had mixed results as far as absolute measurement goes. A Mazda Miata was EXACTLY what I expected, but it seems to read low for my Toyotas. Still it is perfect for the kind of thing you are doing here; relative measurements. I did this test on my wife's car and then fixed a couple of problems and could see that I had gotten about 5 HP and 12 ft-lbs of torque back. Sweet.
The device costs less than an hour on the dyno and is called Auterra Dyno Scan. Here's a link:
www.auterraweb.com/
I'm not compensated by them in any way. I just needed a scan tool and figured it was worth the extra money to get one with this feature.
Good luck to you and everyone reading this.
Thanks for the troubleshooting lesson. While you didn't solve it 100% today, your logic is a sound lesson in the approach.
Jeff , if I was in Oz I’d lend you my racelogic vbox , it’s a video data logger, that combines video , with gps speed and location data, and any data on the can-bus. Simple to hook up, accurate to a fraction of a second. And road runs can be compared with each other and time delta shown against any variable changing for instance AFR, ect. It would make for great TH-cam content. Put a shout out, a local Trackday goer or racer would surely lend you a set up.
On a traditional twin plug car (with rotor) you will get an idle drop if you run only 6 of the 12. If you were getting a misfire on only 6 then you'd know there was an issue with the plug/wire/etc. Maybe the heat range or gapping on the plugs at higher RPM, or could be voltage drop at high load/rpm which can't keep the coils energized
Enjoying the knowledge in the comments almost as much as the video! How nice to come to such consistent technical natter, no drama 😁
I'd be checking the fuel pressure on main rail, perhaps injectors too
Yes for sure - has he got an air-fuel chart from the dyno?
The simplest component in the ignition is the plugs-- plug gaps -- ignition wires also I use dielectric grease on all the wire ends.. Perform a compression test to at least check cylinder performance. .Recheck valve lash.. "cheers mate!!"
I like looking for improvement via data logging. Same road, conditions, run through the same speeds/rpm then compare time logged and look for loss/gain.
One thing that may sap power in a rear engine vehicle is the low air pressure at the rear of the vehicle.
Adding some sort of ducting to capture clean cold air from a high pressure area can add a noticeable amount of power.
I would certainly carry out a dry and then wet comp test, also is your dwell time correct for the coils. Plus.... one feed for 6 coils may not be enough current, I would take a look at maybe splitting coil feeds for each bank.
Also, dont neglect earthing, look at your ecu earth points, there is a great adaptronic video discussing earthing practises
Hi Jeff- I have to imagine your ECU has some datalogging capabilities. Even if you aren't experienced with them, with just a little testing you should be able to log engine RPM when you make your full throttle runs. Comparing your RPM over time (from run to run) on your test track will show improvements in much greater detail than your camera method, and with a lot less labor. RPM versus time does not require vehicle speed or anything else, so it's pretty reliable. Just do each test at the same spot and in the same gear. Can't wait to see what you come up with.
Start from the ground up. Leak down. Compression. Valve clearance. Then look at plugs and voltages to packs. Resistance of plug wires. Flow test Injectors.
How to accurately estimate power in a manual vehicle on the road.
First obtain an accurate G meter. Then obtain the full gear ratios from flywheel to tarmac and calculate what speed the vehicle should be doing at any given engine rpm and gear and what the road speed is reading at those rpm.
Then do several runs in each gear noting the G readings time between gear changes etc (a good ecu should have a data logging ability for this) . How this gives you a good estimate of power. Aside from the mathematical formula that you will need to calculate what the power should be the G readings will tell you what you’re actually putting to the road sans wheel spin.
A reading without spinning the wheels will be a fairly good reading in determining any power gain or loss.
You can use similar math to how horse power is calculated to determine what the engine should be putting out for a particular G reading in a particular gear, you can also calculate what G you should be pulling at a given acceleration, as an example zero to one hundred mph in six seconds might require an acceleration of three G and six hundred hp to obtain that level of acceleration.
Please find the actual math etc I’m just going off memory.
If you hook up your laptop to the ECU and do a log (I always do so with every single parameter added), this will give you some interesting data.
There's things like "Engine Speed ROC" (Rate Of Change) - this can tell you how quickly your revs are changing at any given point in time - might be a little better to pinpoint areas in the rev range that might be experiencing issues that cause it to not accelerate at the correct rate, and might help you to get a better picture than the overall "does it get between these two points quicker".
As for the spark issue... that's a strange one to me! Have definitely you got the right dwell times for the coils? If the dwell times are too short, it could be that they're not getting a chance to fully charge, but between the two sets they might have enough energy to ignite the fuel at lower loads, so when you disconnect one set, you don't quite have as much energy there?
That is something that is easy enough to check, but it hasn't changed between the first and second dyno sesssion.
@@HomeBuiltByJeffI think you mentioned about adding that 3 way fuse board - was that between dyno runs - has that changed the thickness of wire feeding the coils, or the overall length? A thinner (or longer wire of same gauge) could introduce more resistance, therefore less power carrying ability, so the coils need longer to charge? Really just throwing ideas to see what sticks now! :)
Hi Jeff, I think others have mentioned that the behavior you are seeing with disconnecting one set of plugs at a time is exactly what you would see in a light airplane. They are all required to have twin plugs with independent ignition systems and it is part of the run-up checks to look for a drop when switching from the right mag to both and then to the left mag. I did hear a small fast surging at idle. Mabe that is nothing...
One thought is can you test the exhaust gas at higher RPMs (as the torque is dropping off)? If it is lean it would be fuel and rich could be spark (all other things in alignment). Any chance the injector timing isn't keeping up? If you were having spark issues I would expect a bit of popping with excess fuel in the exhaust. Can you log all the timing and fuel delivery to see if that matches what you would expect? Does the manufacture have a way for you to send them the logs to see if they can get you zeroed in on the issue? Just some thoughts.
As for the tach, The only thought I have is a capacitor to ground would eat up some of that bounce. Caps are natural high (frequency) pass filters and if you shunt that to ground it will ground the higher frequencies. The question is what size... Without knowing the whole circuit it would be difficult to calculate the size, but the bigger the capacitor the more the soothing, and the smaller the capacitor, the less soothing.
Just some thoughts... Franny
I have actually found an old thread on the 914 forum where he used a 2200 uF Cap to do this. His was also a 74 and I would imagine the 911 and 914 Tachos were probably the same unit, but he did mention that it may toke some experimentation up and down in cap size to get it just right.
Hi Jeff - not sure what type of plugs you are running, but the one time that I had torque problems at high revs (in a modified rotary, not an upanddowner) it turned out that the centre electrode in a couple of the plugs (both leading ones) had burnt to an oval shape rather than still being circular. Wasn’t massively noticeable at lower revs, but at the top end the effect was significant. It took ages to find the problem because if you’re not looking for it, the difference between round and oval on a piece of metal 2mm wide is hard to spot. New set of plugs and performance was back where it should have been. Just an idea. Otherwise, if you are still convinced it is electrical then, as others have said - heavier gauge wiring and a really good ground. Good luck mate.
Might be low fuel pressure. If spark and air are good. Maybe the spark plug is not the correct one could also be but fuel pressure sounds more likely.
Zero deg here in UK with snow on the ground, I think you maybe fretting unnecessarily it sounds to run very cleanly the extra plugs may be making more complete combustion of the fuel and slight change of note disconnecting one set may be misleading especially as it is identical whichever row .If you have been through all the possible diagnostic checks that come up OK you might just be looking for an error that does not exist . Whatever the power I am sure you do not want a noisier exhaust on a long run. Different barometric pressure/humidity on different days may account for change on the power curve. Instruments are for a specialist experienced outfit with all the test rigs and all the components .Incidentally that sort of speed testing on public roads in UK both invalidates insurance and would earn a driving licence endorsement there are 80 different endorsable charges here in UK - the police would have a field day here if they witnessed it safe though it might have been !Could not be done here because the is always a row of cars in front - now 43 million cars on the roads of Britain a country 1/32 the size of Australia .
The reason I chose 2nd is that road has a 100km speed limit, and that is the speed at the top of 2nd ;)
Coils are need in more voltage from olternator at higher rpm due to your size of cable to earth, get the feeler blade a check gap on all plugs well you there change them you might have a dud when reaching temperature
I would check spark plugs to to see if they fouled out or see if the spark plug gap has changed due to heat
Sorry to hear about the issues .I'd change the plugs and open the gap up 5 thou or try surface discharge plugs .3 prong ones
As for the radio use 2 more resistors inline I had to use 3 on my tach as it was like an Irish riverdancer
I can try some more resistors. Not sure if it will do anything, but can't hurt.
I know the idea of the baseline test. We always do this by pointing a camera at the tachometer and driving through the entire rev range (1,500 - 7,000 rpm) in 2nd or 3rd gear on the same road. Then you can later measure with a video tool exactly what time was needed between 2,000, 3,000, 4,000, ... 7,000 rpm. Of course, this is not possible if your tachometer is defective ;-)
I’d suggest putting in your data log into Megalogviewer HD and doing a HP calculation. Run 2nd or 3rd gear and compare back to back.
Edit: as I watched the rest of your video. I’d be checking for proper grounding of the ECU/Coil Packs.
As your well aware. They are still all firing but getting incomplete combustion. Grounding, plug gap, dwell settings. You got this.
Hi Jeff.
Have you thought about a Digital DC clamp ammeter. It should show any leads are dropping power. Also have you checked for any of the Spark Plugs since the dyno session.
Also another way to check an engine is running properly is to get a thermometer gun and check each pipe on the manifold to see if 1 one of the cylinders has low temperature which will point to that cylinder being the issue.
Love the channel!!
To solve my bouncing Tach. I purchased a tachometer adapter from Pelican called Tach-Adapt. The bounce is caused by the electronic ignition.
Is the charging system working properly? No voltage fluctuations? Steady 14 volts? Using resister spark plugs? Shielded plug wires? Shielded cam and crank sensor leads? Check engine to battery ground at high electrical loads. Lights, heater, rear defrost all on. Check voltage drop across the ground and power leads at high loads. If voltage is fluctuating it could explain clock, tack, and power loss all in one.
Some very good suggestions here regarding grounding and ignition timing. I would do a run with no muffler installed see if it does change your “scientific test”.
I’m sure there is a way to log a run with your ECU and look at your data. A sudden drop at 7k rpms seems like timing related otherwise the drop on your torque curve wouldn’t be so clean. I would really look and see what’s happening with ignition timing and throttle position at those rpms. I would also look at your fuel/air ratio and knocking at the higher rpms. Also the location of your knock sensor (don’t remember where you put) can be picky.
I was trying to recall about, what changes exactly you have done to the engine between 1st and the 2nd tuning session. Can't really recall, but at least you did run on throttle position sensor instead of a MAP sensor the 1st time around. If this is one of the changes (you running on MAP 2nd time), it should be possible to make the car run without MAP again and take it against the baseline you have on video. False MAP readings could explain loss of torque on an entire curve.
Since unplugging either set of coils / plugs results in decrease in rpm, it leads to an assumption that they work ok. The air/fuel mixture is ignited better with twin spark than just one regardless of engine rpm. At least that is my layman's diy theory.
You being as thorough as you are, I'm sure that you get to the bottom of this! Keep up the good work!
Always wanted a Porsche
If you're set on a spark issue pop each plug out and run it individually and observe the color. Might be a good idea to do a compression check while you're poking around.
On your two runs at the start of the video that engine is really struggling to accelerate - try it without the plastic covers on your intakes and without the silencer for a couple of runs and see if it makes a difference. If it's not that I'd suggest the mapping - your wiring (grounds etc.) should be ok if it's running smoothly and revving to 7000. Good Luck !
Jeff, lve had a little exposure to twin spark engines in racing and aviation. Most systems in aviation work as a redundancy for a bit of insurance. Racing applications are very different though. One of the interesting things is that when at idle you isolate either system by removing power for an entire bank of coils that is makes a difference. This should not be the case. There should be no difference at idle unless the the timing moments are taking place at different crankshaft degrees. Im not sure if your management system allows you to split timing moments but this could potentially effect performance.
How about you try this!
Firstly doing power runs in 2nd is useless. Pick a higher gear.
How about doing a power run whilst isolating either coil bank. If your running simultaneous ignition there should be no change. Just a thought.
Having said that lm still not convinced that exhaust isnt causing a problem. It would be nice to know the primary pipe temps at WOT.
The ignition system seems to work just fine in my opinion.
The bores of the throttle bodies are not very big. Hos many hp are they known to support?
Testing with an open header collector system would show the max potential of the current engine setup.
The cam timing check I have seen you perform was the lift at a certain angle as I recall. Have you done an actual measuring of intake/exhaust events? Great efforts on your part as usual.
For engine to work need 3 thing... Air, fuel and spark... Try looking at the spark plug maybe it will show some clue on what going on with the engine
I feel you need to go back to what you did change between the dyno runs - for example I think you changed between MAP/MAF with associated wiring. Also not sure the fact air/fuel ratio is good guarantees enough fuel. Do you still have good compression. Good luck!
th-cam.com/video/YUO29lTTInM/w-d-xo.html
Maybe diagnosing with an exhaust gas tester would help, then you can see how wel the combustion is. My miata once had problems with the valve stem seals and was burning oil at high revs and not al fuel was being burned and you could see this with the exhaust gas tester in "HC" i believe below 100hc is normal. Btw love your channel, greeting from holland!
The car has dual wide bands already ;)
The days when nothing goes to plan are the worst! But keep at it, I'm sure you'll figure out whats wrong soon enough!
Hi Jeff when doing a design of experiments to determine the cause of an issue you have to get back to where you were as a baseline. Can you access the ecu map version at the time of your original dyno run? Can you compare all of the settings / inputs throughout the run? I would start by analyzing all of that data. If not the other way is to draw up a design of experiments listing every and all possible issues. Then investigate one by one. Also, don't make any assumptions, test everything. Good Luck.
Oscilloscope. Just go ahead and put a scope with amp meter on the coil packs main power circuit on each bank,you'll see if one is not not firing as it should. See ScannerDanners channel if you need more info on the topic. Try to log cam and crank relation (even with scope or with link). Check exhaust temperature on each cylinders and do a leakdown test on all cylinders. These are my ideas first. Valve float at higher rpm's cant be a problem for you imo. Also 34 mm for the itb's seems to me a bit small, but I'm not really a porsche guy.
In the end for me it seems like restrictaion related issue, so either exhaust or itb problem..
If you try to ajust the ignition a little earlier and get better top end power, it should be the issue. Have you intalled the MAP in between of the dyno runs? Check the manifold pressure on high revs and full open trottle. It should be near zero or in the best case little positive(dynamic resonance charge). To much negative pressure means to small intake. But you didn't change intake or exhaust after the first dyno run. I think it's ignition issue or cam timing got different because of loose bolts ore bad chain tensioner.
I was thinking - although that engine was so meticulously built, now it's pretty much 'bedded in' it might be worth doing a compression test again to put your mind (and ours!) at ease. ETA >> ninja'd by a couple of others, and anyway, I doubt it hadn't crossed your mind as well (but with that slight sense of dread we all get when hoping for the best but fearing the worst!). ETA 2 >> Great to see some really good info in the comments - hope you're taking notes Jeff!
Jeff what is there a voltage drop over both coils? by that i mean is the supply enough for what they are trying to draw? just remember your alternator may not supply enough above 6k try running a big enough amp wire from the battery to the fuse side of the coil to make sure you are getting enough supply. Second are the coil packs rated enough for what spark power you need? Regarding dyno air density and fuel quality make a large difference.
Thats totally normal to lose some RPM when you disconnect one set of plugs, think of twin plugging any engine as reducing the ignition timing (completing a combustion in less time than a single plug), so it gives the same effect as reducing the ignition timing (hence the RPM loss).
Feels like a red herring the idle changing when half the coils are removed. Exhaust manifold or cam timing is my 2c ‘TH-cam’ guess off the bat ;) How confident are you in the cam designer (do you know duration, lift, centre line, IVO/IVC/EVO/EVC timing events have they used) - because one mans ‘wild’ cam is another’s ‘does that even lift bro’ .....well you get the idea with the analogy!!😂 I’ve fixed a similar looking curve by retarding exhaust cams before - but this is a single cam per bank right? Which means it’s fixed in the grind of the cam if it’s machined wrong or simply not actually that aggressive.
Have you tried the app PerfExpert? It uses the accelerometer, GPS, coefficient of drag, and a bunch of other variables for your specific car to calculate an approximate power / torque curve from a single gear pull. It is not that accurate, but it is very repeatable in my experience, and extremely useful for situations like these.
Maybe you could try using a auto meter or some sort of tach and gut the insides and retro fit the original Porsche tach plate numbers and all?
One idea. Did some muffler packing come apart internally in your exhaust between dyno runs and create a minor restriction? Other than that I'd do a WOT run, then simultaneously kill the ignition and push in the clutch. Coast to a stop and then pull the plugs and take a reading. That should show you what is going on in each cylinder and with each coil at WOT.
Did you check fuel pressure?
Really good video with clear information on the problem. Plenty of discussion to be had on the possible issues. Sounds like what you mentioned that it could be electrical - ignition parts including plugs and ground paths. Have you changed the way the engine is being managed by the ECU and lost power there? Has the dwell time for coil charging changed in the settings? Cam position sensors or other engine inputs to ECU are now different?
No. None of the main settings have been changed, which is what has gotten me scratching my head. It may be the dwell time, but I am just not sure yet.
Because the engine is running/pulling so well up to a certain RPM, then the power curve begins to show losses proportional to the rise in RPM...my money is on valve float. If it is, the good news is that shims are cheap. The bad news is you've got to pull the rocker assemblies and springs to install them. I can't remember if you replaced the springs and tested them before installation. It's got a steeper cam, right? More valve travel and a precipitous lobe drop would require a stiffer spring than stock to keep them from floating at high rpm, right?
Nice number of ideas, above. Is the tach mechanically damped?(not working?). if so, check that aspect, maybe enhance that. Ditto most comments re: one plug v. two firing w/ revs change. Look for the voltage being pulled down to the coil packs at hi revs. Look at afr from the dyno runs to see if there is rich/lean at revs. All in all, you're close. Go out and break in that nice new motor and get to know the chassis, brakes, tires, set the pedals where you are comfortable, get ready for that first track day.
oops. below
I replaced the capacitors in my Benz’s clock last autumn (had the car for over 15 years, clock was broken when I got it).
I gotta say, it feels weird getting into the car and seeing that it’s no longer permanently noon.
Hey Jeff. Are you sure it's not the exhaust? Have you checked the exhaust? 🤣🤣
Fill the tacho with pear juice. That will slow the needle. 🤣😂
Would grape juice work as well?
Hey Jeff, Love your videos. Back in the day when I was a tech for Mercedes we had constant issues with the twin spark engines. Ie the m112 and m113. The m113 is what's in your ML. They use a single coil assembly with 2 leads to each plug. Most of the time when we had misfires it would be one of the leads. Luckily with the MB scan tool we could check each lead to find the problem ones. If you really believe its spark related it could be a bad lead causing an issue. It could run perfectly fine most of the time but under load cause an issue. Another problem could be spark plug gap causing it to break up at higher RPMs. Although if it is a misfire you would probably feel it. Or if you have Knock sensors it would probably pick that up. Data logging should show that. Another thing to look at would be what changed since your first dyno run? Tune? what is the timing set at? Did the Crank sensor move? You could always check your timing at idle with a light and make sure its where its supposed to be.
th-cam.com/video/YUO29lTTInM/w-d-xo.html
Don't worry, you'll be taking engine out again soon, so you can check cams and timing :D
Hi Jeff, You should get a drop on idle disconnecting a set of coils thats normal as you are reducing the efficiency of the combustion process by removing half of the spark per cylinder. I would be interested to know if the ECU you have fitted requires a speed signal at all to coincide with the mapping and timing for targets, I notice in a previous video you mentioned the speedo stopped working. Has the alternator got the power for the twin spark setup is it perhaps starving power to the coils under load ?
Lots of great suggestions from the comments.
Giday Jeff. You should be able to get all those resistors and capacitors from Jaycar for next to nothing. They can even test the components to help isolate what has failed. Worth a try. D
Have you thought about a Dragy? You can then use a 50-100 time in a single gear (depending on how close ratio your box is)
I was thinking along these lines, but I wondered if the ECU had a logging function to record time/speed
If you add 12v with power probe and it cleans up you got voltage drop/resistance in your positive feed. Thats my guess
Power pilots do an engine check b4 takeoff and it is usual and acceptable to find a slight drop in rpm when changing ignition circuits. Why does this happen? At low rpm the air / fuel mixing in the cylinder is not as complete as at higher rpms, lower gas velocities etc, so two separate spark plugs do a better job at more complete firing. I reckon that slight rpm drop is not an issue. What is the issue, why doesn't the engine want to get going above 6000? Maybe, just maybe the timing chain has stretched a tad since you set up the cam, that would throw cam timing off a bit. Anyway, just a thought.
ECU parameter settings??? E.g. rev limiter setting, fuelling pressure set from idle to 7k revs, same with ignition timing throughout rev range - not sure what else is being controlled by your particular ECU, but were these parameters not set and adjusted by your friend in NZ or were these also set and modified on your Dyno runs? Might be worth checking the current settings.
You need to show us the a/f ratio not just say it’s ok, as good for power is quite different. It’s one of the following. So far you have only convinced me on Air in.
Compression
Fuelling a/f
Air in
Gas out
Ignition and timing advance
Valve timing
Love the channel. For sure I would look at the alternator output, battery, ground and the gauge of wire supplying the ecu and coil packs. Only other thing, is I seem to recall there being a knock sensor. Any chance that is causing you grief?
I would be checking the actual voltage at the fuses when the engine is running. Is the alternator putting out the correct volts? Maybe the wiring is too small for the power required, keep in mind that every connection adds to the total resistance as well. 12v wiring is very subject to voltage drop. Also keep in mind that when working out wiring sizes you need to calculate both sides of the wiring, pos from the battery and neg back to it, most forget that power travels in a circuit and needs equal size cables both ways.
Also, is the engine earthed properly to the chassis?
THERE IS A TIME CHANGING KNOB ON THE FRONT OF THE CLOCK, TWIST IT AROUND ONE FULL 12 HOUR CYCLE, THEN CHECK HOW MUCH TIME IT IS LOSING, YOU MAY NEED TO DO THIS A FEW TIMES TO GET THE INTERNALS ADJUSTED.
Maybe it's a combination of issues. The only major engine change I can recall since the last dyno run was that you adjusted the valves. Maybe you got them slightly wrong and that's why you've lost power down low?
As for the lack of power over 6k rpm, I know you're using the same muffler (ie not the new bimodal ones), but maybe the muffler has never had enough flow at higher RPM, but since you weren't revving it that high when breaking in the motor it was never an issue? If worst comes to the worst and on the next dyno run it's still got no top end, maybe drop the muffler and give it a pull?
I would check engine grounding (try to add more grounding points, from the heads, and engine block) and if the spark plug gaps and temperatures are adequate..
Or even use a jump lead directly from -ve of battery to a good (non powder coated) engine contact
So if when the engine was first running the coil pack fuses made no difference at idle compared to todays test then a voltage drop in the wiring somewhere. Optimum alternator output should be 14.4V but at idle, and especially on older vehicles, then 13.8V or more should be what all electrical items on the system should be getting. So test at the battery, then the fuses and then the coil packs. Could be as simple as the engine to chassis earth cable is a bit loose or internally broken so has increased resistance to produce a voltage drop.
If there is insufficient voltage or current then at higher RPM the coil packs won't be able to charge up sufficiently to give a bright enough spark. With twin spark and being NA then this probably isn't showing itself as misfires as the twin spark is still allowing a burn event but just not a hot enough flame front to make the most power from the air fuel mixture.
The tacho may be a case of setting the ECU tacho output correctly as the Porsche tacho could be voltage or current sensing.
For the clock the quartz is normally very long lived and is what creates a stable clock pulse but as the capacitors get old and dry out then the charge and discharge time period changes which changes the frequency of the pulses the quartz sends out. So by replacing the capacitors should fix the time loss issue. Been ages snce my electronics degree but think I've remembered that correctly.
Not the thing you want to hear but I bet the lack of power (relatively speaking) is due to a combination of things. As others have noted, tons of potential electrical areas to try, but I would confirm the fuel rails are getting the right amount to all cylinders, and if you could run it without your exhaust box for a run or two. Having said that, it still doesn't explain the change in power / torque from 1 dyno run to the other, if the set up was unchanged.
Possibly could of swapped the coil connectors when you pulled off the valve covers?
Forget the flow based stuff as the top end power difference isn't the issue. How can you have such a drop in torque everywhere with no changes? Something has changed significantly. You said you set the tappets, are the valves not closing now perhaps? Maybe cam timing has slipped if it can. Also check the oil and filter for bits as you might have picked up something and have a friction increase. Also change the water pump.......
Sorry I can't help with this issue Jeff, but I hope you can fix it soon and fully enjoy your car!
Do you have data about the air/fuel mixture in the area where the torque isn’t delivering?
And could it be the software isn’t allowing the revs climbing as soon as you wish? Although the engine sounds great, it does sound a bit lazy.
One thing you changed that you have n’t mention was you adjusted the valves between dyno runs. I adjusted my valves using the front in method you used and got a decrease in power. Then I used the back end method with two sized shims .003 and .004 against the lobes which allowed me to set the timing perfectly. The Increased in power was very noticeable. Also, I thought my valves were working properly before the adjustment, so just listening to the engine can fool you.
what's front in vs. back end? pls expl. Are .003 and .004 the clearances at full lash/center of base circle? thx
Look up backside method on pelican parts forum. You can get the longer shims from pelican parts as well. Worked great for me!
I checked again and the the two feeler gauges are .0025 and .003.
The twin plug set up will change how it runs when one plug set is eliminated. That’s normal. This is a red herring. The fault is elsewhere.
You need to find someone who has experience with these engines or you are going to need individual lambda and EGT sensors and really deep drive how the engine is running.
I agree w @James T. - in my experience with servicing early 911s w/ MFI that were modified w/ twin plugs, disconnecting one set of plugs would cause the same slight rpm drop @ idle, which was indicative of a properly functioning ignition system. In order to reach your horsepower goals & expectations for Harry, I would first ensure your wiring is a large enough to handle the increased demand of the high powered, dual ignition, and new FI system. Then verify ignition timing maps, and spark dwell times, as well as fuel supply pressure, and fuel mapping such as pulse width/delivery volume in the upper rpm range. Lastly, do you have a larger diameter set of headers & muffler you can test with ?
Good luck with your project! You’ve built a beautiful 911RS tribute, and although these cars can be maddening at times, when they’re dialed in, they’re wonderful!
Peak torque at 7000rpm?? You sure youre not confusing Torque with HP?
Hi Jeff, You have probably already covered this but have you checked the ignition timing map is good above 6K RPM? The curve looks like it could be backed off. Loving your channel.
My boss switch to VAG coils on his alfa 2liter 8valve twins park from a 155 it didn't work before him, his brother and our other boss designed a small module and mounted between the ECU and Coil pack.
But with a newer ECU you shouldn't have that trouble. (My boss runs a 20-22year old DTA ECU)
I agree on Ground is always a good thing to upgrade. And then look at the sparkplugs to se color differenc and maybe it's to cold or to hot. You can probably find a good guide online to compare coloring and if it's to Hot og Cold.
Maybe the feel time on the injectors og coils har to low .
My boss has the benefits of being a engineer in combustion engines and his co owner of the company is a engineer in printb ords and electrics and his brother is an IT engineer. We have a Dyno and tavhey all 3 had raced cares for 25+years. So they have a lot of experience and still they sometimes struggle to find problems...
Great video👍 looking forward to the solution!
Thoughts and prayers. 😉