great stuff! I really appreciate your detailed and clear explanations. As someone who takes care of my engine myself, I really appreciate youtubers like yourself and Cole who have taught me so much
Hi Paul, great vid and info as always😃, What you are demonstrating is Static ratio, A running engine sees dynamic ratio as an ever changing compression due to the throttled valve and cylinder filling of the cam degrees, ie, racier cams need more comp ratio as you will know, keep up the great work dude, thanks, Tony, 😃👍
Great video, and just on time, when I need it :) What I think would be worth mentioning with measuring each chamber separately is, that it might not me the case of head not being resurfaced correctly, but on modified heads (to flow better), it migh be done not exactly the same way between chambers and have such result. In such case some grinding in the "smaller" chambers migh be better option than re-skimming the whole head :)
You are right, I did mention that it was critial that people doing this should measure each chamber and you are right there is a chance if there was a have a go engine builder that the chamber volume could be uneven and as you quite rightly say this should be rectified first before any skimming takes place 👍
Back in "my day" cams never specified a compression ratio. By the way we always used paraffin not water as it gave a more accurate reading, water has a big meniscus.
Yo are totally correct Tony Paraffin would be much better, I was just trying to keep it as grass roots as possible to hopefully encourage a few more people to get out there and give it a try. Regarding Cam Companys not giving out compression figures. Id imagine because that was cutting edge tec back then they may not have had one to hand as it would still be in the trial stages. Now with most cam grinds 30+ years old all be it tweaked in recent years. cam companys have good base line data to work from and give us good starting points
Perfect timing with your vid, plus the Lets Talk S**t on ignition the other day... Just rebuilding my 998 engine after it sitting in the garage for 20+ years (my projects get overtaken by glaciers rushing past ;) ) and its time to figure out a cam/dizzy/comp ratio for it. Basic spec is +20 flat top pistons, 12G295 on std valves, single SU, maniflow LCB. Back in the day I ran it on a Kent 286 and a ported high comp 12G295, fun but not very practical. I want something that will start in the mornings, but still have some zip up top for when it needs it. Thinking either MED RS or Swiftune SW5 but I'm well out of touch with comp ratio's and ignition for running this spec on current pump fuel. Any advice or things to avoid?
I think either of those cams would be a good choice. the Swift cam likes a little less timing at lower RPM but likes plenty at the top end so I would get a dizy as near stock as possible for a std 1275. my experience with the MED RS is that it needs less timing over all so something like the Aldon yellow or the 123 dizy would be very good. Comp Ratio 10:1 on standard Pump gas will be fine for both. you could squeze the MED RS a bit more with 10.5:1 but you would want to be sure of your fuel
The word 'explosion' belongs to a different category of chemical reactions (like nitroglycerin). The compressed petrol / air mixture just burns very quickly (Deflagration). Usually a blast front velocity of
Top Job Pewpewdie, im glad you cleared that up for us. Although Im not sure on your numbers, potently you are talking about low explosive LE at 400ms-1 but the Nitroglycerin you give example of would be classed as a High explosive and detonation blast "velocity" of more like 1400 - 9000 m/s. All that said, when I started talk off the cuff in a manner which is intended to help debunk some of the mystery that is created by people who use complex science to explain. I like to use simple english that people are used to hearing so Explosion seemed fitting 👍
Just a (possibly pedantic, possibly wrong) note on "swept volume". I thought that is only the volume of the area specifically swept by the piston crown? And does not include the area above the top of the piston at TDC. Ie the the swept volume remains the same regardless of what volume is in the head, the gasket etc. Therefore the full the BDC volume would include the swept volume as PART of the uncompressed cylinder volume, but not the TOTAL I would think. (Edit: btw I only say this as I think it was a slip of the tongue, and wanting to check my understanding is correct. I watch to learn from you :) )
That is correct Simon, I left explaining that out as it is taken care of by the software on Coles compression Ratio calculator and I did not want to confuse more people, however you are correct If you where working this out using math forlmua it would be critical that you take this into account
Hi Paul, thanks for sharing! Are the measurements down the side of each piston to the top of the piston rings (i.e. the piston to bore clearance capacity) relevant in the calculation too - or only if you are getting into serious performance tweaks as opposed to what is needed for a road going engine? As always, an excellent video - please keep them coming!
you are on the money, they are important when you start geting into the 12 - 13 : 1 static compression ratios but at 10:1 road going level nothing to worry about.
Just a thought, the head gasket will compress slightly. I guess you could measure thickness of a used gasket when entering the value on the calculator. Will definitely be looking at that website 👍
Hi Paul, another great video, thanks for sharing with us. I’m assuming that the cam designers specify the compression ratio assuming a full stroke from BDC to TDC, rather than from ‘inlet valve closed’ to TDC: in other words, they take the difference between the full stroke and the actual compression stroke into account themselves, so those of us building engines don’t have to work it out. Not sure my trigonometry would be up to it anyway, although I suppose you could use a crankshaft protractor and just measure it. The combination of a late closing inlet valve and partial cylinder filling at high revs must make quite a difference between the notional CR and the ‘real’ CR. Cheers, Will
That’s is correct Will, Basically the cam designer will take into account the Dynamic compression ration and then work that back to figure out the static compression ration, hence why the SW5 cam will run static compressions around 10:1 because it is a very Tame cam with very little over lap and valve opening and closing very close to piston position. Where as somthing like the Kent 286 would run statics around 12:1 but it’s dynamic would still be close to 9:1 like the SW5
Thank you both. I was just about to ask how it relates to dynamic compression - I like a lumpy cam with lots of overlap, and the idea of using a static CR calculation never made sense to me. Cheers!
Aha! ‘Dynamic compression ratio’ and ‘static compression ratio’, two new terms I’ve learnt, amongst a lot more. Keep it up Paul, I love learning! Cheers, Will
@@HREIRL thank you for your response, it's free.. But now that you mentioned that. I will consider to put some money on new one. Maybe SW5.. Thanks again!
Hello, I've just done this too - 23.2cc. I was wondering why you use water as it has a high surface tension so will have a tendency to form a meniscus (sit proud in the centre). Using something like paraffin might be easier? Just a thought - brilliant as ever.
Hi Paul yes Paraffin would undoubtedly be better and somthing I will give consideration in the future. It’s a case of me just doing what I have always done 👍👍
Would it not be easier to adjust the gasket thickness to get the compression ratio figure you want and then subtract that from a stock gasket and that gives you the thickness of meat you need to remove.
You can do it that way, but the combusting chamber is not a symmetrical shape like the gasket. So if you use that as the reference you could risk taking to much off the head
Yes is the Answer Peter, however that cam is very short on lift. In some cases it can benfit from slightly more compression but this would need to be carefully setup and measured. 10:1 would be very safe
There you are again going on about Black Magic. And the wife overheard, shes out there now looking how to take off the cylinder head, I've had to hide the spanners. I keep trying to explain you don't mean chocolates but she's mad on confection and won't have it. Had to go on amazon and buy some head phones so next time I tune in she will not hear you mention black magic.
been there done that.......................now have some fantastic headphones............. trouble is she can hear my headphones lol...........#slightlydeaf
![[LIVE] : ONE ลุมพินี 89 | คู่เอก "ยอดไอคิว vs คิริลล์"](http://i.ytimg.com/vi/Z3vYkHJ_5Ig/mqdefault.jpg)
For anyone looking for the compression ratio Calculator here is a link www.classicminidiy.com/technical/compression
great stuff! I really appreciate your detailed and clear explanations. As someone who takes care of my engine myself, I really appreciate youtubers like yourself and Cole who have taught me so much
A very good easy to understand video on Compression Ratio.
Glad you enjoyed Gavin
Hi Paul, great vid and info as always😃,
What you are demonstrating is Static ratio,
A running engine sees dynamic ratio as an ever changing compression due to the throttled valve and cylinder filling of the cam degrees, ie, racier cams need more comp ratio as you will know, keep up the great work dude, thanks, Tony, 😃👍
you are exactly correct this is Static Compression ratio 👍
Simple and very well explained explanations. Thank you.
Nice clear explanation with no bullshit 👍
Thanks buddy glad you like it 👍
Thank you so so much for these videos!!
Very informative Paul, great video 👍
Great video, and just on time, when I need it :) What I think would be worth mentioning with measuring each chamber separately is, that it might not me the case of head not being resurfaced correctly, but on modified heads (to flow better), it migh be done not exactly the same way between chambers and have such result. In such case some grinding in the "smaller" chambers migh be better option than re-skimming the whole head :)
You are right, I did mention that it was critial that people doing this should measure each chamber and you are right there is a chance if there was a have a go engine builder that the chamber volume could be uneven and as you quite rightly say this should be rectified first before any skimming takes place 👍
Paul
You are taking us back to school, with this usefull Video! 😀
Most welcome Francisco’s
Looks like lab 👍👍
Back in "my day" cams never specified a compression ratio. By the way we always used paraffin not water as it gave a more accurate reading, water has a big meniscus.
Yo are totally correct Tony Paraffin would be much better, I was just trying to keep it as grass roots as possible to hopefully encourage a few more people to get out there and give it a try. Regarding Cam Companys not giving out compression figures. Id imagine because that was cutting edge tec back then they may not have had one to hand as it would still be in the trial stages. Now with most cam grinds 30+ years old all be it tweaked in recent years. cam companys have good base line data to work from and give us good starting points
@@HREIRL Thanks for that explanation.
Perfect timing with your vid, plus the Lets Talk S**t on ignition the other day... Just rebuilding my 998 engine after it sitting in the garage for 20+ years (my projects get overtaken by glaciers rushing past ;) ) and its time to figure out a cam/dizzy/comp ratio for it. Basic spec is +20 flat top pistons, 12G295 on std valves, single SU, maniflow LCB. Back in the day I ran it on a Kent 286 and a ported high comp 12G295, fun but not very practical. I want something that will start in the mornings, but still have some zip up top for when it needs it. Thinking either MED RS or Swiftune SW5 but I'm well out of touch with comp ratio's and ignition for running this spec on current pump fuel. Any advice or things to avoid?
I think either of those cams would be a good choice. the Swift cam likes a little less timing at lower RPM but likes plenty at the top end so I would get a dizy as near stock as possible for a std 1275. my experience with the MED RS is that it needs less timing over all so something like the Aldon yellow or the 123 dizy would be very good. Comp Ratio 10:1 on standard Pump gas will be fine for both. you could squeze the MED RS a bit more with 10.5:1 but you would want to be sure of your fuel
2nd lol. T shirt is doing ok, no shrinkage etc when washed. Wearing it as i type lol
I’m delighted to hear that Paul and great to hear your getting good wear out of it
The word 'explosion' belongs to a different
category of chemical reactions (like nitroglycerin).
The compressed petrol / air mixture just burns very quickly (Deflagration).
Usually a blast front velocity of
I should add that detonation and combustion are different reactions.
Top Job Pewpewdie, im glad you cleared that up for us. Although Im not sure on your numbers, potently you are talking about low explosive LE at 400ms-1 but the Nitroglycerin you give example of would be classed as a High explosive and detonation blast "velocity" of more like 1400 - 9000 m/s. All that said, when I started talk off the cuff in a manner which is intended to help debunk some of the mystery that is created by people who use complex science to explain. I like to use simple english that people are used to hearing so Explosion seemed fitting 👍
Just a (possibly pedantic, possibly wrong) note on "swept volume". I thought that is only the volume of the area specifically swept by the piston crown? And does not include the area above the top of the piston at TDC. Ie the the swept volume remains the same regardless of what volume is in the head, the gasket etc. Therefore the full the BDC volume would include the swept volume as PART of the uncompressed cylinder volume, but not the TOTAL I would think. (Edit: btw I only say this as I think it was a slip of the tongue, and wanting to check my understanding is correct. I watch to learn from you :) )
That is correct Simon, I left explaining that out as it is taken care of by the software on Coles compression Ratio calculator and I did not want to confuse more people, however you are correct If you where working this out using math forlmua it would be critical that you take this into account
Finally understand 10 to 1 ratio ,now I know where you get the figures from . Do you need to know this ratio , to fit all after market / sports cams ?
Most definitely to get the best from them Guy
Hi Paul, thanks for sharing! Are the measurements down the side of each piston to the top of the piston rings (i.e. the piston to bore clearance capacity) relevant in the calculation too - or only if you are getting into serious performance tweaks as opposed to what is needed for a road going engine? As always, an excellent video - please keep them coming!
you are on the money, they are important when you start geting into the 12 - 13 : 1 static compression ratios but at 10:1 road going level nothing to worry about.
Just a thought, the head gasket will compress slightly. I guess you could measure thickness of a used gasket when entering the value on the calculator. Will definitely be looking at that website 👍
Those figures are Compressed thickness Ryan well spotted thanks for mentioning
Hi Paul, another great video, thanks for sharing with us. I’m assuming that the cam designers specify the compression ratio assuming a full stroke from BDC to TDC, rather than from ‘inlet valve closed’ to TDC: in other words, they take the difference between the full stroke and the actual compression stroke into account themselves, so those of us building engines don’t have to work it out. Not sure my trigonometry would be up to it anyway, although I suppose you could use a crankshaft protractor and just measure it. The combination of a late closing inlet valve and partial cylinder filling at high revs must make quite a difference between the notional CR and the ‘real’ CR.
Cheers, Will
That’s is correct Will, Basically the cam designer will take into account the Dynamic compression ration and then work that back to figure out the static compression ration, hence why the SW5 cam will run static compressions around 10:1 because it is a very Tame cam with very little over lap and valve opening and closing very close to piston position. Where as somthing like the Kent 286 would run statics around 12:1 but it’s dynamic would still be close to 9:1 like the SW5
Thank you both. I was just about to ask how it relates to dynamic compression - I like a lumpy cam with lots of overlap, and the idea of using a static CR calculation never made sense to me. Cheers!
Aha! ‘Dynamic compression ratio’ and ‘static compression ratio’, two new terms I’ve learnt, amongst a lot more. Keep it up Paul, I love learning!
Cheers, Will
Thanks for the video. Very useful. Now I need to find what is the right CR for me. Wonder Where can I find the best CR for my 544 old cam.
Hi Moshe, typical you would need 11:1 on a cam like that to be getting any benefit however they can be very lumpy as it’s quite an old profile
@@HREIRL thank you for your response, it's free.. But now that you mentioned that. I will consider to put some money on new one. Maybe SW5.. Thanks again!
Hello, I've just done this too - 23.2cc. I was wondering why you use water as it has a high surface tension so will have a tendency to form a meniscus (sit proud in the centre). Using something like paraffin might be easier? Just a thought - brilliant as ever.
Hi Paul yes Paraffin would undoubtedly be better and somthing I will give consideration in the future. It’s a case of me just doing what I have always done 👍👍
Would it not be easier to adjust the gasket thickness to get the compression ratio figure you want and then subtract that from a stock gasket and that gives you the thickness of meat you need to remove.
You can do it that way, but the combusting chamber is not a symmetrical shape like the gasket. So if you use that as the reference you could risk taking to much off the head
Bravo!
My Cooper S came with (presumably) a AEG148 Cam, so will it work ok with a C/R of 10:1? What do you reckon?
Yes is the Answer Peter, however that cam is very short on lift. In some cases it can benfit from slightly more compression but this would need to be carefully setup and measured. 10:1 would be very safe
@@HREIRL Thanks for the reply Paul. Uneven wear is evident on some cam lobes, so will some form of polishing or reprofiling "repair" its performance?
10:00 i like your light shield but all i see is upside down skirting board lol................once seen unable to not to see lol
Dammit Now I see it! I was thinking about building a bench light over my bench.
@@paullorman8924 lol, i've got the LED strip light but need to fit it above my bench#sonisasparky#nogoodtohisdadlol#
once seen cant be unseen 😜
@@HREIRL Yeah thats what i was trying to remember 😀
There you are again going on about Black Magic. And the wife overheard, shes out there now looking how to take off the cylinder head, I've had to hide the spanners. I keep trying to explain you don't mean chocolates but she's mad on confection and won't have it. Had to go on amazon and buy some head phones so next time I tune in she will not hear you mention black magic.
been there done that.......................now have some fantastic headphones............. trouble is she can hear my headphones lol...........#slightlydeaf
Hahaha 🤣 I need to get a box as a prop Dave and wave them around any time I’m talking about it hahah
@@HREIRL That will be fine shes as blind as a bat.