@15-16 min approx -high vacuum doesn't open secondaries, lack of vacuum does that is why there are springs in the secondary control pots . high vacuum overcomes the spring. however the air dam on a qjet opens by the amount of air flow
High venturi vacuum is a different concept than high manifold vacuum. As air passes through the venturi you get a pressure drop and a passage connecting that pressure drop to the secondary diaphragm “ports” venturi vacuum to operate the “vacuum secondary” which opens using that ported venturi vacuum against the top of the diaphragm to overcome the spring. This is why changing the spring to a softer spring opens the secondary sooner than a stiffer spring. It’s also why using ported vacuum on a vacuum advance is dangerous and can lead to over advanced timing. Yes, the air valves on an AVS or Q-Jet are opened by flow, not vacuum, it’s a different approach to the same goal, but much less refined.
@@TheGT350Garage The vacuum secondary carb uses manifold vacuum right? because there is no port vacuum at idle or WOT. the secondaries open WOT therefore they open lack of vacuum and manifold vacuum keep them closed at idle. ported vacuum is the same as manifold except at idle there is zero vacuum unless the primaries are open too far. I don't know why you mentioned the over advanced timing but that can be limited in the distributor after the vacuum can is selected for cruise. you might want to recheck your video and make sure it clear for your audience is why i mentioned it . if you're happy with it then it's all good.
No. A vacuum secondary carb DOES NOT use manifold vacuum to operate the secondaries. As air is passing through the venturi, it creates a low pressure (vacuum) signal on a passage that connects to the vacuum secondary chamber. As the secondary opens the signal on the primary changes and the secondary will vary how far it opens to maintain the Hughes primary signal possible. The variable nature of the design is what makes a vacuum secondary a true load sensing carburetor. Your reasoning and understanding would make a vacuum secondary carb operation like a mechanical secondary and the faster and harder you open the primary the faster the secondary would open, which would negate the drivability benefits a vacuum secondary offers. Also, if the spring was opening the secondary, you would need stronger springs to open them sooner, but the stronger the spring the later they open.
Great video Walter I'm going to use a Q-Jet on my 469 street 4 speed car. Any time you want to throw out some nuggets in that direction would be welcomed. I really look forward for this project especially the jetting with current pump gas. Good stuff.
I’ve used many Q-jets over the years, on Fords even. They have their place, and I don’t have anything against them. I just don’t have a practical way to do Q-Jet tech at this time.
Awesome car brother! I have a 65 fastback I rescued from years of drag racing. Great site fascinating information on pump gas! I found your info very informative thx!!
For the stock power level that will look and drive great! 1523 was first sold with a Shelby Dual Quad setup using a pair of Holley 4-barrel carbs, that setup is long gone sadly, and it would not be particularly good on the engine I’m building for the car anyway.
Mix you gas with 2 stroke oil. 50 to 1 just like your leaf blower or chainsaw. Watch you ethanol issues disappear. Been doing it for years on engine's without catalytic convertor.
Do you have any experience with percolation and vapor lock avoidance when using a 4150 carb with E10 93 octane fuel? I had a quik fuel 4150 carb on my 351W with 10.5:1 compression, larger retrofit hydraulic roller cam, with the 351W cast iron heads with larger valves installed, and the original 1969 shelby aluminum intake manifold. I had fuel percolation after hot shut off, and fuel would drip down into the intake and flood the engine and fowl the plugs. I tried everything to fix it shields, phenolic spacers, etc, but nothing worked. Ultimately, I installed a holley sniper efi and that fixed the percolation problems because no fuel is stored on top of the engine so it can't boil out of the carb. However, I just experienced an unknown internal failure of the holley sniper and it is dumping a lot of fuel into my engine and my oil smells like fuel. I am thinking about switching back to a carb because the quality control on the holley sniper is very bad - many are having issues and there is a 10 week wait on warranty repair work on the snipers. I am hesitant to put another 4150 type carb on my car because it will likely create the same percolation issues I had before the EFI. Any ideas on which type carb would be the least likely to have percolation and vapor lock issues? Thanks.
The only reason the EFI always fixes the issue is it runs higher pressure in a sealed system. Fuel percolation goes away as the pressure increases. The problem was pretty common with carburetors installed on top of EGR plates (most Ford V8s from ‘73-89). The carburetor gasket for those applications is one of the best solutions I’ve found. Felpro 60390 or Mahle G26183. Your stock carb would be a 4300 Autolite, and they’re just a little too fussy for me personally. The 4150 would be the way to go. I’m not really a fan of the Carter AFB / Edelbrock carbs. There are a couple other little things you could do. Block off the heat crossover at the intake gasket. Requires removing the manifold and using a 1250 Felpro or equivalent to eliminate the crossover passage. Have the manifold cleaned and ceramic coat the gasket faces and the underside with a heat reflective thermal barrier coating (can be done with no visual change to the exterior of the manifold). Increase the vacuum advance at idle and cruise to reduce engine operating temperatures. Install the factory style front spoiler or a small air dam below the radiator to reduce pressure in the engine compartment and pull heat out from below the car, it will drop the engine compartment temps. You can also use ceramic coating on the exhaust manifolds or headers to reduce temps under the hood.
Regarding intake manifolds for stroker 331's. Holman & Moody have a "classic dual plane" for a single 4V and the only specs available are the operating range is from 1000 to 6500. I would like to have an intake that is period correct for my 65 mustang build but dont want to sacrifice too much power. I watched your video on intakes and the Cobra intake would not be good for hp ratings over 300(?). I emailed Holman Moody and they basically said it's a great intake for Ford small block...the recommended intake from AFR heads is to go with the Edelbrock Performer RPM...any thoughts on how decent the Holman intake might be? Thanks for making these videos with lots of detailed info! Much appreciated! Stephen Winfrey
The Holman Moody intake you’re looking at is the Blue Thunder S2MS Shelby Hi-Rise, only it has Holman Moody where it would otherwise say Cobra. That intake is the best of the Shelby style manifolds, but still suffers from the same runner length issues. The Blue Thunder versions will support a bit more than 375hp but you have to be careful with carb tuning and timing. If you are building the engine specifically for a period look, consider falling to Comp Cams about one of their dual profile cams that has more duration on the end cylinders to balance out the engine for mismatched runner lengths.
Clearance is tighter on 65-66 than 67-70, but an Shelby Hi-Rise or RPM Air Gap with an Edelbrock or Holley carb will clear with a HiPo air cleaner assembly using a 3” filter. If you want to run a spacer, you’ll need to subtract the spacer thickness from the air cleaner element height. So a 1/2” carb spacer would require a 2-1/2” filter element. Do NOT use a “Drop Base” style air cleaner base for clearance, getting the air cleaner lid too close to the carburetor inlet can cause drivability and performance loss. Also AVOID filter lids. They can have undesirable effects on airflow and in the event of a backfire.
do you know what carb i have to pick with my engine? 331 stroker at max 6500 rpm with a comp 282 cam . ford racing intake , nkb heads and t5 transmission
Basic starting point is find your potential airflow demand: ((331*6500)/2)/1728=622.5 cfm. Then take a look at the type of use. If you’re just drag racing, a mechanical secondary type carb would be fine and you’d want 650-700cfm. For street use, I recommend vacuum secondary carbs. Exclusively for the street, a 670-725cfm carb would be fine. If it’s more of a street and occasional track deal, I’d run a 750-780cfm vacuum secondary. I happen to prefer the Holley 4150 vacuum secondary to the 4160 models, because 4150s have secondary jets that are easy to change for tuning purposes. So the Street Avenger carbs are a great choice, and they also have Holley’s best carb warranty.
@15-16 min approx -high vacuum doesn't open secondaries, lack of vacuum does that is why there are springs in the secondary control pots . high vacuum overcomes the spring. however the air dam on a qjet opens by the amount of air flow
High venturi vacuum is a different concept than high manifold vacuum. As air passes through the venturi you get a pressure drop and a passage connecting that pressure drop to the secondary diaphragm “ports” venturi vacuum to operate the “vacuum secondary” which opens using that ported venturi vacuum against the top of the diaphragm to overcome the spring. This is why changing the spring to a softer spring opens the secondary sooner than a stiffer spring. It’s also why using ported vacuum on a vacuum advance is dangerous and can lead to over advanced timing.
Yes, the air valves on an AVS or Q-Jet are opened by flow, not vacuum, it’s a different approach to the same goal, but much less refined.
@@TheGT350Garage The vacuum secondary carb uses manifold vacuum right? because there is no port vacuum at idle or WOT. the secondaries open WOT therefore they open lack of vacuum and manifold vacuum keep them closed at idle. ported vacuum is the same as manifold except at idle there is zero vacuum unless the primaries are open too far. I don't know why you mentioned the over advanced timing but that can be limited in the distributor after the vacuum can is selected for cruise. you might want to recheck your video and make sure it clear for your audience is why i mentioned it . if you're happy with it then it's all good.
No. A vacuum secondary carb DOES NOT use manifold vacuum to operate the secondaries.
As air is passing through the venturi, it creates a low pressure (vacuum) signal on a passage that connects to the vacuum secondary chamber. As the secondary opens the signal on the primary changes and the secondary will vary how far it opens to maintain the Hughes primary signal possible. The variable nature of the design is what makes a vacuum secondary a true load sensing carburetor.
Your reasoning and understanding would make a vacuum secondary carb operation like a mechanical secondary and the faster and harder you open the primary the faster the secondary would open, which would negate the drivability benefits a vacuum secondary offers. Also, if the spring was opening the secondary, you would need stronger springs to open them sooner, but the stronger the spring the later they open.
@@TheGT350Garage so it works like an air dam ok cool it wasn't that clear in the video for me thanks
Great info brother
Great video Walter I'm going to use a Q-Jet on my 469 street 4 speed car. Any time you want to throw out some nuggets in that direction would be welcomed. I really look forward for this project especially the jetting with current pump gas. Good stuff.
I’ve used many Q-jets over the years, on Fords even. They have their place, and I don’t have anything against them. I just don’t have a practical way to do Q-Jet tech at this time.
Yeah that’s why su carbs are so good because they are vacuum operated they give the motor air and fuel what is needed
Awesome car brother! I have a 65 fastback I rescued from years of drag racing. Great site fascinating information on pump gas! I found your info very informative thx!!
Great info. My 66 is #1506. Very close to yours. Mine in candy apple red. Putting an original cobra 3x2 carb set up on her .
For the stock power level that will look and drive great! 1523 was first sold with a Shelby Dual Quad setup using a pair of Holley 4-barrel carbs, that setup is long gone sadly, and it would not be particularly good on the engine I’m building for the car anyway.
Interesting! Looking forward to the engine build! Be well! 🤙🤙😎🐍🐍🐍🐍
Mix you gas with 2 stroke oil. 50 to 1 just like your leaf blower or chainsaw. Watch you ethanol issues disappear. Been doing it for years on engine's without catalytic convertor.
Do you have any experience with percolation and vapor lock avoidance when using a 4150 carb with E10 93 octane fuel? I had a quik fuel 4150 carb on my 351W with 10.5:1 compression, larger retrofit hydraulic roller cam, with the 351W cast iron heads with larger valves installed, and the original 1969 shelby aluminum intake manifold. I had fuel percolation after hot shut off, and fuel would drip down into the intake and flood the engine and fowl the plugs. I tried everything to fix it shields, phenolic spacers, etc, but nothing worked. Ultimately, I installed a holley sniper efi and that fixed the percolation problems because no fuel is stored on top of the engine so it can't boil out of the carb. However, I just experienced an unknown internal failure of the holley sniper and it is dumping a lot of fuel into my engine and my oil smells like fuel. I am thinking about switching back to a carb because the quality control on the holley sniper is very bad - many are having issues and there is a 10 week wait on warranty repair work on the snipers. I am hesitant to put another 4150 type carb on my car because it will likely create the same percolation issues I had before the EFI. Any ideas on which type carb would be the least likely to have percolation and vapor lock issues? Thanks.
The only reason the EFI always fixes the issue is it runs higher pressure in a sealed system. Fuel percolation goes away as the pressure increases.
The problem was pretty common with carburetors installed on top of EGR plates (most Ford V8s from ‘73-89). The carburetor gasket for those applications is one of the best solutions I’ve found. Felpro 60390 or Mahle G26183.
Your stock carb would be a 4300 Autolite, and they’re just a little too fussy for me personally. The 4150 would be the way to go. I’m not really a fan of the Carter AFB / Edelbrock carbs.
There are a couple other little things you could do. Block off the heat crossover at the intake gasket. Requires removing the manifold and using a 1250 Felpro or equivalent to eliminate the crossover passage. Have the manifold cleaned and ceramic coat the gasket faces and the underside with a heat reflective thermal barrier coating (can be done with no visual change to the exterior of the manifold). Increase the vacuum advance at idle and cruise to reduce engine operating temperatures. Install the factory style front spoiler or a small air dam below the radiator to reduce pressure in the engine compartment and pull heat out from below the car, it will drop the engine compartment temps. You can also use ceramic coating on the exhaust manifolds or headers to reduce temps under the hood.
Regarding intake manifolds for stroker 331's. Holman & Moody have a "classic dual plane" for a single 4V and the only specs available are the operating range is from 1000 to 6500. I would like to have an intake that is period correct for my 65 mustang build but dont want to sacrifice too much power. I watched your video on intakes and the Cobra intake would not be good for hp ratings over 300(?). I emailed Holman Moody and they basically said it's a great intake for Ford small block...the recommended intake from AFR heads is to go with the Edelbrock Performer RPM...any thoughts on how decent the Holman intake might be? Thanks for making these videos with lots of detailed info! Much appreciated!
Stephen Winfrey
The Holman Moody intake you’re looking at is the Blue Thunder S2MS Shelby Hi-Rise, only it has Holman Moody where it would otherwise say Cobra. That intake is the best of the Shelby style manifolds, but still suffers from the same runner length issues. The Blue Thunder versions will support a bit more than 375hp but you have to be careful with carb tuning and timing. If you are building the engine specifically for a period look, consider falling to Comp Cams about one of their dual profile cams that has more duration on the end cylinders to balance out the engine for mismatched runner lengths.
Do you know if a 289 with a hi rise intake and a 4 barrel will have enough clearance for a stock hood? (in a 65 Mustang )
Clearance is tighter on 65-66 than 67-70, but an Shelby Hi-Rise or RPM Air Gap with an Edelbrock or Holley carb will clear with a HiPo air cleaner assembly using a 3” filter. If you want to run a spacer, you’ll need to subtract the spacer thickness from the air cleaner element height. So a 1/2” carb spacer would require a 2-1/2” filter element.
Do NOT use a “Drop Base” style air cleaner base for clearance, getting the air cleaner lid too close to the carburetor inlet can cause drivability and performance loss.
Also AVOID filter lids. They can have undesirable effects on airflow and in the event of a backfire.
do you know what carb i have to pick with my engine?
331 stroker at max 6500 rpm with a comp 282 cam . ford racing intake , nkb heads and t5 transmission
Basic starting point is find your potential airflow demand: ((331*6500)/2)/1728=622.5 cfm. Then take a look at the type of use. If you’re just drag racing, a mechanical secondary type carb would be fine and you’d want 650-700cfm. For street use, I recommend vacuum secondary carbs. Exclusively for the street, a 670-725cfm carb would be fine. If it’s more of a street and occasional track deal, I’d run a 750-780cfm vacuum secondary. I happen to prefer the Holley 4150 vacuum secondary to the 4160 models, because 4150s have secondary jets that are easy to change for tuning purposes. So the Street Avenger carbs are a great choice, and they also have Holley’s best carb warranty.
@@TheGT350Garage
thqnks for the input
do you have driving vids of the gt350