NEVER put a 750 on a 318........

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Throttle response can suffer from too much carburetion too fast it's a velocity thing but if you have enough gear ratio to allow the motor to wind quick enough it can handle a lot of carburation Mopar race manuals called for an 850 double pumper for a single plane for Max effort for a 340.
When 850 were as big as it got… LOL!!!
 
How's that?
Not in the metering block/plate, just in that other than the earlier 3310(-1), almost all 4150's were double pumpers, except the line of SA's when they appeared....My mind was processing a response to 2 posts at once, lol..
 
Problem is they way carbs are rated, if your engine displaces 500 cfm of air at peak power that will be how much your carb will flow no matter if it's labeled a 650 750 850 or even a 250 they will all flow the same just there will be different amounts of restriction aka hp loss.
 
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Problem is they way carbs are rated, if your engine displaces 500 cfm or air at peak power that will how much your carb will flow no matter if it's labeled a 650 750 850 or even a 250 they will all flow the same just there will be different amounts of restriction aka hp loss.
The only problem is when they are not compared at the same depression with the same method & conditions. If You can get 850 thru' a 250 I wanna see it.....and hear it...
 
The only problem is when they are not compared at the same depression with the same method & conditions. If You can get 850 thru' a 250 I wanna see it.....and hear it...


All 4V carbs are tested at 20.4 inches of water. IIRC that is 3 inches of Mercury. 2V carbs are tested at about 10 inches of water which is 1.5 inches of Mercury.

You can 850 CFM through a 250 CFM rated carb by running the test pressure up.

The biggest mistake in running a bigger carb than the math calls for is not getting the booster correct. You can run a much bigger carb if the booster is carefully selected and not lose a single HP down low and gain from the middle all the way up.
 
The only problem is when they are not compared at the same depression with the same method & conditions. If You can get 850 thru' a 250 I wanna see it.....and hear it...

Thats the real question is depression you want to run at full throttle not how much cfm.

I don't know what a restrictor plate flows but it's lot less then what a nascar engine needs, the air still gets minus the pumping loss hp cause of the restriction. My cousins late model pulls to 6500 plus through a two barrel.
 
All 4V carbs are tested at 20.4 inches of water. IIRC that is 3 inches of Mercury. 2V carbs are tested at about 10 inches of water which is 1.5 inches of Mercury.

You can 850 CFM through a 250 CFM rated carb by running the test pressure up.

The biggest mistake in running a bigger carb than the math calls for is not getting the booster correct. You can run a much bigger carb if the booster is carefully selected and not lose a single HP down low and gain from the middle all the way up.
Actually it's the other way around, but 2V-3.0" & 4V-1.5" are typical, conversion is sq.root of 2; 1.4142. Going "too big" just presents more tuning challenges, but will outperform too little if You've got it right for sure.
 
Thats the real question is depression you want to run at full throttle not how much cfm.

I don't know what a restrictor plate flows but it's lot less then what a nascar engine needs, the air still gets minus the pumping loss hp cause of the restriction. My cousins late model pulls to 6500 plus through a two barrel.
Cam & compression makes that possible, NOBODY chooses that strategy, long aggressive cams give more time & get the port flow up & sustained so they gasp as much as possible. Then You squeeze the poop out of what You manage to get in there. Time-bombs in NAPCAR prompted the rules for locking up the engines & shocks they qualified with.
 
Actually it's the other way around, but 2V-3.0" & 4V-1.5" are typical, conversion is sq.root of 2; 1.4142. Going "too big" just presents more tuning challenges, but will outperform too little if You've got it right for sure.


That’s what happens when you post stuff after bed time!!!! You get it backwards.
 
"You'll lose your lower end!"
"You'll drown it in fuel!!!!!!"
"The computer chart says... cfms's!!!!
"Blah Blah Blah BLAH !!!!!"

I've heard it all, but the wind is out of my sail to continue the beat. I simply walk away. I say "ok", then smile. I will charge to explain it anymore. LITERALLY! You will PAY me before I go rounds again and explain it to you. LOL :D

Shelby, now there's a name. A recognizable name. A name that's tied to performance. What did he know?? Obviously, not much!! Because he put over 700 cfm Holleys on 289's. Yes, if you bought a Shelby 289 Mustang, you got a over 700 cfm Holley.


Yes, those 715 cfm "Lemans" vacuum secondary carbs may not have been optimal, but the fact that they're vacuum and not a DP kept things civilized. What is the cfm rating on the ol' 1987 318 Dodge diplomats' quadrajets? Or how does 1350 cfm on a 440 6-pack's trio of Holleys work? It just DOES!

 
my J headed 318 with wolverine cam, wealiend intake, high com pistons loved the 750dp really woke it up alot compared to the carter avs!!!
 
So you sold them before all the good revisions happened.

I got tired of rebuilding them all the time to keep them running good. Friends raced Super Stock and Stock, kinda opened my mind to what was possible. I stopped reading magazines and started listening. A friend was racing a 396 in a late 60's Chevelle 4 speed and was using a 850 DP Holley. He was running real slow times, so I asked him if he had the original Quadrajet. He did, so I spent a day doing it up right. Next race day we went to the track and he had so much low end power he shredded the clutch right off the line, first run. Well, he blamed me and the Quadrajet and put the stupid Holley back on. He continued to run slow. I'm not saying a Holley won't run good or make more power, but for me, they are not worth the aggravation for little to no gain. Thermo-Quads are amazing.
 
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All 4V carbs are tested at 20.4 inches of water. IIRC that is 3 inches of Mercury. 2V carbs are tested at about 10 inches of water which is 1.5 inches of Mercury.

You can 850 CFM through a 250 CFM rated carb by running the test pressure up.

The biggest mistake in running a bigger carb than the math calls for is not getting the booster correct. You can run a much bigger carb if the booster is carefully selected and not lose a single HP down low and gain from the middle all the way up.
I’ve been saying this for — EVER!
But yet! Some people say there engine only consumes *** of CFM on the dyno, so there’s no reason to use a bigger carb. I give up, run what ever the help ya want, just don’t ask my opinion on it.
I got tired of rebuilding them all the time to keep them to running good. Friends raced Super Stock and Stock, kinda opened my mind what was possible. I stopped reading magazines and started listening. A friend was racing a 396 in a late 60's Chevelle 4 speed and was using a 850 DP Holley. He was running real slow times, so I asked him if he had the original Quadrajet. He did, so I spent a day doing it up right. Next race day we went to the track and he had so much low end power he shredded the clutch right off the line, first run. Well, he blamed me and the Quadrajet and put the stupid Holley back on. He continued to run slow. I'm not saying a Holley won't run good or make more power, but for me, they are not worth the aggravation for little to no gain. Thermo-Quads are amazing.
Same as above! But I’ll add, it’s also amazing how well a factory intake offering will do as well. I’ll suggest it when the combo is right for it, where the focus is driving the car on the road and rpm’s on the highway or down the local neighborhood are low, there ideal. A lot is where the car/engine live and what your doing with it.
 
Yes, those 715 cfm "Lemans" vacuum secondary carbs may not have been optimal, but the fact that they're vacuum and not a DP kept things civilized. What is the cfm rating on the ol' 1987 318 Dodge diplomats' quadrajets? Or how does 1350 cfm on a 440 6-pack's trio of Holleys work? It just DOES!


See posts #27 & #36...
 
I got tired of rebuilding them all the time to keep them to running good. Friends raced Super Stock and Stock, kinda opened my mind what was possible. I stopped reading magazines and started listening. A friend was racing a 396 in a late 60's Chevelle 4 speed and was using a 850 DP Holley. He was running real slow times, so I asked him if he had the original Quadrajet. He did, so I spent a day doing it up right. Next race day we went to the track and he had so much low end power he shredded the clutch right off the line, first run. Well, he blamed me and the Quadrajet and put the stupid Holley back on. He continued to run slow. I'm not saying a Holley won't run good or make more power, but for me, they are not worth the aggravation for little to no gain. Thermo-Quads are amazing.
If you can find a good one probably work for little while.
 
650 is perfect. why bother with a 750 on a street/strip 318. because you can I guess.
 
IMG_0008.JPG


Two Edelbrock 500 AFB style carbs on my 340 - smooth as silk once it warms up, but again (as has been said here more than once) - air demand secondaries.
 
650 is perfect. why bother with a 750 on a street/strip 318. because you can I guess.

I just always had to try different things. I did not care what anyone said. The difference is between a 600 and a 750 was a lot more than noticeable, and I was running a 273.
 
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