Soooo, what if my carb is too big?
1 - 8 of 8 Posts
You'll probably suffer low-end, probably have poorer mpg, and probably have softer throttle response.
My 454 had a 750 VS carb when I bought it. I thought it ran great. For a myriad of reasons, I changed to 650 VS carb. Acceleration, throttle response, and mpg all improved dramatically.
A 454 sounds as though it should have a 750 versus a 650 carb, but my heads are low rpm/high torque. Based on RPM, modification level, etc, the 650 carb was a better match, both on paper and in the real world.
See if you can borrow someone else's carb and do a comparison test.
My 454 had a 750 VS carb when I bought it. I thought it ran great. For a myriad of reasons, I changed to 650 VS carb. Acceleration, throttle response, and mpg all improved dramatically.
A 454 sounds as though it should have a 750 versus a 650 carb, but my heads are low rpm/high torque. Based on RPM, modification level, etc, the 650 carb was a better match, both on paper and in the real world.
See if you can borrow someone else's carb and do a comparison test.
A vac. sec. will run ok -just not the best if it is oversized for the cubes. The vac. secs will tend to only open based on the demand from the engine. I actually have a 750 AVS Edelbrock and alum GM high rise on the 59 Vette w/283 and it runs great. Compared to the original 2 WCFB's, it is a race car! Too much carb with a Double Pumper will make bite nails though. FWIW
Too large of carb venturi for the application causes a poor signal and poor response/atomization.
Ever wonder how GM put 750 and 800 cfm carbs on almost everything?
Ever wonder how GM put 750 and 800 cfm carbs on almost everything?
Joined
·
18,121 Posts
they used a carburetor with really small primaries for a good signal under low load conditions and a vacuum operated secondary air door to move however much air the engine wants at higher load conditions. this same basic carb was installed on everything from the lowly 4.1 liter (252) Buick V6 of the early 80's to the 500ci Caddies of the early 70's and everything in between..
so, as usual, the answer is to just get a quadrajet and be done with it..
Joined
·
1,453 Posts
You have to take consideration that bigger is better when it's not true. It all depend what is the application you are going to use it on. A heavy car or truck may need a smaller carb for torque. A light car with big gears need a large carb for horsepower.
Just throwing a big carb on a motor is not going make a car or truck go faster.
You have to consider the weight, Type of tranny, the size of the converter in a automatic, the rear end gear ratio and tire size, the displacement of the engine and max RPM you will be pushing. All have to work together once you dial it in.
Just throwing a big carb on a motor is not going make a car or truck go faster.
You have to consider the weight, Type of tranny, the size of the converter in a automatic, the rear end gear ratio and tire size, the displacement of the engine and max RPM you will be pushing. All have to work together once you dial it in.
Joined
·
5,676 Posts
lot's of theories out there but i must agree with VENTURI size.
not carb size..
but then you toss in the booster..some boosters are capable of great atomization in a large venturi.
I have a 750 double pumper that has dogleg boosters ..all tweaked of course..will flow way over the rating..
I have installed it on a car that had a 670 street avenger..and 241 gears.
Funny how dialing in a carb means more than the size sometimes..
That car was much quicker all around..and snappier throttle than the smaller 670..
I never ran dominator size venturies so i cant comment on those..
If i need lot's of cfm i go with 2 carbs.
Then tweak them all till there is no more tweaking left to do to them.
People that just bolt on a carb and never really dial it in perfectly , will never know the real story ...
I am talking more than just jets and squirters and pump cams.
get out the pin drills and epoxy and grinder.
Largest i ran(on a small engine) was a 750 on a 240Z..was the largest i had at the time..
ran awesome..that is 2.4 liter. big cam ported head.
shift at 8500..with the 450cfm she would go 6500 and peter out.
22.5MPG is what it got with either carb.
Ran a 600 ?afb early buick on a 280z with 260 head in a 260Z with a home made 4V intake..27MPG..
These guys runnin 600cfm on a 350 tickle me..I guess it works for daily driver ...max R's and power i like more..
1200cfm on a 350 ran awesome..but done it with 2 600's
650cfm on 2.3 pinto's..they loved it..
we are talking RPM potential here.
not carb size..
but then you toss in the booster..some boosters are capable of great atomization in a large venturi.
I have a 750 double pumper that has dogleg boosters ..all tweaked of course..will flow way over the rating..
I have installed it on a car that had a 670 street avenger..and 241 gears.
Funny how dialing in a carb means more than the size sometimes..
That car was much quicker all around..and snappier throttle than the smaller 670..
I never ran dominator size venturies so i cant comment on those..
If i need lot's of cfm i go with 2 carbs.
Then tweak them all till there is no more tweaking left to do to them.
People that just bolt on a carb and never really dial it in perfectly , will never know the real story ...
I am talking more than just jets and squirters and pump cams.
get out the pin drills and epoxy and grinder.
Largest i ran(on a small engine) was a 750 on a 240Z..was the largest i had at the time..
ran awesome..that is 2.4 liter. big cam ported head.
shift at 8500..with the 450cfm she would go 6500 and peter out.
22.5MPG is what it got with either carb.
Ran a 600 ?afb early buick on a 280z with 260 head in a 260Z with a home made 4V intake..27MPG..
These guys runnin 600cfm on a 350 tickle me..I guess it works for daily driver ...max R's and power i like more..
1200cfm on a 350 ran awesome..but done it with 2 600's
650cfm on 2.3 pinto's..they loved it..
we are talking RPM potential here.
1 - 8 of 8 Posts
