327 carburation
#1
06-28-2009, 04:27 PM
327 carburation
HI THERE ,i have a 1967 327 30 over, trw domed pistons, 291 ,202/260 fuelies 300hp cam weiand stealth intake is a 750 carb to big for my set up as i am not sure .thanku .
#2
06-28-2009, 06:22 PM
With the 202's and high compression pistons with all the other bolt ons a 750 should be fine.
Well, you say a 750 but not what make or model carb and they do vary quite a bit but generally a good size carb for a warmed up small block
Is it a vacuum secondary carb or a double pumper? Manual trans or auto?
The reason I ask is that a car with stock auto trans (no stall converter) might bog a bit if you hammer the throttle hard from a dead stop with a 750 double pumper,not so much with a single pump carb and even less with a spreadbore carb like a 750 Quadrajet if set up right.
With a manual trans it's just a matter of finding the right rpm to let out the clutch and mash the peddle.
Well, you say a 750 but not what make or model carb and they do vary quite a bit but generally a good size carb for a warmed up small block
Is it a vacuum secondary carb or a double pumper? Manual trans or auto?
The reason I ask is that a car with stock auto trans (no stall converter) might bog a bit if you hammer the throttle hard from a dead stop with a 750 double pumper,not so much with a single pump carb and even less with a spreadbore carb like a 750 Quadrajet if set up right.
With a manual trans it's just a matter of finding the right rpm to let out the clutch and mash the peddle.
Last edited by Y2K; 06-28-2009 at 06:30 PM.
#3
06-28-2009, 10:11 PM
Join Date: May 2007
Location: Fort Brag NC (no longer in iraq)
Posts: 2,200
He is right on.
With that set up a well tuned in 750 would be right on. But the key word is well tuned in if you dont have a lot of experince you might want to take it over to a good shop with a dyno and let them get it right on for you.
With that set up a well tuned in 750 would be right on. But the key word is well tuned in if you dont have a lot of experince you might want to take it over to a good shop with a dyno and let them get it right on for you.
#4
06-29-2009, 04:53 AM
re 327 carb
hey thanks for replying .. ive been advised that a 650 would be a better choice and the 750 is way to big.. the truck is an auto th350 with 2500 stall . i havent bought a carb yet and am wondering wether its better if it needs it to down jet a big carb or or up jet a smaller carb ? what say u many thanks..
#5
06-29-2009, 08:57 AM
Join Date: Oct 2007
Location: The 'Burbs of Chicago
Posts: 18,306
A recommended carb size is based on cubic inches, maximum rpm's of the engine, and volumetric efficiency of the engine.
We'll use 6,000 rpm as a safe max rpm range, and a V.E. of 95% which is considered a very good breathing engine. An engine at 100% V.E. is far and few between.
The formula would be 327 x 6000 x .95, divided by 2820. That gives you a figure of 661 cfm that the engine is capable of pumping through.
But, keep in mind that's the maximum cfm of air movement through the carb that your engine requires at that rpm. And, the 661 figure is also considered a generous estimate.
Now let's say you never wind the engine past 5,000 rpm. At 5k, your engine can only move 551 cfm through.
Obviously, if your 327 can wind higher than 6000 rpm, you'll need to figure for that. But based on the above calculations, 750 is a little overkill.
We'll use 6,000 rpm as a safe max rpm range, and a V.E. of 95% which is considered a very good breathing engine. An engine at 100% V.E. is far and few between.
The formula would be 327 x 6000 x .95, divided by 2820. That gives you a figure of 661 cfm that the engine is capable of pumping through.
But, keep in mind that's the maximum cfm of air movement through the carb that your engine requires at that rpm. And, the 661 figure is also considered a generous estimate.
Now let's say you never wind the engine past 5,000 rpm. At 5k, your engine can only move 551 cfm through.
Obviously, if your 327 can wind higher than 6000 rpm, you'll need to figure for that. But based on the above calculations, 750 is a little overkill.
Last edited by Camaro 69; 06-29-2009 at 09:00 AM.
#6
06-29-2009, 11:10 AM
Oh,it's going in a truck 'eh.
Yeah C'69 has done the math for ya,a 750 will work but might be a li'l much especially for a truck.
I like the old Holley 650 spreadbore double pumper for a build like that.
Smaller primary circuit for mileage and driveability but packs a punch with those big secondaries and second accelerator pump.
You could use anything from a 600 to a 750 and make it work just fine but a 750 might be a bit much for your application.
Holley 650 spreadbore double pumper
Yeah C'69 has done the math for ya,a 750 will work but might be a li'l much especially for a truck.
I like the old Holley 650 spreadbore double pumper for a build like that.
Smaller primary circuit for mileage and driveability but packs a punch with those big secondaries and second accelerator pump.
You could use anything from a 600 to a 750 and make it work just fine but a 750 might be a bit much for your application.
Holley 650 spreadbore double pumper
