[EricL]

i have a 600 cfm holley carb on my 455.how much of a difference do you think a 750 or 800 would make on it? i only spin the engine to 4500. all of the calculators i've used say at 100% VE a 455 at 4500rpm needs 598cfms.

______________________________
1980 Special Edition Trans Am

1975 2 bolt 455, 6X-8 heads, summit 2802 cam, stock intake, holley 600cfm vacume secondaries and modified adapter(alum intake and bigger carb some time).
TH350 trans and convertor out of a 78 TA, stock 10 bolt with 2.41 gears(3.23s going in soon)

pypes 2.5" exhaust on its way

[EricL]

i have a 600 cfm holley carb on my 455.how much of a difference do you think a 750 or 800 would make on it? i only spin the engine to 4500. all of the calculators i've used say at 100% VE a 455 at 4500rpm needs 598cfms.

______________________________
1980 Special Edition Trans Am

1975 2 bolt 455, 6X-8 heads, summit 2802 cam, stock intake, holley 600cfm vacume secondaries and modified adapter(alum intake and bigger carb some time).
TH350 trans and convertor out of a 78 TA, stock 10 bolt with 2.41 gears(3.23s going in soon)

pypes 2.5" exhaust on its way

[Virginian]

performance wise, and the 600 will have quite a bit better easy driving street manners, especially before it's fully warmed up. Smaller venturis equals higher (i.e. better) mixing velocities at the same airflow. I had an 850 on a 455, and you had to always launch the car a little just to get moving. Wife loved it... in reverse.

"What could have happened, did."

[PONTIAC DUDE]

Here ya go.

http://www.angelfire.com/fl4/pontiac.../MyShadow.html

Made very little difference.

************************************************** ***************************

Build it fast, build it right, build a Pontiac.


http://PontiacDude.cc

[Tom Vaught]

Quote:

"i have a 600 cfm holley carb on my 455.how much of a difference do you think a 750 or 800 would make on it? i only spin the engine to 4500. all of the calculators i've used say at 100% VE a 455 at 4500rpm needs 598cfms."

1) I agree with your calculations except for the
100% V.E. which a stock street vehicle will never
achieve. A number of 85% is probably much closer
for your combination.

2) Pontiac Dudes' testing was based on the difference between two Edelbrock AFB type carbs with air valve secondaries. Because the air valves (on the secondaries) control the total air flow the carb will pass, if your engine needs 500 cfm, (assuming 85% efficiency), in the case of P Dudes' 600 cfm carb the secondaries are about 83% open and in the case of the 750 AFB carb the secondaries are about 66% open. BUT in both cases
the carb only flowed 500 CFM.

If the test were run with a Holley 600 vacuum carb
vs a 780 vacuum carb (750 vac carbs actually flow
780 cfm), both carbs again would flow 500 cfm.

In both cases, the performance would be the same.

If your engine was not limited to 4500 rpm, had a
higher stall converter, had a more agressive cam,
and other mods then again both carbs would still
perform the same up to 600 cfm air flow then the
600 cfm carb would become a "restrictor carb" but
the 780 carb would still have more hp potential.

Tom V.

[BAD ANDY]

With my 600 Holley I switched to a 750 Edlerbrock, not only did I notice more power but I got better gas mileage!!! Both carbs were brand new! Good luck, maybe A friend will let you borrow a carb and try.

[Cliff R]

Considering the adapter plate and the stock iron intake a larger spread bore carb would be a nice improvement, at least from what we've seen here. Despite the "math" and scientific stuff the 455 engine will like a larger carb. On KRE's dyno we always see more vacuum during pulls with small carbs indicating a restriction in the intake. On 455's making in the 450-500 hp range we see about 20 less hp when a 750cfm carb is substituted for an 850cfm carb. This difference on a "mild" 455 would be much less. Even so the smallest carb I'd even consider using on a 455 street engine prepared here would be about 750cfm......Clif

[SJMule]

Cliff, you've got mail.

Mule

1973 Grand Prix SJ455
1969 GTO 428