Carb Size???
Thread Starter
Cruising
Joined: Aug 2007
Posts: 13
Likes: 0
Carb Size???
Hi Guys,
First post from a new member.
I just want to ask,
what size carb do you guys recommend for a slightly modded small block,ie,i have done the following cam,heads,dual exhaust and headers.
I have a holley 600cfm on it now but i think this is a bit small.
What do you guys think should be the wright size carb i should use?
First post from a new member.
I just want to ask,
what size carb do you guys recommend for a slightly modded small block,ie,i have done the following cam,heads,dual exhaust and headers.
I have a holley 600cfm on it now but i think this is a bit small.
What do you guys think should be the wright size carb i should use?
Racer
Joined: Mar 2007
Posts: 306
Likes: 0
From: New Hampshire
It all depends on what you want out of the engine, engine size, cam, heads, ect. A 600 should be adequate for most people, Some people make a mistake and put too big a carb on thier engines.
I wouldn't go much more then a 750 cfm. I had a Cater AFB competion Plus on my 350 and took it off and replaced the Q-Jet that was on it, it ran a lot better. I've also been thinking of going to Fuel Injection just to make cold starts easier, not for power.
I wouldn't go much more then a 750 cfm. I had a Cater AFB competion Plus on my 350 and took it off and replaced the Q-Jet that was on it, it ran a lot better. I've also been thinking of going to Fuel Injection just to make cold starts easier, not for power.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
First of all, welcome. There's some nice, knowledgeable folk around here.
As for your question, depends a lot on it's intended purpose. If you're combo really needs the flow for strong top end, a 750 could well be in order. If bottom end, mid-range throttle response and ease of tuning are higher priorities and you won't be revving, a 650 is a safe bet.
Either way, not knowing more than I do about your car, I'd probably go vac 2nds with an auto and/or dual plane intake, and DP only with a stick and single plane. Just my $0.02. You're sure to get plenty more advice...
As for your question, depends a lot on it's intended purpose. If you're combo really needs the flow for strong top end, a 750 could well be in order. If bottom end, mid-range throttle response and ease of tuning are higher priorities and you won't be revving, a 650 is a safe bet.
Either way, not knowing more than I do about your car, I'd probably go vac 2nds with an auto and/or dual plane intake, and DP only with a stick and single plane. Just my $0.02. You're sure to get plenty more advice...
Melting Slicks
Joined: Mar 2006
Posts: 2,465
Likes: 0
From: Orange Park Fl
Cubic inch displacement x Maximum RPMs x Volumetric efficiency / 3456 = Carb size.
350 x 6500 x .80 / 3456 = 525 carb
350 x 7500 x .90 / 3456 = 685 carb
The first would be a decent street engine. The second a race engine. Your 600 cfm should be fine. God bless, Sensei
350 x 6500 x .80 / 3456 = 525 carb
350 x 7500 x .90 / 3456 = 685 carb
The first would be a decent street engine. The second a race engine. Your 600 cfm should be fine. God bless, Sensei
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Going by that formula, for a dual plane manifold, you should then multiply those #'s by a factor of about 1.2.
350 x 6500 x .80 / 3456 = 526 x 1.2 = 631 (minimum)
...and I feel that 80% VE is a tad low for a mild street perf engine.
Also, a better example of a race engine's VE would be 105%...
350 x 7500 x 1.05 / 3456 = 797
Notice I didn't factor in a dual plane, but here IMHO 7500 rpm is on the conservative side.
These numbers represent an approximante point at which the carb's rated capacity becomes a restriction to be overcome.
350 x 6500 x .80 / 3456 = 526 x 1.2 = 631 (minimum)
...and I feel that 80% VE is a tad low for a mild street perf engine.
Also, a better example of a race engine's VE would be 105%...
350 x 7500 x 1.05 / 3456 = 797
Notice I didn't factor in a dual plane, but here IMHO 7500 rpm is on the conservative side.
These numbers represent an approximante point at which the carb's rated capacity becomes a restriction to be overcome.
Last edited by TheSkunkWorks; Aug 8, 2007 at 07:03 PM.
