Question for C3 Engine Experts
Thread Starter
Instructor
Joined: Jul 2017
Posts: 111
Likes: 9
Question for C3 Engine Experts
My question for engine experts.
If I think I have the perfect 383 engine with tall manifold and 770 carb will I need to or should change anything when I put short manifold on it to fit car?
Like cam or carb?
Thanks for your help.
If I think I have the perfect 383 engine with tall manifold and 770 carb will I need to or should change anything when I put short manifold on it to fit car?
Like cam or carb?
Thanks for your help.
Pro
Joined: Sep 2017
Posts: 516
Likes: 72
From: Modesto California
Is this "383" an engine you already have or thinking of having? A 383" engine only needs a 600 cfm carb unless it has a long duration cam in it and then it would need lower rear end gears too. For a mild 383" the short intake manifold will work perfectly.
Burning Brakes
Joined: Mar 2016
Posts: 1,008
Likes: 163
not true. If it's a hot 383 it could definitely benefit from a carb bigger than 600 cfm. If he is running stock iron heads that don't flow that well, then yes the 600 is fine. But if he is running some good flowing aftermarket heads and a bigger cam, a 700+cfm carb would.most definitely make more power than the 600, especially in the higher rev range where the 600 would choke it a bit.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Why not just use a dropped base air cleaner. I use a two inch filter with the filter top for hood clearance with a tall single plane and 1/2 inch wood spacer
Pro
Joined: May 2016
Posts: 708
Likes: 150
From: Minnesota
In theory you can simply install a lower profile intake - no problem. That said, you'll want the best part compatability to get best performance, so you should know the cam in the motor and attempt to match intake rpm range to the cam profile. As already mentioned, also find out the carburetor installed and determine whether it's the appropriate size. A new intake will need to be square or spread-bore depending on your carb, assuming you use the same one.
Pro
Joined: Sep 2017
Posts: 516
Likes: 72
From: Modesto California
It's The Volumetric Efficiency That Determines How Big It Needs To Be
not true. If it's a hot 383 it could definitely benefit from a carb bigger than 600 cfm. If he is running stock iron heads that don't flow that well, then yes the 600 is fine. But if he is running some good flowing aftermarket heads and a bigger cam, a 700+cfm carb would.most definitely make more power than the 600, especially in the higher rev range where the 600 would choke it a bit.
According to my calculations a 383" running at 6000 rpm with an 85% volumetric efficiency will only consume 566 cfm. As you know it's almost impossible to exceed an 85% volumetric efficiency in a street engine so a 600 cfm carburetor would be more than enough to feed it. That's why the carburetor manufacturers always recommend 1-1/2 cfm per cubic inch of displacement for street engines.
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Team Owner
Joined: Oct 2004
Posts: 81,241
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From: altered state
St. Jude Donor '05
which 383 GM sells a bunch of different ones
youll need a pn link pic something so we can help you out
is it this one?
https://www.chevrolet.com/performanc...s/sp383-deluxe
Those charts were made many yrs ago we have lots better stuff out
youll need a pn link pic something so we can help you out
is it this one?
https://www.chevrolet.com/performanc...s/sp383-deluxe
Those charts were made many yrs ago we have lots better stuff out
Pro
Joined: Oct 2009
Posts: 664
Likes: 89
From: Marysville Ohio
Relative to hood clearance - I have a 79, but previous owner put a 1980 front clip on it. Ive run 383s and 400s with a tall dual plane like i.e., a 7501RPM Performer Ait gap. I ran a drop base cleaner with a 3" filter in both cases. and had no clearance problems - so you can go with a decent-sized intake depending on your air cleaner choices.
Racer
Joined: Jul 2008
Posts: 338
Likes: 4
From: Bowling Green Kentucky
As stated above a RPM Airgap and a drop base air filter will fit with stock hood without issue. I had plenty of clearance with that set up on my '81.
I have now changed to a Victor JR. The Victor JR. is actually not as tall as the RPM Airgap. I don't recall the exact number, but it was a bit over .400 height difference.
Depending on what GM part number the manifold is on the 383 it may or may not have clearence. See if you can find out the part number for the intake and compare the specs on it to the Edelbrock manifolds it would give you an idea. If it it is close in height to the Victor JR. you should be good to go with a drop base air filter.
If it is too tall there is always the option of milling the carb mounting flange to get what you need.
I have now changed to a Victor JR. The Victor JR. is actually not as tall as the RPM Airgap. I don't recall the exact number, but it was a bit over .400 height difference.
Depending on what GM part number the manifold is on the 383 it may or may not have clearence. See if you can find out the part number for the intake and compare the specs on it to the Edelbrock manifolds it would give you an idea. If it it is close in height to the Victor JR. you should be good to go with a drop base air filter.
If it is too tall there is always the option of milling the carb mounting flange to get what you need.
Team Owner
Joined: Sep 2002
Posts: 38,310
Likes: 2,070
From: California
I personally wouldn't spend too much time theorizing about it!
I would put the manifold or config that fits under your hood into the car, and then see how it runs! I would bet that considering the match you have of cam, heads, carb etc to displacement etc, that it won't affect you that much. You will lose a little top end!
I would put the manifold or config that fits under your hood into the car, and then see how it runs! I would bet that considering the match you have of cam, heads, carb etc to displacement etc, that it won't affect you that much. You will lose a little top end!
Burning Brakes
Joined: Mar 2016
Posts: 1,008
Likes: 163
According to my calculations a 383" running at 6000 rpm with an 85% volumetric efficiency will only consume 566 cfm. As you know it's almost impossible to exceed an 85% volumetric efficiency in a street engine so a 600 cfm carburetor would be more than enough to feed it. That's why the carburetor manufacturers always recommend 1-1/2 cfm per cubic inch of displacement for street engines.
Last edited by mobird; Sep 25, 2017 at 12:22 PM.