1984 throttle body cfm question
Thread Starter
Racer
Joined: Nov 2013
Posts: 338
Likes: 8
From: South NewJersey
1984 throttle body cfm question
I always thought that the main restriction in the crossfire system was the manifold but I just read a very informative post from back in 2010 on digital corvette that says " the stock manifold already out-flows the stock throttle bodies" does anyone know if this is true? Also when you port a crossfire manifold that supplies more air does the computer see that and adds more fuel to the or dose it just get more air? Thanks
Melting Slicks
Joined: Dec 2009
Posts: 2,227
Likes: 284
The ecm can add a little, but its assuming that the engine is stock. These early efi cars are a pain to tune & that's why most guys increase the fuel pressure.
The manifold is the biggest restriction. Here's a test that you can do to see if you need bigger throttle bodies, I'd do this after you fully port your intake. Get a vacuum gauge, hook it to a manifold vacuum source (any port below the tbi units), then tape the gauge to the windshield. Go out & drive the car hard, if the gauge shows 1" or more vacuum at WOT then yes you'd benefit from larger throttle bodies. If the gauge goes to zero then you won't benefit from larger throttle bodies.
The manifold is the biggest restriction. Here's a test that you can do to see if you need bigger throttle bodies, I'd do this after you fully port your intake. Get a vacuum gauge, hook it to a manifold vacuum source (any port below the tbi units), then tape the gauge to the windshield. Go out & drive the car hard, if the gauge shows 1" or more vacuum at WOT then yes you'd benefit from larger throttle bodies. If the gauge goes to zero then you won't benefit from larger throttle bodies.
Last edited by ex-x-fire; Mar 2, 2014 at 09:53 AM.
Thread Starter
Racer
Joined: Nov 2013
Posts: 338
Likes: 8
From: South NewJersey
Thanks ...Nice to ask the guys who have already done it. I'm just trying to get the best possible out come. Back in 1983 I had a Z28 ('78) threw some older heads, aluminum intake, Holly carb and a cam...13.3 In 1/4 at Atco raceway on a HOT summer night just waiting to overheat. Ahhh memories 
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
The TBI's are definitely NOT a restriction. I have seen ported intake CFI's go to bored TB's with zero change in performance. The stock TB's are more than enough for a stock or stockish 350.
Who ever made that claim on DC was FOS. Kind of. Each CFI runner flows about 180 CFM, IIRC. If you total all 8, that is 1440 CFM. Stock TB's flow about 480 CFM, IIRC. So yes, 1440 is more than 480. Unfortunately for that poster and his claim, an engine isn't flowing air through all the runners, or all the time. A V8 is partially drawing on as many as 3 at a time, and fully drawing on only 1 at a time. So the actual demand at the TB's isn't going to exceed the flow of the TB's.
ex-x-fire's test is a good one...but I already know what you'll find.
Who ever made that claim on DC was FOS. Kind of. Each CFI runner flows about 180 CFM, IIRC. If you total all 8, that is 1440 CFM. Stock TB's flow about 480 CFM, IIRC. So yes, 1440 is more than 480. Unfortunately for that poster and his claim, an engine isn't flowing air through all the runners, or all the time. A V8 is partially drawing on as many as 3 at a time, and fully drawing on only 1 at a time. So the actual demand at the TB's isn't going to exceed the flow of the TB's.
ex-x-fire's test is a good one...but I already know what you'll find.
Thread Starter
Racer
Joined: Nov 2013
Posts: 338
Likes: 8
From: South NewJersey
There used to be a great site called crossfire vault. I think some of the admins. pop up on here once in a while. They had an archive that was amazing. everything you could think of someone there tried and posted on it ...with pics ... If anyone know how to get at any of that info it would be great.
Cruising
Joined: Sep 2013
Posts: 13
Likes: 1
From: Racine Wisconsin
Intermediate
Joined: Oct 2012
Posts: 39
Likes: 3
From: Lufkin Texas
frankinvett84, I think this is the one you are looking for. All the tech articles and forum questions are still there. Very few go to it anymore, but the history is invaluable.
http://crossfireinj.fr.yuku.com/
Regards,
Ken
http://crossfireinj.fr.yuku.com/
Regards,
Ken
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