Real gains from switching main bodies?
11-07-2006, 08:46 PM
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Car: 1986 IROC Z28
Engine: 350 carbed
Transmission: TH350
Axle/Gears: 3.43
Real gains from switching main bodies?
I was looking in the recent summit and came across this.
Proform Main Bodies for Holley Carburetors: PRO-67101C - summitracing.com
They claim 25-50 hp gained over stock main bodies with choke tower and air horn. As I don't feel the need to switch to a bigger carb but don't need the choke anymore I thought this might be a good buy. Can anyone tell me if this can give me real power gains like this over my stock holley 750?
Proform Main Bodies for Holley Carburetors: PRO-67101C - summitracing.com
They claim 25-50 hp gained over stock main bodies with choke tower and air horn. As I don't feel the need to switch to a bigger carb but don't need the choke anymore I thought this might be a good buy. Can anyone tell me if this can give me real power gains like this over my stock holley 750?
11-08-2006, 12:35 PM
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
I had 2 problems with it, one which isn't Proform's fault, the other which they have since remedied.
Both related to the secondary idle. I've got 2-corner adjustable idle (primaries only), and the air bleeds they included were the large ones on all four corners, which leaned out the secondary idle circuit horribly. I didn't realize I had a problem while I had a mild 270 hydraulic cam in it, but when I went with the XS282, I couldn't keep it running. Somebody's mention of the idle air bleeds here is what finally got me going down the right track.
The other issue involved the throttle body itself (the original Holley part), that didn't have the secondary idle slots cut evenly, so one wasn't uncovered and the other was uncovered too much. Picking at the short one until it was the proper length fixed that problem.
I forget the details now, but I think I also had to file something off of the original Holley parts to get it to fit properly. A minor thing, whatever it was.
I only ran the 650 DP for two weeks before I put the Proform in, so I didn't have a lot of data on the difference. The DP itself dropped 2 tenths off my 1/4 mile ET's vs. what the 750 VS ran, and the Proform dropped another .05 or so. A week later I put in a higher stall converter (dropped 3 tenths), so too many changes too quickly to give hard data on the improvement just from the Proform.
Both related to the secondary idle. I've got 2-corner adjustable idle (primaries only), and the air bleeds they included were the large ones on all four corners, which leaned out the secondary idle circuit horribly. I didn't realize I had a problem while I had a mild 270 hydraulic cam in it, but when I went with the XS282, I couldn't keep it running. Somebody's mention of the idle air bleeds here is what finally got me going down the right track.
The other issue involved the throttle body itself (the original Holley part), that didn't have the secondary idle slots cut evenly, so one wasn't uncovered and the other was uncovered too much. Picking at the short one until it was the proper length fixed that problem.
I forget the details now, but I think I also had to file something off of the original Holley parts to get it to fit properly. A minor thing, whatever it was.
I only ran the 650 DP for two weeks before I put the Proform in, so I didn't have a lot of data on the difference. The DP itself dropped 2 tenths off my 1/4 mile ET's vs. what the 750 VS ran, and the Proform dropped another .05 or so. A week later I put in a higher stall converter (dropped 3 tenths), so too many changes too quickly to give hard data on the improvement just from the Proform.
11-08-2006, 02:49 PM
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Car: 1986 IROC Z28
Engine: 350 carbed
Transmission: TH350
Axle/Gears: 3.43
That's another thing. Should I switch my vacuum secondary 750's main body out, or just pay more to buy a new 750 DP?
11-08-2006, 06:00 PM
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
I failed to note the VS part. I wouldn't spend $105 on a VS carb, personally.
What is your intended use? If just daily driving, just keep what you've got. If 1/4 mile ET's are your primary goal, go with the DP. You can get a 750 Holley HP or Proform for about $500. Just the "normal" Holley DP is over $400, so getting the carb and then putting the mainbody in would cost more than the HP.
What is your intended use? If just daily driving, just keep what you've got. If 1/4 mile ET's are your primary goal, go with the DP. You can get a 750 Holley HP or Proform for about $500. Just the "normal" Holley DP is over $400, so getting the carb and then putting the mainbody in would cost more than the HP.
11-09-2006, 10:13 PM
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Car: 1987 Iroc-z Convertible
one thing I will throw in too I recommend getting the main body from quick fuel as they were the ones that devoloped it. they make sure all is right before it leaves there. I have used them a few times and have been greatly impressed everytime. my 
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