Holley 700 DP

[6.50camaro]

I have an old Holley 4778 700cfm DP. Would there be any flow gain if I went to down leg boosters over the original straight leg boosters. I ask this question because it seems to that the hood across the minor dia . of the booster is reducing airflow slightly. I have tried to use this carb to slow my car down to run a slower index class and it runs .08 off the index. If I could pick up that .08 by changing boosters I'd try it. Dan

[jmarkaudio]

You would want a .450 step downleg that BLP manufactures. It will flow the most air. For a 700 probably a .145 passage thru on gas.

[rgalajda]

[jmarkaudio]

.450 is the hole thru the center. A stock booster is around .380 and has no step, you can get .435 and .450 with steps cut underneath. The steps help with signal and atomization.

[rgalajda]

[rgalajda]

[GTO Geoff]

My understanding is that there is little to no flow difference [ ie, air flow past the booster ] with either type, but the DL booster is more sensitive & flows fuel at a lower pressure.

[jmarkaudio]

There is a gain thru the booster, and a little outside as the booster is machined on the outside as well. I did a 650 body with .450 DL's for someone in Australia, they picked up 15HP on the dyno.

[6.50camaro]

Thank you for your input JMark .

[eric76]

I can tell you I had a Holley 4777 650 double pumper carburetor that I took out the straight leg boosters and installed down leg stepped boosters and it made quite a difference in throttle response and a stronger signal when hitting a quick half to wide open throttle and was a lot crisper and smooth when going from the transition circuit the mains flowing through the boosters. That was my experience doing that. I used a .140 sized inside dimension of the booster tube going through it.