Carbureted LSX forum - The difference between a Holley 950HP vs a 750HP

Recently, I received my Holley 950HP. At first glance the venturis appeared to be no bigger than my Holley 750HP. After a little internet research, a conversation with Jon Bitler of Pro-Systems and a closer look, I can now detail the differences.

http://www.holley.com/data/products/pictures/medium0-82851_v2.jpg

In fact, the venturis are the exact same size at the 750HP. So, how does it flow more air? The difference lies in the base plate, the boosters and the taper under the venturis leading to the base plate.

The base plate on the 950HP shares that larger bore diameter and throttle blades with the Holley 850 Double Pumper. Most Holley Carb affectionados know that Holley 600 through 750 carbs share one size base plate, while the 850 mechanical secondary carbs have a larger base plate with 1.75" throttle bores.

The boosters are thinner having a bigger hole in the middle and some machining on the underside.

And, last but not least, the main body throttle bores taper out more aggressively under the venturis to a larger final diameter to accommodate the larger base-plate throttle blades.

Does all this add up to 200 CFM? Here is what I have read. The 750HP is actually a 780 CFM. Okay. So does it really add up to 170 CFM difference? I have read that the answer is no. From what I understand, Holley used more inches of vacuum to come the the 950 CFM rating than they did to come up with the 780 CFM rating. So, for that reason, some cry foul.

Does it flow more? Sure. How much more? I am not sure.

What I do know is that I will test them back to back on my car in the next month or so and, as always, I will share my results. YMMV.

Recently, I received my Holley 950HP. At first glance the venturis appeared to be no bigger than my Holley 750HP. After a little internet research, a conversation with Jon Bitler of Pro-Systems and a closer look, I can now detail the differences.

http://www.holley.com/data/products/pictures/medium0-82851_v2.jpg

In fact, the venturis are the exact same size at the 750HP. So, how does it flow more air? The difference lies in the base plate, the boosters and the taper under the venturis leading to the base plate.

The base plate on the 950HP shares that larger bore diameter and throttle blades with the Holley 850 Double Pumper. Most Holley Carb affectionados know that Holley 600 through 750 carbs share one size base plate, while the 850 mechanical secondary carbs have a larger base plate with 1.75" throttle bores.

The boosters are thinner having a bigger hole in the middle and some machining on the underside.

And, last but not least, the main body throttle bores taper out more aggressively under the venturis to a larger final diameter to accommodate the larger base-plate throttle blades.

Does all this add up to 200 CFM? Here is what I have read. The 750HP is actually a 780 CFM. Okay. So do is really add up to 170 CFM difference? I have read that the answer is no. From what I understand, Holley used more inches of vacuum to come the the 950 CFM rating than they did to come up with the 780 CFM rating. So, for that reason, some cry foul.

Does it flow more? Sure. How much more? I am not sure.

What I do know is that I will test them back to back on my car in the next month or so and, as always, I will share my results. YMMV.

My old prosystems hp950 flowed around 840 cfm. Most stock hp950's from what I have seen are about 830 cfm. The new redesigned HP carbs are supposed to be a true cfm rating.

Speedtigger... really wish you were closer and could throw on my 750 Mighty Demon and test it against them too :)

I was told the Holleys are dry flow rated Vs. Demons wet flow rating...But it's a moot point with BG closing the doors.

I was told by a Tech that the MD 750 would flow in the low 900's testing on the same Bench and parameters as the Holley does ???? Never checked that out, but can say it made a difference on my 406SBC.
Maybe you have someone local to you that would let you borrow for a weekend ????

As always.....I'm in for your results. Also, for what it's worth, Patrick says my "950HP" Prosystems carb flows a true 846 CFM.

I wonder why they feel a need to use (what seems to be) deceptive advertising???

I have read similar info about the way different carb makers use different "of hg, to measure their carbs flow. That said, my 6.0 seems happy with my 850MightyDemon, I'm led to beleive it flows closer to 1000cfm
looking forward to the results speetigger

Well, every 750 carb I have had was stamped 1.75 on the throttle blades, maybe they were not 750 Carbs?

Well, every 750 carb I have had was stamped 1.75 on the throttle blades, maybe they were not 750 Carbs?

Are you sure the stamp on your throttle blades did not say 172? That is what most I have seen say. The stamp on the 850 and 950 throttle blades will say 180.

is that the street HP carb your bought? 82951??

is that the street HP carb your bought? 82951??

It is a Pro- Systems carb. It uses a holley main body casting. The metering plates calibration and base plate are Pro-Systems.

Are you sure the stamp on your throttle blades did not say 172? That is what most I have seen say. The stamp on the 850 and 950 throttle blades will say 180.

I think i have not looked in so long i do not remember, LOL.