750 vs 850 vs 950 Holley

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skrews

skrews

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Flow tested a few carbs the other day, thought I'd share my findings. The Ultra HP carbs are the older design from around 2005 they are no longer sold.

Holley Ultra HP 750 part#80675
1.375 venturi / 1.687 base plate
819 cfm

Holley Ultra HP 950 part#80676
1.375 venturi / 1.75 base plate
825 cfm

Holley 850 "old style main body" part# 9380
Choke horn milled off, slabbed throttle shafts, annular boosters
1.58 venturi / 1.75 base plate
945 cfm

I'll be replacing the 1.375 main body of the 950 with a 1.45 main body and retesting in the coming weeks.

This test backed my suspicions about the true flow of the 950, as it was only able to make about 5 more HP than the 750 on an upper 500 HP 360 motor. 950 my *** lol, I know Holley took a lot of **** over that carb and the new XP950 has a 1.6 venturi because of it.
 
I have a 80528# 750 HP on my 416 . I also have a 950 HP I was going to try on my 416. You may have saved me the trouble.
 
I responds and works so well with the 750 I hate to mess with it. You can stab it as hard as you want and the response is instant. This is on my 416 68 Barracuda with 3.91's
 
My pump gas 408 ran 9.80's with ease with a new style 750 holley on my Duster. When I switched to alcohol I sent APD and 850 to change over to alcohol for me.
 
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If I ever get my butt in gear this APD 1250 is going on my 572
 
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yellow rose said:
Is that carb for the 275 car you are doing? Or was it a drag week car? I forget.
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(275) 10.5 heads up build. Age and knee condition have caused a near stop but I will get moving. I could finish the engine in three hours and I have the transmission almost done
 
pittsburghracer said:
Yes. It’s a Keith Black I ordered and got in 2009. It went 8.40’s in my 91 Daytona with a pretty mild 440-1 build. I redid it with 7.150 aluminum rods and nitrous friendly pistons.
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Would love to have one but , $$$$ . KB still make them ?? ebay is flooded w/ them from shannons engineering, but $5500 is too high for me , bet he doesn`t sell a whole bunch of them !
 
RAMM said:
1.5" hg correct or 20.4" H20 right? J.Rob
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Converted 1.5" of mercury to 20.4" of water for testing on the bench.

RAMM said:
The 750 HP/XP is one of the best all around carbs for small blocks from 350-400+ cubes I've found. J.Rob
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Agreed. The only thing I don't like is the high location of the idle fuel restrictor jet, but that can be relocated.
 
skrews said:
Agreed. The only thing I don't like is the high location of the idle fuel restrictor jet, but that can be relocated.
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They're all like that now from what I have seen. It causes the idle AFR to bounce back and forth--annoying. Low set IFR's = rock steady afr @ idle. J.Rob
 
RAMM said:
They're all like that now from what I have seen. It causes the idle AFR to bounce back and forth--annoying. Low set IFR's = rock steady afr @ idle. J.Rob
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Interesting.... What do you guys think causes this? Maybe too much air above the emulsion holes? (Oops the idles may not have a real 'tube'..)Or something unstable in the airstream higher up? Just curious....
 
RAMM said:
They're all like that now from what I have seen. It causes the idle AFR to bounce back and forth--annoying. Low set IFR's = rock steady afr @ idle. J.Rob
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I don't know what the reasoning is behind the high IFR. Part of me thinks its just monkey see monkey do engineering.
 
skrews said:
I don't know what the reasoning is behind the high IFR. Part of me thinks its just monkey see monkey do engineering.
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That is exactly what I think as well. I think the idle circuit becomes over emulsified due to the location and the circuit loses "prime" or something and sucks air, sucks fuel, suck air , sucks fuel. Sometimes older is better. J.Rob
 
The engineers 50 or 60 years ago had the holley style carbs right.
Anyone ever flowed a 650 or 750 Mighty Demon?
 
skrews said:
I don't know what the reasoning is behind the high IFR. Part of me thinks its just monkey see monkey do engineering.
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I have one of the queer applications because every time I lower the IFR the car doesn't idle nearly as well. I have spent enough time on it that I gave up and moved them back up and let it go. Everyone I know moves them down, but for whatever reason, mine want to be up.
 
yellow rose said:
I have one of the queer applications because every time I lower the IFR the car doesn't idle nearly as well. I have spent enough time on it that I gave up and moved them back up and let it go. Everyone I know moves them down, but for whatever reason, mine want to be up.
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If you have a BLP carb, those guys probably have it figured out. QFT, Holley, and others not so much. Its more about bling and gimmicks.
 
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