Low vacuum engines.

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Low vacuum engines.

Postby WarWagon » Thu Jul 05, 2018 1:41 pm

I have a 302 (301ci)Small Chevy v8, stock GM rotating assembly (11:1 compression ratio) It has a solid lifter camshaft that is better suited for iron heads vs the aftermarket aluminum heads I have on it now. Also has a mid rise single plane intake manifold (team G). I
used to run a large mechanical secondary Demon carb in the past and it was not perfect but ok, barely idled with the primaries cracked quite a bit and lots of fuel dumping/smell. The engine didn't like running this carb this year. I started modifing a vacuum secondary Holley 600 to run and it us taking a considerable amount of tuning to get right and just to idle. I pulled it off and temporarily installed a Q-jet for the time being, and it actually idles and runs good up to the mid range then it's running out of fuel for the top end. So it's been OK to drive around and do light cruising but is still isn't right. So I'll be getting back on the mods for the 600 Holley. Tuning needed just to get it to idle with the Holley: completely drill out the brass idle feed restrictors, drill two 1/4" holes in primary throttle butterflies, 2.5 InHg power valve. Ignition timing is nearly 40* @ idle speed of 1500 rpm. Last time out with the Holley had it idling well but a fuel dead spot in the mid range and the top end. So up sizing jetting is the next things to try.
Adam Knoll
Fairmont, W.V.
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Re: Low vacuum engines.

Postby Rick Andersen » Thu Jul 05, 2018 3:25 pm

Sounds like a very complicated project! I've been having problems with the Holley carbs I have on a bunch of my cars simply leaking. I am guessing that it has something to do with the ethanol in the gas.

Something to think about might be to try electronic fuel injection. I know you can make plenty of adjustments to those through software on a PC.
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Re: Low vacuum engines.

Postby WarWagon » Thu Jul 05, 2018 5:27 pm

No fuel injection destined for this engine, I'll swap the Chevy out for something much more street friendly in the future. I have tuned with Holley carbs quite a bit on different engines that all had plenty of vacuum and I do like them once they are setup right. Takes much longer to setup and smaller changes make bigger improvements when tuning an engine with little to no idle vacuum. Mine has 3inhg at 1750-1800 rpm idle and 12inhg once engine hits 2500rpm.
Adam Knoll
Fairmont, W.V.
'65 Corsa 140 turbo DD
'66 Crown V8 Vair 5.3 LS
'66 Buick Riviera GS
'84 Isuzu Impulse Buick 3.8
'84 Buick Regal 3.8 blowthru turbo
'13 Suzuki SX4 6spd AWD
'19 Chevy Silverado 4x4 5.3 LT
WarWagon
 
Posts: 100
Joined: Sun Feb 02, 2014 3:45 pm
Location: Fairmont , WV


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