750 Holley too big? will less CFM be better

Status
Not open for further replies.

39F

G-Body Guru
Sep 9, 2019
501
93
Pittsburgh PA
thank you guys,

blades are probably cracked because i lean into it. its brutally worse at of idle,

new set up and car/build. iv run it as much as 42 degrees, back safe at 36 because it wasnt faster or slower. had same issue.

this is the only clean pass, because i floored it slowly:

Sounds pretty healthy ,does the carb got holes in the butterflies?
 

Myles

Apprentice
Thread starter
Jun 17, 2011
80
8
sorry im slow still getting used to this forum, the layout, answering, etc.

yes shes healthy once rolling.

no its doesnt have the holes.

really not trying to run from the problem, but i think trying other carbs might work. just for the hell of it.

the more experienced guys at the track say a vac carb would be good

my q jet car was exact same issue, chased it for years, tightened that stupid flap and good to go.

apparently vac holleys are adjustable also.. with a spring kit i heard.

with the 750 on your higher compression big block 4 speed you mentioned, i feel like mines a little extreme for my dish piston 355
 

39F

G-Body Guru
Sep 9, 2019
501
93
Pittsburgh PA
As fleming442 said get a vacuum gauge ,this pic should give you a good idea of the transfer slots,if everything else checks out and they are open way to far you may need to install small holes in butterflies especially for radical cams
IMG_20200124_230229333.jpg
 

Myles

Apprentice
Thread starter
Jun 17, 2011
80
8
ok sorry, interesting, mine is identical i just checked.

At idle i read exactly 10 with a quality vac gauge, everything that should be plugged is plugged, dont think i have a vac leak, i re installed the intake also and did every test i could think of, heh..
 

1320John$$$

G-Body Guru
Sep 18, 2019
927
93
Pennsylvania
Put a 750vac carb on it the secondaries will only open enough to meet the engines demand you’re then going to adjust the secondaries rate of opening with springs not the CFM
So if It only calls for 650 CFM that’s all it will pull
 
  • Like
Reactions: 4 users
Oct 14, 2008
7,669
113
Melville,Saskatchewan
Get an air fuel gauge and bungs welded in, period. Also your car sounds like a track only special, not a long distance cruiser. Build a 383 short block with proper compression. With the LS craze, 350 4 bolt blocks are everywhere for sale, for cheap. Also a 242/250 cam on 355 CI isn't small.
 
  • Winner
Reactions: 1 user

TURNA

Rocket Powered Basset Hound
Jul 24, 2009
10,955
113
Socialist NY
Dish piston old offenhouser 5000 stall?????????
 
  • Like
Reactions: 1 user

lilbowtie

Comic Book Super Hero
Jan 7, 2006
3,460
113
Canton Mi
this is the only clean pass, because i floored it slowly:

You are kinda answering your own question. You have a miss match engine combo w/ low comp and large heads big cam which is killing the runner velocity which, as mentioned, your not pulling air on the bottom end and getting a poor carb signal. Your clean pass shows you can mask the problem. As mentioned above a wide band tuning and the aid of a down track recorder tells you exactly whats happening
and where (no guessing)
 
  • Like
  • Useful
Reactions: 1 users
Status
Not open for further replies.

GBodyForum is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Amazon, the Amazon logo, AmazonSupply, and the AmazonSupply logo are trademarks of Amazon.com, Inc. or its affiliates.

Please support GBodyForum Sponsors

Classic Truck ConsolesDixie Restoration DepotMike's MontesP-S-TSouthside Machine PerformanceUMI Performance

ContactAdmin@GBodyForum.comfor info on becoming a sponsor