mild mild mild 427
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Joined: Jan 2013
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mild mild mild 427
Hey Guys,
The numbers don't match on my 427/390 4spd 68. Its all stock. Currently dialed in at 12 BTDC per the Lars timing doc.
I need a little bit more oomph. I have a lot of experience modifying fast boosted EFI cars, but not much with carb tech. In a previous thread you guys helped me troubleshoot several performance problems with my car. We ended with saying "Maybe a carb replacement/rebuilt would be good." I'm kind of thinking - if I'm gonna do that anyway, maybe I get something that is a bit of an upgrade?
My first thought was to swap out the intake and carb with something that breathes a little harder. Is that a reasonable mild upgrade for these cars? Will I get any performance? Good value for the money? What is the gold standard in intake/carb combos for this purpose, assuming the rest of the motor stays stock?
Thanks again for your guidance!
The numbers don't match on my 427/390 4spd 68. Its all stock. Currently dialed in at 12 BTDC per the Lars timing doc.
I need a little bit more oomph. I have a lot of experience modifying fast boosted EFI cars, but not much with carb tech. In a previous thread you guys helped me troubleshoot several performance problems with my car. We ended with saying "Maybe a carb replacement/rebuilt would be good." I'm kind of thinking - if I'm gonna do that anyway, maybe I get something that is a bit of an upgrade?
My first thought was to swap out the intake and carb with something that breathes a little harder. Is that a reasonable mild upgrade for these cars? Will I get any performance? Good value for the money? What is the gold standard in intake/carb combos for this purpose, assuming the rest of the motor stays stock?
Thanks again for your guidance!
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
Wouldnt waste money on a carb probably be disappointed
More power air in/air out
hang the valves open longer/farther (cam)
Intake
Headers
Headwork huge +
can still make it mild mannered but nice increase in power.
More power air in/air out
hang the valves open longer/farther (cam)
Intake
Headers
Headwork huge +
can still make it mild mannered but nice increase in power.
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
What would probably give you the biggest "seat-of-the-pants" increase in performance would probably be a numerically higher diff gear and an overdrive transmission to make up for it on the highway, but that's going to cost a pretty penny, so we'll just put that in the "maybe someday" file. Although, it might help people give you better advice if we knew what your diff gear presently is, and if the 4-speed is a close ratio or a wide ratio.
The 427/390 came with a Q-jet carb on a cast iron intake manifold, right? I'd keep the Q-jet, have it rebuilt/tuned by someone with a good rep, someone like Lars Grimsrud. It's a good street carb, your not leaving anything on the table by keeping it.
As far as the intake manifold, I am a big advocate of upgrading cast iron manifolds to aluminum, if for no other reason than the weight savings. I'm not really into BBCs, so I'm kind of talking out of my a$$ here, but as a guess, I'd say you probably wouldn't go too far wrong with an Edelbrock Performer, or equivalent. You say "all stock", so I'm assuming cast iron exhaust manifolds. Headers and a free-flowing dual exhaust would probably be your best bang for the buck mod.
Corvettes are marginal when it comes to hood clearance, anyway, even with the small block engines, more so with the big blocks, so be aware of that when it comes to choosing an intake manifold. You should be able to make some clearance with a dropped-base air cleaner. I'm sure you'll get some more specific advice from a big block owner pretty soon, so just be patient.
Scott
The 427/390 came with a Q-jet carb on a cast iron intake manifold, right? I'd keep the Q-jet, have it rebuilt/tuned by someone with a good rep, someone like Lars Grimsrud. It's a good street carb, your not leaving anything on the table by keeping it.
As far as the intake manifold, I am a big advocate of upgrading cast iron manifolds to aluminum, if for no other reason than the weight savings. I'm not really into BBCs, so I'm kind of talking out of my a$$ here, but as a guess, I'd say you probably wouldn't go too far wrong with an Edelbrock Performer, or equivalent. You say "all stock", so I'm assuming cast iron exhaust manifolds. Headers and a free-flowing dual exhaust would probably be your best bang for the buck mod.
Corvettes are marginal when it comes to hood clearance, anyway, even with the small block engines, more so with the big blocks, so be aware of that when it comes to choosing an intake manifold. You should be able to make some clearance with a dropped-base air cleaner. I'm sure you'll get some more specific advice from a big block owner pretty soon, so just be patient.
Scott
Last edited by scottyp99; Jul 13, 2013 at 10:26 AM.
Instructor
Joined: Mar 2013
Posts: 205
Likes: 20
Keep the the Rochester Quadrajet carburetor. There is not much real estate under the hood and on top of the intake manifold. Have it remanufacture to the specifications you will make to your engine. Another Rochester Quadrajet remanufacturer is All American Carburetors.
http://www.allamericancarburetor.com/
http://www.allamericancarburetor.com/
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
68's came with the Winters Aluminum low rise; it's as good as a Performer. I believe you need a good end-to-end tune, as the L36 is a torque monster. I have one. As posted, Mr. Lars Grimsrud will make your Q-Jet (and engine) come alive. Mine is pretty stock, with a little head work, a mild Crane cam and Hedman headers. I have shorter tires (255/50/16) so the 3.36 rear end acts a little higher.
