Quadrajet?

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May 2, 2010 | 04:05 PM

Ronaldo

Thread Starter

Racer

Joined: Nov 2006

Posts: 379

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Quadrajet?

I found an old qjet I would like to have rebuilded and use on my 68 vette (327 cui, 300HP, auto)

I have this data on it:

- #7041200
- "large main airbleed" model.
- Primary: jets 77, rods 49B
- Secondary: rods BG ( 0.039" )

Is this for a BB? and how should it be setup for my vette?

I'm not rebuilding it myself, just want to make sure it gets the right spec's

Thanks,

May 2, 2010 | 04:39 PM

Peterbuilt

Le Mans Master

Joined: Aug 2006

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From: mount holly NC

2025 c3 ('74-'82) of the Year Finalist - Unmodified

2019 C3 of Year Finalist (appearance mods)

That carb was originally on a 71 Chevelle 402/454 auto, the rods and jets you listed are correct for that carb #.

May 2, 2010 | 05:20 PM

7T1vette

Team Owner

Joined: Jan 2006

Posts: 37,637

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From: Crossville TN

I suggest that you send an e-mail to Lars [Grimsrud] at V8fastcars@msn.com requesting how to best set up that carb for your engine.

May 3, 2010 | 01:34 AM

HamadUP

Melting Slicks

Joined: Jan 2003

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From: Doha

St. Jude Donor '08

I have exactly the same carb on my 454 engine, it was rebuilt by Lars a while ago and since then it works really good. but isn't that carb too big for a small block?

May 3, 2010 | 08:38 AM

Aussie79

Racer

Joined: Mar 2002

Posts: 406

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From: Maroochydore QLD

Quote:

Originally Posted by HamadUP

I have exactly the same carb on my 454 engine, it was rebuilt by Lars a while ago and since then it works really good. but isn't that carb too big for a small block?

Well this is the nice thing about Qjets, because they are metered fuel delivery and they have down draft controlled secondaries they can adapt to most V8 sizes, you just need to use correct primaries and rods for the setup.

May 3, 2010 | 11:23 AM

7T1vette

Team Owner

Joined: Jan 2006

Posts: 37,637

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From: Crossville TN

Exactly. The Q-Jet is self-regulating on the secondaries...the air valve opens 'as needed' by the air flow going into the engine. So, while every Q-Jet has the potential to supply 750-800cfm, only the amount needed by the engine will be delivered.

All that is needed is to set up the primary jets and rods and the secondary rods, and to adjust the air valve spring to accomodate your engine's needs and it will work fine.

May 3, 2010 | 01:28 PM

lars

Tech Contributor

Joined: Aug 1999

Posts: 14,382

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From: At my Bar drinking and wrenching in Lafayette Colorado

Quote:

Originally Posted by HamadUP

isn't that carb too big for a small block?

All Q-Jets are 750 cfm, whether they came off a small block, big block, or a 6-cylinder (yes, GM used 750 Q-Jets on 6-cylinders). The only exception are a few 800 cfm Q-Jets that were used on SD455 Pontiacs, Stage 1 455 Buicks, 500 cube Caddys, and late-70's 400 Pontiacs.

May 3, 2010 | 02:51 PM

73, Dark Blue 454

Melting Slicks

Joined: Mar 2005

Posts: 2,838

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From: Austin TX

A bit of trivia.

On q-jet equipped 400 cid first gen Firebirds, the baseplate would allow the secondaries to open to only 70% at WOT, which meant a max flow of about 600~ cfm. This 'governor' was to prevent the Firebird from exceeding GM's policy of no more than 10 HP per 100 lbs. for it's cars back in the day.

Also, GM thought the q-jet would work fine on the 327,..many were equipped that way; the L-30 for instance.

FWIW

Last edited by 73, Dark Blue 454; May 3, 2010 at 02:56 PM.