Chevy Quadrajet on oldsmobile engine? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-31-2008, 01:07 AM
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Chevy Quadrajet on oldsmobile engine?

Can this be done? Maybe this is a stupid question, but its late and Im confused. I would like to replace my aging rebuilt q-jet on my 350 olds with a newer q-jet. I actually found brand new edelbrock q-jets but they say they are for chevy. I guess the bolt pattern may be different on the chevy q-jet compared to the olds, but if so are there any adapter plates anyone knows about? I could not find any information about if something like this even exists or is necessary. Any info anyone has would be great. Can a chevy q-jet be used on an olds 350 with holley intake?

Thanks

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Old 05-31-2008, 01:35 AM
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4 barrel carbs have two base plate configurations. Squarebore and spreadbore. All Q-jets are spreadbore so it doesnt matter what it came off of. Itll fit any other spreadbore intake. Edelbrock carbs are also spreadbore. Holleys come in both.

As i understand it spreadbore is better for a daily driver/cruiser because the primary side of the carb is alot smaller then the secondary side so under normal driving you wont be sucking in as much fuel. Once you get on the gas though the larger secondary side opens, giving you the extra flow you need.
Squarebores are the same size on both the primary and secondary side. Which is better for performance but not so good for mileage.
Spreadbore gives you the best of both worlds.

So yes, the chevy Q-jet wil fit on your olds 350. The only thing you may have to do is replumb your fuel line. Different models and years of Q-jets had the fuel inlet in different locations. Some were on the side and some were on the front.

Hope that helps
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Old 05-31-2008, 08:42 AM
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Thanks for the response. This is what I figured, but if you read this

Jet Q-jet

It says will not work on Oldsmobile. Maybe they are referring to stock manifolds?
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Old 05-31-2008, 08:49 AM
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You can make any carb work on any intake - if ( and only if ) you can fabricate the necessary adapter .
I just recently put a spread bore carb on a square bore intake by using a spacer and doing a little grinding and drilling on it. Works like a charm . Don't let someone tell you ' it can't be done' .... do it now , just to prove them wrong !
Mike
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Old 05-31-2008, 09:04 AM
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Quote:
Originally Posted by glamaina
Thanks for the response. This is what I figured, but if you read this

Jet Q-jet

It says will not work on Oldsmobile. Maybe they are referring to stock manifolds?
More than likely the Olds,Buick,Pontiac have different fuel line routing, choke type or throttle linkage setup but it can be made to work. The actual intake mount area is the same on all Quadrajet intakes.
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Old 05-31-2008, 09:04 AM
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Quote:
Originally Posted by glamaina
Thanks for the response. This is what I figured, but if you read this

Jet Q-jet

It says will not work on Oldsmobile. Maybe they are referring to stock manifolds?
A statement like this usually means the manufacturer can't be bothered to see if the part even fits on non-Chevy engines.

All Q-jets use the same manifold bolt pattern. The three major differences between the Chevy style and Olds style Qjets are the inlet, the throttle arm, and the choke. All Olds Qjets use a straight-in inlet. The Chevy carbs have the inlet facing the passenger side of the carb. You'll need to fabricate a new inlet pipe to match. The throttle arm may or may not hit the Olds manifold. If it does, you can just use a spacer to jack the carb up to clear. Depending on your Olds, the Chevy throttle arm may or may not have the correct connection points for the throttle cable and kickdown cable. Depending on the year, the Olds could have used a divorced choke (thermostat coil in the manifold with a linkage to the carb) or an integral choke (round canister on the passenger side of the carb). I don't know what this carb comes with, but I'd just convert to an electric choke and be done with it.

Finally, the carb jetting may or may not be correct for your engine and car combo. You'll need to dial that in yourself by changing the metering rods and possibly the primary jets as required.
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Old 06-01-2008, 01:07 AM
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I've seen a Chevy Q-jet whose throtte lever would be jammed up by part of the casting on another division's Q-jet intake manifold. Fuel inlet angles can also be a problem. Lotsa little bugaboos when you change stuff up sometimes.

If the current carb used to work fine, I'd get it rebuilt by a good carb shop. A new one would likely need recalibration for your engine, costing time and/or money that wouldn't give you any gain over what you have now.
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Old 06-02-2008, 08:54 AM
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Thanks again, Now one more question maybe you guys can help me with.

Ive been reading "How to Rebuild and Modify Rochester Quadrajet Carburetors" by Cliff Ruggles. Very good book. He recomends starting with a late model (1976 or above) core and working from there. There has to be a point in which computer controlled carbs were introduced though. Which means, a what point can i no londer use the carburetor on my 72 cutlass. I found an 80's olds q-jet but there appears to be an electrical connection on it. Anyone know if this year carb would work?
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Old 06-02-2008, 08:58 AM
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No, it won't work. Olds started using the computer controlled Qjets on the 307 in 1980. Not sure about the ones Chevy used on the 305s. In addition, the secondary air valves on these carbs only open about 70 degrees. You can file the stop, but it's a moot point. In any case, if there's an electrical connector coming off the carb, don't use it.
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Old 07-28-2008, 03:50 AM
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you would want to try and match the numbers on the carb the q-jets were set up for diff apps i.e. truck, high alt., Cal emissions etc. the carb number decodes into year, type and trans and manufacturer.
http://www.oldengine.org/unfaq/leadfoot/qjet1.htm
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