QuickFuel vs Q-Jet - spacer & manifold

gbody79malibu · Aug 30, 2014

Guys,
I got a standard 305 Chevy engine with the original intake manifold on my 79 Malibu (street car). The 4bbl Q-Jet carb is kind of leaky and shows a poor vacuum result (around 10in hg, dropping to 8 in Drive). That's why I want to exchange the Q-Jet with a QuickFuel 600 cfm Slayer Series (Holley 4160 architecture) - would you recommend that carb, has anyone experience with that one? And should I change the intake manifold as well or could I use a decent spacer instead? Which spacer could I use - it should be fitting the orignial (dual-plane???) spread-bore manifold and the square-bore carb. What about the hood clearance in the case of spacers - what's a good spacer height to be used??
thanks a lot for your hints.
Steven

seawolf18 · Sep 1, 2014

If your going to change a q-jet(spread bore) to a square bore, you will need an intake adapter not spacer. I would change out the manifold, especially if your still using the factory cast iron one. quick fuel makes nice carbs. The Slayer series is their budget carb, and works well for a stock or mildly built motor. On the other hand the q-jet is a good carb. It will also get the best fuel economy, if that's and issue for you. The common thing that goes bad in them are leaky plugs. If you can find someone that knows them and get it rebuilt, they will fix all the common issues with them.

Bonnewagon · Sep 2, 2014

There's nothing better than the original equipment carb and if it's unmolested that's even better. Instead of adapting around it just get it fixed and she'll probably work great for another 35 years.

pontiacgp · Sep 2, 2014

Bonnewagon said:
There's nothing better than the original equipment carb and if it's unmolested that's even better. Instead of adapting around it just get it fixed and she'll probably work great for another 35 years.

x2

jociha · Sep 2, 2014

Not a big fan of the Quickfuel carbs, they use course threads on there adjustment screws so adjusting is not as easy as other carbs, [at least it is like that on mine] so I would use something else. A spacer will only get you a couple HP on a 305 mostly mid and higher RPM so don't bother. If you decide you want a aluminum intake any of the dual plane air gap types will work just fine.

olds307 and 403 · Sep 2, 2014

Get a Street Demon 625 cfm instead. It will bolt right to your manifold and give you better mileage. You need the thin spacer plate with carb being designed for square and spread bore manifolds. The carb is an improved all new castings version of the old Carter Thermoquad.

DoubleV · Sep 2, 2014

olds307 and 403 said:
Get a Street Demon 625 cfm instead.

What advantage would that be over a properly set up Qjet?

foxtrot · Sep 2, 2014

DoubleV said:
olds307 and 403 said:

Get a Street Demon 625 cfm instead.

Click to expand...

What advantage would that be over a properly set up Qjet?

In this case, no advantage that I can think of. Maybe the fact that he can purchase one from the inter web and bolt it on would be faster than waiting for a rebuild (if needed). The one caveat here is that it will need to work out of the box - ha.

pontiacgp · Sep 2, 2014

DoubleV said:
olds307 and 403 said:

Get a Street Demon 625 cfm instead.

Click to expand...

What advantage would that be over a properly set up Qjet?

none, I tried a street demon 670 for a few months just to shut up a holley lover who inssisted I'd be real happy with it but I'll take a q jet over that any day

olds307 and 403 · Sep 2, 2014

None but no wait time and can be bought anywhere. The Thermoquad was very similar to the Qjet. The new 3 barrel Demon version eliminated a few problem areas and and added a much better choke set up. It is a better solution than using those awful adapters. Pony up for Performer style square bore intake if you want a square bore carb.

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QuickFuel vs Q-Jet - spacer & manifold

gbody79malibu

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seawolf18

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Bonnewagon

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jociha

Master Mechanic

olds307 and 403

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DoubleV

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olds307 and 403

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