Right now I've got a Q-jet that I have rebuilt myself. It runs superb I would say, as far as start-ups, driving, power-wise, etc. I did not build it with any 'fancy' parts, just a run of the mill rebuild kit.

I am putting together my 454 soon, depending on when the Muncie 5-spd comes out, it could be ready to drop in around Christmas or so, if the tranny is still scheduled for year end (I think that's what I heard?). What I want to budget in is a carburetor. The Q-jet I got was off a '77 Caddy Eldorado with the 425 CID engine, and I'm pretty sure it's the 800 CFM version. I'm trying to use all the parts I have already which will include the rods, crank, heads (-781), intake, basically everything except pistons and valve train components and cam. The intake is for a square bore carburetor. If I purchase an adapter to put my Q-jet on there, will that cause problems?

The main reason I put the Q-jet on my car (swapped from 2-bbl) is because I found one cheap to rebuild and liked the gas mileage.

I'm curious if the adapter plate for the Q-jet would cause a problem, and would like to know if anyone knows any power VS gas mileage statistics if I just got a new Holley (prolly 800 cfm vac. 2ndary?). While I know some people feel I shouldn't be concerned with gas mileage if I'm putting a 454 in there, I'd just like to know. If a brand new Holley is going to give me 10-20 more HP but only drop me 1 mpg, that's cool, but just curious.

Thanks in advance!

Running an adapter plate is never ideal.

Think of it this way, by running the Qj and not buying a Holley, you can spend part of the money you saved and invest in a spreadbore intake.

I ran a Holley -vs- Qj comparison. The Qj was 2 m.p.g. better with no loss in power.

Mike

I use an adapter with no problems.

Taylor,
In my family, there are 4 vehicles which have a Mr Gasket adapter and Q-jet bolted to a Holley bolt pattern manifold: 51 Chevy with an early Z-18 manifold on a 350, 71 Chevelle 454 with alum GM manifold, 66 Chevy pickup with early Z-28 manifold on a SB400 and a 70 Chevelle with an early Z-28 maniflod on a SB400. The Q-jets in use range from 70 to 73 models.
For daily, dependable, all around street/performance driving, I have zero complaints with any of the four. In fact, the only Holley in my family is the one on my jet boat (on an early Z-28 manifold) on a small block 420. The boat only get out during the summer time and sits the rest of the year. Almost every spring, I have to take it apart and clean it out!

I haven't had much luck with the adapter plates, they just don't seem to work as well as a dedicated manifold. What rpm range is the engine being built for? Heck, if it's a low rpm motor even a basic Holley 600 vacume secondary would be enough, and easily tuned.