Throwing around the idea of swapping a quadrajet onto my 390 to see what kinda gains I get in the mpg area. I've gotten 12mpg at best with my 4160 holley and think I could do better. Anyone running a quadrajet on their FE or anything else? We've got at least 6 quad's laying around upstairs so I just need to get a kit and adapter plate to go from squarebore to spreadbore. Waste of time/stupid idea? Anybody back me on this one?

 

with a spreadbore manifold I'm sure you'd see noticeable gains. however,goofy flow through the adapter plate will hurt.

Other issue is quadrajets like to wear out their throttle shaft bores on the primary. If you have any play, the carb will get a strange vacuum signal and won't run right for anything.

Justin

 

Hey Justin, got a link to your FE in 80s truck swap?

Hijack over

I know it has been done, that guy just liked the Q-J.

It seems like there may have been a spread bore manifold, maybe aftermarket. I'm pulling a blank at the moment.

 

They do make a quad/sq bore adapter. I have one somewhere in the pile. I tried this back in the early 80's with a 302 I rebuilt and someone gave me a quadrajunk. Never did get it installed, used a 600 Holley instead.

 

hypoid- the long of it is in the engine swap forum, but here's the short of it:
http://www.fullsizebronco.com/forum/...&highlight=390

Justin

 

That they do, and if you turn it upside down, you can put a Q-Jet on a square-bore intake - but it's still upside down.

It's meant to put a nice dependable carb in place of a Q-Jet, not the other way around

 

Good one!

Seriously though, didn't Ford use the Q-jet on some cop motors or something back in the 70's. I'm thinking 429's maybe?

 

Ford used the Quadrajet on the 429 CJ for 1 or 2 years. The Q-jet is actually a really good unit IF you have a good core (which are hard to come by anymore) since they haven't been made since 1980.

Best thing to do with one is send it to a reputable q-jet rebuilder and let him have his time with it. It'll typically cost about the same to have one rebuilt as it does to just buy a holley or a performer, so it's up to you.

Justin

 

Ya, I just know that over the years I've liked seeing those teeny weeny primaries and massive secondaries. You've gotta get better miles w/ that thing only allowing that little bit of air/fuel in the primaries. We'll see what my selection of quad's turn up, whether or not I gotta good core to start w/ or if they're all shot. Justin, you know any tuning tricks for these things?

 

i've never really had a chance to fiddle with a q-jet. all the ones i've come across run great and I'm afraid to touch or are so worn out that nothing will help other than a total remanufacturing.

I have a really comprehensive q-jet tuning guide somewhere and I'm looking for a good core to try it out on, i'll dig it up and send it to you.

Justin

 

The Q-jet was also used on some 351C's and 460's. Seems like I saw new Q-jets in Summit's catalog recently. Another good spreadbore was the Carter Thermoquad.

 

Thermoquad is definitely another one that doesn't get it's fair share of respect. A guy I worked with ran one on a 50 Ford street rod, ran quite respectably for just having a stock TQ tossed on it. It finally met the demise of so many other TQ's when the float body warped and started dumping fuel out the top.

And 73F100, send me a PM with your e-mail address and I'll send you the tuning quide. It's about 30 pages long, but it has about everything you could want to know about a q-jet.

And edelbrock is making a new QJ. It looks like the original one, but they did away with some of the metering circuits to make it cheaper and easier to produce so it doens't have quite the economy or part throttle driveability capabilty of the original.

Justin

 

Well to change the tune a bit, what about edelbrocks? Whose running 'em? I was told by a good friend of mine to use an edelbrock on my 390 build a couple of years ago but I was also told by another guy that it would cost me close to $100 to tune it correctly after purchasing all the rods and so forth. I'm no doubt a fan of holley due to its simplicity but not a fan of it's fuel economy or lack thereof. What all is involved in properly tuning an edelbrock? Also, are edel's spreadbore/squarebore?

 

The Edelbrock/Carter AFB carb is a square bore.With the truck in your sig, 15 mpg would be about tops for a 390. What're you getting with the Holley?

 

When i had the 390 in my truck I was running an edelbrock 750 and it pulled down right at 16mpg at a 60mph cruise. I'm going to agree with baddad that that's about all you'll get out of one. But compared to the milegae my 300 got, it was toally worth it.

If you do go edelbrock I could see how it would cost you $100 to get it dialed in if you bought individual rods and jets, but if you buy the calibration kit it's between $30 and $70 and has everything you should need. Also ask around, see if anyone you know happens to have a calibration kit.

When I originally set mine I borrowed a complete calibartion kit off of a repair shop (i know the guy that owns it) with the understanding that i could use it as long as i needed to so long as it came back with all of the same jets and rods that it left with. I got the carb set, bought $14 worth of rods, and got it back to him.

Justin