Question for Quadrajet gurus
 

I have 2 stock 330 quadrajets that I would like to set up for my 454's on steroids so I can run them against my Holleys for power and fuel comparions. I know next to nothing about quadrajets. I do have manuals. Can someone give me some ideas on what to change and good starting points? Engines are M4 454's .030 over, 8.8-1 compression. flat tappet cam-224, 232, .527, .553 at 114 lobe sep, intake timed at 106, mildly ported large oval port heads with 2.19, 1.88 valves, single plane Torker 2 manifold, gil exhaust. Should make 425+ hp. Plugs are very difficult to get at. What do I need to buy and change? Thanks.

"What do I need to buy and change?"

Oh man did you set yourself up with that question:D :D

an adapter...
 

Just install it with an adapter, squarebore to spreadbore. Wire open the choke and make sure the fuel pressure is 7 1/2 to 8 psi (no more). I wouldn't change a thing as far as jetting goes.

The Quadrajets horsepower limitation comes at about 500 horsepower (with a limited amount of fuel flow) through the single needle and seat and single float bowl.

Should be interesting, I have done this before and haven't seen any improvement with the Holleys.

Sincerely
Dennis Moore

Oh, I have done this with an engine identical to these and there was a 400 rpm wot difference betwen the quad and the holley. Thats why I ended up going to the holleys years ago. My manifolds will handle either carb design. Wierd, the quad pooped out at 4600 and the holley would run to 5000 and more, no other changes. However the fuel mileage suffered considerably, obviously.

what holley an 850? i think Dennis is on the money unless you are using a bigger Holley carb [650 are bigger] and you can make the power upstairs in the RPM band pushing more than 500 HP
Mark

I use 780 cfm 3310's heavily modified. Never had any luck with 850's on this size engine, hard to start and sucked a ton of gas and didnt go any faster and accellerated like crap. Took a few years to get the vacuum secondary and all the ports right but I like these now for WOT.

I built the basically the motors you are talking about. I used the 850's and never had a problem. 3000to about 3300 still in primary and never saw a lean condition. Just have to take your time dialing them in. Never really liked a vac secondary on the boat.
Mike

I also built a motor for a guy the same way and he used a Quadrajet because he didn't want to spend money for holley. It seemed to flatten out about 4500 or so. Ran great but could use a little more carb I thought. His is hooked to an alpha. I told him to take it easy on the drive and he does now after exploding four of them. LOL
Mike

Tom-
I went through the Q-Jet tuning process on my engines in the Formula. If your'e short 400 rpm at WOT compared to your Holleys, you can make this up easily with a secondary metering rod change. These are readily available from Edelbrock and can be purchased from P.A.W., Summit, or any other speed shop.
The secondary metering orifices are of a fixed diameter and can't be changed on the Q-Jet, so you simply decrease the size of the metering rod itself.
There are identifying letters stamped on the rods, and once you get into the catalog (or one of Dennis' books) you can figure out which ones you should have in your 'kit' for your sea-trial. The rods are cheap, and can actually be changed with the engine running (I didn't though- I could just see that little hanger screw going down into the carb....). The process takes only minutes for both engines, and you will be pleasantly surprised at the results.
Primary jetting and metering should need nothing.
I gained over 450 RPM by upping the sec. rod size, one size at a time until I saw no more gain, then I went back one size.
Jim

If your looking for Holley carb anserws go to Prosystems.cc and look at his marine carbs. we have used them and dyno'd with them. the idle and mid range is really good, and see tourque and hp on every one we have tried. (15 to 48 hp over holley hp) I like the idle return while docking, the engines don't stall while shifting from rev. to forward like they use to.. If you call Patrick and ask what he does he can explain but he talks over my head...

Anyone that's been associated with drag racing knows the QJ is a great carb if you understand the changes needed to make it perform. Primary jets, primary metering rods, secondary metering rods, hanger, cam etc. These carbs consistently make high horsepower in the super stock classes that require their use in NHRA. 3275 pound all steel SS/HA Camaro with a 350, QJ and a powerglide running 9.90's at over 134mph. I am having my 454mags redone (read: horsepower increase) at present and I'm staying with the QJ's. Maybe not as easy to tune as a holley, but it can be done (as Dennis said, up to about a 500 hp limit due to fuel flow through needle and seat).

P.S. If you check some of the drag racing boards/websites, you'll hear some name dropping on some great QJ tuners (Elisha Boyd is one that comes to mind).

Thanks all, Im real happy with my holleys but with the fuel prices uncertain, I wanted to try the quads as an option.

Thanks Jafo, thats what I needed. So I go smaller in diameter on the secondary metering rod, right? Ill drag one out tonight and go through it.

Dennis Moore andf jafo have the same opinions I do. One more piece of advise, the needle and seat assembly needs to be the .140" version. You can get this from Edelbrock. Also, be sure the secondary flap spring is adjusted properly. Once set up, you can't beat the Q-Jet up to 500hp!!!!

That's exactly right- smaller diameter rod in the same size secondary jet = more secondary fuel = more RPM. After modifying heads, cams, and exhaust, the Q-Jet just needs small mods itself to be able to keep up with the increase in flow/efficiency. It's a great carburetor for up to 500 HP applications when tuned in.:)

Tom,
We have talked about this before. My engine sounds almost identical to yours, and I have fooled around with the q-jet for two full seasons, mostly because of the plugs Dennis Moore has put in for it, and I do like the economy and idle. However, the motor just hits a wall at about 4600 RPM and no matter what I do with the secondary metering rods, that is the best I can do. So, I am going to try a 800 Holley this year. We have looked over everything, and I think there is more there, and my belief is the q-jet is not doing the job on the top end.

Yup, I remember now. My boat started with 2 stock 330. 4650 rpm each. last year, one built with a holley the other stock, 5300+ on the new motor and it dragged the stock one to 4900. This year both built and should run good. But, The fuel mileage was horrible and I was running rich on the holley which I dont understand cause this same setup was spot on in a single engine boat. Thats where the quad did so poorly. Would the load characteristics change that much with twins?

You think it may have something to do with the .140 needle and seat that blown 1500 mentioned above? I dont know whats in the stock quad.

Start with a secondary metering rod with the designation 'AU'. Chances are this will be rich enough. If not, go to 'AX', and finally 'CC'.

Chances are the AU will be fine. Q-jet's are awesome carbs set up right. Definately change out the needle and seat for a larger one. Adjust your vacumn secondary till the any bog goes away, and your done. You'll never hafta touch it again.! :D

The engines in my Excalibur are Exactly the same as yours: I used all same compression, same cams, large oval port heads with the bigger valves only difference is I searched out and found the first gen Edelbrock Torkers. My buddy gave me the Qjets off his Cyclone 400s. I rebuilt them, replaced the floats and used em. I had to use a 1 inch thick spreadbore to square bore adapter. I had to do a lot of cleaning up to the adapters, so they wouldn't impede flow.
Anyway, 3.5 seasons (so far) and the motors will spin up to 5100 if I'm running my mirage 25s.
Decent gas milage, I'm not changing to Holleys anytime soon, if I did it would be to 750s nothing bigger.
Good Luck,
DS

So, your Qjets are probably set up for the 330s with .069 primary jet and .042 primary rod with DP secondary rod (a pretty lean secondary rod)

Merc set up the 454Mag Qjet as .068/.041 and DA secondary rod. That would seem to be the place to start. The DA rods give about a 21% increase in secondary flow area over the DPs.

The secondary rods used by Merc stack up like this (from lean to rich): DP (7.4L), CL (5.7L & 305), AY, CH (350Mag), AU, DA (454Mag), AX, CC, DC (502 Mag).

Good Luck