Croozin2

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).

formula31

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.

blown1500

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!!!!

jafo

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.

Whiteknuckle

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.

formula31

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?

formula31

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.

Madmax

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.!

Zanie

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

220BR

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