MN71W30

I'm running a 455 with a manual transmission, 1971 quadrajet carb, AU rods and 71 jets. The car has never run better. The problem I have now is wondering if there is a better combo for a car running low 13's @ 103mph. Is there anyone out there that has experimented with different combo's and could save me alot of time and trouble? Or has gotten a q-jet too rich?
Thanks for all the help.
Dave

Bobsw32

A common speed trick mistake is to always install thinner (richer) secondary rods. Some engines and carbs will produce a secondary “lag” if the rods are too thin. On about half of the engines I work on, I obtain better performance by installing fatter “non-performance” rods. Again, a quick road test is the only way to set this up, so go back to your 300-foot stretch and make a few runs with rods both richer and leaner. Once you have found the rods producing the smoothest secondary transition and the best numbers, you can start unwinding the secondary airvalve spring. Relax the spring tension in 1/8 turn increments until the car stumbles on acceleration, then tighten up 1/8 turn again. You have now determined the quickest secondary opening rate that your engine can handle, and your secondary mixture is set.

Note that secondary metering rods come in three different tapers: long tip, short tip, and medium tip (see Figure 3). Most of the available after-market metering rods have the long tips, and these will produce a full-rich mixture upon the slightest opening of the secondaries. Many street engines will produce better performance by using the short tipped rods. A short tipped rod does not allow a full-rich mixture until the secondaries are opened quite a ways, keeping the mixture a little lean initially. This can produce smoother and crisper performance in many applications. Next time you see a junk Q-Jet laying around, make sure you yank the rods and jets out of it: many old truck carbs have some really good short-tipped secondary rods in them.


I would try a set of DA rods and or AX rods and see if the motor responds to more more fuel....

Bobsw32

If this were mine I would have a separate carb for the strip that I would eliminate the primary metering rods and plug the inlet for the power piston and then run a 57 or 58 jet and then run something like an AX secondary rod. I would grind about 1/8th inch off the top of the accelerator pump rod, eliminate the internal fuel filter and put a large window needle and seat.......these mods will help

MN71W30

Wow, I hit the jackpot!! Great info. After I installed the AU rods and 71 jets, I did notice a sight problem that acts like a bad accel pump. I figured I may have damaged it. Is the the lag you mention? I had AK rods and 70 jets before. I'll read through your post a few times and, yes I plan on modifing another q-jet for performance.

MX442

400 G block, .040 over. 9.75:1, Performer intake, 212/224 .472"/.496"

1977 Chev q-jet
73 mains. .044" custom rods (Ruggles)
DA secondary rods. K hanger.
2800' altitude.
I may go leaner to 72 or 71 main.

I still have some fine tuning to do. Need a wideband or dyno to get it perfect.

dc2x4drvr

461, Edelbrock 04B, 800 CFM Q-Jet: 73/41/AX rods on a G Hangar.
Modified secondary pulloff. Built by Dean Oliver.

4speedBench

I'm in the midst of this myself. My 455 is a stock '71 motor & 4speed. QJ was re-done by Sparky but it has a stumble at partial/light throttle but if you put your foot into it..WOW. I'm thinking I need to go richer in primary metering rods since I noticed it runs best (and smooth) at cold start up (rich via choke) and WOT.

Suggestions on rods?

Thanks

firefrost gold

Dave I have cliffs book and a old mag from 70 or 71 were they NHRA set up a q jet for a 442 if you want I can dig them out and drop them off let me know.

J-(Chicago)

I ran a bone stock 72 455 carb with a stock fuel pump. Car went 13.16, no problems.
secondary rods were AU.
It was only a 9:1 compression setup though.

Run to Rund

Try to find Doug Roe's book on Rochesters. He ranks the size of secondary rods. Beyond that, for a given altitude and camshaft, the best approach is to test different stuff. For street, I got good results with DA secondary rods; primary jets depended in part on what metering rods I could find.