Hey guys, Just wondering if I should be changing the secondary metering rods in my quadrajet. I have CD in there now. Qjet 7040240. The motor is a 71 455, I believe a mild cam in it, seems to run well. Could always use more power though Sent from my iPhone using Tapatalk
It is difficult to measure improvement with secondary metering rod changes unless you are on the dyno or at the track. "Seat of the pants" testing is difficult, unless one metering rod size is WAY of the mark. The other problem is that different metering rods have different upper section diameters, taper, tip size/length, etc. So simply changing from one to another can hurt power in one place and help it in another, unless you are using different height hangers and/or custom machined rods from the same cores for your testing. The cam listed is pretty "small" for a 455 build, even a low compression one. A cam change would really wake things up for the big 455, something with more seat timing, about 10-15 more duration @ .050", and wider LSA. If the exhaust is full length and no X or H pipe, and less than 3 diameter head pipes, a split duration cam would also be a good idea......IMHO.....Cliff
Thanks, I have stock exhaust manifolds, full dual exhaust but no X or H pipe, 2.25" OD pipe. Sent from my iPhone using Tapatalk
DA, rods used to be readily available, and they are rich, me and the group I've run with since the 80s, have used em 100s times, the biggest improvement you can make, is experimenting with the tightness, or looseness of the secondary air door, until you have it perfect for your car, just find a isolated road, and do full throttle launches till you have it perfect
that 268h is a good choice for the exhaust and comp your running, just know, if you upgrade exhaust, and induction, a different cam would make more power, but with out those upgrades your fine,
Thanks! So how much HP gain can I expect from a cam change alone? Also, does changing my rods make a huge difference? Are my existing ones starving a stock engine now? Sent from my iPhone using Tapatalk
You have a CD .0567" long tip. The next step richer that is available is an AU rod that is a .0527" long tip. (also CV and CK were the same size) That is what a factory 455 Buick Stage 1 engine used, (also the big 455 Olds W series engines) and will be about 1 or 2 percent richer than your CD rod. Long tip rods are harder to find than Short and Medium. Stay with long tips or it will become a comlicated mess of switching out hangers to compensate for extreem variations in air fuel mixture. Your current air fuel ratio is likely close now.
with the combo you have now, you can expect the car not to run as well as it does now, with a change to a larger cam, its all about the combo, improve all the externals first then go to internals, the order I would take is, 1 maximize ignition spark and timing curve 2 Fully science out mandrell bent 2.5 xpipe system, with headers or ported manifolds 3 suspension, shocks, sway bars, bushings 4 Brakes you gotta stop 5 Cooling system more power generate more heat 6 transmission Refresh or shift kit, improve the converter, and driveshaft/ u-joints 7 fuel delivery, pump and lines for more power 8 Cam and intake, 9 new more powerful engine IMO, this plan has been successful for me, and others, many times, good luck
The closer to the letter A you get the higher it lifts the metering rods out of the hole and richens the mixture only under wide open throttle, if you pull that hanger, and compare it with a different letter hanger side by side you can see, that the holes the metering rods hang in, are drilled either higher or lower in each hanger, there is a lot of really good quad info floating around, BUY cliffs book, modify your secondary air flaps with a little notch, like cliffs book points out, lots of little stuff to do, if you really get into twisting and tweaking on your quad and your HEI, you will be amazed how well your stuff will run, once you start learning and get a feel for which way to go, good luck!!! ask questions and self educate, and by all means change those rods, change that hanger, Twist that distributor and have a ball playing with your car!!!! Sent from my iPhone using Tapatalk[/QUOTE] Sent from my iPhone using Tapatalk[/QUOTE]
The cam being used would simply be OK in a 455 with 7.5 to about 8.5 compression, but it is DONE way before 5000rpm's with only 268 degrees seat timing and 110LSA. If the compression is higher for sure it's WAY too small. I build a good many engines here, and dyno all of them. Just helped another "builder" with his first 455 (Pontiac), he had called Comp and used 276 duration HR cam on a 110LSA. Compression was 9.5 to 1. They were experiencing detonation, crappy idle, and WAY down on power for the combination of parts. I recommended much bigger cam on a 114LSA instead of 110. The new set-up idled better, more power at every rpm, no detonation on pump gas, and it cranked out nearly 90 more HP on the dyno and 50 more ft lbs of torque over an additional 1000rpm power range. BTW, 2.25 pipes and no X or H is WAY undersized for a 455 of any make/manufacture. These big engines LOVE 3" head pipes and at least 2.5" after the muffler, X or H is an added bonus.......FWIW....Cliff
So I could go to a CK metering rod or an AX rod. Both would allow more fuel but the CK looks pretty close to my CD. Or do small changes in these rods yield bigger results than I'm thinking? http://quadrajetparts.com/mobile/qu...0-diameter-mp-163.html?redirectCancelled=true
AX are no longer made (that I know of) and difficult to obtain. We use DA's here, and machine smaller rods from those cores when the customer needs a set for tuning at the dyno or track.....Cliff
Thanks, it looks like AX is available at quadrajets.com Do you think the AX will be too rich for a mild 455? Another option is CK, which is supposed to approximate a stage 1 AU rod. Just wondering how much difference there really is in actual performance. Sent from my iPhone using Tapatalk
The CK is the same as an AU .0527" used in the stage 1 455. The AX is about .0397 and DA is about .0440. Experimenting with these 3 should cover all you'll ever need. Sometimes there are surprises out there. Some strong engines have used (leaner) CD or AY .0567" for best power. However, most stock or mild camed engines can count on AU or DA rods to be sufficient. Use only long tip rods, like the ones above and make sure your hanger has a high lift like a B or G, and be sure the cam that lifts the rods is not worn. If the taper is hanging into the .136 jet hole, your air fuel can be way off in the opposite direction. Your best bet is get Cliffs rods with long tips and careully machined taper that stair steps the sizes evenly above the straight tips. Stock rods go crazy in the tapered area.
Unless all the rods being used for testing are some upper section diameter, taper, tip length and angle leading to the tips it's difficult to compare them. I've been on the dyno and switched to rods with smaller tips and went leaner since they were not from the same cores. It also helps to be on a dyno or dragstrip for testing these things, and to be armed with a nice selection of rods and a few hangers as well. I have absolutely no faith in "seat of the pants" testing with these things especially when the metering rods are very close in dimensions......FWIW.....Cliff
