What hanger and secondary and rods should I use?

[RC81]

If anyone has changed theirs from stock please post up what you installed. I dont know if there is much to be gained by changing. Thanks.

 

[Peer81]

If you don't know if your running rich and how much then it's hard to say.
I was thinking the same thing a few days ago and came to the conclusion that with the new exhaust system I let them weld on the left and right side a opening for a co bug. Then on the right side I can plug in a co bug attached to a fuel air ratio meter to see what the mixture is under load etc etc and adjust the carb to get is perfect.

But maybe it's also possible to datalog from the ECM but that I don't know.

Greetings Peter

 

[Tom Bryant]

This is an interesting topic. I'll be interested to see what is said on this.

I did this on my wife's '77 Trans Am years ago. I just couldn't believe that a 400 inch engine could be that sluggish. It was low miles and in excellent tune. Knowing that emissions era carbs were severely leaned out I figured that going back to pre-emissions secondary rod sizes would make a difference for the good. I didn't mess with the primaries since it ran and drove beautifully.

I ordered secondary rods for a '68 or '69 400 Firebird or GTO engine from GM and they were drastically thinner than the fat boys in the carb. I had the desired hanger in my stock of Q-Jet parts and installed that also. (don't have any record of the numbers) I had already played with the timing a little so this was the only change at the time.

I could feel a little increase in acceleration and my stop watch 0-60 mph and 50-70 mph time dropped slightly. Drivability didn't change at all nor did mpg.

I think what I learned mostly from this excercise was that there was not going to be any shortcut to performance for this engine. With the fuel and timing sort of optimized there was no place to go but inside the engine. The '77 400 had only about 7.5- 7.8 actual cr and very small valves and ports. A camshaft change to one that would increase cylinder pressures would have been the next step but the heads were the real performance killers. I had no desire to take the engine apart so this is all the further I ever went with it.

Also my wife had a test tube (replaces the cat) on the car and it rusted out. Very thin and cheap steel. I put the cat back on and experienced no change in 0-60 or 50-70 times. 0-100 was off just a little.

Tom

 

[damoroso]

If your in stock trim, I don't think there's going to be anything to be gained. What problem are you trying to solve?

 

[Sensei]

There are several performance upgrades that can be made to this carb, including secondary rods. But just a rod change by itself will probably not make a noticeable difference. You might try a set of Edelbrock 1951 (CE) rods and see what happens.

God bless, Sensei

 

[RC81]

If your in stock trim, I don't think there's going to be anything to be gained. What problem are you trying to solve?

I dont have any problems actually. I have a rebuilt carb from National I recently put on, then I spent several days dialing and setting it up. I set the TPS voltage to the correct setting, the choke the way I want it, the idle speed to the rpm I desired and the air valve to open when I wanted. After much on the road testing it runs great. I have Doug Roes book and he goes into detail on the secondary circuit and I was wondering if there was anything to be gained by making some changes. Without testing on a dyno its probably hard to know. Seat of the pants feel is sometimes deceiving as we want to believe the changes we make are actually making us quicker!!

 

[damoroso]

Sounds like you're well on your way! I agree with Sensei, you can try the Edlebrock rods, Edlebrock actually makes a tunning kit for these carbs (actually for the Edlebrock replacement, but the parts work!) that has several sets of rods and other parts. I've used Cliff Ruggles book and spent some time on the phone with him and he too goes into detail on the secondary circuit, so there are certainly mods that can be made. Aside from mods/adjustments to the air flaps, I'm still not convinced changing rods will help on a stock engine, but hell, I've been wrong before, just ask my wife!! I'd be interested to hear if you do gain anything, let us know what happens.

 

[RC81]

The only mods to my car is a mild cam and some exhaust work, so maybe I should leave well enough alone. Sometimes I have a tendency to fix things untill there broke!