Hey guys I have just finished replacing a colapsed lifter, ajusting all the lifters, and setting my timing to 36 deg at 3000 rpms. I had to back off on the timing as it was set up near 40 deg. total. I put my car on the dyno and it put down 417 hp at the rear wheels with a 100 shot of nitrous. The fuel curve was just right up to 6200 rpms so my jetting is OK. My question is that when I run the car for 45 seconds at 2000+ rpms the #5 & #7 header pipes start to glow orange a little bit. My engine temp is a cool 170 deg. during this event. After I bring the car back to idle the orange glow goes away.

I spoke with a fellow racer and was told that the glow was a result of being too rich. The unburnt fuel burning in the pipes. I am running a colder than normal plug as I run with a 100shot of nitrous most of the time. If I increase my initial timing, I will also increase my total timing. I want to keep the timing at 36 total. I would appreciate any ideas that you all may have as to how I can stop those two pipes from glowing.
Thanks in advance,
Daniel

Get a temp reading of 6 and 8 also.
compare these with the rest of the header pipes.
If 6 and 8 are much hotter, I would say you need a larger plenum area in the intake. You could do that by a tunnel ram or different intake. Also, it could be that at 2400 or so, your secondaries are not open and you are leaner in the rear of the manifold. That in combination of retarded timeing will make headers glow. You did not say if you are running a vacume advance or not. If you are, you cant set the total to 36 with the vacume connected. It will be way retarded at idle.
I have never heard of too much gas making anything hot let alone enough to glow.

Just some ideas here. I don't really know the solution for sure.

Dave

Too rich... that sounds like to lean to me. Unburnt fuel will cool the header. Lean burn will send extra O2 out the header and make it very RED HOT. Can you change the fuel to air ratio?

You are running lean, nos systems have been known to have bad fuel balance with under carb plates, try running without nos and re-check. Also check those plugs and see what they look like, you need to be carefull here, taking off the end of the plugs off or worse the top of the piston, Rob...

I had just run the car on the dyno and the air/fuel ratio was right on the money with and with out the nitrous. My timing is set to 18 deg. initial and 38 total. The car is running cool and has plenty of power.
Danny

What was the timing at 2000 rpm? Do you have vacuum advance? What was the a/f ratio with and without the nitrous?

Daniel,

You likely don't have enough timing advance at the RPM at which you are seeing the headers glow. Advance the timing at the RPM you are experiencing the headers glowing. If that fixes the problem you will need to adjust your timing curve accordingly.

You can do this by increasing initial advance and limiting the amount of additional timing added by the distributor. There are several different ways you can go about this. Vacuum advance is another solution.

Example: At idle you have 16 degrees advance. At 3000 RPM and up you have 36 degrees. Therefore 20 degrees of mechanical advance.

My question is that when I run the car for 45 seconds at 2000+ rpms the #5 & #7 header pipes start to glow orange a little bit. My engine temp is a cool 170 deg. during this event. After I bring the car back to idle the orange glow goes away

Is this in a loaded or no load condition like fast idling at 2500??

I don't use a vacuum advance, and the 2000 rpm test was done under a no load condition. I tested the car on the dyno and had an appropriate air/ fuel ratio on motor and when I used the nitrous, the engine was a tad rich on the top end.
I have been doing some road testing and the car seems to be running very well. Since the fuel curve is slightly rich on the top end, then I should be ok, as the car is a 20% street car and a 80% strip car. It launches at over 3000 rpm, so it will not be hanging around at 2000rpms for very long.
How can I take a stock HEI and limit the timing to 38 degs? If I increase the initial timing, the total will also increase, creating problems when I use nitrousl.

We use an a/f ratio meter on our chassis dyno and it actually gives the ratio as a number. It will plot the a/r ratio for the entire run, so you can see what happens at any rpm. Terms like 'okay' and 'a tad rich' are not very informative. Since nitrous oxide contains more oxygen that air, the a/f ratio requirements for a nitrous engine will be different than those for a n/a engine.
The lack of vacuum advance probably causes a retarded timing situation in the lower rpm range under low loads, causing your headers to glow.
You can limit the total timing in an HEI distributor by limiting how far the weights rotate. CHP has a little tutorial on this.

http://www.chevyhiperformance.com/howto/46178/

If it is a no load condition it is completly normal for headers to glow. We see it all the time on the dyno during break in.
As soon as you load the engine the power valve or whatever circuit your carb uses will richen the engine.
If you put it in gear (automatic :D ) & foot brake it it should go richer.
I believe what is happening is you are confusing the carb.
You have high vacuum at 2500 with no load so the power valve is not opening & you are lean.
When you load the engine the vacuum will come down & it will richen up.

Thanks for the help and the tutorial. I'm sorry I did not provide the actual air/fuel ratio numbers during the run. I had the owner of the dyno checking the numbers through out the run. He verbally told me what was happening on each dyno run.
He sponsered the Street Rod class that I won last year, so he gave me 3 dyno runs and about 5 hours of tunning time for a total of $25. I just didn't have the heart to ask him to print out my runs, on top of everything else. We only looked at the computer data and discussed it.

Originally posted by Wolfplace:
My question is that when I run the car for 45 seconds at 2000+ rpms the #5 & #7 header pipes start to glow orange a little bit. My engine temp is a cool 170 deg. during this event. After I bring the car back to idle the orange glow goes away

Is this in a loaded or no load condition like fast idling at 2500?? Mike You are sure a good reader. I thought for sure he was talking under laod... nice catch! graemlins/beers.gif

Thanks Paul, we be tryin' :D