Exchanges on my 930 Getting Red Hot

[rboylan]

Boys,

Its always something.

I completed the exhaust update on the 930 motor today. I recently updated the exhaust on my '79 930. I replaced the thermal reactors and exchanges which were originally installed on my '79 with 86+ exchanges and crossover pipe less Catalytic Convertor. At the same time I upgraded to a K27 Turbo.

I completed the work this evening. I ran the car at idle for about 10 minutes. While running I noticed the Exchanges(inside the shell) were getting red hot on both sides. I noticed becuase I did not hook up any heat in the car and I could see thru the holes in the rear of the exchanges. There appears to be normal flow from the exhaust and the temperature gauge is not reading a high temp.

What could be causing this ? Any help would be greatly appreciated. Thank you.

[dean]

Lean mixture or retarded timing. It might be a normal cond. I have never looked at mine. So I don't know. If I were you I would check the mixture and timing.

[Doug Zielke]

Well, I'd guess that running at idle, with not much air flowing around the pipes, might get you some red heat.

[rboylan]

After checking the plugs, the mixture condition is more on the rich than the lean side.

I never looked inside an exchange before so I'm not certain whether the condition is abnormal.

It definitely doesn't seem right.

[A Quiet Boom]

It is very difficult to read plugs with todays fuel blends, I suggest either installing fresh plugs and then taking a reading or invest in a AF meter, they intall in the exhaust with an O2 sensor and have a digital readout on the dash, about $90 from a speed shop and very useful. If it's not lean then it's either an obstruction or retarded timing, if you're only idling the turbo is somewhat of an obstruction and could be causing the heat build up but I don't think it should be red hot since that would eventually anneal the metal and severely weaken the exchangers. On the other hand this could be somewhat "normal" with the factory figuring the air from the heat ducts would cool the pipes enough. Many factory turbo cars use either heavy guage tubing or cast iron manifolds as opposed to porsche's thinwall tubing so this is a possibility. Wonder what the headers on a GT1 look like after extended idling?

[lukeh]

Mine glow red after running the car hard and was told this is normal. I also seem to remember on thread on this subject. I don't know if this would be normal at idle though.