J Tubes/exhaust system

[ScotMcLean]

Anyone have experience w/ J tubes?

I live in sunny (too much at times) Arizona and thinking the removal of the heater boxes might allow more air flow and a cooler running engine.

Thxs - Scott #3078 69 912

[Scat(\/)an]

I don't have any direct experience with a 912 exhaust - I assume it's similar to a Type I VW setup.

The construction of the heater box is such that the outer shell is considerably cooler than the exhaust tube inside it. If you ran j-tubes instead, you would have a larger source of heat running directly under the heads. As a result, the heads run hotter. You could wrap the j-tubes in exhaust wrap and insulate them as much as possible.

I don't think removing the heater boxes will increase airflow, but It will remove some weight.

[ScotMcLean]

Hi - Thanks for taking an interest. I have heard and see your point of view, but there seems to be conflicting stories. For example, on the 912 Registry site (great site Rick) at:

http://www.912registry.org/tech/exhaust.htm

Exhaust and heating systems are discussed and two 912er's say they use J tubes with cooler results. I've also read about using a VERY thin coat of high temp black paint.

If the pipes are surface rusty, would rust convertor (changes rust to a polymer, looks black) be good or would the change actually retain more heat?

[mein12]

Regarding heat, you can ceramic coat your exhaust and reduce heat as much as 30% in the intake area. You will also reduce heat flow to the block. Flow gains will also be realized using this coating.
The best part is that the coating is almost polished aluminum in color and does not fade away. Check out this link www.hpcoatings.com.

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68' 912/5 modified brakes, suspension, limited slip trans, hi performance engine.