993inNC

Stedge, those sheilds are .....aluminium (correct Bill) which disperses the heat prior to cooking the V.cover. And as far as the wrap, Roberts correct, that header wrap will rust a set out in no time. Yoy'd be better to get the Jet hot coated and go for the heat shields. I did my cover gaskets recently and they are bone dry still. The only thing I disagreed with on I think it was that P-car DIY was that the author recommended coating the gaskets in oil before installing them in the cover......? Why? Won't that just lead to the gasket drying out and or allowing new oil to follow the oil on the gasket and right out the cover..? Just my .02 cents

k00k

I'm not sure, but I think its to get a nice positive seal on the gasket when you tighten them back up.

cheers
Mal

deltawedge

An old British (both car and person) mechanic passed on a trick he used for those total loss oil lubricated vehicles the British used to sell in the 50-70's. He put a glaze of wheel grease around the rubber gasket for the valve cover. This also had the benefit of holding the gasket in place while you got the cover in place. The wheel grease doesn't thin very much when it gets hot, so it isn't as likely to let the motor oil out. Just another data point, for what it's worth (I know, nothing).

chris walrod

Robert and others, you are right-on about the header not lasting long. Yes, the thermal wrap works great, but headers dont last for more than a year or so of driving.

The heat-sheet is a cool idea, but much more effective if made out of Ti..

User 4221

Thanks for the feedback guys. Very logical about the headers deteriorating. I think I will skip this step on re-assembly.

Chris,
I was looking at the Heet Sheet and noticed it was made from stainless steel...... Pretty hefty stuff.

Thanks again guys.

Toga

We will arrange something. Monique is not far either. A rennlist meeting in Belgium? Why not? As soon as you have the dates we could start a topic on that!

duc916

I would think the best material would be carbon fiber. As it does not transfer heat (compared to aluminum or allow steel), even thought it is black and be more apt to get hot due to radiant heat. The aluminum can still get hot (radiant heat from the headers and convection heating from the hot air off the headers) and radiate the heat back to the valve cover. And for the **** retentive weight / cool factor it would be the lightest also.
Chris, you have much more experience with CF (since it is not allowed in our series very much), it this contrary to your experience?

Dan


Dan

chris walrod

One would think that c/f would be best at heat rejection, but we have found this not to be the case. At least not the case with the epoxy composite resin systems that are commonly utilized in the racing industry. Phenolic resins would be best, but we dont see the demand to tool-up, so to speak, for this type of resin. We do make some parts of the sidepods (near exhaust headers) from a high-temp epoxy prepreg, which requires post-curing and its messy, knarly, PIA product to trim and fit.

For areas near turbos, headers and crossover tubes, we have found Ti sheeting is still best for heat rejection. Not saying there isnt a better material, but given cost vs. availablilty vs. workability, Ti, so far, is best from all standpoints (for us). It is difficult to machine due to its work hardening personality, but we keep the Ti design criteria in the fabricated catagory

duc916

Chris,
That is very interesting. The reason I figured the CF would work is I have CF exhaust cans on my Ducati and have seen them on a CRF450. The can is warm to the touch, but never as hot as aluminum or stainless steel cans after a ride.
We have used them for heat shields above the exhaust below the valve cover for 24-hour of Lemans with no issue, but I have no knowledge of what resin they where constructed with.
Do you have coefficient of thermal conductivity for the CF, I have data for Ti. I would expect the coefficient is magnitudes larger for Ti vs. CF.

Dan

chris walrod

Soon, I will ask our composite engineering staff about the Ctc for typical CF. Definitely would be interesting to look into..

chris walrod

Following is something I found online: I will find out more tomorrow..

Properties for Carbon Fiber
Property Value
Material XAS,HTA,T300 34-700, T650/35 UMS2526 HM HS40 P25 P100 F180 F500
Coefficient of thermal expansion - Longitudinal x10-6 K-1 -0.1to-0.5 -0.6 -0.7 -1.3 -0.5 - -1.5
Coefficient of thermal expansion - Transverse x10-6 K-1 +26 - +37 +25

Thermal Conductivity W m-1 K-1