1.6TD Long runner heat shield

[moTthediesel]

This relates to Jake's great thread on intake manifolds, but I thought it might be best to start a new thread as a sort of side bar.
I'm putting an A2 long runner intake on my hotrod Quantum engined Porsche 356. I'll be using a VNT 15 turbo, and as I've be dealing with clearance issues between to two manifolds, I've begun to think about heat transfer from one to the other. Now it's true that the aluminum long runner manifold is certainly not an ideal heat exchanger to capture heat from the exhaust manifold, but I am worried that the charge air, so recently cooled by my Buick (of all things!) GS intercooler will be significantly reheated by radiant heat from the exhaust manifold. They are very close to one another after all.
How much do you all think this should be a concern? The charge air will certainly not spend much time in the manifold, and only a very small percentage of the air will make contact with the walls of the casting, so should I just not worry about it? On the other hand, I'm thinking that I could wrap the exhaust runners with the available insulating tape and then form a shield of say, 20 ga. stainless between the manifolds without too much difficulty.
Do you think it would be worth the trouble  :?:
moT

[greggearhead]

I think it is an important step - the whole 10 degree temp reduction equals 1% power increase rule of thumb.  If you think of all the surface area of the plenum and runners, that is a significant amount of contact area for air to absorb heat out of the aluminum.  

I would suggest a couple things.  There are some DIY ceramic coatings that work well.  Using it on the outside of the cast iron manifold and turbine housing WILL help, as well as using temperature to help keep velocity up.  The wrap stuff is a decent idea and works, but it does promote corrosion.  You could also use the ceramic coating on the intake manifold as well.

Now, if you are confident in the product and the application, you could also put it inside the intake and exhaust manifolds for even more benfit, but if it chips or flakes off, it could be very hard on the turbo or rings, etc.  

I think coating them and making a stainless heat shied would be a very good thing.  It has good potential to help, and no chance to hurt, and should not be very expensive.  Win win.

[fspGTD]

For my purposes, heat shielding is very important.  In autocross we take a run, then return to grid and wait several minutes (sometimes more like 20-30 minutes!) before its time to take the next run.  In those few minutes of letting the car sit, especially if the engine is turned off, the intake manifold can heat up STINKING HOT!  What I've noticed, is when it's "too hot to touch", it noticeably makes a negative impact on performance.  I tried all kinds of things... spraying water on it (lots of work, works only so long as the water doesn't evaporate off the manifold) setting a bag of ice on top (very effective!  But have to buy the ice and store it in a cooler until its needed... still lots of work), keeping the hood shut and idling the engine instead of shutting it off, while the radiator fan is manually switched on (I found this actually works amazingly well.)  But when a heat shield I made that went between the turbo and intake manifold broke (from fatigue/vibration stress), it was nearly impossible to keep my intake manifold cool.  I'd imagine the problem would be even worse with an unprotected long-runner intake manifold reaching over the top of a hot turbo... with all that surface area directly above the turbo.

If performance consistency is important, I would probably add a heat shield of some sort under that long-runner manifold.  While I don't think ceramic coatings beat a true metal heat shield with air gap on both sides, ceramic coating are very practical in that they don't rattle, fatigue/break from vibrations, and you don't have to work around then when maintaining the car, etc.  So they have a lot going for them.  A heat barrier coating applied to an intake manifold however might trap heat in, so if you were considering that route you might want to only coat the surface that is near the turbo & exhaust manifold.

[VWRacer]

I agree that heat shields will definitely work and are worth the effort on a racing or street/track car. For normal driving, though, you may not see any difference to your engine's perfomance. FWIW, just as important as the shield itself is ensuring that cool outside air is routed to and swept across both sides of the heat shield. The air carries away heat much more efficiently than radiation and conduction working alone.

Remember that in basic physics there are only three ways for heat to escape: radiation, conduction and convection. Radiation is what you feel when you place your hand several inches from a hot turbo and can feel the infrared radiation (heat) coming off of it. Conduction is heat transfered from physical contact (the intake manifold direcly touching the head and/or rubbing up against the exhaust manifold). Convection is the transfer of heat from a liquid or solid directly to the air, and the more cool molecules of air you bring into direct contact with a hot object, the more rapid the cooling effect. That's why autocrossers virtually all open their hoods between runs - to encourage natural convection. Well, if you use some dryer hose to route a column of air to the interface between the exhaust and intake manifolds you can take advantage of all three cooling effects. That's what I do on my race cars. Oh, and I glue the header tape to the side of the heat shield facing the exhaust to form a thermal barrier between the exhaust and the shield, further cutting down heat transfer to the shield, and hence to the intake.