Since the exhaust manifolds on our cars are prone to cracking, I was wondering if anyone had tried ceramic coating? I have watched a couple of Wheeler Dealer shows and they had it done to a couple of cars including an older Jag.

The benefits seem to be lower underhood temperatures, slight increase in horsepower but the main benefit may be a lowering of manifold temperatures and the resulting decrease in extreme temperature fluctuations that may lead to cracking of the cast iron. My exhaust manifolds seem to be crack free and I was thinking about getting this done as a matter of maintenance as a lot of them do crack with age.

Any thoughts, feedback on this?

 

Haven't seen 'em and know nothing of them, but your thermodynamics is not working out for me. Ceramic materials are generally good heat insulators, which would explain the benefit of lower underhood temperature. However, coating the outside of the manifold with a material with a low coefficient of heat transfer should not have any effect on the heat produced by the engine, that being a function of load, ambient temp and fuel-air mixture. Therefore, from the mainfold's perspective, "Same heat in as before, less heat out...I gotta get hotter.."

Therefore, the exhaust manifolds themselves would be experiencing higher ultimate temps, if anything, rather than lower, because the heat is released more slowly to the atmosphere through the ceramic coating. However, the cool-down time would be slower, so depending on your cycle-time between drives, you may have a lower number of critical-cycles (movements in either direction between hi/lo temps that matter to the cast-iron, whatever they may be..)

 

i had mine done about 5 years ago,due to several cracks in the old manifolds. I had the new manifolds treated in a silver ceramic coating,both inside and outside,yes the engine area temp is lower,i dont know if i got beter horsepower or torque, but no more air leaks.

 

 

If you coat them and they still crack? Ouch!

 

Something else I was thinking about on the exhaust manifolds was shot peening. I know that this is done on connecting rods, cranks and rear end gears to toughen up the surface and to prevent cracking. I was reading online that this can also be done on cast iron.

Any thoughts on this?

 

I very much doubt it. Cast iron, by definition has flakes of graphite in a microscopic network. This is weak and no amount of shot peening can improve its strength.

 

Actually if you do a google search for "can cast iron be shot peened" there are some interesting reports and papers written on the subject. There is a paper written by 3 engineers in England about the benefits of shot peening and also machining to strenghten cast iron. From the little I read on it it seems that besides the composition on the cast iron, the surface finish (which on most cast iron is very rough) has a lot to do with the formation of cracks.

According to their tests shot peening of the as cast finish or machining the surface of the cast iron and then shot peening resulted in stronger parts that were not as prone to cracking.

The reason I even did a layman's search was that I remembered seeing it somewhere that cast iron could be shot peened, also this time of the year in the winter I am bored and cannot work on the car and reading the posts almost every day makes me happy.

 

when i had my manifolds ceramic coated,i was told that the insides would be smoother along with the coating,so far ..so good..www.jet-hot.com.

 

works for me,, 22 years and counting, NO cracks or leaks,ceramic coatings.

 

Very interesting. It's on my list to check if mine are cracked and if so try the "boiler flue sealer" as mentioned in another thread as a cheap fix and I've used that literally on a boiler flue and is tough stuff even if one has to reapply it every few years.

But if I can find some relatively inexpensive uncracked headers I'll send them off to get coated... can't hurt, sounds like it might help and I generally have exhaust parts coated by JetHot anyway.

Thanks for the feedback/tip, as maybe this is the "fix" we've been looking for?

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