Some say that it is better to not use exhaust manifold gaskets because it would slow down heat transfer from the manifolds to the heads. What is the theory behind that? Would it cause for a higher risk of cracks in the manifolds if gaskets are used? Thanks.
I have read that the heads and manifold expand from heat at different rates. That is why most gaskets eventually fail. It would be better to not use a gasket if you have a good seal (straight paralell surfaces) between the head and manifold. There is no benefit that I can think of to better metal to metal heat transfer. The manifold heats up from the exhaust gases.
Lay them on a surfacer and they will be shiny and flat in a minute. Then install without gaskets. Never unbolt them untill they are totally cool. Never had problem with my 400, 430, 455's.
I stand corrected - the heat transfer occurs from the manifold to the head causing it to run cooler. From another thread:
Understood. But when headers are used there is a gasket installed, so in theory it would run hotter. I am still not sure if it is a big deal or not.
The use of the proper ramp lock bolts, torque to 18 foot lbs, is critical for long term success with iron manifolds and iron heads. Surface both the heads and manifolds for the best results. JW
Gaskets hold moisture and rot, causing the manifold surface to pit and degrade too. Also, putting those soft gaskets in will cause the manifolds to warp due to only being torqued down on those two corners. Then you start breaking ears off, etc. I’ve had two cars in here this summer that have had exhaust manifold leaks, all because the gasket went tits up and blew out. Surfaced manifolds and reinstalled with no gaskets. Problem solved.
Thanks. If original without gaskets is that good i wonder why my factory original RH side exhaust manifold suddenly started leaking at the firewall side?
True......i was thinking that the california climate helped to prevent from leaking a very long time. The car is here in The Netherlands since january/february 2006 although stored inside but unfortunately not climate controlled. It would probably still be good when still in California??
Be careful getting them surfaced....I gave a nice pair to a machine shop and they called me and said after surfacing they were all cracked and they went in dumpster. Was pretty pissed.....surfacing equipment hard on them? Would have liked them back or see them...WTF? Maybe someone else needed a pair. I don't have good luck with machine shops and bodyshops...... I dragged out another pair and surfaced them myself using a piece of plate glass and progressing sanding....took a while but perfect. And no cracks....
cracking should be no issue, the proper equipment to service and flatten exhaust manifolds is a big industrial size belt sander.. JW
