Cracked Exhst Port Ceramic - how bad?
10-04-2013, 08:14 AM
#16
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It has nothing to so with heat or steam pockets.
The ceramic liners were used to keep the heat in the exhaust to help spool the turbine faster.
Which is also the same reason the turbo head has the hump on the exhaust port floor (which is to increase the velocity of the exhaust gas).
On the race engines we used the N/A heads which don't have the ceramic nor do they have the hump on the exhaust port floor. This because we could get better exhaust port numbers from the N/A head vs the turbo head. Excess heat was never an issue.
That said, I see no reason why he couldn't just remove all the ceramic and have the exhaust port ridges (where the ceramic meets the aluminum) blended and call it a day.
TonyG
The ceramic liners were used to keep the heat in the exhaust to help spool the turbine faster.
Which is also the same reason the turbo head has the hump on the exhaust port floor (which is to increase the velocity of the exhaust gas).
On the race engines we used the N/A heads which don't have the ceramic nor do they have the hump on the exhaust port floor. This because we could get better exhaust port numbers from the N/A head vs the turbo head. Excess heat was never an issue.
That said, I see no reason why he couldn't just remove all the ceramic and have the exhaust port ridges (where the ceramic meets the aluminum) blended and call it a day.
TonyG
Is it possible, that ceramic is there to keep the difference in temperature between the exhaust valve and head?
Isn't it true, that in order for sodium filled valve to transfer as much heat to head as possible, port and guide should be as cold as possible, so that temperature can transfer faster and more efficient?
Could it be, that part of ceramic solution is actually ex. valve cooling?
10-30-2013, 09:36 PM
#17
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A fellow racing buddy installed a freshly rebuilt head that was discovered to have some ceramic cracks so as not to miss a racing weekend. After a few track sessions, the car was fired up for the next session and ... zero power! The car had hardly enough power to load itself on the trailer. You guessed it, the ceramic broke up and fully jammed the turbine. Luckily the turbo survived, possibly due to the low RPM at start-up. Below is a picture of the head where you can just make out the missing ceramic - basically the whole floor of the port sloughed off!
The car ['87 turbo] is now under my ownership after spinning a rod bearing on the track later in life!
John
The car ['87 turbo] is now under my ownership after spinning a rod bearing on the track later in life!
John
Last edited by vette951s; 07-19-2015 at 12:07 PM.