rad_951

Got the head back from the machine shop and found the exhaust port sleeve were chipped near the valve. Was this done by the machine shop or can this happen with normal wear? Without the sleeve intact, is the head no longer worthy of track use or street driving?
Thanks in advance for any advice.

Tony

largecar379

regardless of how it was done, take them both back to the machine shop and have them all removed. you do not need them, and removing them will add flow if you port to match.





--Russ

ptuomov

I think that not everyone agrees with this approach. Some people feel that the low-rpm, low-boost throttle response requires higher exhaust port velocities. One group of that school of thought is here:

Quoting from http://www.lindseyracing.com/LR/Parts/LRHEADS.html

The exhaust port is a different story. A good exhaust port design should flow in the 600 FPS range. The stock configuration of the 944 Turbo is well shy of this, in fact it is less than 400 FPS. One option that some shops have tried is to take the 944 NA head and port and polish it on both intake and exhaust ports. The correct porting of the exhaust can increase the velocity as well as the flow. This is all well and good, but what is missing is the ceramic port liner that Porsche built into the Turbo head.

We felt that it would be beneficial to retain the ceramic liner if possible so Lindsey Racing has been testing different combinations on the 951 head to try and increase the port velocity without significant loss to the flow numbers. The problem is that the ceramic liner that is inside the exhaust port on the Turbo head cannot be altered, so porting the exhaust cannot be done. There is an alternative and we have discovered what that is. We now have found a combination that the exhaust flows 185 CFM with the velocity increased from a miserable 390 to an impressive 566 FPS! That is a 45% increase in velocity with only a 3% loss in flow rate!

Imagine what will happen to the Turbo when you hit it with hot exhaust gases that are moving so much faster. You guessed it, quicker spooling and increased HP. You expect more from Lindsey and you get it! This very affordable option is available on all 2 valve heads from Lindsey Racing.

The head is first disassembled and cleaned with a close inspection to make sure that the head is a good candidate for the upgrade work. One major problem that is noticed on about one in five heads is the ceramic\ liner in the exhaust port has begun to break up. This is a serious problem. Debris breaking off from the liner could damage the Turbo, and regrettably means the head is not worth going any further.

rad_951

Thanks for the responses.

You folks are smart! I accidentally posted this in the 928 forum and you knew it was a 951 head. I will contact Lindsey to see if they can help me out.

Tony
86 951
86.5 928

BC

The 928 heads for the early euros also have steel liners.

toofast928

Porsche used the steel sleeves in the 928 head to protect the head from exhaust temperatures. The 951 Porsche advanced to ceramic lining that is prone to crack.

A N/A 928 can operate without the sleeves. On a engine that is 20+ years old the sleeves are probably loose and falling out.

On my blown hybrid I decided to keep the sleeves. Removing them would increase the exhaust port, only to larger diameter than the exhaust manifold. This would disrupt the exhaust flow.
Last year I pulled 405 HP so I must be doing something right.............
Tony