Vilhuer

Yes, GTS pistons are only ones which do not have them fully drilled from the factory. There was reasoning for that but it wasn't very successful idea.

Vilhuer

IIRR they should be ...xR as they are casting numbers. Raw casting can be made to many different cams and thus there is separate number stamped at read end of cam to show what exactly they are.

Vilhuer

This means connecting rods are still older and weaker type. See DR's message for how to tell old and new style GTS rods apart. If you have also S4 rods they could be used except that they are much heavier and crank would need heavy metal included.

https://rennlist.com/forums/928-forum/356382-16-995-93-gts-on-autotrader.html#post4247681

Boomerang Baba

Ok.
What exactly shall I do ones we start to really overhaul the engine?
Any specific information as to how to drill those holes? Once I have everything in bits, any tips on how to get more hp? Porting the tops I guess....! Anything else?

Tails

Erkka,
Correct, 1992 first introduction of GTS, however Boomerang Baba gave the engine type as M28/50 which, was first introduced in the European model GTS in 1993 whereas the 1992 GTS had a M28/49 type fitted.

I made a mistake with the valve lifts, inlet lift was 9.5mm changed from 10mm and exhaust lift was 8.5mm changed from 9mm.

I must have been drinking some of your high alcohol beer and not reading correctly. On my first trip to Finland I was drinking your great beer, however, I was getting a little under the weather and I asked for a Light Beer. To my surprise I was getting drunker and when I asked to see what type of light beer I was drinking I discovered that that was its name and it still had the high alcohol content. Heavy head next morning, but that night I was introduced to your Finnish White Wine.

Tails 1990 928 S4 Auto

Tails

SwayBar,
You asked for my source of information, 8 years of owning a 928, doing extensive reading and all my own maintenance and repair work, however, most of my technical information comes from Jim Morehouse's Technical CD, the WSMs, Technical Specification booklet, Service Info Tech books and the web.
Tails 1990 928 S4 Auto

Louie928

Since you have the heads disassembled, don't use the GTS exhaust cams. S4 exhaust cams work better. For even better performance, use GT cams.

IcemanG17

Or even better performance get Devek B1 cams like Louie and Tims monsters are running!

Vilhuer

M28/49 is manual gearbox engine for all '92-95 GTS while M28/50 is automatic engine for all years. Only difference is vacuum line to automatic gearbox and maps in LH and EZK box. Piston and piston rings were changed in '93 MY and connecting rods in '94 but this didn't have any effect on engine numbers.

S4 has 9mm intake and 8mm exhaust while GT has 10 intake and 9 exhaust.

http://www.928developments.com/stree...t_packages.htm

SwayBar

I've been wondering about this very question: do you know whether the S4 exhaust cam indexes properly with the GTS intake cam? In other words, can they be mixed and matched and retain their independently stated valve timings?

And one step further: does the GT exhaust cam index properly with the GTS intake cam?

I wonder how that big cam will run with a smaller 5.0/5.4L engine?

Boomerang Baba

Hi,
I do have a complete S4 engine in bits. Mostly in good shape...
Can I just slide those S4 exhaust cams right in with the the rest?
Oh by the way I just delivered my S4 manual `89 to Henrik Fries in Gothenburg to complete the work on the supercharger install! He is going to map it up and install antoher brain...!
I will get it back next week. Should be fun!
His heavily modified `78 racer was in his garage. Impressive work. Screw compressor on a 4,5 liter block. Light weight. Nice.

Cheburator

Funny you should say that - I finally took my MY1995 GTS pistons out of the block to get them cleaned and balanced. The oil return holes are there and they have been drilled by Porsche. Am I missing something here? Can try and post pictures if you need them

Alex

Louie928

Use the stock GTS cam timing. The S4, or GT, exhaust cam will be "close enough". After it's all running, you can advance/retard the cam timing to get the torque curve you want.

Vilhuer

Are they drilled all the way through or are they blind? If they are all the way through those pistons are not normal GTS parts. Normal GTS pistons have eight blind holes, at least early version.

Hopefully in few weeks I'll have another early GTS engine to compare. Sadly it has suffered similar block death as my first one. Block has cracked due to head gasket failure. If I'm lucky, crank, heads and seven pistons are all ok.

Cheburator

The pistons have 8 holes, which are round in shape, and not oval like on some GTS pistons and go all the way through the material - just like on earlier S4/GT pistons. The pistons do have Porsche Part Nrs on them, however I don't know what material they are made of, since Porsche installed dry liners in my block in the factory. Remember, my engine is one of the very last ones. The liners' material seems to be steel, but I cannot be sure.

Another interesting fact - the most wear on the conrod bearings was observed on cylinders 1-5 and not on 2-6. The only barely visible singns of wear on the piston skirts' was observed on cylinders 3-7. The engine had done 20,000 very hard (service on schedule, but pedal to the metal at all times) miles before I bought it.

I do intent to re-use the original Porsche bearings - too many bad stories about Glyco being too tight on this list. I am not so sure about re-using the conrod bolts, but there is a part of me thinking that I will get away with it just once Opinions?