Hi Guys,
Sad to report my GTS engine is kaput! (170,000k, auto,Murf- Vortech 2 supercharged)
No. 2 cylinder has a nasty Y shaped crack extending the length of the bore(of sleeve). I was suprised to find all cylinders had been resleeved and the cylinder itself had also cracked in a straight line along the sand seam.
The symptoms occurred within 5 minutes of starting up after an intake manifold refurbishment, including some over revving(not excessive) as a result of a misaligned cable clamp on the throttle cable bracket.
It is still a mystery as to cause, suggestions are, The engine may have been seriously overheated at some time in it's life, the resleeving process has taken too much out of the cylinder or water has entered from an external source. The coincidence of it happening straight after Manifold refurb is inescapable yet it started and ran before water vapour appeared in exhaust. The vehicle has been driven quite sedately in spite of the SC and I don't think it is a factor in this event.
I intend to rebuild the GTS motor from 91 S4 block, as far as I can tell the only differences I need to address are
1 Replace crankcase studs with bolts
2 Machine 3 passive oil drain holes in block .
I would appreceate feedback from anyone who has "been there, done that'' or any comment on rebuild in general. Especially with regard to what else should be renewed or improved 'while I am in there"
I read other posts suggesting it may be necessary to machine block to take con rod movement in lower half of crankcase, is this the case??
TIA

Ray
94 gts/S4

 

One interesting alternative would be to go for a block from an early '87 engine with the oil squirters.

Speculation in previous threads about the squirters is that they were added when Porsche was considering making a boosted 928, for additional cooling of pistons and in turn the cylinder head.

A search for "oil squirter" will bring up a few threads:

https://rennlist.com/forums/showthre...t=oil+squirter

https://rennlist.com/forums/showthre...t=oil+squirter

 

if the 87 had oil squirters, they probably tapped into a high pressure oil line inside the block. That line is probably there in every 928 block, you just need squirters and you can potentially machine a hole and add the squirters right.

I dont know how the 928's system worked, but i was very familiar with BMW M60 M62 and the M5's S62 engines. The M version used the stock block but added squirters, what you could do to the stock 4.0 and 4.4L was machine a way to mount the squirters (which just look like little tiny spigots pointing up) and you have "oil squirters"

Again not sure if you could modify a later 928 block to do this. I think they run constantly and would then only reach the bottom of the piston when it was at BDC.

 

What about the 928 engine block that was sleeved on the outside of the cylinders for strength needed for boost applications. It is in perfect shape and will not be used in the rennlist sponsored
engine buy for the Holbert racer. I believe Murf is going to sell it, or build another stroker for boost with it.

Murf???

mk

 

Hi Sterling,
I have actually got the '91 S4 engine already. I went for a later model, thinking it may have less wear. I was also advised that the S4 block was the best match for GTS crank and pistons etc.
Thanks for your suggestion
Ray

 

Mark,
That engine also has a custom bore so stock pistons will no longer work. Not to mention shipping an engine block to Austrailia can get expensive.

Not saying it will not work, just a few obstacles getting there and using it.

 

Read up on this thread as there is lots of GTS-centric information there:

https://rennlist.com/forums/928-forum/368494-wtb-gts-rods-late-model-revised-style-only.html

Ryan, they crack open at 3.5 or 4.0 Bar oil pressure.

 

Well, just a thought! Arent there already pistons in the block? so, you would need those and some special rods to fit them with a GTS crank, right?
by the way, since the sleeves are on the outside of the cylinders, what pistons are being used? special with the speical coating that a 928 piston would have?

thanks,

mk

 

No need to. You can use studs and its good to use them in SC car. '92 MY GTS engines use them too.

No need to. They are nice to have but they are not just drilled holes. Block casting around holes is also different and this means drilling earlier block might cause problems.

Its possible they are not needed. Only way to tell is to put bottom end together and see how much space there is.

Most likely you will need at least one piston to replace one which was in broken cylinder. Unless you use 5.0L pistons. In which case you obviously need to use crank from '91 engine also.

I have seen two S4 engines where all eight cylinders were sleeved with Alusil. They were beautifully done and I suspect where done by factory. Both blocks were standard S4 blocks without anything special in them. There is no point in sleeving all cylinders unless block material is somehow wrong mixture and sleeving can be used to save the block.

 

Hi Erkka,
Thanks for the comments on S4 block conversion.
I guess I'm starting to doubt the prudence in supercharging a GTS after reading of so many problems with them.
I am now considering supercharging the S4 engine(currently installed) and continue researching the suitability of rebuilding my spare S4 into GTS for supercharging. If it turns out to be worthwhile I can make it a long term project and take my time.
I would be keen to hear your thoughts on supercharging a GTS also would there be any problem with using the GTS intake manifold/throttle set up on the S4 engine(using GTS wiring harness)
Many thanks for your help.
Ray
94 GTS/S4

 

Your '91 S4 and GTS intakes are identical IIRR. Without checking I would say even engine wiring is exact same.

Really beneficial parts for SC build in GTS are heads but virtually all '91 S4 and GT engines have them too. Late S4 which use different style pistons than early S4 have true 10.0:1 compression while GTS has 10.4:1. So in your case its down to if you want to modify S4 or GTS pistons to lower compression ratio. In the end .4L displacement difference doesn't mean much and in my opinion it would be very good good to modify pistons in both cases. I would go with S4 parts as they are much cheaper and easier to find. Not much point at bolting SC if it needs to be run on only few psi boost and thus low CR is really a must.

 

Hi Erkka,
I think the difference in wiring is only the throttle position sensor -gts having dynamic kickdown.
My style of driving and road limitations here means I would probably only get to boost on rare occasions - it's just comforting to know I can when I need to. Considering this use is there any downside to reducing compression ratio and would it be possible with rings alone.

Cheers
Ray
984 gts/s4