Raceboy

edited title for clarity - RV

This is somekind of cross-road to me as I'm really tempted to buy a '87 S4 that is listed near me and I always fancied the idea of a turbocharged 928 32v.

I bought those pistons for my 2.5 16v turbo, but it's not too often when you get a hold of 8 of them.
Also, I have brand new KKK K31 turbo that suits fine on the 5.0liter engine, has twin-inlet turbine and nicely designed compressor wheel.
As I install VEMS engine managements and done this on 928 also, that won't be a problem also.

I have the skills, facilities and even a bit of cash to throw at it, just my other projects are not done yet. Then again, I've got almost all that I need for proper turbo conversion.....

I'd appreciate if you guys pint me in the right direction or just a wake-up call

BC

The 951 pistons are a bit short. You will either need to buy some custom rods, or figure out how to offset the pin on the current 928 rods to move the piston UP.

Vilhuer

There is third option, take out 2mm from the block deck. This will create whole other set of problems, especially in S4, but they are solvable.

BC

Yeah, I restricted my comments from that, as it does cause issues. Maybe taking enough out of both the head and the block, but then that raises compression even more.

I was reminded Via PM that there is a working motor doing this exact thing with stock everything with the 951 pistons, which makes that one in Green bay, and one in LA. Both have a very very low 7.3 or 7.5 compression ratio.

Raceboy

...in the meaning that it results in a way low CR or upsets squish area by too much?

Custom rods are quite a hack to the wallet but I could get my machinist to make the offset bushings as he purchased new coordinating bench for this kind of work.

EDIT: Ok, got the CR info, thanks.

Milling down the block is not a bad idea since there are adjustable cam pulleys and it can be dialed out. Correct me if I'm wrong.

Vilhuer

Has anyone done calculations what CR decking block to piston top level have in 951 piston + S4 head combination? 8.0:1 perhaps?

Vilhuer

S4 intake do not line up to heads just right as heads move closer to each other. That is only semi serious problem I can think of. Thermostat bridge is more minor detail.

Raceboy

Intakes will be in any way custom units made of aluminium so that issue can be ruled out.

Tony

http://www.marcus3.com/engine1/engine1.html

Raceboy

Thank you Tony! Excellent gallery!
Any more info about the engine? I mean, I've always concerned about the longetivity of a Nikasil/Alusil cylinder wall coatings when they are not freshly treated...

And here's some pics of the K31 turbo I have. It flows a nice 76lbs/min and has perfectly sized turbine for 5.0liter engine.

martin D

Woooooaaaa.............Just in case you've picked up one of the many myths about the 928 blocks (applies to the 951 as well)........Nikasil & Alusil are two different things. Nikasil is nothing to do with the 928 (unless you get the bores plated with it). Alusil is the material the 928 blocks is made out of, it is NOT a plating /insert/liner. It seems to last forever eg 200,000 miles & no bore ware.

Raceboy

Sorry for the not very accurately asked question.
I have pretty good experience with 944/951 blocks and they tend not to wear for some time and then a sudden disaster. Cause: coating is just worn out.

If I understand correctly, 951 and 928 blocks have the same treating?

martin D

No problem, yes944/ 951 & 928 blocks are made out of the same material , Alusil.
It is not a coating/treatment, it is what the blocks are cast out of , just like a cast iron block would be made. The pistons of the 944/951/928 run directly on the bores, the alusil bores.
"and they tend not to wear for some time and then a sudden disaster. Cause:coating is worn out" , in what way ? .
Down load the Reconditioning of Aluminium Engine Blocks
That should help in explaining things far better than I ever could

Raceboy

Thank you.

ceedee

is the cell phone there, in order to dial in the turbo?