This was my Plan:

5.0L conversion of my 4.7L 83 EuroS which is starting out with 300HP, maybe 335HP with my nickle coated MSDS headers, Borla free flow exhaust and bored out thottle body. Then the extra "cubic inches" that 5.0L would maybe bring it up to 350HP.

Then comes the Vortec Supercharger. I am starting with an S4 block which would have lower compression than an 85-86 block and pistons, about 8:1 , so crank up the boost to maybe 12 psi and I figure about 525 crank HP - 450 RWHP .

Only one problem and its major.

Two cracks in the lower block girdle of the S4 motor. I am trying to find out if they are able to be welded.

I will try to post some pix, next.

 

Here is the car and donor S4 block

 

Another shot of a beautiful beast!

 

Please take a pic of the cracks and post them. Ive done some block repairs and diagnosis on aircraft engines, that was my business for a while. would like to see them to tell how they may have developed and if they will spread.

 

I thought that only the '85-'86 block would work with the early heads. Is that wrong?

 

Gerry,

...as you know, I too was going that route...and I'm changing my mind towards supercharging the S4 motor instead...and every now and then I reconsider the initial plan...but wanted to point out the following:

Are you sure you will yield 8:1 compression in mating the S4 bottom end to 16v heads? when I considered this in the past, I spoke to some people, and the conclusion was that it would yield 7:1 compression. I could be wrong of course, depending on how you got to compute the resulting 8:1 compression

Now also remember that you lose at least 3% per compression ratio point.

Assuming your 335hp figure is correct, 3x(3%) loss will knock you down to 305 hp at the crank.

Your plan might still be a more affordable way to go, but it seems to me (in my case) that supercharging the S4 would yield better results without having to mess with engine management or convert to MAF, or lose low end crispness due to low compression ratio...not to mention the room under the hood for an intercooler in the case of the S4

 

Yes, that's incorrect. There was at least one around with either an '89 or '90 5-liter block and '83 Euro heads and intake on it.

 

The S4 pistons will yield a low compression when used with 16V Euro S heads. You can use any 5.0L block as long as you use the 85-86 US pistons. Gives you a bit over 10:1 compression.
I think it's between 7:1 to 8:1 using S4 pistons. You would be better off with 944 pistons if your going to turn up the boost. Just remember that the motor will be a dog at 7:1 until the boost comes on.

 

Warren:

Can you fix this one? It is in the Girdle only and one like it on the other side. The engine was roled over on its alternator in the shop was what I was told and could not be seen until the brackets where removered by me.

 

Maybe the way to go would be to use 944 turbo pistons!

 

Gerry
It would depend on where the cracks end on the inside of the girdle, as you can see on the Left (drivers side LHD) there are oil passages.

 

So it works, but without the pistons there's likely a loss of power.

Also, I've heard that the '85-'86 pistons must be notched.

This is a popular upgrade. Anyone made a reference for it?

My engine is likely coming out this winter and depending on how the bores look I might be considering this.

 

That crack started at the bolt hole. Yikes, that's ugly. It's as though someone over torqued (which is unlikely in alum.) or they used a bolt with unthreaded shoulder. But it could be that another source, altogether, caused the force neccisary to crack it.

 

When I considered this option, this characteristic was an advantage, as it allows for comfortable street driving and better fuel economy. And this was comfirmed to me later when driving Eric's Dvorak's supercharged S4 with stock engine internals. The thing wants to JUMP all the time and is difficult to drive slow. Pretty annoying actually. I do believe 7:1 CR is worth looking into for smooth driveability as well as safety at the upper boost/critical temperature limits. That's what the 911's have, so it's not unheard of. Then again, I don't know of a boosted 928 with 7:1 CR out there. We'll see if Gerry or I will be the first to do it

This DOES bring up another inquiry I have: Mating a GTS block with 16v heads. Anyone knows the resulting CR? I'm guessing in the 8:1 - 8.5:1 range. But just a guess

 

Pistons: 944 turbo pistons should solve the compression dilema. They are deep dished and strong and should yield about 8:1 compression and are proven under heavy boost.

Girdle Repair: Has anyone out there done a crack repair on this thing or should I just find another block which is rather hard to do? Jim from 928 Intnl says you cannot inter change a girdle from another engine because they are mated for life.

I will separate the block in the morning after I remove the heads and pistons and will post more pictures after much needed sleep.

To be Continued!