Yes, pin to top of piston is like nearly 4 mm difference. I would never do that, besides the 951 pistons are just outrageously priced and why install some used pistons anyway?. You could install a longer rod and it would work. I'm planning to pick a conservative CR for my twin turbo S4...but not sure what just yet. I know where it is now is too high for the power I want to make. If you want the engine to make a lot of power and not be a hand grenade, then forged pistons are an absolute must. Remember, the turbo car will offer full boost much earlier than a centrifugal car...so the pistons will be seeing a lot more boost with turbo induction as compared to centrifugal. It is a function of load.

8:1 is probably very safe...but I think those heads can handle more cr and still allow a lot of boost to be run. 8.5:1 might be a real nice combo...remember, you still have 5.0 liters of displacement on that car. I'd highly recommend you go Nikasil plating on the block, then have a custom Wiseco, JE, Arias or the like made...then you get precisely what you want. Doing that gives you an entirely new combustion wall and pistons and still will be less $ than the 951 new piston and longer rod option.

What turbos are you planning to use? Tammons is dead on...you must do timing control as you add boost. Lowering CR is only part of the picture, you balance ignition advance, fuel octane and boost pressure. If you try to run full ignition advance and all a lot of boost you will have issues. With stock guts I would not run over 7-8 psig.

 

Personally after running 2 different 928 setups, I would run 9:1, Custom forged pistons/liners, rods, somewhere around 50# injectors, water to air intercooler, stock heads and cams, and a Tec III with a wide band and a fluidyne 3 core radiator.

Its not that hard to install the TecIII. The hardest part is getting the trigger wheel mounted to the balancer. I had originally planned to build a 32v turbo motor, but just thought it was too much hassle and expense. With a setup like that you should be making around 600 hp or enough to blow transmissions and clutches.

 

Hey...breaking parts is what it's all about! I'm not crazy about stand alone for street cars...my setup will keep all the stock injection in place for excellent economy and the ability to get it certified if I go that far. 9:1 I agree with...I think that is a good number for the 4V heads, though I could push more boost with 8.5:1. I'm not sold on the air-H20 and I think I'll be doing air to air on mine. I'm also not a fan of liners on the 944/928 motors...you can run much tighter with Nikasil and the cost is a lot less...the ultimate would be a custom piston compatible with the 390 block..but they just don't exist.

I don't see where the 32V will cost more than a 16V conversion...same stuff just different! The nice part is you can blow out serious power and you don't need a fancy exhaust system to do it.

Hey...that tranny just may hold more than you think...though the clutch is a different ballgame...most likely need a twin disk.

 

A general rule of thumb for any turbo car is better flowing exhaust= less lag.

"Fancy" exhausts are most definitely very helpful in turbo cars.

 

Just my opinions after building and driving 2 different T 928's so....

The tec III ran just as good on my 928TT as my 951 runs with stock FI. If you take the time to set it up correctly on the low end it will put around all day, just like a stocker.

The stock injection setup will not handle 600 hp. As a matter of fact you will need to run dual fuel pumps and dual feed lines, for over roughly 400-450 hp and thats at the engine. You can set the second one to turn on at low boost with a hobbs switch or I think the tec III can do that too. Also for anything over 6-8 psi timing control in manditory. Take my word for it. If you want to make serious horsepower, sell your stock computers mass air sensor etc, and put it towards a stand alone. It might save you a lot of $ in the long run. All you need to do is blow a head gasket and you could have paid for a tec III.

My TT 928 with a tec III and 42# injectors got 19 mpg on the highway and it was not really running that lean. Actually it was so tame and tunable i could set it up for 6 psi and run it on 87 octane all day long, or just reload a new map, turn up the boost and run 93, but you cant do that with a stock computer or without timing control. Also if you were really nuts and had a fresh engine and big enough injectors, you could reload a race map, fill it up with race gas and turn it up to 24 psi and really break some parts. You need to control the fuel obviously and you can do that with a rising rate FP regualtor etc, but no timing control is more likely what will lead to detonation and a blown head gaskets IMO.

Also IMO there is really just not enough room to get a good sized air to air IC in a 928 without running the feed pipes under the front radiator support. I ran 3 different air to air setups. Probably the best way to do it is either just copy the calloway setup, or better yet install a narrower 3 core radiator that leaves enough room on the side for the IC pipes to go by the side. I ran my car with that calloway type setup and everytime I hit a speed bump, I would lose a pipe. Get out reconnect it, it was a real PIA. Also you could also run over the top of a custom radiator with some custom tubes. That part of the setup is a real PIA.

The early 928 4.5L motors can handle 10-12 psi all day long stock with after market FI, so that it what I opted for. It was just a lot simper option. Its basicaly just drop it in and go. If you want to go over 10-12 psi, you need forged pistons. The way I drive 12 psi was plenty enough to get me in trouble. My car was a rocket.

From what I understand the 5 speed gives up at about 5-600 hp. Call mark Anderson on that one. You will definately fry a single disc clutch, but the fix does seem to be a twin disc. He also pointed me to that and mentioned they would handle around 600hp, although the intermediate plate may give you problems.

There was a turbo builder down here that built a TT to4 s4 back in the early 90's that was supposedly making 950 hp. I think that # was a little overstated, but at any rate when I asked him about his build, they had basically broken every part in the drivetrain and gave up when they started blowing trannys. That was after melting pistons, bending the stock rods, frying numorous cutches and going ceramic in the end, and having a custom driveshaft built. When I asked him what he thought of my plans to build a TT928 he said I should be driving a 930 ! Of course I ignored that and built them anyway.

Since I have sold both my T 928 cars and now drive a 951. If I ever decide to build another T 928 it will be an S4 similar to what I described in the last message on a 5L 32v block. Its very expensive to do it right though.

 

Herr-Kuhn

Hey I just realised my response was to you and not the original poster. I am sure you are dialed into the whole turbo 928 thing, so just take all my opinions with a grain of salt.

If you ever do want to buncce some ideas send me a PM, as I have been into that engine bay with turbo crap, more times than I would like to count.

One thing I will say is I never realized how much room is in a 928 engine bay, until I bought a 951.

 

Hey...it is just about knowing where to go and what to mount and how...that is the trick! I won't tell on my plans for fuel and ignition...but it will be slick for sure...

 

Interested. Keep me posted.

 

The new 2.0 liter 4 cyl for audi/VW is 10.7:1 compression with 12psi comming from a quick spool turbo. I think with proper charge cooling compression can be raised pretty high, comparibly, and still hold together very well.

 

Is that 10.7:1 turbo the direct injection engine?