OK. (My post #13 explains a bit more what I'm thinking about -- easy to miss I know when skimming through threads.)

Don't know if S2 rods are forged or not.

If the 8V head lowers CR to 9.5:1 or so, and then a wide HG possibly a bit more again, would you think would I still need the custom pistons for a low-boost application?

 

This is very interesting reading. Maybe I shouldn't discount the 16V head so quickly. BTW, The premium pump fuel here about 93 in US octane rating.

By low-boost, I was thinking of something that would get me to about 300hp at the crank... < 10psi I would guess?

 

S2 rods are cast Patrick. But with only 300hp & 5psi I stick with the stock engine 16v head and a simple standalone EMS so you can set up the AFR's and timing adjustments...

Benefits perfomra like a 3.0 still with heaps of torque and the kick of the turbo from 2800rpm, I thought mine was great as a daily driver in that config (for a while) - but got greedy, the boost got me

 

got a set of forged rods here to. I'm making a 16v turbo inlet right now i guess i could do another about 800 au i would think ..
you can can sacifice your inlet and have one made from that you should be able to have that done for around 600 or less .
And old mate of mine has a work shop some where in bris and plenty of go fast crew i can talk it out with him if you like he knows plenty of fabricators and tuners up there ..

 

Any truth in the rumour that you can safely machine a dish of up to 2mm in the S2 pistons? not that it's necessary for low boost/high octane, just asking...

 

Yay Mike from Sydney is back give us an update mate and please send me a message if you need any parts or advice on who what and where ...

well on the advice of my Piston guru buddy i would say no there is simply not enough crown in them ...
but correct me if I'm wrong mate "Mike's turbo cab" made 400 hp @10 psi on 96 octane fuel from a standard S2 engine...
and now 98 octane is available all over ....
you can get a few cc's from pushing the valves back in the head and afew from the gasket ..

 

So is that what you did, Mike? 300 hp at 5psi with a stock S2 engine on 96 fuel?

So where did your "greed" eventually lead you?

 

Mark, I ran 5psi for a few months until I had it all dialled in then went up to 9psi, that was on a totally stock unopened engine, I was happy to play and if it broke wasnt too worried. At 9psi it was fantastic, was great at 5psi too.
After a while I popped the headgasket, but that was really I think just age 20 years old. I had some wear on the pistons, so I went totally stupid and rebuilt/remachined just about everything, forged rods/pistons, ported head, manifold and lots more, then did all the brakes suspension and on and on....spent a lot of money since

 

Mike, was your setup intercooled?

 

...and again he drops from the clouds....so Mike I know you've had some interruptions but are you continuing the rebuild? Where are you up to?

 

Rogue, yes I had a 951 intercooler on the orginal build, TO4B 60-1hifi, stage 5 #10 hotside

Hey Patrick, yeah back into the Porsche, it was finished ready to register, but last week decided to put a front mount in so its got the nose off at the moment, must stop playing and start driving

I seem to have missed what happended to your lovely grey car - its changed, was it a track incident?

 

"Deus Ex Machina" is the phrase that springs to mind.

Nice timing to make a return!

 

Mark,

There is an article in May 911&PW regarding a 3.0L turbo build. They started with a 1990 turbo 250bhp model. They used a 968 block with crankshaft and pistons, machined the piston crowns to drop CR to 8.5:1. Then added a 2.7L cylinder head (8V), a 2.7 water pump (to increase cooling capacity of the bigger block), then all the rest of the bits from the turbo car. Power output is 300 hp and torque 350 lbs/ft. The engine has not been further modified except for adding bigger injectors. The "test" car has covered over 200,000 miles without problem.

 

That's it? You don't even need boost for that. 300 horsepower is nothing from a 104mm bore, 4V engine. You familiar with Racer's Edge? Karl's 944 S2 race car puts down 240 at the wheels (~275 crank). He has headers and a full exhaust. I believe he sells the header.

I'd keep it NA if that is your power target. Increase the intake valves to 39mm, port the head to match, intake if possible - considering your budget, I'd think about a custom short runner one. Go with a 12mm lift cam. That's on the inside. On the outside, larger tube headers and 3" exhaust, and do whatever you can to get rid of that god-forsaken swing door air meter.

Other comments.......if the pistons for the 2.7 are the same as for the 3.0L, then there are some engineers at Porsche that should be fired. The piston should have some definition for valve reliefs, which means a 2V and a 4V piston will look very different. Also, you don't want to sink the valves into the head if possible. Bad for flow. How much/if you can machine a relief into the piston will depend on how the dish is shaped, and what the bottom looks like. For example, if you have a D-shaped dish, but the bottom is uniform, you can turn that D into an O pretty safely, but that's about as far as I'd go.

I had Diamond make some pistons for me for an old 2.3 turbo Ford, but it had traditional cylinder walls. You might give them a call and see if they can do something with the proper coating for ours. My cost was about $500.

 

You can with the 968 pistons, I guess that means you could with the S2 as well. Both are forged.