Bengt Sweden

I hope some will be interested to follow my discovery journey towards a 3 liter turbo. Any advice is appreciated.
I have started to look at the modification necessary to use an 8-valve head on a 968 block.
This picture show the difference in waterchannel location and the following pictures an already modified head bought from the US by a friend. I must say I am not impressed this time by the workmanship. The picture doesn't show but the channel is very narrow inside.
Bengt

Bengt Sweden

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Bengt Sweden

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Bengt Sweden

Next step is to get the right Compression Ratio. Stock is 8:1 on 951.
With unmodified 968 with 8-valve head we get 9:1 which is a bit too much for serious charging. The head is 56cc the head gasket is 9cc the piston is relieved 28cc = 93 cc. Bore and stroke is 104X88 =748cc.
748/7=107cc. I will need 14 more cc to get to 8:1.

Here is a picture of a piston modified in a lathe, which together with some milling around the plug area in the head will be sufficient. I am hesitant though since I want to keep the squish area. Any ideas?

Bengt

BoostGuy951

I really like your attitude of doing the hands on type projects to make do with what you have (ie. putting the piston on a lathe to gain cc's). I'm the same way.

I don't see a problem with using the 8v head if you can fab the correct water passages, and you dont mind the subsequent drop in VE.

One problem I see is the use of the factory 968 pistons. These arent optimal for turbocharging, as they are cast. I think this would be the place where I would go ahead and spend the money for a good aftermarket unit. I would so hate to see you go though all this work only to have a piston fail.

Good Luck!



Edit: as well as the stock rods too.

fast951

If you tune the car correctly 9:1 CR is not bad...

Bengt Sweden

Thank you for the advices!
Yes I am on limited budget and actually prefer that. The other day I visited a friends shop when a customer handed in a new GT3 with all the upgrades to have it tuned. How much sport is that? What drives me is to gain the knowledge needed to find the short cuts to more power. I also prefer "sleeper" looks.

I plan to use 951 rods as I have written here
good rods?

To use the 16v head would be dramatically more expensive and tedious. I am quite sure that the eventual difference is not worth the trouble. Porsche shared the same opinion.

I didn't know about the pistons being cast but I believe there are advantages with casting. Temperature deformation is less and therefore play can be kept small.
Anyone had piston failure without knocking ?

9:1 is nice for quick response and modern turbo cars often have that CR, but it means less boosting. Perhaps I'll just do the relief in the head, leave the squish areas on the piston and end up somewhere in between.
What about a thick copper head gasket?

What CR and boost do you run 968turboS?

Bengt

TurboTommy

I run 9:1 compression. You can use a larger turbine hot hausing and not have a mushy laggy feeling off boost; it's the best of both worlds. What octane do you have at the pumps where you live?

TonyG

Issue #1: Although the 2.7L head will bolt on, the 951 intake will not. And you'll spend some money for sure to splice together the appropriate intake that will bolt on.

Issue #2: Squish area. The problem you have right now is that you don't have a squish area. The 968 pistons are designed for a different combustion chamber. If you examine the 951 piston, you'll clearly see the squish area on the piston which matches the squish area in the head. Even before you cut down the piston, you didn't have a matching/proper squish area. What you've done is to cut the little squish area there was... out.

The squish area is one thing you never want to mess with.

Bengt Sweden

Thank you for the answeres. No I am not discouraged and I don't have a problem with people who can afford to buy the latest stuff. However I would soon be boored if I were in that position.

What is the difference with a turbo RS block?

Tony, the pistons on the picture are not mine and if you read carefully you'll see my own doubts about removing the squish band. Let's see how far I can come with just prepping the head (although I don't want to remove the squish areas here either).
Why is the squish by the plug recessed? Can I safely mill away 1mm of the piston top in the bowl? Are the Mahle low compression pistons adapted to 8 v heads? And what about a thick copper head gasket?

Bengt

fast951

Stay away from copper headgasket. Every one I have seen leaked coolant... However, I hear some people use them without a problem...

michael2e

could someone please explain what would be involved in using a stock 968 head and block for a 951 turbo project and what the probable cost might be. much appreciated

fast951

To turbocharge a 968 engine (with 16V head) you will have to deal with the followings (and then some):

- Come up with pistons to lower the compression.. Sleeving or Nicom the block will be required. And Aftermarket pistons...
- Modify the exhaust to adapt the turbo
- Modify the intake
- Modify the head to eliminate the variable timig..
- Figure out a way to tune it...

Not a very easy task.. It has been done, but requires plenty of work...

PorscheLars

Tony G

Can you explain more what the risk is to combine the senter detonation 968 piston with the 8v head and the squish area.

I see the missmatch.. but what happends.. exhaust left over.. ?

Boostguy. are you 100%sure about the pistons?

The rods for the 968.. weak? dont think so.. 99.99% af all rodfailure is caused by other things.. or..

Bengt.. I have a 3.0 (Lars fra Norge. 1 havari fra en Sanden bygd motor allerede) engine and had to rebuild it after 10 000 km.. and all the enginejob was done before I entered Rennlist. So you have started the right place for knowhow. Unessesary to tell but I should wish I could turn back time 2 years.

My engine runs well and pulls 0 - 200 kmh around 15 sec @ 14 psi but the longlivity will be the next experiment..

(I have bought a spare 2.5 turbo engine with snatched belt to build a spare engine ;-))

fast951

Raj,

The new 104mm turbo pistons that Andial offers are designed to work with the 8V head not the 16V. My post was addressing the 16V head...
The 968 Turbo used a modified 951 head (8V).
As of now, sleeving or Nicom are required to get low compression pistons to be used with the 16V head..

Variocam can be adapted, but it's just another variable to add...