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skygrounder
08-31-2004, 09:09 AM
Planning on converting my Porsche 968 to run a low boost turbo setup (so i can keep the varioram) using a K26 turbo. Does anyone know how much boost I can run safely without lowering the compression ratio? The stock compression ratio is 11.1:1.

JustinL
08-31-2004, 09:18 AM
Try www.968.net. There is some valuable info there andI think some of those guys have gone FI with thier 968s.

C4S
08-31-2004, 09:49 AM
ASK RAGE ! :D

rage2
08-31-2004, 09:53 AM
Very little boost on pump gas. There's been various 968 Turbos built, and they all need high octane fuels to run to it's full potential. You'll also NEED a full standalone setup to properly dial in the turbo setup, meaning a full MAP conversion. You will not get the full potential of the 968 motor by staying high compression.

The K26 turbo is not a good candidate for a 968 Turbo, it can only flow a max of ~290whp, not very suited for the 3L 968 motor. You'll get full boost at like 2000rpm with that tiny turbo, but it'll die off past 4000rpm (roughly).

The proper way to do it is to get the very rare 968 Turbo S pistons that work in the aluminum bores... Andial I believe made a small run of 20 sets of these suckers, and they're all gone now. Very strong pistons, no need to do anything to the block as the drop right in with the aluminum bores.

Since those aren't available, you can sleeve the 968 block and drop in forged aftermarket pistons (like I did with my 944 turbo). Bonus is with the 968 block you can move up to ~3.2L safely. From there you would have to either build a custom manifold that works with the 16V variocam head, or move to a 8V head to use the 944 turbo's exhaust manifolds.

If you want to buy bolt on parts and stay with high compression, powerhaus has built several 3L 16V turbos, including custom manifolds. It's easier to do yes, but you won't make as much power, and probably pay just as much as a low compression custom setup.

Lemme know if you have more questions, I know quite a bit regarding the 944/968 and turbocharging both.

skygrounder
08-31-2004, 01:30 PM
Thanks alot rage, dude i was wondering what you meant by 'sleeving' and 'a full standalone setup', and couldn't i just dish out the stock pistons to lower the copression or get the turbo s pistons from my porsche dealer also what turbo do you recommend i use.

There were 2 reasons I was gonna do a low boost setup the first was i wanted the car to be reliable as it would be my only car and used daily and secondly this is what John anderson from andersonmotorworksinc.com suggested. I did look at the powerhaus conversions and was pretty impressed by the huge power figures but this was gonna cost me $25k for that money (if i had it) i would probably sell my car and put the cash towards a 993 carrera . ultimately if I get around 350 bhp out of the car i'm a happy man.

The only other problem is that I only have a budget of around $7500 but could afford more the longer I left it. One of my good friends has a garage over here called quarter mile and will be able to do me a deal on the the labour plus I live in dubai where the labour costs are ridiculously low compared with the U.K or the U.S for that matter. What do you think is the best way of spending the cash?

rage2
08-31-2004, 02:04 PM
Sleeving (Iron sleeves into a 2.5L 944 turbo aluminum block) :

1. Bore out existing cylinders.
http://www.virgeweb.com/rage2/944t/20030323-Block%20Prep%201.jpg

2. Get some sleeves and pistons
http://www.virgeweb.com/rage2/944t/20021203-2.8L%20Pistons%20and%20Sleeves%20from%20AMW%2001.jpg

3. Install Sleeves and bore sleeves to match piston size, gaps, etc.
http://www.virgeweb.com/rage2/944t/20030325-Sleeved%20Block%201.jpg

4. Install pistons.
http://www.virgeweb.com/rage2/944t/20040303-Engine%20Assembly%2016.jpg

Standalone... it's basically a replacement ECU where you can adjust every parameter yourself. Since you can not adjust the stock ECU's fuel/timing/boost map/fuel cut/revlimit parameters, replacing it with an aftermarket Standalone ECU will allow you to tune your fuel and timing maps for your custom setup.

You can not just buy lower compression pistons and slap them into your block. It's an aluminum bore with alusil coating, so you must get special pistons for it. Porsche only made something like 20 968 Turbo S's... they were never production vehicles, so the pistons are rare. Porsche Motorsports *may* have a set somewhere, but nobody has been able to find them. edit - The Porsche 968 Turbo RS pistons wont work, they're not Alusil compatible. The 968 turbo had a different block than the 968 (nikisil vs alusil), and thus pistons are not interchangable between the two because the required coating is different.

To use any aftermarket pistons, you must go through the sleeve process to install an iron cylinder sleeve to use forged pistons. There was a very small run made of 104mm 968 turbo s alusil pistons last year, which would drop right in, but those are all gone now. Doesn't make sense to get those anyways, if anything went wrong, you would NOT have any replacement parts.

John Anderson is a really great resource. I bought my 2.8L sleeve + JE pistons through him. I'm one of the VERY few people with reliable 2.8L all bore setup. His prices are genearlly better than Powerhaus, but I'm not sure how many 3L FI applications he's done.

If you have a budget of $7500, I'd say save up. These cars are not cheap to build up. Or sell the 968, and get a 944 turbo. You can easily make 350bhp with bolt on stuff for way less than $7500. Turboing an NA car is never cheap, especially with Porsches.

rage2
08-31-2004, 02:23 PM
Here's the thread on the last set of the 104mm low compression pistons for Alusil blocks. There were some 104.5mm overbore ones available at that time (March) but they're long gone now.

http://forums.rennlist.com/rennforums/showthread.php?t=120963

If you go with the sleeving route like I did, you would end up with 3.11L using 106mm pistons. One guy went 3.2L with 108mm pistons.

skygrounder
09-03-2004, 05:08 PM
Thanks alot dude gonna start saving!

rage2
09-03-2004, 07:31 PM
haha yea, it's not exactly cheap! It took me 2 years to pay for the build on that block.