Lorax

It's not really any secret that I am trying to build a turbo 2.5l 16v engine out of a 944S

Unfortunately I am not knowledgeable enough to figure out all this on my own. So I am trying to get advice who know more about the subject.

So here is a list of issues with turbocharging the 944S motor.

1. Exhaust: Pretty easy fix... cut off flanges and rotate them then modify bolt holes to line up with xover pipe. At least I think that would work.

2. Intake: Weld a turbo intake onto an S2 intake flange/runners

3. Rods: Factory rods are cast, replace with forged turbo rods or other aftermarket

4. Compression: Here is the big one... 944S compression ratio is 10.9:1. If I went with an extra thick HG that would bring it down to around 10.5:1. Still pretty high.

I have been told that the 951 piston with the 944S head would be about 9.5:1, which is right where I want it to be. Can anyone verify that? The only issue is whether or not the pistons would clear. I have also been told that the design of the 951 piston is not optimal for the 16v combustion chamber, but that's ok with me.

CAN ANYONE TELL ME FOR SURE - Will the 951 pistons clear the valves of the 16v "S" head WITHOUT using shorter rods, or machining the pistons? I really don't want to use shorter rods.


On more question. Assuming I am running 20-23psi on the turbo compression, how can I calculate how much I would have to drop the boost to just use the stock 944S compression? I know it is also affected by the differences in the comustion chamber and etc, I only want a rough estimate.

333pg333

Well for one you can't use an 8v piston with a 16v head so you'll have to get some custom pistons made I think. That will make life a lot easier as you can get them made to suit your intended c/r. Going with an extra thick h/g may not be the best solution, depending on how thick too.

RPHARRIS

Do yourself a favor and Google the word Quench. That will get you thinking about some of the important issues here. The 16v head has a better combustion chamber design than the 8v. You want to take full advantage of that, especially if you really want to run a 9.5:1 CR.

theedge

Id talk to Chris White about getting some custom Wossner pistons. Theyre pretty affordable, and lightweight too.

Chris White

and I have made up a few sets of the exact pistons you need! Design is already done.

Lorax

I was hoping you would chime in here.

So are you confirming that the 951 pistons will NOT clear the valves when used with the 16v?

333pg333

The cams / timing would have a bearing on this also. From what I've seen of the later Wossners they are cheap (in a good way), light, and very customizable.
What are you planning to use to control all this?

Lorax

I understand, but I'm trying to pinch pennies here.

In the future custom 16v cams, pistons and lightweight rods are all dandy but for now I would like to be as resourceful as possible.

Lorax

Hey, thanks for your replys.

This is not a track car or anything like that, it's simply a platform for me to experiment.

To get the most of the 16v head I really need custom cams and a turbo that is spec'd properly for the application, that is true.

My goal right now is to find the easiest possible way to assemble a 2.5L 16v engine. Once I get that performance baseline, I can begin improving it.


As far as EMS, I'm using vitesse vflex software with the smt6. Also going to be running his wasted spark ignition too.

Chris White

Nope....I am confirming that I use custom piston for the job.
16v engines are not usually the basis for a 'cheap' build! I can understand trying to make a build on a budget but using the incorrect piston design as the core is not a good way to go.
If budget precludes the custom pistons my recommendation would be to build a really nice 8v instead.

Lorax

It' not that I can't afford them.... you have a PM

Chris White

Since you are shooting for the 16v project there is another plus for the Wossners –
They are over 100g lighter than the stock 951 pistons. If you are doing a 16v engine it means that you will need to run the rpms up more. An 8v engine will work better up to about 4krpm and then the 16v will perform better – so if you want to take advantage of the 16v head plan to run at a higher rpm range – where piston weight is an issue!

Lorax

That's another on of the reasons I want to use higher compression... Hopefully I will keep more low end with the 16v that way. Also Will allow me to stretch my smaller turbo out a bit more into the rpm range since I will be running less boost. Is that correct? And of course it will spool quicker with the higher compression.

RolexNJ

Ryan, you should see if you can contact Mike (MPD47) as he has a very similar build, at least I think so. Maybe he will grace us by poping by.

Lorax

Mike?? That dude doesn't know anything....

He drives around in a chopped up car with an N/A motor and talks about having another turbo motor someday... I think we all know that is BS.