16 valve pistons in 8 valve motor???

fastfredracing · 07-28-2006, 06:05 PM

Anyone ever used 16 valve pistons in their 8 valve motor, I think they are a whole compression point higher. Maybe have to eyebrow the pistons for valve clearance???. Just wondering

Zero10 · 07-29-2006, 10:23 AM

If you are running a full standalone system you could get away with bumping up the CR, but on the stock DME, you will probably get lots of knock.

Looking at a set of 16V pistons side-by-side with N/A 8V pistons, it actually looks like the 16V pistons would yield a lower compression ratio, unless they moved the wrist pin location. It's tough to tell.

nynor · 07-29-2006, 11:18 AM

just move the DME adjuster to retard the timing a couple of degrees...

carsontc · 07-30-2006, 07:32 AM

using 16v pistons with a 8v head was looked into several times before (no surprise). the 16v head's valve chamber volume is less than the 8v head’s volume. so it's the 16v head that is really responsible for the higher compression ratio…not the piston.

Quote:

Originally posted by Zero10
Looking at a set of 16V pistons side-by-side with N/A 8V pistons, it actually looks like the 16V pistons would yield a lower compression ratio, unless they moved the wrist pin location. It's tough to tell.

actually this is a fact. IIRC using the 16v piston with the 8v head reduces the c/r to somewhere around 8 to 1

Zero10 · 07-30-2006, 07:35 AM

Putting a 16V piston side-by-side with a turbo piston, the dishing is pretty similar. I would say that 8:1 is a fair estimate. The wrist pin location is indeed the same, I checked.

CJFusco · CJFusco's Garage

Ahoy there, Fred. Good to see you on Pelican.

Porsche-O-Phile · Porsche-O-Phile's Garage

Why not simply get the 8v head shaved with your stock pistons. You can jack up the c/r all you want that way.

Zero10 · 07-31-2006, 11:22 AM

You can't deck the head very far before you require an adjustable cam gear to keep the motor in proper time.
That said, you will see a marginal gain in CR even by doing so,
i.e. 9.6:1 - 9.7:1
Custom pistons are the way to go if you must crank up the CR, but I am really starting to wonder why you would want to.

fast924S · fast924S's Garage

Just get a set of 88 pistons or some euro's. Im swaping my 87 924S 9.5cr pistons to the 88 10.2. Im thinking with high octane gas I should be ok

Brando · Brando's Garage

By high-octane, you mean 91?

I have a feeling though, you won't have a knock sensor to retard the timing...

Zero10 · 08-01-2006, 12:33 PM

^^^ Exactly why I suggested standalone. Knock starts to become an issue with the higher CR.
IIRC, the S and S2 motors had a knock sensor.

fast924S · fast924S's Garage

True, I think it all depends on how much higher you go, My thinking is running 10.2 with 91 octane, I should be ok, But If Im not I can always turn the FQS back one, Or find a piggy back from split second to chang up the timming. Ot as Zero and many others have said just go stand alone