3.0 compression ???
 

Rebuilding a 3.0 motor. going with 48 PMO's and Dougherty DE40 'Mod 's' cam, electromotive spark control. keeping the 95mm cylinders. have 2 scenerios: 1. using big port SC heads and 1.5" euro style headers or 2. using 3.2 head and 1 3/4" headers. These 3.2 heads have been twin plugged. Having a questions about compression. would like to use JE either 9.5 or 10.5 stuff. only have a single spark electromotive now. Looking at making this a stump pulling street car. ??? which heads, which pistons, do I need twin plug for the higher compression?

General consensus here is anything over 9.5 : 1 needs twin plug because of the uncertainty of fuel. I just built a 3.0 with 46 Webers and GE 60 cams using a 1 5/8 header. It uses '78 SC heads with race springs and retainers. This motor is an ass kicker. I'd bump the compression to 10.5 and add coils to the Electromotive stuff you already have and twin plug. You might want to talk to Dougherty about a different cam choice unless you already have them.

PMOs come in 40, 46 & 50 mm. I think you meant 46 mm PMOs, right?

Lindy

thnks. do you know your torque numbers on your engine?

check the CR on your JE's . they're known for being off on the stated CR.

if you want a stump puller, check this out. John did me a wicked cam and the torque 'curve' is more like a straight line. I told John I wanted an engine that pulled like a truck and I wasn't concerned about power over 6K. I got a serious 'stump-puller' .

http://forums.pelicanparts.com/porsche-911-technical-forum/502996-3-0-dyno-day-pleasant-surprise.html

The J&E pistons will be exactly what you order. The said compression ratio for the 9.5:1, is based upon an total stock configuration. The final compression ratio is based upon your final combustion chamber volume. So if you are not changing anything the 9.5:1 will be fine with premium street gas but anything up to 10:1 taking a chance and should be twin plugged.

You should do all your machine work fist, then CC everything, then custom order your pistons from EBS. Call EBS they are professionals and will help.

To get the most out of your engine, if you all-ready have the 3.2 heads for twin plugs, that will give you the best performance. You could have the heads ported for larger intakes and exhaust.

You will be leaving a lot on the table by not taking advantage of a displacement increase. If you are going to do all this then why not up to 98 mm P&C's.

Shane