Je piston question plss....

[damian911]

In reading some of peoples comments here and reading the 911 engine rebuilt book im a little confused...I would like to built the "upgrading the 3.0sc engine" to his spec's...meaning the 964 cam and JE 9:8:1 pistons....but ive recently looked at je site and they dont make a 9:8 cr piston, and ive also heard that you can tweak here and tweak there to obtain this comp.ration...so does this mean you actually buy a lower comp/rat and tweak it to obtain this??? or do you have JE custom make you a 9:8 piston?? thanks---damian

[Henry Schmidt]

Buy higher compression pistons (10.5:1) and adjust compression as required.

JE will also make any compression you want but if you need to replace one later you will have to buy at least 4.

With the "self" piston you can buy one at a time.

BTW: a dyno would have a hard time measuring the difference between 9.5:1 and 9.8:1.

Street gas tells us error towards the lower end.

[jdm61]

what do you need to do to run 10.5:1 pistons in a '85 3.2? All of our super unleaded here in Florida is 93 octane. The $850 or so for the JE's sure seems a lot more reasonable than the $3000+ for the 10.3 Mahle Euro Carrera pistons and cylinders or the $4600+ for the 3.4's. Am i missing something? Would I need to twin plug the heads?

[Steve@Rennsport]

Jdm:

You'll need twin-ignition to run close to 10.5:1 on any pump gas. To me 10.25:1 is max when 92-93 octane fuels are to be used.

For sure, JE's are far cheaper but don't expect them to last as long as Mahle's will. You get what you pay for.

[Henry Schmidt]

It is important to remember that camshafts will also effect compression ratio as it relates to detonation.

10.5 : 1 static may be less likely to detonate than 10.0 : 1 if the dynamic compression is less. Cams will always effect dynamic compression.

[damian911]

Henry i have just dropped my engine and about to take inspect the inards here shortly....its a 3.0sc with the typical problems, rings and broken bolts...and im just like the others who wants lil more hp and doesnt want to bet the farm..Since the cylinders prob. need rebor/honing does it make since to go from 95 to 98mm pistons?, is it possib. to keep the cylinders? and would i make since to then make it a shor-stroke3.2?, could i keep then the cis?
If the cylinders need to be changed then ill prob. stick with them..so then would u say go from stock cam to 964?, and u said to buy the high compression je like the 10.5 and to have the c/r decreased?, where does this adjustment come from???? thks damian

[Jeff Alton]

If you are staying with the stock bore....... 9.5 pistons and 964 cams and CIS makes a nice motor. Espescially with a backdated exhaust....

The last 964 cammed 3.0 I built was a really nice strong motor, just like a normal SC but a little beffier everywhere in the power band.

Cheers

[matty74]

How long will JE's Last?

[cnavarro]

I've had customers with over 100,000 mi on JEs just re-use and not even have to re-ring them.

[matty74]

well that pretty good durability I'll buy them and save a few $$ on Mahles

[cnavarro]

It's all in setting the proper clearance. Too tight, they seize. Too loose, they clatter themselves to death. If you want to err on the side of tight, it's always a safe move to have them dry film coated - the coating wears in where added clearance is needed.