beepbeep

We were thinking about using JE-pistons kit with pistons and cylinders for rebuilding 3.6TT engine after it compes home from Nurburgring. There are 100mm and 102mm kit's as well. Using 102mm would give us 3.72L displacement and lower boost treshould approx. 180RPM.

This is the kit:
http://www.jepistons.com/pdf/2006-je8.pdf

Are there any problems using 102mm P&C's from reliability stand? Do we have to enlarge spigots or anything like that or is bolt-on?

What about using Perfect Bore - barrels? Anyone that uses/used them?

Thanx!

P.S. Which dome volume should be used for ~7.5:1 C/R? 40 or 45cm^2?

Geoffrey

The 102mm cylinders come in two styles, slip in that fit directly into the 107mm case spigot of the stock 3.6 case and bore in which require the case to be bored out to 109mm. If you are looking fore reliability, I'd suggest staying with 3.6l due to the cylinder to head sealing surface. The link you references shows only N/A pistons with a compression ratio of 11.5 and 12.5:1. You'd need a net dome volume somewhere in the 10-12cc range (from memory without doing the calculations) to obtain a 7.5:1 compression ratio.

beepbeep

Excellent advice!

You don't happen to know a source of forged 3.6 turbo pistons fitting a 3.6 with acceptable dish volume to support 7.5:1 C/R?

So you don't recomend going to 3.72L? Engine has 700+ hp and we haven't had reliability problems so far except for cracked head beacuse of backfire.

beepbeep

P.S. Our heads are flameringed so unless it's impossible to fit flame rings in 102mm barrels I don't expect any leak issues with smaller head sealing surface as surfaces aren't doing the sealing job, rings do.

So 10000$ question is: are 102mm P&C's inherently less reliable than 100mm job in highly stressed engine?

We could do well with higher displacement (to cure turbo-lag) but reliability is important.

Geoffrey

My recommendation is to take a Mahle N/A piston and mill it to your deisred compression ratio. I am not a fan of JE pistons for a number of reasons that result in a reduction of longevity and reliability.

You can flame ring the 102 barrels, however, you need to consider the heads. The bottom fin is thin and has little support for sealingo on the head. The more you increase the bore, the less structure that is there on the head. You can/should weld the bottom two fins on the head for added structure.

Are you racing or street? For street it is probably Ok, although I would rather build a more efficient 3.6l engine. In the racing engines, there have been other issues such as pistons cracking at the wrist pin area and case webbing cracking, and cylinder to case sealing issues (3.8l) when using high boost (1.2/1.3bar) and high HP.

beepbeep

Engine has H-beam rods, flamerings and 993TT pistons. It worked well but jugs are worn oval and pistons are nagged and worn from countless rebuilds.

Plan is to replace pistons and jugs with something new and hopefully, better. My idea is to use JE pistons in order to lower the reciprotating weight.

We will either go to 102mm or keep stock 100mm jugs depending on reliability issues. Using Mahle N/A pistons sounds like a risky bussines as engine runs up to 2 bar of boost when on drag strip. Wouldn't milled N/A piston have quite a thin dome? OEM turbo pistons worked really well but it's time to replace them.

What issues did you have with JE regarding reliability? Only issues I heard of is extensive piston slap when cold, due to different thermal coeficient of material used.

Regards,
Goran

Geoffrey

You may or may not be aware that the 102mm Mahle N/A pistons have a deaxised wrist pin by 1mm which helps piston wear on one side of the engine but accelerates it on the other. I "think" the Turbo pistons are made from the same blank, you may want to check on that. They are also heavy. You may check with Ninemeister who has a much sturdier piston than Mahle or JE and their N/A 103mm piston weighs 400 grams without the wrist pin. I believe Colin can manufacture the pistons with different pin heights and compression ratios. You can also use a longer rod with his pistons to help the terrible rod/stoke ratio.

The JE pistons use a generic blank and the wrist pin boss area is weak and tend to be 25 hour pistons in a normal race engine (1.0-1.2bar not 2bar). They also have had the piston slap issue you noted due to larger clearances required. I know JE has very recently developed a new casting for Porsche to address some of these issues, but have not seen it.

beepbeep

Hmm, interesting.

I'm aware that pistons have their bolt axis off-center. Are JE piston axis symetrical compared to OEM/Mahle? I've sent a mail to Ninemeister, hope to get reply soon.