JE/LN 3.8 vs. Mahle Motorsport 3.8
 

So it's rebuild time. Decided to fix the leaky head issue and get the whole engine gone over so I can start fresh. Decided to go 3.8 since it's only another 2k while I'm in there. My question is which p/c set would you use and why? My mechanic says the JE's are noisy. Can someone verify how much? Does this make the engine sound like crap at idle? This is a street car, so I am concerned. Option 2 is the Mahle Motorsport 3.8 set, I would have the heads shaved to bring them up to 11.3:1 like the JE's would be. I know they are heavier, but quiet and maybe longer lasting?

JMHO, but I think your mechanic offers you 24kt gold advice.

If maximum durability & longevity are the most important aspects of the engine build, you will be better off with the Mahle P/C's.

Do not raise the CR unless you intend to run 94 or better gasoline. The stock CR permits one to use performance software as well as provide a margin against detonation during hot weather.

Dave, where are you in Ohio and who is doing your work??... if you don't mind sharing. Planning engine modifications really needs to be thought out as a complete system. You can do a lot with 3.6 liters by upgrading to a reasonable cam, exhaust, and software for a reasonable amount of money. You can do relatively little (on top of that), by making radical cam changes and small increases in displacement, stand alone ECU's etc etc for infinity more dollars. $2k extra for bigger cylinders and piston's isn't chump change. I think you would notice that expenditure more if you did something more creative with it, like working on changing the gearing, or shaking off some weight. Either way, I am still working my way down this path, but I have some documentation from my build process that could be e-mailed if you were interested.

Steve,
After all my bragging about 94 octane in Ohio it seems that Sunoco has eliminated it from their product line :( We still have 93 in many locations. The times they are a changin'. As a side note and hijack to this thread, I ended up deciding to keep my hotrod track/street engine. I'm going to work on building my own muffler for it, and continue to learn as I go. I built a data cable to tune my Autronic, and I learned that to some "professional tuners" building a "race car" is an excuse to cut a lot of corners! I bought an LM2, and I'm pretty much starting from scratch. One of these days I'll probably be calling you to talk about backing off the camshafts a little, and probably cutting down on the CR. That may be a ways in the future as the economy still has a choke hold on my fun budget.

I was going to raise it to the factory spec of 11.3:1(or make sure it is there), if I go with the Mahles, as I understand they don't make the advertised compression. And yes, 93 is not a problem here in Ohio. I don't think Sunoco makes 94 anymore? :mad: Anyway, this is the route I am leaning towards, as is my mechanic is more comfortable with Mahles for street use. Thanks for the reply.

Cleveland area, and Steinels Autowerks. I realize 2k isn't cheap, but I was planning on a newer chip anyway which is part of that, and hopefully I can regain some of that by selling my old p/c's. I also just wanted something a little different then everyone else. I will get port work done as well, and am deciding on an exhaust(see other thread). I too afraid cams will take away driveability, a mild grind might be okay, but probably not worth the cost? I'll gladly take any info you have, pm me for email. Thank you.

Hi Ryan,

I was pretty much afraid that 94 was NLA anywhere in the US now, due to stringent EPA regulations about fuel. Good call on the LM-2 as thats an integral tool for what you are doing. :)


Dave,

JMHO, but a real 11.3 CR & 93 octane fuel doesn't safely permit performance software to be used without putting pistons and rings at high risk in summertime temps. BTDT, too many times.

The actual compression ratios of 10.4-10.7 is precisely why performance software works well in these engines when using pump fuels in this country. That affords the headroom to permit changes to the timing maps for improved throttle response and torque. Caveat Emptor on such changes.

I do some performance software for Steinel's. :) :)

Lastly, stock ports support well over 300HP; something you'll not likely exceed by much using the stock intake system and RS cams. Those components typically yield something in the 290-310HP range with a decent exhaust.

Dave, I'll send you a PM... My car is what the bottom of the rabbit hole looks like. The PDF file I have isn't really a "how to", but its a write up I made to try to help me change careers, or land an assistantship with a university to continue studying mechanical engineering. As far as driveability is concerned; thats a personal thing. My car is running 3.8 RSR cams. Some people would say they are not streetable, but with a standard flywheel I don't mind the cams at all. As far as usability, I don't make any real power until I'm over 4k RPM. That can be frustrating, but I still have just as much or more low end grunt as a stock 3.2 Carrera. Unless you are going to spend the money for aftermarket rods, and valvetrain parts you will want to keep your powerband located within the boundaries of the stock redline. The more you push your cam selection, the more you are going to wish for that little extra compression for low end and mid range. You may still open yourself to some hot weather preignition concerns at high RPM though. It seems that most people who actually measure and calculate the compression ratio on a stock 964 usually come up with something less than 11:1.

I trust that Eric will do whatever he safely can for me, given my budget restraints. I may be misinterpreting what he is telling me he can do. I am open to ideas of what can be done for minimal costs to get that little extra out of the engine while they are in there? I'm having the bottom end done too, just so you know.

The JE forgings I've seen are heavier than the Mahle 3.8 pistons which should be 11.3 - 11.5:1 compression. The JE pistons require larger piston to cylinder clearance than Mahle which is why they are noiser, especially when cold. The Mahle are not without their issues, however, for a street car, I would use factory Mahle over JE any day and agree with Steve and Erik's comments.

Looks like I am going with the Mahle. I probably wouldn't be happy hearing piston slap on a street engine that I just spent a mint on rebuilding. Besides, Porsche uses them, so they must be good?

To be fair though, the piston slap reputation of JE is from a long time ago. I can't remember the last time I heard cold piston slap from a JE engine.

My builder says it exists, especially with the 3.8. He also said that he had one set that was so bad, he couldn't let it go out, and re-rebuilt the engine with Mahles. After sending the pistons back, they were found to be defective. Not something you want to hear with new, expensive parts that could cost him a reputation and the car owner a catastrophic failure. I'm sure this was an isolated event, but I wouldn't want it to be me. If he is happier with Mahles, I will be too. And from the looks of the replies, others agree, for the street, anyway.

If going w/ Mahle, try to get a set w/ correct L/R pin o/s