Geoffrey

Don, then you have the wrong pistons for your application. What is the cc of your cylinder heads. and the net dome volume of your JE Pistons? A stock one is about 94.6cc with W4CS twin plugs.

I'm curious about the math you are using to work out for the compression ratios you are stating. For instance, for your engine, assuming for a moment a stock head with chamber volume of 94.6cc and a .069 deck clearance. You would need a net dome volume of 26cc to acheive a 8.05:1 compression ratio. Now, if you decrease the deck height to .039, the compression ratio is now 8.57:1 or a very small change for a .030" change in deck height clearance. .5:1 compression is a far cry from 2:1. Also, a net dome volume of 26cc is large by turbo standards. The stock Mahle 7.5:1 pistons have only a 7cc net dome volume. If you reduce your chamber size from 94.6 to 84.6 the compression ratio raises only 1pt. The heads must be cut substantially to have such a high compression. I'm just not following the math.

Win Rice

Dang it, Geoffrey, you beat me to it

I was working on the math, but 0.030" doesn't add up to a 2 point increase in compression. Somethings wrong here. The heads and piston domes need to be carefully measured to see where you stand, Then the new replacement JE's need to have the proper dome volume to give the compression you want, while maintaining the proper squish band and clearance of around 0.040".

Not sure about Porsche engines, but semi-hemi 2-stroke combustion chambers want to maintain about a 0 to 1 degree difference at the squish band between the head and piston surfaces, with the tight side next to the cylinder wall.

JE should be able to make the proper piston, but you may have to give them pretty exact requirements.

Win

125shifter

Don, everyone's covered my tech thoughts and then some. I just want to offer my admiration for your perseverance. I'd have pulled all my hair out by now. Good luck.

DonE

The reason my statements do not make any sense is that I am echoing parts what my machine shop is telling me. He has done all the measuring from the case to the head including combustion chamber volume and has come up with these numbers. I've spoken to him nearly daily since this happened (again) based on all your comments and he still sticks to his math and DH recommendations.

No offense, but I have to take the advise of someone who is successful in building, tuning and racing these motors over what I get over the internet. I sincerely respect 99% of what I hear from you guys.

The best course of action for me right now is to learn and understand what all this means and measure it myself. Please understand the more people I talk to, the more confusing this gets. For example, I spoke to Joe Essa about this the last time I had a problem. He sets his deck height on some cars at 0 because he says he is taking expansion into consideration. He has some very powerful cars out there. My machine shop says 069. You guys say 040......

I think I need to take some time off from the lists and investigate this on my own. Thanks

Win Rice

Don,

I'm with David, a lesser man would have given up long ago.

10 engine builders, 10 opinions, you've been hit with plenty. Have a beer and think it through. Been there. Being a rockheaded DIY guy myself, I usually find the old saying 'Third time is a Charm' to be true.

Hang in there.

Win

srf506

Don, I guess I'm a little confused as to what you got myself. Only one piston is showing this abuse? (And I didn't mean you were doing anything wrong by that term, its just what was happening to that piston in the motor.) The plugs looked okay with no spalling? If the other five are clean, and seeing what little I can see in a photo, I would think that piston had a defect, either structurally, a crack, or ding, or, metallurgical, a void, tempering or casting issue. Go to the library or a good bookstore and find a reference book with the math in it for engine rebuilds/mods and check it out yourself. The math isn't that hard. Just remember the mantra "measure twice, cut once". I don't think any of us can really give you causual information because we don't have the parts in hand. Good luck, I hope you find the cause of the problem real soon.

edpurplett

Don,

I hear you on trusting your tuner... anyway.. as menitoned it appears you have an anomoly with one cylinder... IMHO.... and it virtually has to be fuel or previous hidden damage as mentioned... it's a little tough for timing variance :-)

... but to tuners... I hear Essa is good and I regard Todd Knighton as god... but the crew here is AMAZING...I would trust them... anyone having done work for you with 2 blow-ups MAY have butt coverage issues to contend with.. so be careful as you know...though it is not obvious they had anything to do with the problems....(fuel issues to one cylinders obviously are far out of their control)

I have been building turbos for 24 years and unless your machine shop specializes in Porsches I would listen to Geoffrery and others... and as a matter of fact when it comes to 'endurance' longevity and racing issues Geoffrey's advice is as good as it gets... he sees SOOO many configurations and sees the harshest conditions possible... Even Todd (and i think Joe E) tune for mainly HP and street driveability and can do racing style tuning.... but as you know street/short run duration cannot expose issues like racing.. point is, get your guys to disprove the folks here... if they can't explain to you why they're right and the folks here are wrong change who's doing your work .. just MHO... ( I worked at 2 speed shops when younger and there is huge variance in machinest's math skills ;-)..).. so unless Joe tells you he has run those deck heights (for example) in racing (road)engines I'd defer to the crew here..

... not trying to stir things up at all but the knowlwdge base here is astonishing and the willingness of folks like Geoffrey, PHD, ViperB and others to share is heartening.. and I also feel you pain.. I would of gone insane with 2 poofs in 5k...

btw, doe sit make sense to try to test teh injector for that cylinder... it sure would nbe nice to see defined culprit.. so you don;t lose sleep and worry every time u run boost...

Ed

edpurplett

.. and btw one other thought.. any possibility a tight ringgap caused the problem...(though I doubt it).. BUT I'm a little, a lot actually, confused why the ring is bending UP into the piston break versus down..let alone didn't blow out or break... is this a clue ?? makes me think of previous damage to piston to be honest....

e

Dknebes

I may be missing something here. Joe Essa did not build or recommend the deck heights. He put the car on a dyno and ran safe a/f and timing. If Joe Essa built this engine he would stand behind it. I admire Don for his ability and feel for the problems he has gone through but his problem is some thing like an intermittent fuel pump or something that is plugging the gas tank or one bad cylinder. Don had a problem before and it probably is the same thing that caused the second problem. This can be frustrating because he could rebuild and have it happen again if it is not corrected. I would look at the fuel delivery.

edpurplett

Dave,

No offense intended dave!! I hear wonderful things about Joe.....in general my point is make them defend what they are doing .. so many shops play all sort of games when they don't or can't explain things... and talk over folks... the fact that these folks here share their knowlwdge in invaluable if used correctly...

ANyway.. who has a guess at the ring bend (up) issue... how can that be???

Dknebes

Ed,

No offence taken. I hope some one can find the problem for Don. I would be very frustrated by now.

senna21

My guess was, and still is predetonation.

Here's what I think happened. The piston had a hot spot (on the intake side- apparently). Some have said probably due to a lean mixture. As this spot heated up and began to head toward a melting point the hot spot created a cycle of predetonation. It got hot and the predetonation began at that spot, causing it to get hotter, which increased the predetonation at the spot, which caused it to get even hotter, which increased the predetonation at the spot, which caused it to get even hotter.... this continued until the piston was deteriorated to a point that the resulting predetonation occurred when there was a hole in the piston. The resulting predetonation (still on the upstroke) blew the piston sides and ring upward as there was equal too or greater force still pushing the piston up.

If the detonation had occurred when it should have the piston simply would have been forced back down the cylinder (transferring the force to the crank) and the walls wouldn't have been blown up toward the cylinder head.

sand_man

I think Don is running the iron cylinders from JB Racing that allow the use of molly rings...or are they iron rings? Can't remember exactly, but his cylinders allow the use of a ring material that is different from OEM spec. This might explain why they bent instead of broke.

DonE

In the time since my last post, I've spoken to 2 TEC3 tuners (plus one independent), 2 engine builders and JE Pistons. According to all the tuners, there was nothing that stuck out that would have been a problem. Of course, no two fuel maps on custom motors is the same, but again there is nothing jumping inconsistent with their similar tunes on similar motors.

Two different builders reviewed my build (including deck height) and had no problem with any part of the engine - clearances, pistons, intake, cams, cylinders, timing, turbo, ignition, plugs and so on. JE Pistons looked at the damaged piston and echos what senna21 states.

The only part that does not make sense is the fact that the car ran inconsistently. For example, there were mornings that I had to turn the engine off after 15 min of driving to get rid of the rough cruise and no idle. Once cycled, it ran perfectly until I got to where I was going. Another example was setting the fuel map on a very nice dyno (where you load the engine) and a couple weeks later it is as if I never tuned it (AFR's not even close at cruise and idle - other than temp change, how does that happen?). I've actually called the shop I bought this from while cruising trying to set values, only to have the car run horrible a week later (after no changes of course). When I could occassionally contact electromotive tech support, the same thing happened, but mostly with the (lack of) idle. One last comment, I paid two separate TEC3 tuners nearly $2500 (total) to tune the motor with similar results.

So, what am I going to do? Right or wrong, I am selling the electromotive ECU and coil packs in favor of a Link ECU and bosch coils. Everything else will remain exactly the same.

BrianKeithSmith

What is a "Link" ECU?

Brian