good luck on getting it fixed.

 

UH OH........don't pull me into this!!!! I can see where you are going!!!

The piston that I mic'd up was from a different build of Jet's. The piston did seem to have a fairly healthy taper to it......I ended up mic'ing the piston several times to make sure I was getting accurate readings. I thought it was odd, but maybe that's how Arias likes to machine ther pistons. Anyways, that was over a year ago. MAybe, it was a bad piston...don't know. I have no idea what these pistons are like, but Jet's engine builder will be checking and measuring everything when he takes apart the short block. I am curious to see the results.

 

Larry, can you post some close up pictures of the contact marks you are seeing?

It's unlikely that the pistons themselves are to blame. These types of pistons have been used literally 100 or so buildups, between FP, GTM, IPP, PF, and others...and race pounded and abused by many people.

Pistons will rock back and forth in the bore slightly...this is normal. Piston to wall clearances are crucial to a well behaving piston. GTM assembled the shortblock, and have plenty of engine building experience at their disposal, so that's not going to be the issue.

Second point, is that you are running the UTEC and tracking the car. AF ratio is just one element of the tune. Personally, myself and a lot of other tuners don't like racing with the UTEC, or pushing it too hard, becuase it doesnt offer the level of control or comfort that a Haltech or FCON would provide. I am by no means saying the tune is at fault. I am just saying that the UTEC can do funny things...particularly at high boost.

Detonation also has one other effect, that we often overlook: It hammers the pistons and violently rocks them at the top of the bore. With really strong piston like the ED, you may not see other signs, like chipped ring lands. This could be a contributing factor to any marks you see. Also check the cylinder bores for taper. If they are enlarged at the top of the bore...bingo....there is your issue. When you pushed your pistons out of the block during disassembly, did it take a lot of force, or did the pistons just pop out?

But I would like to seem some pics of these marks.

 

Sharif,

Larry took the short block to the the machine shop in "assembled" condition, so he never took the pistons out of the bores.

also, here's a couple camera phone pics of the #2 cylinder combustion chamber. It looks like there may be contact on the exhaust side of the chamber.

 

Hmmm... would be very interesting to know if the cylinder bore was out of spec at the top vs. the bottom. Inherent flaw of running boost with an open deck design?

JET, you used Evans this past season, correct? I remember you had a thread early in the year about it...

EDIT: Just saw the pics quadcam, and I see discoloration but I cannot make out a mechanical disruption - looks smooth. Could you feel something?

 

rcdash.......it may have just been "kissing" the surface. definately, doesn't look like the piston "crashed" into the head!

I think Larry is more concerned with the deteriorating ring seal after only a few thousand miles of driving.....This is a secondary problem. What's done is done......I am curious to see what the tolerances and clearances are when the engine builder performs the disassembly.

 

What are you smoking?

I have Ed pistons, fawk my life

 

I don't smoke. No point agonizing over this until the full teardown is complete.

 

I think he meant open deck failure. Our FP S1 shorblocks are all open deck with Arias ED pistons.

 

To the readers of this thread just to be clear. I am not implicating that there may be a problem with the ARIAS ED pistons. It's just a factor that several people picked up on upon a very rudimentary inspection without tearing the motor down. Don't forget we are looking at a cold motor. The top of the piston will expand when at operating temp.

The piston shows absolutley no signs of detonation at all and neither do the spark plugs.

There are definite signs the pistons are hitting the heads. Why? We don't know yet.

 

Jet see the light spots on your pistons? Is that where you think the contact is occuring?

 

Yes.... and there are coresponding marks on the cylinder head. All the marks are on the top and bottom side of the piston parallel to the wrist pin. This is what the machinist said it was. Cylinder #2 was particularly bad.

 

Sorry to hear about this....I have the same pistons and use the car in the same manner as you. I will wait to see what the findings are....I am really hoping its not the pistons.

 

Larry you have had the worst luck with your project, I sympathize with you, and hope you can be back on the road ASAP, let me know if there is anything I can do to help.

As far as the GTM short block we shipped to Forged Performance for Larry this was his second build as most of you already know, therefore the block has been decked twice by us. That will definitely effect how much clearance the pistons have relative to the cylinder head. Usually in this case scenario we always install a thicker head gasket to compensate for any machining done to the heads and block. Keep in mind that the factory gaskets and HKS gaskets are virtually the same thickness (measured by us in house).

As far as the piston rocking in the cylinder hole, this is normal in a high performance engine. The piston on the top is always smaller by .0040" meaning if you measure a brand new piston out of the box, unused, at the highest point it will be .0040" smaller in diameter than the lowest point.

Our pistons are designed to be .0023" below the deck, to accommodate for expansion and piston lateral movement. So if you press on the piston on one side, and measure the height, you will get ~.0011" from the deck to the highest point of the piston.

If you take that into consideration, with the block being machined twice, the head gasket will play a very important role in the cylinder head to piston clearance.

This brings me to the next point, another reason a piston could make contact with the cylinder head, is if the pistons had expanded abnormally, this is something that your teardown inspection should reveal Larry.

We have had reports of GReddy turbocharger failing due the consistent high EGT's of road racing, as you can see from the teardown your turbos did not last very long. We believe this is due to the older design and no water cooling available. If you notice anyone who road races their G35/350Z on a regular basis, they more than likely are using a turbo system which utilizes a water cooled turbocharger, like Garret. As a matter a fact, I believe Sharif went through 2 sets of turbos on his Z when he was road racing with his GReddy kit.

Personally, I would recommend not using the GReddy turbochargers/turbo kit again if you plan to continue road racing with your car.

You have my cell, anything you need please do not hesitate to call me.

Best of luck,

Sam
GTM

 

About the Watercooled vs Non Watercooled....that is a fact in road racing....This is why 99.999% of the Porsche teams use Garrett turbo's.

 

I chewed through a couple of sets myself roadracing, but they were all after-market upgraded 20G wheels. Still on my first set of Garrett's.

 

+1

-George
GT Motorsports

 

18G's probably wouldn't have been much better, since they are basically the same. I would actually assume the 20g's would be better since they flow more air.

-George
GT Motorsports

 

so we already decided its the turbos fault?




either way ... garrett ftmfw!

 

I think Sam said its because the block has been decked twice