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I agree with jw you may need more cooling capacity. In the interim try to encapsolate and duct air directly through the coolers.

My car only has a measly 270 hp and after 25 minutes of track time my temps starts to creep over 240.

Great car. I forgot it was Don's until I saw it in your sig.

Enjoy that beast.

Tinker
Old 10-08-2011, 07:44 AM
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Question for Chris @ Turbocraft...

Hello Chris,

Could a slipped cam chain sprocket on 1st bank of cylinders, cause a temporary sine wave in the timing chain that could affect the cam timing on the 2nd bank of cylinders?
If so, would it be enough to affect cam timing enough to cause the damage to 1 cylinder on the opposite side of the engine, as shown in the first set of photo's??

Mark
Old 10-08-2011, 06:06 PM
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Is there a rev limiter on that engine? If the answer is no (or it is set too high), then you know what happened. Your well-intentioned friend either missed a shift (it happens when you change cars for a few minutes) or he just let the revs go past the safe point (possibly his car has a rev-limiter and he is used to it) and the valves floated for a moment; that's all it takes in an engine like that.

In any case, I would verify with JB Racing that the valve springs used in that engine were each tested and found to be up to the task at any RPM that could be expected (or unexpected). There is no indication of detonation in that engine in my opinion regardless of the fuel mixture or the ignition timing used (you said it was running well, things like that don't typically change suddenly).

Mark
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Old 10-08-2011, 06:43 PM
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[QUOTE=totle;6297093]Hi guys,

]

After talking with Mike Bruns at JB racing he was sure this was caused by detonation.
He suspected that the right side was damaged as well, so I removed this side as well to find this.



The pistons are black due to that the engine was running some time with fat mixture due to that MAP pressure was way off and gave wring fuel table reading.



Engines running fat don't burn up





I had to order new parts and do a rebuild.
If the engine was original, I could sort parts from my local dealer, but the engine is quite modified.


I talked with Mike Bruns again and he was really helpful in sorting out new parts.

New 98 8:0:1 JE piston was ordered (same as the engine had)
He ordered the new pistons with the top piston ring further down to get more strength on the top of the piston.





Here in lies the real problem

Hot rod engine builers can get special pistons made with nonconforming ring locations to increase compression. The top ring land was located to high, there is not enough metal between the ring land and the valve relief cut in the top of the piston.

Send 1 of your failed pistons to JE and see what they say, if it's a stock piston they may help out with repairs.
Old 10-09-2011, 04:40 AM
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I agree with Paul's comment below on further investigation.

I took a drive with Don in this car a couple months before you purchased it. He was making in the 550rwhp area and we did several runs up to ludicrous speed. Car ran great and I know Don used the car daily for several months afterwards.

Assuming nobody played with your tuning map, and all of the fuel delivery components were functioning properly, I can only imagine detonation being caused by a differential in fuel quality. Here in Georgia, we use 93 octane (US Grade) fuel... I know Europe's numerical values for fuel equate to a lower knock rating, but don't recall the comparison past that. If the car were tuned for a higher fuel quality, your comments about ignition advance might be right on the lower quality fuel.

As your friend was driving the car while the damage occurred, it's hard to know for sure what happened. Are you positive the car was fully up to temp before your friend revv'ed it out? I seem to remember Don telling me he rebuilt the motor once in the past due to not letting the car get up to operating temp - if I remember the story correctly, in that incident he saw contact with the valves.

Regardless of the cause, I can attest to the car being in great working order when I saw the car here stateside.
Best,
John


Quote:
Originally Posted by 911nut View Post
Look closely at the adjusting slots on the sprocket pictured. There's witness marks where it was in one position and is now indexed a few degrees.
Also, you can clearly see the contact between the broken piston and the valve. There's a crescent shaped indentation on the piston top which should be a dead giveaway. Furthermore, the valve is bent from the contact.
You need to ask yourself how it was that the previous owner was able to drive the car and never blow up the engine if it was truly was too lean.
Not arriving at the right root cause may cause you to rebuild your engine more than once.
Old 10-09-2011, 09:19 AM
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Quote:
Originally Posted by lucittm View Post
Is there a rev limiter on that engine? If the answer is no (or it is set too high), then you know what happened. Your well-intentioned friend either missed a shift (it happens when you change cars for a few minutes) or he just let the revs go past the safe point (possibly his car has a rev-limiter and he is used to it) and the valves floated for a moment; that's all it takes in an engine like that.

In any case, I would verify with JB Racing that the valve springs used in that engine were each tested and found to be up to the task at any RPM that could be expected (or unexpected). There is no indication of detonation in that engine in my opinion regardless of the fuel mixture or the ignition timing used (you said it was running well, things like that don't typically change suddenly).

Mark
The rev limiter is set in the ECU. Set to cut off at 6800 rpm

Well car was running well. But I am not sure that the mapping was done in a dyno. From what I remember the mapping was done with log files from road test.
If that was the case, I believe that the setup in high rpm was not set correctly when engine was under stress
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1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
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Old 10-09-2011, 09:43 AM
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Quote:
Originally Posted by turbo owner View Post
Here in lies the real problem

Hot rod engine builers can get special pistons made with nonconforming ring locations to increase compression. The top ring land was located to high, there is not enough metal between the ring land and the valve relief cut in the top of the piston.

Send 1 of your failed pistons to JE and see what they say, if it's a stock piston they may help out with repairs.

I did send one piston to JB racing, and had JE custom made the new pistons
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Trond R.
1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
1972 914-6 GT replica project
1986 944 Turbo
Old 10-09-2011, 09:47 AM
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Quote:
Originally Posted by JBurer View Post
I agree with Paul's comment below on further investigation.

I took a drive with Don in this car a couple months before you purchased it. He was making in the 550rwhp area and we did several runs up to ludicrous speed. Car ran great and I know Don used the car daily for several months afterwards.

Assuming nobody played with your tuning map, and all of the fuel delivery components were functioning properly, I can only imagine detonation being caused by a differential in fuel quality. Here in Georgia, we use 93 octane (US Grade) fuel... I know Europe's numerical values for fuel equate to a lower knock rating, but don't recall the comparison past that. If the car were tuned for a higher fuel quality, your comments about ignition advance might be right on the lower quality fuel.

As your friend was driving the car while the damage occurred, it's hard to know for sure what happened. Are you positive the car was fully up to temp before your friend revv'ed it out? I seem to remember Don telling me he rebuilt the motor once in the past due to not letting the car get up to operating temp - if I remember the story correctly, in that incident he saw contact with the valves.

Regardless of the cause, I can attest to the car being in great working order when I saw the car here stateside.
Best,
John

John, there is many issues that can go wrong.
Of course there could be a over-rev if shifting to 2'nd instead of going to 4'th.

As mentioned earlier, I don not blame Don at all.
I have a good confidence that the build is well done.

As I recall Don mapped it for US 91 octane, equivalent to 95 oct in europe. 93 US octane is equivalent to 98 eur octane.

I have rebuilt the engine and it has been running well all summer.
Just wanted to share my story. Did not want to blame anyone
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1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
1972 914-6 GT replica project
1986 944 Turbo
Old 10-09-2011, 09:56 AM
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Quote:
Originally Posted by totle View Post
I did send one piston to JB racing, and had JE custom made the new pistons
Not wishing to stir up a hornet's nest here, but those pistons were doomed to fail. You're right about the top ring land being too close to the valve-cut crown. But, if you look at the area where the fracture occurred, there is very little material at the outer edge of the valve cut to the interior section of the ring land, maybe several millimeter's? Once that cracked started, the area would start to lift........BANG! Valve contact., catastrophic failure.

With all due respect to JB Racing, that was NOT caused by detonation. That is a piston design flaw.

Totle, I know you're not trying to place blame, but illustrate an engine failure. I respect that, just thought you should know a more likely scenario.

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Old 10-09-2011, 11:43 AM
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Hi Dave.
Thank you for your comment.
This scenario has also been in my mind. Maybe you are right here.
If it happened on a build I had put together, I would probably look more into this.
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Trond R.
1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
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Old 10-09-2011, 12:59 PM
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Quote:
Originally Posted by 911nut View Post
Look closely at the adjusting slots on the sprocket pictured. There's witness marks where it was in one position and is now indexed a few degrees.
Also, you can clearly see the contact between the broken piston and the valve. There's a crescent shaped indentation on the piston top which should be a dead giveaway. Furthermore, the valve is bent from the contact.
You need to ask yourself how it was that the previous owner was able to drive the car and never blow up the engine if it was truly was too lean.
Not arriving at the right root cause may cause you to rebuild your engine more than once.
Full agree with your analysis !

Detonation is not responsible of this damage.

I would not use these adjustable sprockets.
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Old 10-09-2011, 01:18 PM
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Quote:
Originally Posted by WERK I View Post
Not wishing to stir up a hornet's nest here, but those pistons were doomed to fail. You're right about the top ring land being too close to the valve-cut crown. But, if you look at the area where the fracture occurred, there is very little material at the outer edge of the valve cut to the interior section of the ring land, maybe several millimeter's? Once that cracked started, the area would start to lift........BANG! Valve contact., catastrophic failure.

With all due respect to JB Racing, that was NOT caused by detonation. That is a piston design flaw.

Totle, I know you're not trying to place blame, but illustrate an engine failure. I respect that, just thought you should know a more likely scenario.

I am also agree. This is possible scenario either !

The piston builder should make a wider radius transition to avoid weakness in this area. (From picture ,I am even not sure there is a small radius )
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Old 10-09-2011, 01:24 PM
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I see signs of detonation on those pistons. It's showing up as fine pitting erosion in the aluminum mostly around the edges of the JE piston and in the edges of the valve pockets.
Look at the new JE forged pistons. They have a smooth shiny machined finish and the broken ones are not a smooth machined finish anymore, instead they show fine pitting and erosion mostly around the edges of the valve pocket the very outer circumfrence of the piston where it comes up close to the squish band in the combustion chamber. That is from the extreme heat of detonation melting the aluminum on the surface of the pistons where the detonation is origonating.

I've installed 10:1 forged JE pistons in a normally aspirated 3.5 liter BMW motor and seen them again thousands of miles later when pulling the head to replace a rocker arm and that motor detonated a little bit sometimes under full acceleration but not alot. After cleaning the carbon off the tops of those pitons while they were still in the block the crowns looked no different from when they were brand new out of the box. They were perfectly smoth and the fine machine marks were totally visable, and there was absolutley no pitting and erosion from extensive detonation.

Thats not what killed your motor though... the intake valves and pistons hit each other either from your friend over revving it when he shifted gears or maybe the adjustable cam sprockets came loose and the cam timing changed. I doubt that though.. If that happened the cams would have gone to the fully retarded or late cam timing postition those sprockets allowed and then the exhaust valve would be closing alot later and the piston would come up and hit the still open exhaust valve as it reaches TDC on the exhaust stroke.

But, your valves are lunched on both sides and it's really unlikely that both cam sprockets came loose at the same time - that is extremely unlikely.

So in the end.. I think your buddy that is used to a much newer design faster shifting shorter throw Getrag gearbox with fast light acting borg warner synchros screwed up his up shift, missed the gear, and overreved your motor destroying it.

..do you think he would admit to that?
Old 10-09-2011, 02:53 PM
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LOL!
Sure can tell the builders from the drivers from that last post!
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Old 10-09-2011, 03:07 PM
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Quote:
Originally Posted by JFairman View Post
I see signs of detonation on those pistons. It's showing up as fine pitting erosion in the aluminum mostly around the edges of the JE piston and in the edges of the valve pockets.
Jim, since there were pieces of piston bouncing around in the combustion chamber (some which passed out through the exhaust valves and on to the turbo), that is the most likely cause of the pits that you see in the photo.
Sometimes the damage is so extensive it can obscure the root cause of the failure. In this case, however, there isn't substantial shrapnel damage, which can simplify the investigation.
As for the cog slipping, that most likely have been the result of an overrev. I didn't realize that both banks of valves had kissed the pistons.
Trond, it appears that your buddy owes you an engine......
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Last edited by 911nut; 10-09-2011 at 06:06 PM..
Old 10-09-2011, 06:03 PM
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I'm betting the cam gear slipped when the valves hit the pistons, not before.
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Old 10-09-2011, 06:15 PM
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In the pic above looking partway down the headstuds it looks like combustion gasses were leaking out between the heads and cylinders on the intake side.
The shiny ARP headstuds show it up.

Glad to hear it's running good now.
Old 10-09-2011, 06:54 PM
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