Muckman’s High Compression Super Build

Muckman

Not a M0derator
I have bad news to report. It turns out the pistons are contacting the head at high rpm. There were no signs of this during the 100 mile break in but I only revved to 8000rpm. Once we revved to 9000rpm on the dyno it was obvious something was wrong. A look inside with a borescope showed evidence of piston to head contact. Last year .035" piston to head clearance was adequate but apparently it is not enough this year with the heavier pistons. I am in the process of pulling it all apart to inspect for damage.

We only made 4 pulls to 9k before we stopped. We had pulled the wastegate spring to make it easier to tune the vacuum tables. The engine made 238whp (STD CF) @ 0psi with a turbine wheel flapping in the exhaust.
 

Nick_C78

New Member
Damn man. Do you think it has to do with the stiffness/weight of those wrist pins? I know the pistons themselves are beefier as well, but it seems like the wrist pins is the most significant thing you changed in terms of weight and strength.
 


Muckman

Not a M0derator
95B18BTurbo said:
If there is no significant damage to the head, do you think you could save it with a thicker Cometic gasket?
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Yes. Thicker Cometic is what Im looking at now.

Nick4dei said:
Do you think it has to do with the stiffness/weight of those wrist pins?
Click to expand...
Both the piston and the pin increased in weight.
piston 279 vs 338
pin 68 vs 108
total 347 vs 446
difference 99g or 28%
Thats nearly a 1/4lbs. At 9000rpm thats a lot of load.

Aussie said:
You had some stout rods, can't believe they stretched that much.
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Me either. But everything expands from heat and stretches from centrifugal force. The hard part is calculating how much.
 

Nick_C78

New Member
Yeah man, that is a lot of load. Especially per rod. Hopefully the Dart head isn't that dinged up. I doubt it is, because from the way you describe it sounds like it is just kissing it. Good thing you guys were "careful".
 


Aussie

Zoom-Zoom
Muckman said:
Me either. But everything expands from heat and stretches from centrifugal force. The hard part is calculating how much.
Click to expand...
You think the fact that you weren't running any boost had something to do about it. I remember something about higher cylinder pressure from forced induction countering stretching
 

Muckman

Not a M0derator
No, that wouldn't work. There is only cylinder pressure under the power stroke. All the cylinder pressure would be vented on the exhaust stroke.
 

Aussie

Zoom-Zoom
Yea that's true, but combustion starts on the upward stroke, and while it is exiting the exhaust it's also pushing down on the piston or else you wouldn't be making power.
 
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Muckman

Not a M0derator
7/13/13: Dyno day - had 100 miles on the new 2013 motor. On 4th pull to 9500rpm a rod flew through the block and about 3k went down the drain.
8/15/13: Bought back up block to salvage seaason, sleeved GSR, low compression tho. Put my Dart head on it, same cams, turbo etc.
Tuner dicked me around all summer, couldnt get back on dyno. Season lost.
10/8/13: Son was born
11/3/13: Tried to salvage something so I did a low vs high compression dyno comparison at 0 and 5psi levels.
1/18/14: Sold backup block.
 

Nick_C78

New Member
How did the low vs high compression dyno look? I am interested in those curves.

Congrats on your son being born. Even though it is very late. lol Is he robbing you of sleep yet?
 
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