Losing Compression On Dyno, Any Ideas?

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05-05-2004, 07:54 AM

#81

rx794

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Join Date: Dec 2002

Location: Long Island, NY

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This is true Ito, didn't think about it, too much retarded timing will cause really high EGT's, did no one check this?

05-05-2004, 10:16 AM

#82

j9fd3s

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Join Date: May 2002

Location: California

Posts: 22,465

Quote:

Originally Posted by Judge Ito' date='May 5 2004, 03:10 AM

The more I sit here and think about it. I'm almost sure the car is having a timing issue. Not enough timing will cause egt's to go seriously high and damage seals. Since proper fuel pressure was checked, injectors cleaned and balanced proper fuel pressure under a load. I going to say timing needs to be addressed with a timing light under a load.

High egts will melt apex seals. High egts come by easier with not enough timing then a lean air fuel mixture.

well maybe the oil temp or something is a little high, and the timing is a little retarted, and maybe a little of something else. it might not just be 1 thing

05-05-2004, 02:47 PM

#83

RETed

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Quote:

Originally Posted by Judge Ito' date='May 5 2004, 03:24 AM

Mike I remember you telling me the turbo melting due to high egt's I think we might have found the problem. I have also played around with negative timing on the race car and seen a faster apex seal damage(warping) then damage from a lean condition.

Whoa, melted turbo?

Did I miss that somewhere?

If the turbo was melted, this really points to overly retarded timing.

I concur with Ito.

-Ted

05-05-2004, 02:52 PM

#84

94touring

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Coolant temps should be noticable higher too with retarded timing. Although if its just under high load, then you may not notice that as much if you only make short burst.

05-05-2004, 02:59 PM

#85

RETed

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I had to reread everything, since this intrigues me also...

Oh crap, I just reread what pluto said in the first page...

Quote:

The only thing I could really think off is the exhaust port or the shape of the port causing it to run higher EGT than normal. I couldn't verify that w/o knowing what the port looks like but after looking at the worn out apex seals (after the tuning), it seems like that it couldn't have been caused by lean a/f ratio but rather very high EGT at the manifold or the exit of the port. I wish we could have made another pull on the dyno to see how hot the exhaust manifold. Also the turbine wheel and see if there are any abnormal wear caused by extreme thermal conditions.

EGT doesn't lie.

I bet the coolant levels could've been a little high (good call 94touring), but the oil temps should've been down.

This all points to a timing problem or retarded timing.

This all kinda makes sense now. Fuel igniting out the exhaust is violent on the engine (and apex seals), and this explains the apex seals rocking and producing the weird wear patterns.

My money says the ignition timing is messed up or too retarded...

-Ted

05-09-2004, 02:43 AM

#86

pluto

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Join Date: Dec 2001

Posts: 98

I"m pretty positive that it is caused by extremely high EGT. The only thing that confuses me is the fact that it only happens when I lean out the a/f ratio closer to 10.5:1 and above. Why would running richer a/f ratio prevent it from losing compression? Since I was the one that did the tuning and I know my timing map pretty well, There wasn't a time where the leading timing gets below 10 degrees in advance. Split timing should be around 6-14 depending upon where it is in the map matrix. Retarding the timing a little helps spool up because of increase in heat to help move the exhaust velocity faster but it doesn't maintain at 10 degrees of advance through out the rpm. I have been using this timing map for over 100 cars and there were only two cars that seems to lose compression after a WOT pull. One is mike's car and the other is Russ's car.

Hey Ito, How early does the exhaust port open? The reason why I asked is because opening the exhaust port earlier serves similar purpose as allowing hotter temperature out to the manifold to help spool and maintain boost.

I wonder if the combination of my timing map and early port timing causes too high EGT?

Ihor's engine was ported down at least 5mm from factory port and I have never seen his engine loses compression. I guess mike's car is one of those ringer that doesn't want to stay running for too long...

05-09-2004, 04:46 AM

#87

RETed

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Haltech or Power FC?

If it's Haltech, I would just double-check the ignition map.

Glitches on an upload can cause for bad data and corrupt the map and/or settings.

Sorry for stating the obvious - just trying to cover all the bases.

-Ted

05-09-2004, 09:26 AM

#88

Badog

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It's a PFC.

Hey Steve or Mike, got the logs? Point me to them or compare recorded against actual. There are factors in the PFC that will cause the ignition to retard beyound what is intended. Thinking that could be part of it.

Tony