GM Reman Engine Question

[truckins10]

Would any know what compression ratio my engine would be running with .030"over piston?? This is what came with my truck, its a reman from GM. I wanted to know to put my KR problem to rest. Anyone knowledgable on the subject?? Thanks Fern

 

[sytyguy]

What vintage is the engine? If it's post '98-ish, I can almost guarantee you that it has incorrect parts in it. The compression ratio might be correct, but the main caps, head gaskets, etc......could all be wrong. I do know that when I tore down the longblock that was in my truck back in '99, it had incorrect head gaskets, grey iron main caps, and L35 heads. It did have the correct pistons.....though that comes as no surprise since they're shelf items and readily available. GM's replacement offering has only gotten worse over the years.

I would say that your compression ratio is probably close to correct (maybe as high as 8.5:1) if it has the correct pistons. With standard LB4/L35 issue pistons, it would be closer to 9.0:1. Only way to know for sure would to tear down and take measurements.

How bad is the detonation (degrees)? Could it be something else? Could it be false? Does the engine burn oil?

If the knock is indeed real and uncurable, then PLEASE take it easy on the engine and prepare for a rebuild. The weaker main caps cannot handle the stress of a healthy engine, much less one that's detonating.

My advice........peel back the boost, train the foot, and start stockpiling rebuild parts.

HTHs

Hood

 

[truckins10]

Thanks for the reply,
The engine was done near the end of 98 if I remember from the tag on the block. Whats differant about the head gaskets, are they thicker to lower compression, or differant material??? Would the compression still be as low as your guessing even though it has been bored .030" over??
The engine is in great condition and does not burn oil. I think it is false knock but cant prove it. I posted this before but, when in park and I rev the engine, scantool shows 4-7KR. I disconnected the KS wire right from the ecm harness, same thing. So I thought maybe it was the ecm, got a spare from a 89 turbo sunbird and samething. I dont know, these guys seem to think thats normal, that with the KS wire disconnected the ecm set KR to 4. :-? NEWAYS thanks Fern

 

[turbodig]

Thanks for the reply,
The engine was done near the end of 98 if I remember from the tag on the block. Whats differant about the head gaskets, are they thicker to lower compression, or differant material??? Would the compression still be as low as your guessing even though it has been bored .030" over??
The engine is in great condition and does not burn oil. I think it is false knock but cant prove it. I posted this before but, when in park and I rev the engine, scantool shows 4-7KR. I disconnected the KS wire right from the ecm harness, same thing. So I thought maybe it was the ecm, got a spare from a 89 turbo sunbird and samething. I dont know, these guys seem to think thats normal, that with the KS wire disconnected the ecm set KR to 4. :-? NEWAYS thanks Fern

Try plugging your Knock sensor line into the input on a tape recorder, and recording it. It tends to work a lot better if your recording device has something to limit input level.

A laptop mic is usually too sensitive... it clips off as soon as you get on the throttle.

Haven't tried it, but an old passive stereo EQ might work nice to lower the input level, and you could even filter out some of the frequencies you didn't need.

Once you get a good recording, your ear will tell you whether it's deto or not.

I've seen, more often than not, that the fuel lines get bent/screwed up
right near the trans bellhousing. You don't want fuel lines, tranny fluid lines, or the like contacting the block anywhere.

DP contacting the frame is another source of false knock.

Serpentine belts can sometimes whine and fool knock sensors.

Wrong timing chain/gears can do it too.

Our ESC cal chip doesn't seem to be very tolerant of outside noise influences. Somebody really needs to do a DSP filter circuit that could go between the sensor and the ECM and filter out the crap...

Later,

Dig