DAPSUPRSLO

iTrader: (14)

I have been tuning on a friends 99 h/c c5 corvette and have been running into kr no matter if I set the wot timing at 25, 27, 0r 30. We have been running into kr with a ported stock maf sensor and then an untouched pro auto tech maf sensor.

When he put the cam in with his heads which are milled 30 thousanths he decided to flycutt the pistons. When he cut the pistons he cut them too deep and decided to fill them ever so slightly with epoxy. My thoughts are that the epoxy is causing hot spots on the pistons which in turn is causing pinging and kr.

I have been using a LM1 Wideband and his a/f ratio started off at 11.8-12.0/1 to a now 12.5-12.7/1.

P.S. We are pretty much getting the same kr and pinging at all different timing levels. Also, this pinging and kr is only at wot, although I did see a very short occurence at part throttle.

What are your guys thoughts.

Dope

iTrader: (2)

He used epoxy? Seriously?

That just sounds like a really bad idea, but maybe I've just never heard of that.

Dope

Another_User

What a stupid idea. He might as well have used play-doh. I bet if you check the epoxy has blown right off (hopefully not getting caught on any valves on the way out, and is not only causing hotspots, but also much much more damage. Nice.

Scalpel

iTrader: (4)

It depends on the type of epoxy material. Some can withstand great temps and pressures but I doubt he used the correct kind.

sleeperstyle

iTrader: (4)

im thinking false knock- but there is such a thing as rich knock..

Scalpel

iTrader: (4)

Rich knock? Do you mean having too much fuel (a rich condition) can cause knock (detonation)?

If so, that's incorrect. More fuel resists detonation. Thus if you're adding more fuel you're less likely to have knock.

DaleMX

iTrader: (4)

The epoxy must be vaporized by now. I think the good stuff is good to like 350 degrees, but the pressure and heat expansion have destroyed it without a doubt, and I would doubt that any damage occured.

Sounds like a bad knock sensor, or an aftermarket pulley to me.

Dale

sgarnett

iTrader: (1)

I doubt if the epoxy has completely vaporized. It has probably carbonized and probably cracked. Even "normal" carbon deposits can increase the compression ratio and act like the glow plugs used to start a diesel.

There are probably big ol' glowing hunks of carbon where the epoxy used to be, causing pre-ignition.

If there's enough carbonized residue on the valves, they may not be sealing properly and could be glowing too.

Textralia

Put your tools down and back away from the car! Wash

DAPSUPRSLO

iTrader: (14)

This is not my car guys. Actually my car runs 11.62 with nothing more then a cam, boltons, m6, and at 3545 raceweight so I can assure you mine runs fine. The car I speak of is a 99 corvette.

This nock is not false, I can hear the car pinging. I will have to get back to him and get back to you guys on the kind of epoxy he used and its heat qualities. I still think this is his problem.

Anybody ever had any experience with the pro auto tech maf sensors? I don't think this is his problem but I am just curious.

DAPSUPRSLO

iTrader: (14)

Anybody else have an opinion?

Another_User

Well, who can be sure what is moving back and worth through those red hot holes in the pistons. I would imagine (somebody correct me if I am wrong) that they will start to burn the pistons up and get bigger.

Run the engine and pull the oil cap and see if she's smoking inside (keep your face away from the hole). You can also check the cylinders and see if they lose compression.

slow

iTrader: (7)

pro auto tech maf sensors .... more info on this product?

most likely this has something to do with your detonation problems.

Ryan

DAPSUPRSLO

iTrader: (14)

I don't know much about these maf sensors, they seem to be a corvette only product. We had pinging with a stock ported sensor also. I will check on it. Hell, maybe I'll try to get him to find a stock maf and try that although I don't think that is his problem but hopefully for him it is. Thanks guys, keep the replies coming.

MyLS1Hauls

iTrader: (2)

I would say its hot spots caused by the epoxy...Holy crap...I can't believe he used epoxy on his pistons. Combustion temps would immeditately soar way beyond the limits of any epoxy. Also, who knows how the epoxy (or whats left of it) transfers heat, so again, localized hot spots.

Another_User

PLEASE post pictures of the engine's innards after you guys disassemble it. It should be any day now...

I am dying to see what happened to the epoxy. It will be very educational for us all.

un4giv3n

off topic... what cam are u running?

J-Rod

If you went through the piston, that is very very bad. I can't honestly believe anyone would use expoxy. I'm honestly suprised its held together. Have you thought about putting the stock MAF on there to check for KR with it. But no matter what, the motor needs some attention...

BTW, What was this guy thinking. Most valve reliefs are .60 to .80 at the most. The piston is like .220 -.250 so you have to really try to cut that deep...

DAPSUPRSLO

iTrader: (14)

Custom grind that I came up with. 230/236 107lsa 107icl 576/574.


We are going to try the stock maf and see if that helps although I don't see how it could as his a/f was never leaner then 12.7 to 1.

He is going to be running the 402 slp shortblock soon anyway so it is no big deal but if he pulls the heads I would be glad to take pics. Thanks guys.