Quad Four tuning help! Engines blow after one race, every time.

[Gerrot]

Hello all,

I tune a lot of IMCA Sport Compacts. Generally I tune the ECOTEC engine, however I have a guy that now came in with the Quad four engine in his Caviler. He stated the engine had blown up twice before bringing it to me. The pistons are a forged Wiseco, and they still scratch the walls and the engine looses compression. The engine itself is a 2.7 Liter stroker engine. He along with two other guys are having this same exact problems, they always destroy two pistons(Unsure what exact cylinders).

He brought the car to me with a fresh engine, ran ok. We tuned it. Had zero knock, solid 12.5 AFR and made great power. He went to the race's and within 10 laps, engine had the exact same problems, loosing 2 cylinders/pistons. Has anyone ever had this problems, seen this problem or even heard of it? I'm lost, this cars scans show great, EGT on the dyno are even, not to hot by any means.

Is there a known issue when doing the 2.7 swap? Should I be doing something special?

[5FDP]

Sounds more like maybe an oiling problem than a tuning issue.

[Gerrot]

Exactly what I was initially thinking.

[gmtech16450yz]

Ring end gap too tight? Did you get to look at exactly what the "scratched" walls looked like?

[Dr. Nopps]

This may be more of an engineering/design problem than anybody could really "fix" on theese motors. I was going to build my own Cavalier with one, but was talked out of it by a well respected technician who warned me of their many inherent flaws. From what I can barely recall the cam chain setup was a nightmare of a joke when compared to almost any other Over Head Cam engine setup. But more importantly in regards to what you're experiencing he also said somethig about the balancer shaft causing problems because the oil had to be channeled all the way through it or something, setting it up for further possibility of disaster (starvation) when it doesn't line up correctly or gets plugged. And personally every single time I've ever popped the hood open on one that had been running for even a short drive, it felt like it was overheating or damn close to it.

[JMHZ2401]

This may be more of an engineering/design problem than anybody could really "fix" on theese motors. I was going to build my own Cavalier with one, but was talked out of it by a well respected technician who warned me of their many inherent flaws. From what I can barely recall the cam chain setup was a nightmare of a joke when compared to almost any other Over Head Cam engine setup. But more importantly in regards to what you're experiencing he also said somethig about the balancer shaft causing problems because the oil had to be channeled all the way through it or something, setting it up for further possibility of disaster (starvation) when it doesn't line up correctly or gets plugged. And personally every single time I've ever popped the hood open on one that had been running for even a short drive, it felt like it was overheating or damn close to it.

A factory 2.4 does have a balanced shaft setup. But to get a 2.7 stroker you are not using that setup It is a combo of 2.4 and 2.3 parts.

I'm saying this is a engine build/builder problem.

[Dr. Nopps]

Now you've got me wondering if it "almost" is. My engine machinist would add some extra clearance specificly on engines that were going right to race off a fresh build. (without a propper break in period) If theese guys are all racing off of freshly build engines without a good break in, that might account for the same damage even whether the same builder was being used or not. Even with different shops, actually the better they really are they should all be using the same initial specs showing up on race day with almost the same engines. (internally) But I still won't trust those engines ever and the fact that it's happening to only two cylinders on all of the cars, I don't know the only other thing I can think of is not being properly torque plate honed during the bore/hone process.

[cobaltssoverbooster]

just a note:
when a balance shaft is deleted the front journal is left in the block with its bearing so the chain gear has a mounting location.
the rest of the journals get the bearings pushed out and new ones are inserted in a rotated position to prevent the oil holes from spraying off excess pressure. oil does not flow through the balance shaft.

[Gerrot]

Just a follow up on this thread. I have tuned another "5" cars with this engine configuration, but different engine builder. NONE of those have had any problems. Only the engines coming from "X" shop/builder have had problems. So I'm chalking it up as a builder failure. What he is doing different, I don't know. But I do know now it's not me and I'm happy about that!

BTW, for anyone looking to do these Stroked Quad tunes. Beware they will make more power than you think! I had one make 252whp the other day!

[* _ *]

solid 12.5 AFR.

cars scans show great, EGT on the dyno

Are these readouts grouping all chambers or individual port recording?

[se_sun1997]

a crap ratio rod/stroke can easily break piston....

[Gerrot]

Are these readouts grouping all chambers or individual port recording?

Individual readings on each cylinder. 4 EGT and single wideband.