setup is 2.3,hta86 ss, stock head,intake & TB, 3.5" intercooler,aem ems,comp 272 cams, fidanza gears.

so heres my problem. i got it running and tuned with the cam gears set to 0,0 @ 23psi. car felt like TOTAL crap. lots of midrange power but falls off hard on top. quits pulling hard by 7500. so i retarded my cam gears together 2 deg at a time. each time i did i had to add around 4% fuel to keep it from going lean up top. car was pulling harder and didnt loose and midrange power,spoolup and did not get rich. so i did another 2 deg. same thing. so i ended up at -7,-7 on the cams and the car was feeling awsome! pulled hard from 5K to 8.5K. i ran a 10.9 on street tires spinning like hell. so all was well. at 23psi i only had 2deg. timing at 5.5k and 6deg. @ 8500. way low timing! but i was still getting detonation sometimes. a/f holding around 11.5.... so after about 1500 miles i was racing a bike and bam. burnt a hole right through #2 piston. i had david buschur look at my tune and he didnt see anything that was cause such a thing. so my question is..... is it possiable to retard the cams far enough where i wouldnt have any ign. timing but it is wanting to detonate? i have never heard of such a thing but thats the only thing on my setup that was oddball. also after each time i run the car hard i could hear some piston rattle. come to find out it was a hole being burnt in my brand new piston. anybody got any ideas?

 

-7/-7 is extreme. I would have recommended something like -2/-2 or -3/-3 for that cam set for drag racing. If you need more than that, you should be looking at a different cams, as that Comp Cam set isn't really timed for all out power.

Holing a piston is usually the result of a lean mixture and ensuing detonation, but enough retard on the exhaust cam can create piston/valve contact. As for hearing 'piston rattle' after each run, I'm not convinced that's what it was, but I am convinced that noise (whatever it was) contributed to the problem.

 

well ted, i guess i thought that i could keep moving them if they kept making power. so thats what i did. it was never lean on my aem guage controller. 11.5 afr and it seemed to be consistant too. i can send you some datalogs if you would like to see them. i agree -7 is extreme. but damn it was running good! LOL my valves look fine and i dont see any piston to valve contact. i see a piston completly melted through on the intake valve cutout. through the rings and all.i heard knock sometimes too. but i wasent sure thats what it was. guess i know now. what i ment by noise was, after everytime i ran the engine hard it got a little louder. like more piston rattle. usually signs of piston scuffing or in my case melting down.
i just cant figure out why this happend when it had plenty of fuel and no timing. 2-6deg.
i should have been more like 2-11. i think it was detonating alot over time and finnaly it poped a hole in the piston. i heard it knocking when it let go too. but it was never major. it was very light detonation. i have heard a boosted motor knock hard and it sounds off.
i dont think it was knocking when i had the cams set to 0 but im not sure. im just lost.......

 

anyone else got any ideas?

 

The car can det at -2 degrees timing... just because your timing at peak torque was 2 doesn't mean the tune was safe. How were you monitoring the engine for det when tuning it?

 

knock sensor. how could i need -2 deg timing? negative timing is bad. if i had a crap load of boost then i could see it knocking even with low timing. but 23psi? i see people with the same setup running 30psi. what gives?

 

Well to give you an example, on the same fuel and same boost, my buddy runs about 10 degrees more advance than I do, yet my car is faster. The more cylinder pressure you are able to create, the less advance you will be able to run in general.

But to answer your question... you said the car was detonating sometimes... so there is your answer. You kept driving and racing on a tune that det'd sometimes?

I'm not sure if retarding the cams like you did could cause a situation where the car would be more prone to det, but even if it was, if you tuned it so there was no det, you wouldn't have had a problem provided there was no piston to valve contact.

When you say "knock sensor", what do you mean? Do you mean you would watch the knock sensor voltage datalog on the AEM? Were you able to pull a log off the AEM after the burnt piston incident?

 

i understand what you mean about the timing. but i swear it would detonate at 18psi with 1 deg timing! thats wack! LOL yes, i datalogged the stock knock sensor on the aem but i was not logging when it let go. it was knocking though. i could hear it. i wasent sure thats what it was but i am sure now!