Twin Turbo LS1 - Page 2 - Lateral-g Forums

Blown353 · #11 06-06-2009, 08:33 PM

Jason,

If the bearings are smoked but you managed to get 12K miles out of it my guess would be very, very light and probably intermittent detonation and not continuous sky-high cylinder pressures.

It takes a LOT of force to push the hydrodynamic oil wedge between the bearings and reciprocating parts out of the way and get metal to metal contact; about the only thing that will do it is sudden and severe shockloading... and that would be detonation.

My guess is the thing pinged so lightly you couldn't hear it, it was below the resolution of the knock sensors (if you're still using them), or it was transitional knock that only occurs very briefly under specific loading conditions but it was just enough that over 12K miles it hurt the bearings.

How do the plugs look? Any little itty bitty tiny black specks on them? That's a sign of very light detonation-- not enough to pull metal or deform the ground strap but just enough to rattle the rings so they lose seal and release tiny droplets of oil that then get baked onto the porcelain.

Sucks for sure any way you slice it, but I'll take damaged bearings over hurt or ejected "hard parts" any day!

The thicker head gaskets, while lowering the compression ratio, increase the quench distance and can actually increase the chances of detonation.

Another possibility that I dealt with in a Mustang 5.0 with a Kenne Bell blower: it would hurt head gaskets from time to time and the plugs showed very light pinging no matter how much timing the guy pulled out of it or how much fuel he added at steady state WOT. I dinked with it a while and found that there wasn't enough acceleration enrichment which is VERY critical on an instant-torque (i.e instant cylinder pressure) roots type blower. It would just lightly rattle every time you stabbed the throttle to the floor hard. After a couple months of that it would push the headgaskets. I increased the acceleration enrichment and no more problems.

Jason, if you're going to go back through the motor I would do a +.005 overbore and torque plate hone it. The factory doesn't torque plate hone them. You can pick up some ring seal. Also, if you change the head bolts for studs the rehone should be a requirement anyways as changing fasteners can actually have an impact on the clamped bore distortion. Better safe than sorry!

gearheadgarage · #12 06-06-2009, 11:28 PM

Thanks for the input Troy. Looking to pull the engine out & assess in the near future. Although all knock sensors are in place & there has never been any hint of detonation through any of the tuning sessions, I agree that that may well be the issue. On the way back from Pleasanton I was WOT and pulling solid boost for a steady period of time (140+ mph?) I felt the car jerk 2x as I started to romp past that and subsequently lifted back out of it and cruised a steady 80mph the remaining 20 miles back to Sac.

I don't think the bearings failed at that point specifically.....not likely. I would expect to see some ring lan issues, piston problems or the like if HARD detonation occurred. The fact that I felt it proves to me that there was indeed some sort of detonation, likely not the 1st time. I run it hard & often, and can't say for sure that it hasn't been detonating at inaudible tones.

I am, however, happy to not have experienced catastrophic engine failure. At least now I can study the situation as I disassemble and look for clues. I appreciate the good word-

Any opinions on the rumored poor oil return in the ls1,6 &2 blocks? Another possible issue? Should I repair & re-tune as my wallet prefers or should I dive in deeper. I know the answer, but just asking!!!

mazspeed · #13 06-07-2009, 12:48 AM

Quote:

Originally Posted by gearheadgarage

YUP!! I tried to cheat it by using thicker head gaskets and a cam with more overlap to effectively reduce dynamic compression.....

Guess I might have to get a stroker kit: crank, rods, dished pistons and then run more boost? OH NO, maybe I am gonna have to have a little more giddyup under the hood now?

Reccomendations anyone???

Was this on your red vert Jason?

gearheadgarage · #14 06-07-2009, 07:07 AM

Yes Sir!!

gearheadgarage · #15 06-15-2009, 09:08 PM

Nothing like throwing away good parts! Actually, it could be worse- I blew the top of a piston on cyl #5, and wasted the cylinder/sleeve on both #3 & #5. Resulted in a few cracks in the block too!

Looks like the heads survived virtually unscathed. Ordering up an iron 6.0 block, boring it and running a Callies crank & rods kit likely with Wiseco pistons. This time we'll use a dished,, forged piston in order to accomodate the SuperCharger. I'm amazed how nice all of the bearings and the rest of the bottom end looked- might've lasted forever w/o boost. Guess the block wasn't good to 600 hp+.

Blown353 · #16 06-16-2009, 12:33 PM

Quote:

Originally Posted by gearheadgarage

Nothing like throwing away good parts! Actually, it could be worse- I blew the top of a piston on cyl #5, and wasted the cylinder/sleeve on both #3 & #5. Resulted in a few cracks in the block too!

Looks like the heads survived virtually unscathed. Ordering up an iron 6.0 block, boring it and running a Callies crank & rods kit likely with Wiseco pistons. This time we'll use a dished,, forged piston in order to accomodate the SuperCharger. I'm amazed how nice all of the bearings and the rest of the bottom end looked- might've lasted forever w/o boost. Guess the block wasn't good to 600 hp+.

Ouch... pretty safe to say now it was probably detonation. Were any of the other top rings pinched?

Probably leaned out and rattled on your high speed / high load blast. Make sure you don't have a fuel system deficiency before you toast a new engine!

Look on the bright side, at least parts didn't vacate the confines of the block and dump oil all over the road and under your back tires at 140-something.

Jason, one thing you might want to consider is to give Kurt Urban a call. He can mod the blocks for piston oil squirters which helps out with piston temps and thus detonation resistance-- a good thing especially on pump gas forced induction. Kurt did all the machine work & stuff on my LS2 including adding the piston squirters. I went the extra mile and did thermal coating on the pistons in addition to the squirters.

gearheadgarage · #17 06-18-2009, 08:22 PM

Planning on coating the pistons....will look into the squirters! Cheers.

scamaro355 · #18 07-20-2009, 07:49 PM

Those 6.0 blocks are a dime a dozen at the local bone yards anymore, supposed to be able to support over 800hp in factory form...

camaro2nv · #19 07-20-2009, 08:28 PM

Quote:

Originally Posted by gearheadgarage

Don't forget that big boost combined with factory high compression will eat up bearings if driven hard and often. I just smoked my bottom end after 12k miles on my 520rwhp MagnaCharged LS2.......I'm PISSED!!!

That sux to hear Jason, sorry to hear it. Man how I wanted to do something later on with my LS2.

LSXZ28 · #20 10-04-2009, 04:33 PM

I would agree - make sure the fuel system is up to it! Too often, it holds AFR on the dyno for short pulls, but then it isn't up to the task for a long WOT haul... Put a wideband in the car, and you can watch it while doing those kinda runs...

And I would definitely consider adding a meth kit on any boosted car running pump gas!!