Need some advise on how this happened. I got into it 1/2 to 3/4 throttle, spun the tires, traction control engaged, and i heard a loud pop. From that point a loud tick started. I thought for sure valve train but ended up being the rods.

Does anyone have any idea why this would happen?

Thanks for your help!!

 

Mighta had something to do with the boost.

​​​​​​​What was the tune you had on it at the moment?

 

The car has been together for 20+ thousand miles. First issue I've had. It was tuned with hp tuners, but I don't know the specifics of it.

If it was a tune issue wouldn't i have seen this already?

Thanks!

 

Are you saying that you bolted an LSA blower on an LS3 engine? Correct me if I'm wrong but LSA engines come with forged internals, and for good reason.

 

LSA and LS3 have different compression ratios for one and the LSA blocks have better bay to bay breathing which makes them more suited for boost but my thinking is the higher compression LS3 engine with the cast rods and pistons didn't fare to well when you got into it.

 

Correct, LS3 engine and bolted LSA blower to it. Yes I'm reading about the differences in the LS3, and LSA engines.

I bought the car already built.....

So do you think the boost could bend a rod? I've seen high teens in boost numbers.

Thanks!

 

Boost can definitely bend a rod, especially if there's too much timing at low RPM. Or detonation. LS3's are 10.7:1 compression. Add a blower and you're getting into some serious cylinder pressure.

 

Ok so any suggestions for fixes? Forged rods and pistons be good? Or does the compression ratio need to come down as well?

Thanks for the help!!

 

I'm running Summit ProLS pistons and rods in my Firebird, and they're holding up well. 10.5:1 compression in a 5.3 with a turbo, and I've seen up to 23PSI of boost. With a positive displacement blower, if you're running pump gas you definitely want to drop compression. 9.5:1 would be fine. If you can run E85, a set of flat tops with valve reliefs will probably put you at 10.5:1, and it would make a lot more power. But you'd have to have the fuel system to support it.

 

Yes. Not necessary maybe, butt good.

That'd be a GREAT idea. Boost effectively MULTIPLIES the "compression" part of "compression ratio". There's only just so far you can go with that before the mixture inside the cyl lights off on its own, aka DETONATION. Which is probably what bent your rods. Unfortunately, the OTHER part of "compression ratio", which is, the proportion of expansion that the hot gases after they burn can expand through (i.e. the part of "compression ratio" that makes power), gets compromised in the process. It's always a balancing act. Butt no matter what, survival needs to come before max power, if this thing isn't putting money in your pocket by professionally racing it and earning enough money via purse or sponsorship or whatever (which it doesn't sound like to me), to buy parts and pay your crew for constant rebuilds.

 

Thanks everyone for the info. It was making 720rwh on e85, so the fuel system is good I believe.

Just need to figure out if I should spend the coin to upgrade the rods and pistons or just go back stock. Obviously I don't want to do this again. Not sure if just a better tune would be enough!

Thanks!!

 

With the Summit pro I assume you had it balanced with the stock crank?

 

On E85? Damn!

Aftercooler? Was it functioning properly?

 

I thought all LS engines came with forged rods? Aren't the PM rods forged in a die under very high pressure? They may not be forged billet rods, but they seem to hold up pretty well in FI engines. The high silicone content hypereutectic pistons also work pretty well, but can't withstand much detonation, and probably shouldn't be used in a FI engine. If you run stock LS3 pistons, they have too high of a compression ratio to live in a FI engine. I suspect the 2 pistons failed and then bent the rods...

 

If you have an aftermarket cam it would allow for higher static compression ratio, but your dynamic compression ratio would be lowered due to the cam having more duration. A stock cam with a blower or turbo, combined with 10.5:1 compression is asking for trouble in my .02, e85 or not....

 

SBE LS3's generally handle boost fine with proper tuning and fueling. Not uncommon to push them 800whp on E85. Without seeing a data log and tune file it's hard to say. My guess would be too much timing around peak torque for the amount of boost.

 

Did you lift a head when this happened?

 

100%

He added boost without tuning it.
It was set up to run well for 20k miles NA
--that tune was not made for boost.

simple mistake.

add dish pistons, drop compression, retune..

 

Yes, stock crank. Steve Morris Engines did the balancing and it needed nothing. He said he was surprised, they spun it up and it was the same as stock. Apparently Summit has done a good job getting the weights right.

I agree 100%. The much earlier intake closing of a stock cam would create far too much cylinder pressure.

 

The LSA blower will make boost right off idle. They will make all the boost by 2k rpm.
LSA tune has very low timing in those areas.
If this is a stick shift car, that amplifies the issue.

Those rods can bend without you knowing it. Once they bend to a certain extent, the pistons **** in the bore and the skirts break. Then you know it!

Guys think the knock sensors will save ya. But the knock retard you see in a log file is just the response of the ecu. The knock has already happened…..