1991Z07

I've been lurking for a while in both the Z06 area and here picking up tidbits of information about the Achilles Heel in the LS7 and the search function (while good) hasn't helped me out much...

I'm building a C4-based ZR1 track car. Picked up the chassis minus engine/trans and my intention is to drop an LS7 into her and do a variety of events (HPDE, AutoX, Open Road Race).

So far...from everything I can see the 2 biggest weaknesses in the LS7 are the valves and the dry-sump system.

Since I'll be buying a salvage motor...I'm going to have it rebuilt before doing anything. I'm shooting for 650-700 HP N/A on E85...I'm getting tired of the GT3's & Z06's pulling away on the straights then catching them in the corners...my '91 just doesn't have the HP to keep them behind me on those LONG drags @ CotA.

What other areas should I look at besides the heads and dry-sump?

LateBreak

Better pistons can't hurt, the stock ones aren't great.

1991Z07

Yeah...I was resolved to getting forged ones already. I've not had great luck with hypereutectic's...and certainly will be squeezing the C/R on this build to take advantage of the E85.

Bill Dearborn

Since this will be a heavy duty track car the only thing I can think of is doing what my shop and Katech have recommended to me. Go with bronze guides and Ti/Mo intake and exhaust valves. They will more durable to the higher temps experienced during extended high rpm wide open throttle operation. My builder says to check the valve springs often for the proper tension. He believes most of the on track valve drops are more likely caused by the usage weakening the springs with the resultant lowering of the engines high rpm capabilities and subsequent bouncing of a valve off a piston at high rpm. The dry sump size isn't that much of an issue if you are not going to encounter any long high g left hand turns where you are carrying lots of revs. However, if you have room it doesn't hurt to add oil capacity by increasing the size of the sump. Probably the Lingenfelter mod is the best way to go but that all depends on the room you have.

Bill

1991Z07

Thanks Bill...

Fortunately...CotA is a right hander, but it doesn't mean I don't need to consider other venues. I'll be hitting some NCCC events and they run all over the place, so insurance is the name of the game.

When I built the motor for the '91 the first time...I took some shortcuts and ended up doing it all over again after spinning 3 rod bearings and cracking the crank in 2 places.

It was a hard lesson learned...I'd MUCH rather spend the money up front for the added reliability in the dry-sump department...as well as adding more capacity.

1991Z07

What about the clutch? What are most of you using in higher HP setups? The ZR1 clutch? Or have you gone to a third party supplier (like McLeod)?