Join Date: Nov 2007
Location: Whitmore Lk., MI
05 6 sp. with 4.56 gears, ZR1 clutch, Edelbrock intake, Lunati cam, Crane rockers, C6 modified pan
After a month and a half of deliberations, I finally pulled the trigger and ordered my new clutch today. I never really had issues with mine in 45,000 miles of driving, but I didn't beat on it much. It would shift clean @ 6600 rpm and at least go through the gears one time. I never pressed it more than that. Others, I know, have had several installed. Some have problems with the pedal sticking to the floor and some have slipping issues. The stock unit is made by Luk and is attached to a dual mass flywheel that is shock absorbing. The disc itself has an unsprung hub and is organic faced. The same setup is used in the Caddy CTS-V and their owners, for the most part, seem unhappy with their clutch performance, also. My first concern was some groaning, on take-off, from I'm guessing the flywheel. Also the thought of spinning a 2 piece cast flywheel up close to 7k rpm makes me nervous. My first car, a 65 Mustang, had a stock flywheel come apart and it almost sawed the car in half. I won't take the chance of that happening to the R!
The first option I considered was the LS7 clutch, but for my application it wasn't the right choice. It is also made by LUK, and in looking around the Vette forums they have some of the same issues that we do. At high rpm they will stick to the floor. In spirited driving they slip and boil the fluid and won't release clean. They have real nice street manners, as they attach to a lighter single mass flywheel and have a sprung hub disc with an organic lining. For a street driven, unmodified R it's probably a reasonable choice. Also, the setup is not real expensive.
My next look was at all the aftermarket clutches, and they all have mixed reviews behind LS engines in Vettes, GTOs, and CTSs. The entry level units tend to chatter and be harsh with slightly heavier pedal pressures. Monster Clutch possibly has the best following along with Spec clutch. It seems they are both reliable for racing, but are not really that street friendly. Prices are around the same as the LS7 package. They also have available twin disc units that are expensive and tend to be noisy.
A friend of mine works out at the GM Proving Grounds, close by, in Milford MI. He talks frequently with Mark Stielow, one of the test drivers there. Mark is well known in performance circles, and his latest 69 Camaro is currently making the rounds of all the car magazines. He runs a lot of the top end challenges and road and track events, for street cars. Anyway his latest ride has most of the current ZR1 Vette drivetrain in it, including the dual disc clutch. It seems GM realized the problems of the LUK clutches and went in an entirely different direction with the ZR1. They went to a German company named ZF Sachs, that does a lot of Formula 1 development on clutches, shocks, and harmonic balancers. They asked for and received a dual disc clutch with tremendous holding power, yet light pedal pressure and consistent feel. After nosing around a bit, I discovered a couple of the premier high performance shops in the country are endorsing and selling this clutch. Katech Inc and Lingenfelter Performance have both recently developed retrofit flywheels for mounting this clutch in just about any Gen 3 or 4 powered vehicle. The stock ZR1 flywheel WILL NOT work in anything but an LS9. The LS9 crank has a 9 bolt flywheel flange, where as all other LS cranks use a 6 bolt flange. I ordered the LS9 slave cyl., but it's just possible our stock slave may work - I'll measure both once I receive the new one. I wanted the LS9 anyway because of the mileage on mine and the desire to run an remote bleeder. The cost of this package is significant because of the custom flywheel, but either the billet steel Lingenfelter unit or the billet aluminum Kateck piece gives me piece of mind when I hit the strip! You can expect to pay $1300. - $1500. for one of these setups. I should have it in hand by the weekend and I'll post a few pictures then.
"Strive for perfection in everything. Take the best that exists and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough."
Sir Henry Royce, of Rolls-Royce