Ran my 94 6 speed last night and only managed a 13.7 at 98. I had some terrible clutch slip in 4th gear. I don't seem to get that slip anywhere other than the track. I have decided to upgrade the clutch so I can run some drag radials or slicks. Car is driving 95% on the street. A 355 or 383 with new heads & intake are in the future. Any suggestions? Pros and cons of going to a one piece Camaro flywheel & what pieces are needed to do that.

 

Bump.

Looking at the Centerforce Dual Friciton set up with Centerforce flywheel OR the new RAM set up with a push style pressure plate release?

Any thoughts?

 

Hi. I have a 93 lt1 6spd.

Are you 100% sure your issues in 4th gear are clutch slip and not optispark issues?

I remember back when I first got my 93 lt1 and, whenever it would get hot, the optispark would 'stumble' during hard acceleration - like at the dragstrip.

One other time, I had it doing 106 MPH (on the racetrack), and it just wouldnt go any faster. It was like I hit the wall.

It was all related to the optispark. The higher gears are worse.

One clutch test you can do is put on your parking brake (assuming it works ok), and try to accelerate. I wouldnt try super-hard to go anywhere, but if the clutch just spins, its definitely a clutch issue. If the car tries to move, lurches, and bogs out /stalls - then you got a healthy clutch.

The good news is the optispark is a little easier (still not simple though) than the clutch to replace, if this is your problem.

All this said, if you are confident you have a clutch issue, I can share with you that Ive had good luck with SPEC stage 3+. This is a streetable disk type (stay away from fan-blade puck clutchs like the SPEC stage 3).

SPEC stage 3+ is a sprung-hub clutch which will be necessary if you replace your dual mass flywheel w/ a single mass flywheel. Theres aluminum and steel single mass flywheels - a subject for another debate. I run the aluminum flywheel and love it. The dual mass flywheel is difficult to resurface and not available from GM. This is why people go with the single mass flywheels. The good news is you will save rotating inertia weight from the 40 lb hunk-of-weight dual mass flywheel by going to a single mass steel (20 lbs) or aluminum (12 lbs) flywheel.


I had a SPEC stage 2 kevlar clutch, and it worked great until the center broke out on me.

I am a fan of SPEC clutches as they are different than centerforce or OEM clutches that feel different as they wear down. My experience has shown they tend to keep that same release point in the pedal even as they wear.

I had a centerforce on a difft car and I was unimpressed how the release point changed (just like on an OEM clutch) as more and more miles got put on the clutch.

Good luck.

BTW. be aware of cheap clutch foreign parts (even in AC Delco boxes) such as throwout bearings, etc. made-in-china vs. new-old-stock stuff.

Call up Jim Jandik at power torque systems. He has bought out many of the New old stock parts for our cars (quality parts) and would be happy to talk to you about clutch options.

That ram clutch you mention is interesting. I know nothing about it, Jim would.

 

I agree with everything dizxiz24 said about Spec Stage Three plus clutches.

Don't waste your time or money trying to adapt a camaro style flywheel; Spec makes three C4 specific flywheels: heavy billet steel; lightweight billet steel and aluminum. In the case of my LT4 everything was a bolt in.

One caveat; when you replace the throwout bearing, make sure it is the right one, there are two different inside diameters; I believe the early one's (yours is the ZF "black label" ?) takes the bearing with the larger i.d. Also there are three different height clutch fork mounting studs available...people on this forum have suffered non ending grief after installing the wrong one; but all this can be checked during installation of the clutch BEFORE the transmission gets plugged in.

 

on the subject of RAM clutches, I have run a series of their metallic clutches over the years and they performed magnificently. My only hesitation about installing one in a C4, is that a LT uses a pull style pressure plate and not a push type (like nearly every other clutch in the world) which means that a RAM clutch (or any other push style installed in an LT) must use a (expensive) combination throwout bearing and clutch slave cylinder, all mounted as a single unit, inside the bell housing.

As big as a pain as corvette clutch slave cylinders are to bleed (dozens of threads on that subject), at least they are mounted on the outside of the bellhousing where they are accessible. SPEC clutches are stock pull style clutches and use stock hydraulics.

 

on the above advice. Stay away from machined Camaro flywheels. Just a bad idea.

Test out your clutch to make sure it is the culprit.

What was your 60' time?
What track where you at and on what day? Time of Day?
What is the Density Altitude or DA?

FYI, my stock 93 ZF6 with manual fan switch, cat back exhaust on street tires runs 13.38@105. That is at Pittsbrugh Raceway Park with DA around 1500.

 

Guess I need to add some more info. 94 six speed, 103K on the clock. Hooker shorties, Magnaflow cats, Corsa cat back, open lid. I have a new MSD Opti installed less than 5K ago. It's a second generation. First MSD failed and was rebuilt by MSD. I replaced the flywheel and clutch with factory Delco replacements about 20K ago. I also have new master & slave cylinders along with new line. I have bled it several times with conventional means and a power bleeder. There is a VERY narrow take up in the travel.

During my runs down the strip in 4th gear the tach was in the "red" zone at 98-102 mph. My 60' was in the 2 second range (lots of tire spin on street tires & untreated track and my slip is in the car in my garge) No idea on DA. It was about 90 degrees, 60% humidity about 10pm. Steet style race (www.thursdaynightlightz.com). I actually saw 103 on my speedo before the massive slipping and saw 98 at the traps. I have 3.56 gears so I should have more gear left. I have tried all the normal clutch slipping tricks with no slippage. On the street I can bark 4th if I'm mean to it. Side stepping the clutch at 40mph in 6ths doesn't give me any slip. One thing that came up in conversation today is my seating position. When normally driving my head only has 1/2 clear to the headliner. Putting on a helmet forces me down in the seat. I am actually starting to wonder if being forced down is taking away space for me to get my foot all the way off the pedal. In which case I would feel like a complete idiot. BTW - the guy that knocked me out in the first round was driving a mid 90s Integra with a Greddy turbo kit and ended up finishing second to a 2011 Z06

 

Honestly, I'm wondering too if your not riding it. Even with the gears, which are not much from the stock 3.45's you should have tons of RPM left.

Stupid question, does the engine feel like it runs out of breath on the top end? At 100K+ and hard driving I would think the valve springs could be a little suspect?

 

I think the pedal riding is looking more like the culprit. There is such a narrow window of engagement that it would be very easy to ride it and not know it. First time down strip in 6 years racing for money had my nerves way up plus being stuffed down in my seat. The thing pulls like a boss in all gears up to the limiter with no hiccups at all. In fact on the way home myself and the other guys I went with were messing around (An 89 L98, a 12 C6, 86 Mustang GT loaded with GT40P goodies, and an 01 Mustang) and I was able to pull all of them excpet the C6 halfway into 5th. How would I know if I dropped a spring? I have a sound that sounds like a tiny exhaust leak to me but have been told by others it sounds like main bearing, exhaust leak, short in plug wire, a lifter, and even a spring.

 

Walked the dog and got my slip.
R/T 9.398 (street style race. both yellows then a pretty girl in heels & a skirt drops her arms)
60' 2.095 (street tires, untreated track, lots of wheelspin)
330 5.922
1/8 9.019 at 79.95mph
1000' 11.643
1/4 13.774 at 99.78

 

HOLD OFF ON THE NEW CLUTCH. First, if it won't slip at WOT on the street, in 5th or 6th gear (heaviest load that you can put on the clutch) then the clutch is likely fine.

The problem? I would believe it, except that I've SEEN it happen to two close friends of mine after it happened to me. In the excitement of being at the drag track, some folks do not remove their foot from the clutch pedal completely and immediately after shifting. Either the pressure of their foot on the pedal (resting or otherwise), or the hasing from the slow release, causes clutch slip....NOT a "bad clutch".

Before spending money to replace a clutch that may not be bad, I'd go out, get going on the highway, and see how well the clutch grabs in 6th gear...even w/a little made-up abuse. If it holds, it's still good.

 

OOPS! I "walked on you" by posting before reading the whole thread. Sorry. My bad.

What ^he^ said.

 

[QUOTE=Tom400CFI;1581219649]HOLD OFF ON THE NEW CLUTCH. First, if it won't slip at WOT on the street, in 5th or 6th gear (heaviest load that you can put on the clutch) then the clutch is likely fine.

The problem? I would believe it, except that I've SEEN it happen to two close friends of mine after it happened to me. In the excitement of being at the drag track, ...........

I think you're right! Going to head back next Thursday and try it again.

 

You'd think a 42 year old car nut that has steet raced, autocrossed, dragged raced, and driven a stick since he was 14 could do better.

 

IDK...Adrenaline really gets going. People are watching, there is someone in the next lane....if you get limited runs at your track, then EACH pass becomes "too important" -"this pass HAS to be the ONE!!" thinking. I've been there, many times...even with a pretty long history of plentiful track time. It IS nerve wracking.

Build (or re-build?) your "routine". Learn from each pass and adjust that routine. Remember that you can shift the ZF6 FAST!! As fast as you can possibly clutch pump...that is your "shift speed", b/c the that trans sure isn't going to slow you down. If you can get enough passes, start w/low "expectations" and work on your routine. Good driving, great launch, easy passes...then as it starts to come together, add in the elements that make for "bottom number" runs; flat foot shifts, lightning fast shifts, at-the-limiter shifts (just an RCH before, actually), and so on. When you're good driving routing becomes a HABIT, then adding in the final elements becomes far more likely to produce successful low-number passes.

My 150k bone stock '92 has done 13.6/104 at Vegas (2200') in 95*+ weather. I managed a 1.9 60' on street tires using a 4000 RPM launch starting point and a lot of deliberate clutch slip so that full engagement occurred w/the motor still "on boil" at about 3500 RPM. I've probably got over 40 passes though, just in THAT car, so far. Good numbers didn't happen on the first pass.

 

What I mean is, given age/mileage/use weak valve springs could be causing high RPM valve float and hence the car not "pulling to redline."

I would try it out again and see what happens.

@Tom400CFI, remember this thread.

Might intrest you dchildress.
http://forums.corvetteforum.com/c4-t...en-dies-3.html

 

Did I miss something (again! ) Why the talk of valve springs and Opti, when he said this:EDIT: Yep. I missed that you linked the third page. LOL.

 

I think that we both need to learn how to read...

Regardless I would try the runs again DChildress and make sure your foot is off that clutch pedal. Then go from there.

 

Heading to the track again this Thursday. Been trying different seating positions. I have short legs and long torso (think Popeye) and finding a good position with my helmet on is hard. Tried a borrowed Simpson helmet, my Shoei & HJC motorcycle helmets, but my ATV helmet (DOT approved too) seems to give me the most room. I am sure that I was not getting my foot off the pedal all the way. Bolting on some drag radials and dumping in some race fuel for this run. Look for numbers on Friday.