How To Drag Race Your M6 - Clutch Slipping Techniques...

[Matt @ FSP]

Clutch Slipping 101...


Wait a second, I do not want my clutch to slip? Oh yes you do! Let me explain:


As most of you manual guys know, if you go out to the strip or the street and dump the clutch it makes a nice smoke show but goes no where. OR you dump the clutch at a lower RPM as to not spin, and the car just bogs down. Along with the supporting mods, you can fix this issue with a good clutch selection, some practice and possibly a 2-step (Launch control) to help!


Let me try to break this down as best as possible. The clutch is the only buffer between your power at the motor vs. the power applied at your rear wheels. Of course there is other driveline items such as driveshaft, rearend, axles, etc. but this is the item that can govern power apply from motor to rear tires from the ****pit. The higher the power of the vehicle, the more important it is not to apply 100% power from motor to tires while there is no vehicle speed. This will just shock the tires, and spin them.


Without trying to go into the dynamics of how a clutch works because we will be here forever. I'll break it down “simply” put, but there is a lot more to it. Your clutch pedal is hooked up to a hydraulic line that provides the fluid displacement from clutch master cylinder to clutch slave cylinder. This activate the slave cylinder with the throwout bearing on the end that pushes on the inside “fingers” of the clutch. This then moves the “fingers” or “levers” of the clutch applying friction to the disc(s) of the clutch. If this clamping force (Friction) is applied too rapidly for the track and/or suspension/tires at a higher RPM this is where you get the tire spin. If the clamping force is applied too rapidly at a lower RPM, this is where you get the “bog down” affect. This can be taken into further account with tire shake, which is usually not an issue we need to get into on these particular cars (This is for big HP/big tire guys). So I'll leave the tire shake part of this out of it. Thus leaving us either a tire spin condition from too much power applied or a bog situation where too much friction was applied without the power.


Ok, so we have now pointed the problem out... How do we solve this? Easy answer, shove an automatic transmission in it and go racing. Well, if you have not noticed the fastest cars out there (Fuel/Mods) mostly are all clutch driven, there are a few reasons to this such as less loss through the drivetrain, more reliability in controlling spin or shake and of course class rules govern this also. Also take into account that Top Fuel cars have no transmissions, they work off of 1-speed forward and 1-speed reverse (I'll leave this for another time too!).


So, now we are stuck with your manual trans and clutch so let's make it work!


Here's a quick paraphrase of what we are looking to do here: Do not fully disengage the clutch while coming off the line until you have a bit of vehicle speed and then fully apply the power.


Let me break this down into a few different items:

• The clutch is the only buffer as we explained earlier, so we need to use it to apply the percentage of power at the given moment. This can be harnessed by inducing clutch slip by not fully disengaging the clutch on launch. For example, when you leave the stop light with that huge cam and you slip the clutch out so that you don't bog off the stop light and look like an idiot, well that's the same goal we are aiming for at the drag strip!
• I cannot give you the exact “percentage” of how much clutch to hold back, as this will be individual to each vehicle, track conditions, motor combination and clutch combination. However, a general rule of thumb is to “hold-back” about 10-20% of the clutch disengagement on launch and apply the engagement as you gain vehicle speed. Now this can be done in the clutch itself; a “slipper” clutch that you guys may have heard of. This involves disc material, disc height, counter-weights and a few other dynamics of a slipper clutch. Of course this will not be the clutch you want to put in your daily driven or weekend warrior car, so we need to use a mainstream clutch and use the hydraulic pedal to make it a slip.

What we are trying to accomplish here is to apply the maximum amount of power, with the minimal amount of clutch slip to harness the power to the back tires as to not spin or bog. Once again, to repeat myself, I cannot give you this magical percentage of how much clutch to slip because there are varying factors like I had said from vehicle, power combination, and clutch combinations. Generally I would try to hold-back about 10-20% of the full vehicle power, this figure will change per track conditions and temperature conditions. This is why you will see the crews changing up clutch discs/floaters during a NHRA event day. The change of temperature from a few degrees from an over-passing cloud or dusk starting to set in will change these parameters of how they are setting up and applying the power. There is a lot of R&D put behind this and there are only a few real clutch experts out there.


The best way to practice this method is at the strip with controlled conditions and proper preparation. Of course this is hard to do on a street night where you may only see 2-3 runs, so you can start working on this on the street. I'm sure by now you already know that magic spot on the clutch where it starts to disengage, this is where you can apply some power via throttle to get the car moving without a large buck or stall. This is the same way we are going to slip our clutch at the strip. In general:

• Bump the first stage beam, start revving your car up and bump the second stage beam so you are now double bulbed. Rev your car up to your RPM launch point, and start releasing the clutch upon bulb drop, however, do not fully let it disengage. Ride the clutch out for however long it needs to hold back the power (Generally a few feet up to the 60'), allowing more disengagement as the vehicle speed starts raising. When the tires are already moving, its a lot harder to shock them to spin vs. shocking them from a dead-stop. You can start releasing the clutch pedal a bit more as you are moving until full disengagement for full power from motor to rear tires.

Now, to help in this induced clutch slip, and to have more consistent launches, you can add a 2-Step box (Launch Control). This will do a few things for you:

• Maintain same RPM launch everytime as you are presetting the ignition or fuel cut (Most LS boxes use ignition as the cut-off, however, standalone ECUs will allow ignition or fuel cut – Once again most LS motors will use the ignition vs. fuel cut)
• Load the motor, so on boost vehicles especially, you can start raising boost levels at the line as with the “rev it up” method will produce little to no boost until there is load on the motor (Off the line).
• Induce clutch slip. As I said above, this will allow you to load the motor and start making some HP before you launch the vehicle. This additional power can help you with clutch slip (Especially on a high clamping force load clutch) by overpowering the clutch off of the line along with displacing the power level (Induced clutch slip by driver).

Personally, I have had the most success with this technique in the LS vehicles using the Mantic 9000 twin series, Mcleod RXT or SPEC clutches. That is not to say that the other brands are not adequate, this is just what I have my experience in having installed & drag raced LS vehicles for years.


Well once again, this is not the end all be all article and I do welcome any inputs or adjustments to the statements that I have made above. Now you can think twice about yanking that 6-speed manual out for the automatic every time you go to the strip!

[maxdmax]

Great post, just wish slipping the clutch just right consistantly was as easy as it sounds. The other option is launching the car and getting enough wheel spin to keep the motor from bogging yet not too much that you spin the tires more than a few feet. If you watch pro stock cars this is exactly what they do. Either way works but your technique is the easiest on most of the parts for sure with the exception of the clutch. Both techniques have their challenges and with our heavy cars both are difficult to master but can be done successfully with enough practice.

[ckaram]

Hey madmax, I watched your run on the video you posted on the other thread...you can drive, brother! Your car's got some stones...

[MANNYS2SS/RS]

Maxdmax I agree with you, its not as easy as it sounds. I smoked my stock clutch 2 weeks ago at the track. Now I am debating instead of spending $1,200 to $2,100 on a clutch. I should just put a T400 or a 4L80 and be done.

[Matt @ FSP]

Originally Posted by maxdmax

Great post, just wish slipping the clutch just right consistantly was as easy as it sounds. The other option is launching the car and getting enough wheel spin to keep the motor from bogging yet not too much that you spin the tires more than a few feet. If you watch pro stock cars this is exactly what they do. Either way works but your technique is the easiest on most of the parts for sure with the exception of the clutch. Both techniques have their challenges and with our heavy cars both are difficult to master but can be done successfully with enough practice.

Correct about the tire spin. You need a bit of induced tire spin, as to also avoid tire shake. If you do not get enough power OR too much power down (There are a lot of theories to tire shake) before the suspension unloads, the tire will go out of round basically causing a bouncing effect that is violent and is an aborted run at that point. No good, so yes tire spin is part of the equation.

- Matt

[maxdmax]

Originally Posted by ckaram

Hey madmax, I watched your run on the video you posted on the other thread...you can drive, brother! Your car's got some stones...

Thanks, just wait until we get things lined out. It may take until the spring but we got some good things planned to get this thing down the track.

Originally Posted by MANNYS2SS/RS

Maxdmax I agree with you, its not as easy as it sounds. I smoked my stock clutch 2 weeks ago at the track. Now I am debating instead of spending $1,200 to $2,100 on a clutch. I should just put a T400 or a 4L80 and be done.

You just said the bad word in our "MAN STICK" thread, go buy a clutch and drive that thing. Yes a man pedal car is a lot harder to drive, takes more skill and is harder on parts but it is so freakin much more fun to drive!

Originally Posted by Matt @ FSP

Correct about the tire spin. You need a bit of induced tire spin, as to also avoid tire shake. If you do not get enough power OR too much power down (There are a lot of theories to tire shake) before the suspension unloads, the tire will go out of round basically causing a bouncing effect that is violent and is an aborted run at that point. No good, so yes tire spin is part of the equation.

- Matt

I agree with you, I am just pulling 1.6x 60's with the clutch slipping technics, but to get into the 1.5x and 1.4X 60s it is going to take a lot of things setup right and a fairly hard launch to get these big cars to 60 the way they need to! Just my opinion......

[Supercharged SS]

Let me get this straight. The author of this yanked his M6 to race with a Turbo 350!!!! Hahaha. Matt you dope.


You did a great job with the write up. Way over my head and once you mentioned a manual I started day dreaming!.


No doubt guys like Jim will gain some knowledge!

[maxdmax]

Originally Posted by Supercharged SS

Let me get this straight. The author of this yanked his M6 to race with a Turbo 350!!!! Hahaha. Matt you dope.


You did a great job with the write up. Way over my head and once you mentioned a manual I started day dreaming!.


No doubt guys like Jim will gain some knowledge!

Hay who knows maybe getting board with the auto already

I will be the first to say a auto car is far superior to a stick car on the drag strip I hear it every time I go to the track. The fun factor is what does it for me, I love to watch those auto cars but I love to drive my stick car a lot more......

You auto guys just got too much of that fast list and we need some more stick cars on there. I'm an underdog just got to work harder......

[Supercharged SS]

Originally Posted by maxdmax

Hay who knows maybe getting board with the auto already

I will be the first to say a auto car is far superior to a stick car on the drag strip I hear it every time I go to the track. The fun factor is what does it for me, I love to watch those auto cars but I love to drive my stick car a lot more......

You auto guys just got too much of that fast list and we need some more stick cars on there. I'm an underdog just got to work harder......

Btw, you lost another stick guy to an auto. Teds 800+ rwhp whipple car in MD, which he's been racing all year with the stick, RacerSSRX (or something like that), is bring his car back for a turbo 400 this winter.

[maxdmax]

Originally Posted by Supercharged SS

Btw, you lost another stick guy to an auto. Teds 800+ rwhp whipple car in MD, which he's been racing all year with the stick, RacerSSRX (or something like that), is bring his car back for a turbo 400 this winter.

I know seems to be the in thing to do, when I get older I will likely switch too but for now I just can't. The excitement of all that goes on in that first 330' just does it for me right now. Yes maybe it doesn't optimize my ET but at my age it is about right there on the excitement factor.

[Supercharged SS]

Originally Posted by maxdmax

I know seems to be the in thing to do, when I get older I will likely switch too but for now I just can't. The excitement of all that goes on in that first 330' just does it for me right now. Yes maybe it doesn't optimize my ET but at my age it is about right there on the excitement factor.

Come to the dark side......I mean the fast side!! Hey, if you are having fun who gives a shit how fast it goes. After what occurred on Dec 14, a day at the track with my father well over rides a 9 second pass (10 sec for you )

[maxdmax]

Originally Posted by Supercharged SS

Come to the dark side......I mean the fast side!! Hey, if you are having fun who gives a shit how fast it goes. After what occurred on Dec 14, a day at the track with my father well over rides a 9 second pass (10 sec for you )

You Sir are correct, I took my 88 year old Dad to my Aunts 80th birthday party tonight. A day with dad seeing him smile is priceless at any speed! He is blind and we laughed the whole way, he kept saying if I don't slow down I am going to get a ticket in between telling my about all the tickets he had gotten lol

[MANNYS2SS/RS]

Maxdmax don't get me wrong driving stick is alot of fun, and it does take talent to run consistent times. I am just a little frustrated with my driving. Here is a video of my Buddy(Z69), who like you can drive stick. He has a M6 ZL-1 with just bolt on, no suspension mods only skinny up front and 17" drag slicks. He has been running consistent 1.59 to 1.63 sixty foot.

[maxdmax]

Originally Posted by MANNYS2SS/RS

Maxdmax don't get me wrong driving stick is alot of fun, and it does take talent to run consistent times. I am just a little frustrated with my driving. Here is a video of my Buddy(Z69), who like you can drive stick. He has a M6 ZL-1 with just bolt on, no suspension mods only skinny up front and 17" drag slicks. He has been running consistent 1.59 to 1.63 sixty foot.

I am challenged a lot right now too, I was pulling about the same 60s on drag radials with a hundred less RWHP than I am doing now on slicks. I have only had about 10 real passes on the new setup and have a long way to go. It takes a lot of working at it to get where we want to be with a stick car. Results will come.

That guy in the video can flat out drive that car! He is the biggest part of making that an awesome pass more than the car that is for sure.