Launch Control Strategy

I'm running a factory ecu with a daughter board that has some additional capabilities added to it like launch rev limits and ignition retard on an SR20DET. The ecu can also store two different tunes and toggle between them with the flip of a switch while the engine is running. I'm looking at how to best leverage the available features for launch and traction control, and potentially flat shift. My plan is to hook up the clutch switch to the ecu so that the ecu uses one tune when the clutch is depressed and the other tune the rest of the time. Each tune has the following parameters/limiters available:

Launch Rev Limit, ignition Retard - RPM at which ignition is retarded to a set value

Launch Rev Limit 2, fuel cut - RPM for fuel cut limiter

Ignition Retard value - definable ignition angle value for limiter

Launch speed cut off - definable speed for deactivating launch limiters(limiters inactive above this threshold)

Normal Rev Limit, Ignition Retard - main limiter using ignition retard

Normal Rev Limit, fuel cut - main limiter using fuel cut

So basically I have the potential of two sets of discreet launch and main rev limiters as well as the ability to switch between rev limiters based on a clutch switch or driven wheel speed, and I can specify the amount the timing is retarded when the limiter is active. What would be a good strategy for setting these limiters to be more effective than just a conventional 2 step limiter?

Here is a little of what I'm thinking. The tune that is active when the clutch pedal is depressed would be used for the stationary rev limit and to build boost before launch. The Normal rev limits on the same tune could be used as a flat shift limiter. The second tune could use the launch limiter to retard the timing and reduce torque to prevent excessive first gear wheel spin. The Normal rev limiter of the second tune would then be used to limit max overall RPM.

Any ideas on a starting point for these parameters?

Fwd or rwd?

street radials, drag radials or drag slicks? Size?

Gearing?

surface?

Launch control is going to be mostly about properly controlling clutch engagement to ride the fine line between bog/spin. Controlled clutch engagement makes higher launch rpm possible, which will in-turn make it easier to make boost on the line. Here's a link to a device I make to control clutch engagement- HitMaster 2-Stage Clutch Hit Controller

Traction control should more accurately be called power reduction control, it should be your last resort after you've ran out of other adjustments.

Grant

I have seen numerous clutch control devices obliterate clutches. There has yet to be a time where I couldn't tune a setup well without one. 

Paul_VR6 said:

I have seen numerous clutch control devices obliterate clutches. There has yet to be a time where I couldn't tune a setup well without one. 

I suspect the clutch control devices you are familiar with are likely the Magnus, Tilton, and ClutchMasters types. They are good for reducing drivetrain breakage, but the hit is poorly controlled and waay too lazy, which leads to poor reaction times and excessive wear and tear on the clutch. 

I'm courious as to what you are using as a standard to compare your launch tuning ability?

Grant

Used all those as well as some electronic proportional control valves on some pretty serious clutch cars (crowerglide). No matter what there was always a better way (quicker times) than controlling fluid. 

Paul_VR6 said:

Fwd or rwd?

street radials, drag radials or drag slicks? Size?

Gearing?

surface?

-Rwd

-Hoosier S80, SM7, or A7 (I'd love to try drag radials or slicks but I don't have budget for new and used are difficult to find in the right size)

-205/50-15, 225/45-15, or 245/40-15 depending on availability.  (Currently I have 245/40-15 Hoosier S80)

-3.73 differential, 3.321 1st gear, 1.902 2nd gear

-prepped or unprepped drag strip

-weight < 2300 lbs with driver

Paul_VR6 said:

Used all those as well as some electronic proportional control valves on some pretty serious clutch cars (crowerglide). No matter what there was always a better way (quicker times) than controlling fluid. 

Doesn't sound like you've ever used the HitMaster to control the hit of a clutch. Instant soft hits from any launch rpm without compromising the clutch's ability to hold power. The high dollar adjustable clutches can't do that for you, neither can the Magnus, Tilton, ClutchMasters clutch controllers. I don't see a way to do it with an electronic proportional control valve either.

Grant

In reply to weedburner :

Can I build one for $20 out of junkyard and hardware store parts? If not, although the device sounds great, it is not a valid solution to the problem at hand.  I'm trying to improve launch and traction on a Challenge car. There is just simply not another $400 in the budget for clutch modulating device. Adjusting ECU parameters is free so that is what I am pursuing first. Although I have considered getting a clutch delay valve out of a BMW to help prevent part breakage if the tires hook.

bigben said:

In reply to weedburner :

Can I build one for $20 out of junkyard and hardware store parts? If not, although the device sounds great, it is not a valid solution to the problem at hand.  I'm trying to improve launch and traction on a Challenge car. There is just simply not another $400 in the budget for clutch modulating device. Adjusting ECU parameters is free so that is what I am pursuing first. Although I have considered getting a clutch delay valve out of a BMW to help prevent part breakage if the tires hook.

Clutch delay valves cause more problems than they are worth, especially if you want to flat shift.

$20 budget you say? Here's a link to my DIY Hillbilly Clutch Slipper...

$20 DIY Hillbilly Clutch Slipper Webpage

Here's a later webpage that does a better job of explaining how it works...

GSS Clutch Slipper Webpage

Here's a link to the current version I call the "ClutchTamer"...

ClutchTamer Homepage

It works so well that the $2200 Black Magic clutch guys got it banned from NMRA's sealed engine Coyote Stock class, after they started getting beat by off-the-shelf clutches controlled by it. The ban was quickly reversed the next day after an emergency rules meeting when half the field threatened to quit. Turns out the the ability to compete with an off-the-shelf clutch was a good thing for the class overall. Today there are 5 different clutch brands that are competitive in the class thanks to the 'tamer, and I'm proud to say every single event this year was won using it.

If you take the time to build your own DIY version you won't regret it. Midland Hardware is probably the cheapest place to source a new cylinder, around $12. The Delrin slide bushing isn't really required, it's just there to protect the theads on the adjustment rod. The detent features and fancy knob on the current ClutchTamer are not necessities either.

Grant

Those tires will stick when rolling but the hit won't be good. You are best off setting spark cut with a retard so power comes in relatively soft. On the shift won't matter as much. 

In reply to weedburner :

Wow! I was drooling at the HitMaster a while back, but somehow missed the hillbilly version-it's perfect for the challenge. 

I'm bringing a 91 CRX (FWD) to challenge and the transmission is a known weakness for drag racing. I was told I'd need to "pre-load" the drive train before launch by pulling up the handbrake and releasing the clutch to take the slop out of the drivetrain. 

But with the HM, this isn't necessary; you just let your foot off the clutch, correct?

Paul_VR6 said:

Those tires will stick when rolling but the hit won't be good. You are best off setting spark cut with a retard so power comes in relatively soft. On the shift won't matter as much. 

I ran the S80 tires at 18 psi and heated them up like drag tires.  They stuck well enough to snap the front u-joint on launch. (I probably let the clutch out to quickly.)

I can set a timing retard and/or a fuel cut limiter. Spark cut isn't an option I have to work with. 

In reply to weedburner :

Thanks for the tip. That Hill Billy unit looks pretty easy to build. I'll have to try it out. 

I'm bringing a 91 CRX (FWD) to challenge and the transmission is a known weakness for drag racing. I was told I'd need to "pre-load" the drive train before launch by pulling up the handbrake and releasing the clutch to take the slop out of the drivetrain. 

But with the HM, this isn't necessary; you just let your foot off the clutch, correct?

That's generally true of almost anything, even cars with automatics (thus why transbrake cars break stuff that footbrake cars dont, all else equal). In fact, MOST driveline parts breakage you hear about was caused by the operator through the clutch pedal. I suspect you're right that the device would allow you to not take the slack up 'manually', but unless you have a good reason to avoid 'best practices' I'd just try to work them into your normal routine at the drag strip.

You can try fuel cut but I generally don't like them. Even with pulling timing it likely won't build boost. 
 

You are best learning how it likes to launch on the pedal first. You want some spin but not too much. You can pull the front end up, but not too much. You can let it bog, but too much and it snaps things. 
 

Preloading will depend on the tire and clutch. Necessary on street and drag radials for most fwd. Slicks it depends, if you have good axles/clutch its not needed. I don't anymore and cut low 1.5 60s. 

CrustyRedXpress said:

In reply to weedburner :

Wow! I was drooling at the HitMaster a while back, but somehow missed the hillbilly version-it's perfect for the challenge. 

I'm bringing a 91 CRX (FWD) to challenge and the transmission is a known weakness for drag racing. I was told I'd need to "pre-load" the drive train before launch by pulling up the handbrake and releasing the clutch to take the slop out of the drivetrain. 

But with the HM, this isn't necessary; you just let your foot off the clutch, correct?

You don't pre-load with the HM or the CT, as you have full control over how hard the clutch hits the drivetrain.

Grant

Preloading will depend on the tire and clutch. Necessary on street and drag radials for most fwd. Slicks it depends, if you have good axles/clutch its not needed. I don't anymore and cut low 1.5 60s. 

I mean, it depends on whether you want to actually find out the answer to 'will a clutch dump break something on my car'. If you don't really want to know, you'll take up the slack yourself. If you're running a slick with a lot of sidewall it can soak up a lot of mistakes, and while i don't disagree  with Weedburner that the clutch device can remove the need to take up the slack manually, I still think it's a bad idea to NOT learn how to drive the car properly in the first place before deciding whether you 'need' to drive it properly, or installing devices that can cover up bad habits before you're aware that you've formed them. So i agree with you about learning to drive it first and THEN deciding what you need. 

Vigo said:

Preloading will depend on the tire and clutch. Necessary on street and drag radials for most fwd. Slicks it depends, if you have good axles/clutch its not needed. I don't anymore and cut low 1.5 60s. 

I mean, it depends on whether you want to actually find out the answer to 'will a clutch dump break something on my car'. If you don't really want to know, you'll take up the slack yourself. If you're running a slick with a lot of sidewall it can soak up a lot of mistakes, and while i don't disagree  with Weedburner that the clutch device can remove the need to take up the slack manually, I still think it's a bad idea to NOT learn how to drive the car properly in the first place before deciding whether you 'need' to drive it properly, or installing devices that can cover up bad habits before you're aware that you've formed them. So i agree with you about learning to drive it first and THEN deciding what you need. 

 

 I'd say the bad habit comes when you learn to "drive the car properly" and end up leaving .50 or more ET on the table. 

Grant

I'm all for your device as long as it's not crutching someone along who then steps into another car and immediately breaks something because the only car they've ever taken down the dragstrip had a stupid-proof clutch pedal.  Those are long odds, but the thought makes me cringe.