Autocross launch

I assume everyone knows about the Zoomboni by now.  Almost immediately I discovered when I started running it that AX launches were a little weird.   Between V-8 power and T-5 gearing and a 4.3 torsen rear end, first gear is uselessly short and the run takes place in 3rd gear.  So I just launch in 2nd.

But sunday that meant my 2-3 shift was right at the start of the slalom and upset the chassis just when I didn't need that.

So I tried something absurd: launching in 3rd gear.   Decent revs and quick off the clutch means I'm racing a one speed.   30' of light wheelspin and it goes 0-70 in one shot, no shifting during the entire run.

Shaved 1/2 a second off my time.

Anyone else have weird launch techniques?

Ive been launching in second as well. V6 t5 4.1 miata. 

May have to try third!

Here's some launches I filmed:

The Boxster is way too long-legged to launch in anything but first. The Cobra I launched in second for one event, but the clutch wasn't too happy about it. Way, way back when I had my P71, I would leave it in second for the whole run and it was faster than doing 1-2 or leaving it in D. (It had a modified valve body)

Years ago I took my heavily modded Yamaha RD350 to the drags; 1st was utterly useless, it needed second as well and you had to be far enough forward to keep the front end down but not to far it it would spin the rear tire. I suspect running 3rd might have been feasible with using wheel spin as the clutch.

The technique on my 125 GP bike was simply pin the throttle and slip the clutch; if the motor bogged slip the clutch, if you got wheel spin (not likely on a bike geared for 125-130) slip the clutch.  Naturally I replaced the clutch plates after every weekend.

This past weekend I was experimenting with the Datsun; there is one section of the track where I can run 3rd or 4th. In 4th it's only pulling 5000-5200 rpm, in 3rd it's pulling 6900-7100 rpm. Due to the higher RPM the chassis is very pitch sensitive and so it's much easier to get it wrong and start scrubbing speed.  

Im dumb and slow so I always leave the same way I do at the drag strip. I take my cars to the drag strip regularly and generally have the launch down, so when they go to an autox they get a full bore drag launch, im usually grabbing second in the first kink right out of the gate.

Definitely not the fastest way but it is fun.

People really underestimate the launch in autox. 

But it is free time all the way until you first touch the brakes - which as noted can be a lot.

On warm days My s2000's tires stick more than my clutch does so launching often ends up being an exercise in futility and clutch smell. I'll even try to launch on the dirty line that develops to try to get some kind of wheel spin.

In reply to freetors :

Jeeze dude that's a E36 M3 clutch.  Time for a replacement.

I've always thought for a dedicated Autox car a direct drive with a torque converter seems like the perfect solution.  Just have rear gears that do 0-80 and enough torque to need traction control at low speeds.

Robbie (Forum Supporter) said:

People really underestimate the launch in autox. 

But it is free time all the way until you first touch the brakes - which as noted can be a lot.

There's a reason why all Nationals courses take an immediate 90 degree turn...

The whole point is to negate the value of a nasty hard launch.. you can still launch hard.. but the turn means it has minimal value..

one of the key points of the Roger Johnson course design handbook.

 

spacecadet (Forum Supporter) said:

Robbie (Forum Supporter) said:

People really underestimate the launch in autox. 

But it is free time all the way until you first touch the brakes - which as noted can be a lot.

There's a reason why all Nationals courses take an immediate 90 degree turn...

The whole point is to negate the value of a nasty hard launch.. you can still launch hard.. but the turn means it has minimal value..

one of the key points of the Roger Johnson course design handbook.

 

Yeah, but then there is ProSolo which does the opposite :P

I like that in Autox, your 'trap' as your cross the starting lights is what matters, not your 60ft, so you can use whatever means needed to get up to speed quickly, including a ton of wheelspin.

In reply to ProDarwin :

Right, it's part of what separates prosolo from regular autocross, it's a huge high when you get it right, but it can also be a lot harder on the car.. especially the clutch..

which is why Roger pushes against it in normal autocross.

So is something like my ClutchTamer or Hitmaster clutch hit controllers legal in these autoX classes? There are rally cars that use them for standing start launches, but not sure this sort of thing is on the typical autoXer's radar. The 'Tamer and Hitmaster were originally developed for drag race launches on no-prep surfaces, I would think they would work here as well. Here's a link... clutchtamer.com

Grant

weedburner said:

So is something like my ClutchTamer or Hitmaster clutch hit controllers legal in these autoX classes? There are rally cars that use them for standing start launches, but not sure this sort of thing is on the typical autoXer's radar. The 'Tamer and Hitmaster were originally developed for drag race launches on no-prep surfaces, I would think they would work here as well. Here's a link... clutchtamer.com

Grant

 

Which classes?  I am too lazy to look int he rulebook, but I'm sure in upper level builders classes, these are legal (XP, etc.)

The hitmaster looks like a factory CDV with an electronic timer on it.

So a guy driving a Zoomboni talks about weird launching techniques? 

What a great forum!

I can't even get close to being so bizarre!

ProDarwin said:

Which classes?  I am too lazy to look int he rulebook, but I'm sure in upper level builders classes, these are legal (XP, etc.)

The hitmaster looks like a factory CDV with an electronic timer on it.

Not even close to a CDV. Here's the type of TOB pressure graphs you get with a factory style CDV, various traces are different levels of simple restriction...

Here's the type of graph you get with the Hitmaster...

Basically it's like being able to release your foot almost instantly to the exact same level of partial clutch engagement every time you launch the car. This gives the car time to accelerate without either bogging the engine or spinning the tires. After the launch timer times out, clutch operation returns to normal for the shifts.

Grant

I'd expect this would translate well to autocross, but when rallycrossing the Jeep (4sp auto), it gets launched in 1st, grabs 2nd pretty quickly and I keep it locked to 2nd for the rest of the run, basically using the torque converter as a CVT.  The 1-2 shift doesn't upset things much as there's no power cut on the shift.  Works quite well, and it's got enough power that I never lean on it hard enough at low speed to get a downshift back to 1st.  With taller gearing in the axles, I could do the same in 1st and have it truly never shift, but as-is, it'll top out 1st in a fast slalom, plus the engine braking is excessive. 

IMO, autocross and rallycross are both better suited to a good auto than a manual. 

rslifkin said:

I'd expect this would translate well to autocross, but when rallycrossing the Jeep (4sp auto), it gets launched in 1st, grabs 2nd pretty quickly and I keep it locked to 2nd for the rest of the run, basically using the torque converter as a CVT.  The 1-2 shift doesn't upset things much as there's no power cut on the shift.  Works quite well, and it's got enough power that I never lean on it hard enough at low speed to get a downshift back to 1st.  With taller gearing in the axles, I could do the same in 1st and have it truly never shift, but as-is, it'll top out 1st in a fast slalom, plus the engine braking is excessive. 

IMO, autocross and rallycross are both better suited to a good auto than a manual. 

I'm not sure it makes much difference.  In rally cross the Subaru gets shifted into 2nd and pretty much lives there the entire run.  I was dangerously close to redline many times last even (should be 55-58ish mph in the top of 2nd, but who knows.  I was too busy setting up the sharp S curve after the high speed section.  If there is only one gear change, does it really matter auto vs manual?  Probably not much if at all. 

I'm going to set up the 96 Camaro for CAM class, and it'll probably be more of the same, shift into 2nd and stay there most of the time.  With a 3.42 final drive ratio, I will be surprised if 3rd gets used often at all.

AnthonyGS (Forum Supporter) said:

I'm not sure it makes much difference.  In rally cross the Subaru gets shifted into 2nd and pretty much lives there the entire run.  I was dangerously close to redline many times last even (should be 55-58ish mph in the top of 2nd, but who knows.  I was too busy setting up the sharp S curve after the high speed section.  If there is only one gear change, does it really matter auto vs manual?  Probably not much if at all. 

I'm going to set up the 96 Camaro for CAM class, and it'll probably be more of the same, shift into 2nd and stay there most of the time.  With a 3.42 final drive ratio, I will be surprised if 3rd gets used often at all.

The auto won't save you much time in the shifting department, but it'll let you use a wider speed range in the same gear, as the torque converter will help you out at the lower end of the speed range.  So you can gear for your highest speeds and have less chance of wanting / needing to downshift for more power coming out of a slow part of the course. 

In reply to rslifkin :

Ohio has a strict no spinning tires at launch rule, at rallycross.

Turns out, it's faster.

One event where I was having shifting problems, I decided to leave in 2nd.  Just some clutch slip and a little bog.  Ended up not being any slower, compared to leaving in 1st and upshifting.

I tend to throw a bunch of RPM at my launch, like 4000-4500rpm, and then sidestep it in First, because if I don't hit it hard, it gets some really nasty wheelhop that feels like its going to break things. I then snap it into second before the first element and just leave it there the whole run, unless there is a section that requires clicking it into third.

weedburner said:

ProDarwin said:

Which classes?  I am too lazy to look int he rulebook, but I'm sure in upper level builders classes, these are legal (XP, etc.)

The hitmaster looks like a factory CDV with an electronic timer on it.

Not even close to a CDV. Here's the type of TOB pressure graphs you get with a factory style CDV, various traces are different levels of simple restriction...

The concept is pretty similar.  Not downplaying it, that is pretty clever & effective tech. 

In reply to ProDarwin :

On my F-Dat (bike engined challenge car), the clutch is still on the hand lever like the bike. ECU has launch control feature, where you get to set the 2-step RPM, as well as a 'delay time' for the ecu to ramp up to full power. 

I have considered hooking up a stock MC steering damper (since they are basically free) to the clutch lever so that the release travel is super consistent. Then you should be able to tune in some pretty consistent launches. 

Not unusual for someone to shave .5 off a 60' time with one of my clutch hit controllers during launch, especially on surfaces that have not been treated with traction compound. Better 1st gear acceleration rates without compromising wheelspin, no parts breaking due to wheelhop, and more power available as the clutch doesn't pull the engine down/out of it's power range. Also more consistent and less wear/tear on the clutch over trying to accomplish the same thing with your foot.

Grant

The Foxbody 5.0 mustangs were bad about grenading t5s at the track, I saw a guy come up with a cheap and clever solution. He used a screen door shock on the clutch pedal. Lessened shock and progressively loaded the tires. I guess its the same theory as a CDV, but a much more GRM solution.