maschinenbau
maschinenbau SuperDork
9/9/19 12:40 p.m.

I'd like to know what I'm doing wrong, what I could improve on, and what might be wrong with my setup. I don't know drag racing very well, but from what I'm told, that MPH is way too fast for that ET. 

  • RWD V6 5AT
  • Weight with driver assume 2550 lbs
  • 80 to 100ish wet shot (want to go up)
  • Spraying at top of 1st, holding it to the end
  • 25" Hoosier drag radials, high teen's PSI
  • Crossing like at 5600 in 4th gear. Redline is 6600
  • Launch technique is just stalling converter to about 1800 RPM then flooring it at green
  • Optional tiptronic mode? Just letting it shift itself for now.

No idea what launch looks like, but I assume I'm spinning. It bounces the rev limiter several times during the 1-2 shift.

Lower tire pressure? Burnout harder? Something else?

Dusterbd13-michael
Dusterbd13-michael MegaDork
9/9/19 12:48 p.m.

More nitrous. 200 shot. Im sure it'll be ok.....

 

Joking! 

Sounds like youre spinning hard through 1st, and maybe part of second. 

Will it let you launch in second? 

dropstep
dropstep UltraDork
9/9/19 12:53 p.m.

Certainly seems to be spinning. The mph for an easy 12 is there but the 60 foot could use some work 

Robbie
Robbie UltimaDork
9/9/19 1:03 p.m.

Have you played around with tire pressure? Might still be too high, maybe?

Also, by stalling the converter to 1800 - you mean left foot on the brake and and right on the gas, correct?

Robbie
Robbie UltimaDork
9/9/19 1:03 p.m.

Also, nice work in general!

z31maniac
z31maniac MegaDork
9/9/19 1:14 p.m.

That is a pretty high trap speed for those ETs. 

For reference, the few times I took my sportbike to the drag strip, I was running 11.18 to 11.30 at ~119mph. 

maschinenbau
maschinenbau SuperDork
9/9/19 1:15 p.m.

Yes, I'm left-foot braking and throttling up on on the pre-stage line as high as I can until the wheels want to spin. Maybe I could use the parking brake for more stall? 

Can only launch in 1st. Electronically controlled trans that integrates with the ECM. Might be a way to trick it though.

eastsideTim
eastsideTim UberDork
9/9/19 1:18 p.m.

How does it feel?  I’m agreeing with spinning on launch, but it’s possible there is some wheel hop, but I’d think you’d feel it.  I’ve never drag raced an IRS-equipped car, but I seem to recall some of them are prone to wheel hop.  I know your weight is a lot lower, but if you haven’t checked already, may want to see what the drag racers on the G35/G37/Z car forums are doing.

You’re pulling hard in the last 1/8th, so I think it is pretty much down to your launch.  Do you do a quick burnout to get a little heat into the drag radials?

 

Ranger50
Ranger50 UltimaDork
9/9/19 1:38 p.m.

It just doesn’t 60’.

What does it weigh? How much is on the rear? What suspension? What gear?

At 3000#, I had a 13.24@100 slip on drag radials. It also 60’ in 1.55 sec.

AngryCorvair
AngryCorvair MegaDork
9/9/19 1:42 p.m.
Ranger50 said:

It just doesn’t 60’.

What does it weigh? How much is on the rear? What suspension? What gear?

At 3000#, I had a 13.24@100 slip on drag radials. It also 60’ in 1.55 sec.

was that in an AWD car?   because 1.55 60' is insane for a 13.24@100

AngryCorvair
AngryCorvair MegaDork
9/9/19 1:44 p.m.

In reply to maschinenbau :

what does it do if you don't "stall the converter" at the line, ie short burnout, stage, hold brake to keep it from rolling, but don't mash the throttle until the last yellow.  ECU might be pulling timing when it sees big delta between driven and undriven wheel speeds.  assuming you have wheel speeds available to the ECU.

maschinenbau
maschinenbau SuperDork
9/9/19 1:44 p.m.

It feels very smooth and steady, no hopping or anything. 

A spectator in the crowd told me the exhaust was shooting flames between shifts, so that would be the rev-limit I guess.

eastsideTim
eastsideTim UberDork
9/9/19 1:46 p.m.
maschinenbau said:

Yes, I'm left-foot braking and throttling up on on the pre-stage line as high as I can until the wheels want to spin. Maybe I could use the parking brake for more stall? 

Can only launch in 1st. Electronically controlled trans that integrates with the ECM. Might be a way to trick it though.

If you're spinning, you're launching at a high enough RPM already.

Javelin
Javelin MegaDork
9/9/19 1:56 p.m.

Your short track is where all the issue is. My car runs 13.3@104 with a 1.8 60', and that's a stick on street tires. You have too much pressure in the rear tires and not enough heat. An automatic that traps 110+ on DR's should cut low 1.7's and 330 a lot harder.

Drop air pressure to 12 psi and try a longer burnout. Leave all other variables the same. Keep playing with tire pressure and great until you can launch at the same RPM with no wheels and a solid 60'.

If you go from a 2.1 to a 1.7, you'll be in the 12.8's with no other changes, but I imagine the car will pull harder throughout and net more like a 12.6-12.5. You can't completely rely on your MPH because you spray, and not out of the hole.

maschinenbau
maschinenbau SuperDork
9/9/19 2:17 p.m.

Thanks everyone for the feedback! I can always count on GRM to make me go faster. So in summary:

  • Lower tire pressure
  • Hotter burnout
  • Don't worry about stall as much
  • Control spin in first - either by not spraying, or modulating throttle, or both?

 

Vigo
Vigo MegaDork
9/9/19 2:23 p.m.

That trap speed would max out in the low 12s, et-wise. Traction is the big variable there, followed by gearing and power 'under the curve' so to speak. Main thing for you would be 1st gear traction, although if you're spraying in 1st while already spinning I cant imagine it hooks up in 2nd right away. Definitely don't spray until it's hooked.  

As far as what to do about it, main thing would probably be better tires. Those are street-tire 60 foot times for a RWD car. You can try getting them hotter  or dropping pressure and see if they improve substantially but they may not. You could potentially optimize your suspension to work with those tires but it would cost you somewhere else that is probably more important.  So the easy button is just get real slicks. You could also do some software solutions if you wanted to go down the rabbit hole trying to make those tires work, but  it sounds like you're using a stock pcm so your options there are either really limited, or require a huge upfront investment of time, money or both. 

Launching in 2nd almost never helps. It may help traction but it won't help your ET. That calculus only changes when you are making enough power to spin huge actual slicks (this is the point where drag cars start using powerglides which basically do start in 2nd compared to anything else)  or when you have a ton of ratios like an 8spd Hellcat.  You don't fit either of those categories so i'd purge the thought of starting in 2nd completely. 

Paul_VR6
Paul_VR6 Dork
9/9/19 2:25 p.m.

The Hoosier radials don't like (or need) a ton of heat compared to the BFG from what I have seen. If you do a giant burnout your tire pressure will go up, so you need to take that into account. Generally DR will like lower pressures that you are using, so keep dropping by .5psi until your trap speed starts to hurt. That will generally be the sweet spot. Again, you NEED to keep the burnout consistent or check pressure after the run as well. 

If you can knock the tires off without the nitrous, leave it off until you can't. 

I have cut 1.81 60' on 225 BFG with a FWD manual trans, similar weight, and ended up with 13.22@104 ... you should be able to easily be in the 12.6-7 range just working the short track. 

Streetwiseguy
Streetwiseguy MegaDork
9/9/19 3:01 p.m.

My 82 Camaro has way too stiff suspension because it was done with autocross in mind.  As such, it won't hook worth a E36 M3, plus it's on street tires that grip better on 8th Street than the track. 2.5 60 foot, 13.6 ish at 104.  Should et better than that.

I would suggest all your trouble is in the 60, just like mine.  My solution would involve making the car way worse at almost everything else, so I just suck it up the few times a decade I go to the track.

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