Sorry if this has been answered already, I did a search but couldn't find anything conclusive.

So this Friday, I'm taking my '17 AWD R to one of the local tracks for a community 1/8th mile event (Fast Lane Fridays at Miami homestead track http://www.homesteadmiamispeedway.com/Guest-Info/Fast-Lane-Friday.aspx). I've drag raced before in cars with far fewer nannies and never in an AWD. So my questions for those of you who take yours to the strip regularly -

1. How do you warm up the tires, since doing a straight-line burnout is nearly impossible in this thing?

2. Optimal launch - I understand that you just mash the pedal from a dead stop. No revving in neutral, no ebrake, just standing still one moment and moving the next. Is this correct?

Thanks, guys!

 

1. Don't. If you're stock you won't need to worry about grip even cold. If you get some slip, lowering tire pressure helps.

2. Launch from idle. You can play around with brake torquing the launch, but the general consensus is that this only slows you down.

 

Since you have been drag racing before, you know that there is a water box for doing burnouts. Drive around the water box. If you can, once you're around the box, try to mash the throttle to spin the tires a little bit. This will scrub the tires of any debris. Back up, stage your car, and then when the lights go green, roll into the throttle as fast as the tires will allow without wheel spin. You may be able to brake torque the engine by having the car in drive, and pressing the brake and gas at the same time. This will pre-load the drive line with torque and you can get off the line faster (in theory).

 

Is it better to let the car do it's own shifting?
CRS

 

Probably. Otherwise if you have the pedal presses all the way through the de-dent, then the paddles tend not to work.

 

That was my plan. My worry was actually getting the tires to spin free even in the wet. Maybe turn DSC off? I've tried burning out in the wet before and no luck. The only times I get appreciable wheel spin is if I floor it right before jerking the wheel into a sharp turn.

 

But this has proven to not be the case. The vehicle pulls engine torque when you do this and is slower.

 

That's only an issue if the car has the ability to downshift, which during a drag race it would not.

 

Seriously, don't even try. AWD cars are not meant to do burnouts, and its unnecessary at stock power level

 

I first did a number of V-Box 0-6 runs on my 2016 R. The difference between idle and ~2k power brake was not great, but for sure the best runs were with power braking (maybe by a few hundredths at least, on average).

I then ran a number of 11.4 sec. runs at the strip, bone stock (good air though too). The best runs were with power braking, 2-2.5k. 60' times were about 1.73s.

I did have a couple of occasions where the car backed out of the throttle while staged. I suspect it was because of wheel slip from damp tires, and it went away after fully disabling DSC. Normally I would not recommend turning off the all nannies for RWD, but it is perfectly safe with drag-strip traction and AWD (anywhere near stock at least).

Traction didn't really enter into the equation, at least if I could keep as far from the water box as possible. As Mueller recommended, do a short full-throttle burst after the water box in an attempt to clean gravel off the tires.

Heat soak is a real problem, and the car will slow greatly in all but the coldest weather. Best times come from 1-2 hours of hood-open cooling between runs.

It was a fun day at the track. The Hellcats were grumbling loudly about traction, and I didn't see any on DOT rubber that could keep up. The car got lots of compliments, and people couldn't believe how fast it was running.

 

Surprised to hear about your heat soak issue. Did you forget to take off plastic engine cover?

This is not normal unless it is 120 degrees outside and you are continuously running the strip. You possibly have a cooling issue with your car.

 

It's not engine heat soak, its cat heat soak. The cats get hot and the engine goes super rich to cool them down, which reduces power. Same problem I'm having.

That being said, you're the second person to run ~11.4 flat bone stock. I'm getting increasingly frustrated with how poorly my vehicle does at the strip. Best I could do was an 11.63 stock and 11.39 tuned/lower pulley.

 

On the bright side you didn't pay Hennessy through your nose to get the same time as a car off the lot.

 

Would the 200 cell sport cats help with this issue?

 

They certainly would; less surface area to collect heat. Its something I am considering for sure. I wanted to get back to the track with the colder spark plugs before thinking about that order however.

I'm also dealing with wheel spin in 1st and 2nd gear with the extra power.

 

Engine cover is off. Although I have yet to do any serious logging with this car, I have tuned a number of engines, and analyzed many hours of data. I have never seen an engine that didn't pull timing as the coolant temperature increases. The Corvette V8s I have been used to would cool reasonably between runs, but there is so much mass to this Ford and TVS supercharger, it is too hot to touch the intake even after 1.5 hours with the hood open on a 55F day.

Cat over-temp normally occurs after long-duration or very frequent repetition, typically not with even 15 minutes between runs.

Cat over-temp is calculated (at least on GM, Ford, Chrysler), so 200-cell cats are not expected to help. The temperature is not measured, and even disabling the rear O2 sensors or gutting the cats typically does not result in elimination of COT (as observed by power and AFR). Tuning can - but it is not recommended to fully disable COT as it can be an important protection mechanism.

I have purchased a Mongoose cable (genuine) and hopefully I can soon back my expectations with solid data.

Some things I may experiment with:
* Manual cooling fan switch
* Reduce intercooler-to-engine coolant loops cross flow with an orifice.
* Port the supercharger/intake (other applications of the same TVS are getting huge gains). I would do it myself, with inspiration from web photos, and guidance from an ultrasonic thickness gauge.

 

If you haven't tried already, test not enabling dynamic mode in order to maintain more front torque bias. This also leaves the shocks more compliant, and gives more weight transfer to the rear.

A small possible side benefit of power braking: The rear swats a bit at the line, and as such some weight transfer has already occurred.

Even my 11.4 runs at 55F didn't have any wheel spin that I recall, and this was even on the crappy OEM tires.

Soon Michelin PS 4 tires will be installed, and maybe my car can finally corner almost as well as a Camaro. :-(

 

Keep in mind I have 60-80 horsepower more than you. I don't get it every run, but I'm very clearly on the edge of grip. I've been meaning to experiment a bit but haven't had a chance to go back on a week night so i can get 6-8 runs in a night.

As for the cat discussion, VelocityAP's testing has shown the 200 cell cats eliminate this problem if memory serves correct. I was getting real time cat temp data in my logs, so it very well may be measured in this vehicle.

 

Although ET suffers from wheel spin, trap speed - not so much. As we are trapping the same speed, I would say the HP is rather close for those 123MPH runs. However, I don't know how the density/altitude run conditions compare. For same conditions, maybe you are much quicker.

I am pretty sure the real-time cat data is calculated (just like fuel consumption and others), there is no temperature sensing on the cats. I hope to have the car up this weekend, may be I can get some cat pics.