This is new info on what not do when getting the car ready to beat the Mustang in the opposite lane.

Have you ever done just that little burnout to heat the tires a bit? Or it might have been just a little smoke 'em bit to intimidate the Mustang in the other lane? One of the usual methods to break the tires loose is to get the car rolling, back out of the throttle just a bit and then nail it. Wrong thing to do. It seems that the PCM (not sure if ECMs do this or not), is set up to compensate for this maneuver. In fact, doing this fools the computer into thinking that the engine is close to detonating. The PCM immediately yanks the timing back costing hp and low end torque. In fact, the way the PCM recovers is to yank bank the timing and then slowly add advance, too slow for your next coupla runs down the 1/4 mile. In other words, by doing that quick maneuver, your engine just lost enough advance to affect your 1/4 miles times and speed in the traps. There is no way to recover from this except disconnect the battery cable for maybe several hours so that all short term curves are reset to default.

What happens is that the MAF, which is measuring the airflow, sends the PCM signals telling it how much air is flowing. The MAP which has lots to do, contrary to popular belief, is busy comparing reported air flow by the MAF with absolute pressure within the intake manifold. The MAP, when the gas is backed off, will report a high vacuum (in comparison to ambient air pressure--it's sort of an altitude compensation), then just as quickly report a low vacuum when the throttle is nailed. The figure that the MAP reports is what is used by the PCM to govern how much advance is generated for the engine. By backing off the throttle, then nailing it, the PCM is told that the engine is generating enough dyanmic compression to begine detonation for whatever cause. To protect the engine, the PCM then hauls back the timing and there goes your 60 ft times, the overall ET and the speed thru the traps.

The trick as I see it, is to get the other guy to do that.

yup sounds on the spot to me, I assume this doesn't happen with a speed density car!I also don't think it wouldn't with a custom ECM program. I have seen people do short burnouts and then run thier quickest times, but on a stock ECM sounds good. Also you say from a roll and then a burn out, would the same thing happem if you just nail it from a stand still?

Doug

Nail if from a standstill and wreck the timing? Shouldn't affect anything. Not sure if an ECM does it, since it doesn't use a MAF. This might be only a PCM function since both MAP and MAF are required to give the PCM the necessary info.

Also, the combination of letting off the gas, which drives the vacuum up, and then hitting it again really quickly, which drops the vacuum down to almost zero, is what signals the PCM to immediately retard the timing. However, according to the website, the engine must be equipped with a MAF since the MAF can actually measure air density, and that is what is used by the PCM to compare with the output of the MAP. Got that? Whewww......

Caught this bit of info on a wonderful web site (darn if I can find the web site at the moment, but it is a long read anyway). The guy spent tons of internet bytes explaining how the PCM works and the little tricks on how to work with it. I thought that was interesting, and it explained what happened to my car when I did that little maneuver showing off a bit in 4th gear. The car ran awful for some time after that.

I've always done my pre-race burnouts by jumping on the throttle from a stopped position, without power braking. Last summer, I raced my neighbor's 2001 Mustang GT convertible. On our first run, I started with cold tires...spun about 100 feet. He got several lengths ahead of me before I let off (to save my car from stone chips). Next two runs, I warmed the tires a bit and got him by about a length and a half. I don't know if I lost any timing advance with the burnouts, but the traction I gained was worth it if I did.

.........so should we just roll up (around the water-box), and then just get on it off the line??????

I never go through the waterbox, I do a small burn out to warm em up, then go.

Doug

I've always skipped the ole box too.....but I do spin the tires to get rid of any gravel/oil that may be stuck to it..........would this hit of the throttle affect the way the car is tuned/will run down the track!?!

okay so what is the best way? cause my 60 ft time is crap! I try to hit off the light and burn out for ever so what it the best technque