1/4 mile: questions!

[felixkk]

Mark Imhof and I have signed up for the quarter mile end of September. He has a MkII Interceptor and I've got the C-V8 MkIII. Both of our engines/cars are pretty much stock- both being the 383. Mark's Interceptor is quick- I've chased him up a pass and just barely managed to keep up. The C-V8 is a bit lighter. Mark's girlfriend will be driving (which compensates some of the weight difference).

Any tips? I've read that one should deflate the rear tires, remove the spare wheel and drive with a half empty tank. Two pedal start (have to practice that), but one shouldn't rev the engine in gear for more than 3 or 4 seconds. Start in 2nd I assume? Note to myself: must remember to change gears

I've found the time for the C-V8 in a period road test: 15.2s. Haven't found the time yet for the Interceptor. I don't know what to expect but this being the first time, anything below 20secs I'll be happy. I don't even know how fast we'll be at the finish? Someone said 130 or 140 kmh.

Anyone dare to make a wager on our times? Closest time(s) wins a box of chocolates...

[AH1951]

Why would you start in 2nd?
I think the tyres would soon be ruined if you deflated them.

[bkbridges]

Felix,
That sounds like fun! From my personal experience with 9272 getting a good launch is the most important thing to a good 1/4mile time, provided the car is in good tune and doesn't fall over at high rpm. On street tires I would leave the inflation pressure at 28-30psi. If your limited slip differential is working well you might be able to preload the torque converter to around 1200rpm and then when the starting flag drops wood the pedal and jump off the line. More likely you will incur a lot of wheel spin. If this is the case, try launching without the torque converter preload. Flag drops, hit the gas. Worst case you will still be spinning, so youll need to pedal the car a bit to get traction into second gear. Once you hit second you should be able to keep it to the floor without having to do much driving. If your throttle pressure linkage is set up correctly just leaving it in drive should get you to the end of the track as quick as anything. With the stock gear change mechanism it is too easy to shift into neutral at the top end... not good. Racing with street tires can be tricky, so Id recommend cheating by purchasing a set of DOT approved racing tires. MT streets work well. Also, don't wait for the green light/flag to drop before hitting the gas. The key is to hit the gas early enough so the car just starts moving as the light goes green/flag drops. I leave the spare in and run on whatever gas Ive got at the track. Im not hot lapping for the quickest time or racing other Interceptors though. A little weight reduction is a good thing, but it would be better to take it off the front instead of the rear. Working on high 11s in 9272... best so far is 12.3sec @ 109mph. My MT streets are still waiting to be used for the first time.
Have fun!
BKB

[felixkk]

Adrian, no additional points are given for burnouts

[felixkk]

Thanks Bruce. I'm a bit relieved that I may not have to start with both pedals- although I'll have to try that out beforehand on an empty street. I'm not sure how we'll be starting- it's quite informal. Timed but I'd think without lights. We won't be anywhere near your times, that's for sure.

[Richie]

Cannonball is your man for this... Sounds fun fun fun...

[AH1951]

Is there some kind of gunk you can put on the rear tyre treads to increase traction?
Buying racing tyres seems a bit drastic and probably expensive?

[bkbridges]

Just waiting for Cannonball to reply!
VHT traction compound can help the launch, but may not be allowable depending on "sanctioning" body. It leaves marks...
BKB

[Philip Lochner]

I'm no specialist in this kind of sport, never done 1/4miles and hardly ever do quick starts, so what do I know?

I do consider myself a boffin when it comes to off-roading. Now you may argue that off-roading has nothing to do with maximum acceleration but I beg to differ. When I had the 205's on my car, I gave up trying to do traffic light dices (the few times I did attempt it) because I just end up spinning the wheels (looks of disapproval from all around) and go nowhere. Now that I have the 245's on the car, it has become quite hard to actually spin the wheels and I can confidently jump on the gas - not that I do that often.

Max acceleration has EVERYTHING to do with traction (amongst others). If you end up spinning your wheels in the first "5 meters", you have lost. Done. Same with off-roading (except in mud)

With off-roading, lower tyre pressures = more traction, ALWAYS.

So, if I were to make any such race attempt, I would 1) run the rear tyre pressures as low as possible, but just high enough too make sense at the speeds you will be doing towards the end of the run, the fronts as hard as possible for minimum rolling resistance and 2) run with the widest tyres you can fit to the rear. On 205's I would say you are wasting your time, fuel, tyres and car. Should be entertaining though.

[felixkk]

Makes sense. Thing is, I've never done a full throttle standing start, so I don't even know if the wheels will spin. Must find a quiet road to give it a few tries.

[Richie]

I've done one full throttle standing start...details are hopefully in the imminent edition of the JOC Mag to serve as a warning to all...

[AH1951]

I acquired a bad habit of making fierce standing-starts in my souped-up Humber Sceptre.
It had wider wheels with radial tyres all round and many engine & carb mods.
It was a manual gearbox car.
I would drop the clutch from high RPM in first gear, followed by a bit a bit of tyre squeal and the car would step off very quickly.
However, after doing this a few times, the bolts in the differential fastening the sun gear to the carrier sheared,
moved out of position, splitting the diff casing and dropping oil on the road.
After that, with a replacement diff fitted, I drove more gently.

[Richie]

here's the end result of my 'moment'...

could so easily have been so very, very much worse. Could literally have easily been tragic.

It sounded fantastic running like this!!!

[Philip Lochner]

here's the end result of my 'moment'...

A very interesting failure to result from a hard pull-away. Any ideas as what caused this failure ? (besides stepping hard on the gas)

What exhaust setup do you have going under the car?

What is the condition of you engine mounts?

[Richie]

To cut a long story short...The failure was caused because I pressed the wrong pedal! Instead of coming to a gentle stop in a car park, I accelerated full bore into a temporary parking barrier, which I then ran over. This caught under the car at the rear silencer, pulling the exhaust backwards...
I'm eternally thankful that no people were in front of me...