JCP911S

At LRP the 2.7 911s are almost as fast as the 3.0s....

At WGI they get left for dead....

LRP is not a HP track

analogmike

Lime Rock is a momentum track, HP does not get you much.

I know of a stock 2.7 that got a 1:11 at the Glen
Momentum from T1 exit to the bus stop will help a lot there, too.

Weight loss does not give as much improvement as you think, as the extra weight ADDS grip to the tires. More weight on a tire = more grip, just not quite enough to offset the disadvantages of having to carry around that extra weight. But a heavy car seems to brake nearly as good as a light car, check out the autoweek braking distances, and how a 2800 pound GT3 cup can outbrake most 2000 pound cars.

Flat Top

Mike. Be very careful of how you state your case. There are many innocent eyes reading material posted here and you may inadvertently mislead some.

It is true that weight adds grip BUT in a racing car there are other dynamics that come into play and that is acceleration, braking and cornering. In track cars it is balance of these factors that generate your lap times. For a track car you want the lightest possible car that you can get.

The advantages of having a light car mulitpies - amongst other it allows you to run softer rubber which generated more grip - the need for heavy brake rotors and calipers diminishes (see Formula Ford Disks) - when you fall off the track you have less damage.

With regard to the braking abilities of the GT3 you need to take into consideration that these cars run a very sophisticated braking system. All things being equal the lighter car with less momentum will stop first.

Thanks for your response, even if we may not agree on some points.

Johan
www.almost.co.za

SundayDriver

To be blunt, a general model that looks only at HP, regardless of vehicle dynamics and track, is pure JUNK. A model should work at the extreme cases, and if it fails there, then it doesn't work. If it passes, then maybe it works.

Put a car with 200 hp on a cicrle and get your best lap time. You are running only maintenence throttle. Add 200 hp and the lap time will not improve at all. Formula and concept fails miserably.

Now make the track full of twisties and very short straights. Limited opportunities for acceleration. Again, the model does not much apply. Now use a track ot four slow 90 degree corners followed by 1 mile straights. HP is everything and handling will have a very limited effect.

Acropora

Any thoughts on if one shaved lbs from 3400 to 3200; how much would it lower track times on a course like Gingerman, 1 second?

Larry Herman

Test it empirically...just take a passenger and see how much time you lose.

analogmike

That's the point

You have to think for yourself, and a lot of what you read is wrong.
I like to take the opposite to the norm opinion as it often has as much merit, so people can think for themselves.

Here's some data to support what I wrote:

When I run in E class I am 150 pounds heavier, full fuel tank and ballast. Times do not change by more than a few tenths of a second at Lime Rock, a momentum track. Would be more at the Glen, accelerating up the hill through the esses and other long straights (coming out of the toe of the boot).

Acropora

No no no, that makes too much sense. How 'bout the diversion fudge factor from the passenger yelling how you should be driving..

TheOtherEric

I don't think your argument supports your conclusion. I think we'd all agree that this "6th power rule" doesn't work at the extremes. But it doesn't appear to be intended for use in those circumstances. So I'm just saying it MIGHT be useful for some range of track types. It assumes some ratio of straights-to-curves but we don't know what that ratio is.

BTW, has anybody measured their change in lap time due to adding a passenger?

SundayDriver

I agree that there is almost certainly some car/track combos where that calculation works. But I suspect it is something like 1 out of 1000. I have a clock that is right twice a day - that doesn't make it useful because it can not tell me which two times it is right.