chancecasey

It's funny 'cause it's true...

sjanes

all you need is new ratios for the 915, not a new gearbox.

John H

I LOVE my re-geared 915. It completely changed the car. IIRC it was less that $2500 and that was with a brand new 4th and 5th (3rd was okay from a previous re-gear). I did not drop the tranny or put it back in either.

ZAPmobile

If this is a track only car after re-gearing 3-5, there is really only one way to make it faster. LOSE WEIGHT

Alan Herod

Near track only -- full cage and Sparco Circuit Pro makes entry and egress only an occasional exercise. Still licensed.

Weight loss is definitely in the picture, includes smoother bumper cover/valance with more brake cooling.

kurt M

Air ducts induce drag. Put a 996 FG front end on it.

Noel

Alan,

THe front and rear Carrera spoilers actually reduce drag compared to no spoilers at all, per the book "The 911 Story". It should also reduce lift. The facts I remember reading, was that a non-spoiler 74-89 car at 140-145mph produces about 400lbs of total lift. However, with the front and rear Carrera style spoilers, the total lift generated at that speed is only 35lbs. Pretty dramatic.

JackOlsen

Reducing drag is fine, but it sounds like the issue here is your 5th gear ratio. I don't think there are any tricks you can do with drag that will change the fact that a stock 5th is too tall for most track use.

kurt M

Even after stuffing in mo power? Alan's car has has had a transplant.

JackOlsen

My car's got a transplant, too.

I'm sure Alan's car doesn't have any trouble hitting redline in 5th gear, if he's got enough road. It sounds like the issue is how quickly he can get there, in track use, which is a different thing. My car has plenty of power relative to its weight -- it's a 3.6 in a 1972 tub -- but we went for a 134 mph redline in 5th, which is the max speed I want to hit at all but one of my local tracks. Because of that, I get to use just about all of my 5th, which is what you want. Gears 2-5 should be as close together as possible for track use; there's no lap-time benefit to leaving any gearing on the table.

There's a trade-off, of course. On the street, my car is at 4000 rpm in 5th when I'm going 80. My mileage is still fine, but the buzz of 4000 rpm is not exactly relaxing on long cruises.

Larry Herman

Wow, you must run some short tracks. Your car should be faster than mine and I have a G50 with an 8/32 which gives me 143 mph at 6800, and there are a few tracks where I am right at redline.

Alan Herod

Thank's for the tips -- Looks like gears are the answer -- I emailed Steve Weiner for some tips on the tranny since that is where I got my suspension. It seems like I would like a slightly taller fifth then Larry's. It sounds like my fourth is the same as Jack's fifth; but, I don't think I want to hit red line until the end of the longest straight (VIR and Watkins Glen.)

Larry Herman

Alan, terminal velocity at VIR is significantly higher than at the Glen, so keep that in mind. In my GT3 I was doing 156 at the Glen, and 165 at VIR. I think that I would top out at VIR with the 8/32 trans. That's why I have a spare trans with Daytona gears.

ZAPmobile

As I said before short gears 3-5 are great, that's what we have in our car.if we keep our foot in it all the way to OUR braking point on VIR"s back straight we are at around 6600 rpm in 5th. But the real key is lossing weight in the car, the car just gets better and better as you drop weight. Our car is a track only car.

mark kibort

The drag you are thinking of reducing is a pretty small part of the equation. in doing tests with a rear wing. (much more drag than most all the little things on the chassis can cause) we found that we had 80lbs more downforce by using the real wing vs the stock wing at less of a angle of attack.

so, what did that 80lbs of downforce cost as far as drag? well, at 100mph, in 3rd gear (a ratio of 4.5:1)
an air foil will have (generally) 10:1 lift to drag (or downforce to drag). so 80lbs of downforce comes at a aero cost of 8lbs of drag, 8ft-lbs of torque on the rear wheels. with a ratio of 4.5:1 or so, the engine torque costs would be near 2ft-lbs even if this happened at 150mph, 4th gear at 3.2:1, would cause 8 / 3.2 = near 3ft-lbs. Now, can 3ft-lbs of torque really make a differnce in top speed on the track? based on doing dyno runs and seeing this kind of variance between runs, i dont think it would be noticable. time would be better spent mazimizing HP applied through use of the right gears, or changes in tire size to optimize time spent at near max HP.

Remember, this information is regarding 80lbs of downforce, and 8lbs of drag. you could put your hand out the window and see how much drag an aero mirror has at 100mph. I would guess the difference of an aero mirror and stock mirror would be less than a couple of lbs.

I think the splitter just basically redirects air around the car, rather than underneath. I guess the downside of that , is more rolling friction as the cost for more downforce. Im sure there is some drag associated with them as well. However, if you can come off a cornerfaster, you probably will be able to get more top speed down the straight, even with the 2ft/lbs of torque lost.

mk