Tom W

There was a thread a few months ago discussing how much time could be gained via weight loss. I have some data to share as over the winter I had the Turtle converted from the Mark 2 version to the Turtle Mk3. The major changes were the loss of 300 lbs from 2650 to 2350 (with driver, off-the-track weight) and switching from a 5-speed to 6-speed gearbox (G50/05 to G50/32).

Thunderhill is a 3.0 mile, 15-turn track and it's the one I drive the most. In the Turtle Mk 2, my best times last year were 2:01.9 (going over turn 5) and 1:59.9 (with the bypass). I got my first drive in the Turtle Mk 3 a week ago. Best time on Saturday, with the bypass, was 1:56.5 - a 3.5 second improvement. On Sunday, my best time was 1:58.4 - a 3.5 second improvement.

So, I got 3.5 seconds in 3.0 miles by dropping the weight 300 lbs (12%) and changing the gearing. I was 8.8 lb/hp and am now 7.8 lb/hp (class rules limit my hp to 300 by restrictions to intake and header size).

I have Traqmate data for both versions of the car and it shows slightly faster corner speeds, more g's in the corners and much better acceleration (pretty much what might be expected).

My previous best at Infineon/Sears Point is 1:47.8. Over the 2.5 miles I'm expecting to see a 2.9 second improvement. So my target for next week is 1:44.9.

DrJupeman

Very cool, thanks for sharing and congrats. Btw, I also like the "Mark 2" and "Mark 3" terminology.

DanR

good write up - just lik my wife.........weight is the enemy!!!!!

BrianKeithSmith

That is very much of interest to me. Thanks for posting your results.

After attending the club race at Atlanta last week, I quickly saw firsthand the effect of lower weight and better gearing. My car weighed in at close to 2500 lbs, and I have a stock 930 tranny (tops out at like 200mph with my tire size - craziness) - anyway, my goal is to shed some weight on my car.

Just out of curiosity - what kind of gear changes did you make - what did you swap from - to???

Thanks for the info Tom.

earlyapex

Tom, you are a moving target.

BrianKeithSmith

Nevermind on the gear swap Tom - I reread your posts and see what you did with the tranny!
Thanks!

IcemanG17

Great results....2350lbs is LIGHT....nice......1:58.4 is VERY fast at Thunderhill.....for a car with "only" 300hp..... I wonder how much of the improvement was weight and how much was gearing?

I remember hearing a general guidleine that 7lbs = 1HP....so its like you gained 42HP!!

Your times at Sears are also very good.....in last weeks SCCA ITE race there the top cars were running 1:46-7's So your new setup would be up there!!

I hope my 20 year old bone stock automatic 928 S4 (3500lbs + driver) can hit a 2:20 at Thunderhill in a few weeks at Got Guts at Thunderhill.....

Tom W

A few comments on weight versus gearing. I think almost half of my improvement comes from the gearing.

When I changed from the Turtle Mk 1 to Mk 2 (and the weight change from about 3000 to 2650 lbs) I saw a significant improvement in lap times, but not that much change in acceleration when in 4th gear. I would go through turn 8 at Thunderhill at about 95 mph and gain very little speed on the uphill straight to turn 9, despite being in the power band. Now I accelerate briskly up the same straight. While I'm 1-2 mph faster in the turns, I'm 10 mph faster by the time I hit the braking zones. The speed at which the shift lights illuminate is quite fast!

The car without driver is 2150 and I can't imagine any way to lose any more weight in a 964 tub without compromising safety/integrity in an accident. We paid very close attention to every pound when it was stripped down for the new cage and removed everything not essential. The new cage is heavier than the old bolt-in it replaced, but it's a lot stronger by design. We even removed the stock dash (and all the supporting structure) and replaced it with a light weight aluminum dash. All stock gauges were replaced by a simple MoTeC dash. Gratuitous pic attached... [The passenger seat is removed for races, it was in for instruction/rides at this event]

Brian P

A long time ago I did a regression analysis of various cars in club racing and found that 100 pounds is worth approximately 1 second (at a track like Watkins Glen). YMMV.

Racerrob

Interesting data. I have similar findings. When I converted my 944 from an "I" stock to SP2/944 Cup it lost about 300lbs. So far, I am aobut 2-2.5 seconds at most of the tracks that I drive (the Glen, Mid O, Mosport, Summit) I don't really notice the acceleration but I do notice the cornering speed. I need to get a traqmate.

race911

Yep, exactly the range I would predict.....and I'll bet you're down below 1:55 next time. And then with the repaving in July, watch out! And I agree the gearing is huge. The yellow car even with a stock 3.6 wouldn't be much slower. When I hop in the RSA and its stock gearing, ugh.

JackOlsen

And here's the thing, your times will probably continue to drop even lower as you get more and more used to driving the car with all three improvements (increased chassis rigidity, lower weight, better gearing).

Good work. Those laptimes are awesome.

DJF1

I cant believe this is the same car you took me for a ride 5 years ago! Cool...

chancecasey

Nice work, Tom! Probably some more on the table getting used to jetting into stuff faster now, but you have definitively established that equipment is not an issue.

I just got the rear frame *actually* straightened today - so much for the $550 I paid to the frame guy. We put a bottle jack with a welded-on ERW tube in the back to get it straight, welded in the back cage feet, and it's sitting nice and straight now. I'll put up a part 3 or 4 to my online saga (not sure what I'm up to now) showing every step of the cage - but remember I'm working on beer time.

chancecasey

Since I don't have enough progress to make a thread of my own, I'll horn in on Tom's.

A little preview of Budget C2 Racecar part 3...