mobonic

John, your car is so light i think a brisk wind at willow will turn it over :P

Im going to try to get my car down to 2800 with driver and cage.. then ill go the composite route to shed the last unwanted lbs.

I hope someday my car will be at 2600, but I think thats a bit optimistic with a 997.

jrgordonsenior

2800 would be almost too light for your 997 if you plan on racing with me in GT3. Did you dyno the car Saturday at Willow Springs? Assuming you're putting about 320 to the wheels, your minimum weight would be 2880 (320 x 9)....

I dyno'd at 267 whp so I could run as light as 2403. I doubt I could get more than another 40 lbs if I really worked at it so I think I need some more HP....

Wilder

It would seem to me that the lighter the car gets, the more the effects of weight reduction (reduction being equal) would accelerate returns, not diminish them. Diminishing returns are financial (as I'm sure you know) which is why most people stop themselves short after the free weight is off the car (not to mention it take cojones to hack your car). That's why people like mobonic, JR and my buddy Mark (just took 500lbs out of his E36) are the exception and not the rule.

Great thread NJ-GT!

lowside67

It is only intuitive that taking 500lbs out of a 5000lb car should be substantially less noticeable than taking one of out of a 2500lb car since one reflects a 10% weight reduction and the second a 20%. By that same logic, if you pull 200lbs out and it is a 1 second improvement, the next 200lbs should be worth more than a second. However, I dont know how this theory holds up in actual practice, will let you know this season!

-Mark (currently at 2320lbs, last season weighed in at 2890).

mikymu

Passenger/Time penalty

180 lbs average Joes +3 seconds
118 lbs blond -3 seconds
180 lbs mooty -10 seconds
my mom +10 seconds

Derik Royal

Hey NJ-GT,

It was cool to meet you and your passenger this past weekend. You are likable dude for a guy that drives a Fiat. It's been a while since I had a ride a long. I took a 200 lb+ish passenger out with me for the last session. It was startling how different every part of the track was with the extra ballast. I thought I was just driving like a turd, your thread makes me feel better. Happy holidays! I hope to see you at Homestead.

911SLOW

The change in acceleration (velocity) with which an object moves is directly proportional to the amount of the force applied to the object and inversely proportional to the mass of the object.
According to Newton's second law of motion a = F / m

So reducing weight will always give the same benefits no matter the current weight of car.
Ergo the advantage of a weight reduction in a car is much more important, and the benefits are steadier to monitor easier to apply and affect many other areas of the car (way it handles, brakes,wear etc), than just increasing horsepower (change the force). Besides car engines are not producing a steady power * force output considering their narrow power band delivery, gearing etc.



So we can sum it up with a paraphrase: Peak power sells cars , weight reduction wins races. : )

Erik

LOL, standard joke when people ask for a ride "I don't know, what do you weight". And if I'm battling with someone over the weekend, I tell them I'll only take them if they have a fatter friend that can go into my buddies/competition's car.

996FLT6

I had a 250 lb passenger friend in my 1750lb vw gti(including me plus 1/2 tank of gas). Did my usual line at t2 at ls. Kept going wider and wider and gravel here I come. Mike

silverboy

I read somewhere that for every 120 lbs saved is equal to a gain of 17 BHP at the crank.

Also, for every 1 lb saved in rotational mass is equal to 10 lbs in static weight saved.

TraqGear

And being a great driver JR! That is also a major factor.

enthusiast

For Porsche street cars the estimate that many go by is 1 second slower per 100 pounds over a road course lap distance of about 2.2 miles.

.

NJ-GT

Last weekend, my 25 gallons fuel tank (157 lbs heavy) was a little over the middle (6 bars) during my fastest session with a passenger, each fuel bar in the Fiat is 2.0 gallons (10 bars), plus another 5 gallons left when all the fuel bar are off (reserve).

Weight with passenger:
Fiat on HRE wheels 295/315 tires (no fuel): 2,983 lbs
Driver: 180 lbs
Passenger: 180 lbs
Helmets, jeans, shoes, video/data equipment: 30 lbs
Fuel: 87~ lbs (106 lbs estimated with 6 bars on dashboard, minus 3 gallons consumed in 6 laps, as lap 7 had the fastest lap time with a passenger)
Total: 3,460 lbs
Lap Time: 1:27.950

Weight without passenger:
Fiat on HRE wheels 295/315 tires (no fuel): 2,983 lbs
Driver: 180 lbs
Helmets, gear, video/data equipment: 20 lbs
Fuel: 62~ lbs (started the session with 3 bars and posted fastest lap time in lap 2)
Total: 3,245 lbs
Lap Time: 1:25.654

Notice that the lap time difference was 2.3 seconds for a weight reduction of around 215 lbs. The track is 2.03 miles long and flat as a table. This was just a 6% weight reduction.

Removing the laps with traffic, and using average top speed per segments, the car with the extra 215 lbs is 3-4 mph slower in each segment. This is a lot. It has to do with carrying a lower exit speed, plus lower acceleration and having to brake earlier.

NJ-GT

Hey Pal. The event was great, hopefully next time they let me register in HPDE-4 and obtain my Time Trial license, as I have more fun running against the clock than driving flat-out.

Here are a pair of videos from last weekend.

Session with passenger video ==> http://vimeo.com/17627105

Session with no passenger video ==> http://vimeo.com/17627019

If a TV show thingy doesn't go trhough, I'll be at Homestead. Both things are happening the same weekend (plus an autocross in Fort Myers).

trophy

Don't forget, you will not drive quite as hard with someone in the car as you would by yourself... I find very similar data as you Nj-GT, drop in side and acceleration g's, not so much with breaking (sometimes a little higher). usually see a drop in speed of around 3-4mph at end of main straight, slower entrance speed combined with less acceleration.

Weight loss is the ultimate.

I see people talk about the 'Effective' gain in hp, but this is not a logical or calculable number, it would depend on the starting weight of the car. 120lbs off a 3500lb car is going to give a different result that 120lbs of a 2400lb car. Percentages could be considered, however it still doesn't give more HP. The only way is to do what NJ-GT did and get some back-to-back lap data and compare.....

Get light, go fast.... Nice vids by the way.