power to weight ratio advantages

[challenger&viper]

What are ,or where are the gains when reducing 200 lb from a Viper.
The stock genIV viper is 3454 lb and rated 600 hp with power to weight ratio of 5.75 lb/hp.
Reduce 200lb then the ratio is 5.42 lb/hp.

So, 5.75 lb/hp vs 5.42 lb/hp.

When all things being equal ( hp, weather, driving skill,.. Etc) ,How is that ration going to affect :
*Handling/ cornering.
*1/4 , 1/2, and 1 mile times and trap speed.
*Roll start from 40-60 mph to up to 160 mph time in seconds.

Share your experience/ knowledge

 

[01sapphirebob]

Don't they say for every 100lbs taken off the car you are a tenth of a second quicker in the quarter mile?

 

[Sonoman]

I like to look at things like this in terms of percentages. You are talking about 5% (roughly) reduction in weight and the resulting 5% increase in power:weight ratio. Many of the car's performance functions will improve by about 5%, but some, which are traction dependent, will not. One of the things I observed when I owned my own speed shop years ago is that most customers could easily observe a performance gain (in this case HP) of 10%. It was obvious with a 10% boost in HP that the car had more performance. At 5% most people could tell the improvement was there, but it was more subtle, and while satisfying, not exactly the seat-of-the-pants thrill they were hoping for. Less than 5% improvement numbers start to mingle with day-to-day variations in performance due to things like changes in temperature and air density. So, a seasoned butt dynamometer could detect these small (say 2%) changes in a car they drove frequently, but there was always room for error here-- and just a sunny day and a freshly washed car makes people think it is running better!

Think about it-- when you take on a 200 pound passenger, how much different does the car feel and drive? I believe you will find the 5% weight loss to be noticeable but unless you are racing, not a great bang for your buck. I would go after unsprung and rotating weight first, like forged wheels and lightweight rotors, then move on to more esoteric improvements such as racing seats and carbon fiber body panels. I also believe that in most cases reducing weight X% is better than increasing horsepower that same X% since you also make the car more nimble and reduce fuel consumption and "wear & tear" with the weight loss. Of course, extreme weight loss would require suspension re-tuning as well to keep things planted, but most of us never get that far...

 

[ninjakris]

I did a 1/2 mile event and with or without my wife ~145lbs, it didn't make difference. However, there was a guy with a new 5.0 mustang that removed his rear and passanger seat and was running a few mph faster then other 5.0's out there. I think he said it was a couple houndred pounds lighter.

How would you cut 200lbs? carbon fiber?

 

[Sonoman]

Longer speed runs are more drag-limited than weight-limited. In the eighth-mile your wife likely makes a difference. As the car approaches its top speed, most of the power goes to simply pushing the vehicle through the air; reducing weight just gets you up to speed quicker. Little things like removing the outside mirrors from the car can be more beneficial on a mile run than kicking the passenger out of the car.

 

[TrackAire]

What are ,or where are the gains when reducing 200 lb from a Viper.
The stock genIV viper is 3454 lb and rated 600 hp with power to weight ratio of 5.75 lb/hp.
Reduce 200lb then the ratio is 5.42 lb/hp.

So, 5.75 lb/hp vs 5.42 lb/hp.

When all things being equal ( hp, weather, driving skill,.. Etc) ,How is that ration going to affect :
*Handling/ cornering.
*1/4 , 1/2, and 1 mile times and trap speed.
*Roll start from 40-60 mph to up to 160 mph time in seconds.

Share your experience/ knowledge

I think your 200 lb reduction would have a very big effect on braking distances and how long your brakes last on a road course environment. The longer the session, the better you're braking will be with a 200 lb reduction. So, if you reduce 200 lbs from your car and burn 6 gallons of gasoline in a 20 minute road course session, you'll be about 236 lbs lighter than the before the weight reduction. To me, that is substaintial number. Putting on lighter wheels and rotors will help a lot too (not only braking, but acceleration and handling).

Cheers,
George

 

[Viperless]

I think your 200 lb reduction would have a very big effect on braking distances and how long your brakes last on a road course environment. The longer the session, the better you're braking will be with a 200 lb reduction. So, if you reduce 200 lbs from your car and burn 6 gallons of gasoline in a 20 minute road course session, you'll be about 236 lbs lighter than the before the weight reduction. To me, that is substaintial number. Putting on lighter wheels and rotors will help a lot too (not only braking, but acceleration and handling).

Cheers,
George

I was told by a pro at the NARRA Road America event that 200lbs is worth at least a second on lap times. Maybe more on a long track like RA.

 

[Viper X]

I was told by a pro at the NARRA Road America event that 200lbs is worth at least a second on lap times. Maybe more on a long track like RA.

I would agree, all things being equal.

I've found that I can run almost as fast with a 200 lb passenger as without, but I have to push the car harder, brake later, accelerate sooner and carry more speed through the center of the turns. This works OK for a few laps as I never run at 10/10's, but if you run more than a few laps, the brakes and tires take more of a beating.

Having to accelerate, turn and stop the extra weight multiple times IS noticeable on a road course, some more than others.

Someone above said it, better to cut the weight than add a bunch of power. Car stops, turns and goes better when lighter.

Dan

 

[Allan]

This thread is making me want to strip my car's interior, a/c, radio,...and stop eating ice cream.

 

[challenger&viper]

Great info. Guys.
How is the weight reduction going to affect a roll from 60-160 mph ??

 

[Viper X]

Great info. Guys.
How is the weight reduction going to affect a roll from 60-160 mph ??

Probably just a little bit. Pushing through the air takes more hp / tq than adding a little bit of weight from 60 -160 mph.