power to weight or just more HP????
06-10-2008, 02:21 AM
#16
Rennlist Member
I dont know why the previous poster's head was hurting. 
basically, just keep in mind the "Three Factors". depending on the track. (said already by a few already) the factors need to be looked at more closely.
What i like to do, is find situations where emperical data can be found.
Well, look no farther than the SpeedGT world challenge again. there has been two, and now 3 porche turbo 996s that have run. I know that many of them can get near 500rwhp with only a few mods, some of which are legal. their 3200lbs weight vs the GT3 cup cars with the upgraded engine having weight under 2900lbs and RWHP in the 420 range. 300llbs can be worth near 30hp, and close ratio gear boxes might be worth a few more. The weight however, helps in braking and cornering. These becomes the major factors.
With your comparison of two very different cars, and near 450lbs of weight difference, with only 35hp as a power difference, the turbo would get smoked in every possible way. Even if the power difference was greater, the lighter car would have the advantage in 2/3s of those dependant factors.
Ive spent a good part of the last few years competiting against cars fitting in both ends of the performance catagories. The C5 i race with is 250lbs heavier, but has 90more hp. His bigger tires and more effective downforce, gives him some near same handling, but underbraking, i have a sligth edge. Sure there might be driver differences, but over 100s of laps together , you start to see some of the differences. on the other side, i had an S2000 and a M3 that were much lighter than i was on smaller tires, but were able to spin the same lap times with only 15 less HP. (the S2000 being 300lbs lighter and had 50 lessHP. The point here is that there are a bunch of trade offs.
Back to your turbo, if you can gut it, pull out the FWD and bump up the HP , you could have a real monster on your hands. But, the GT3 with most of its weight already out of the car, might be a better place to start and build from.
mk
basically, just keep in mind the "Three Factors". depending on the track. (said already by a few already) the factors need to be looked at more closely.
What i like to do, is find situations where emperical data can be found.
Well, look no farther than the SpeedGT world challenge again. there has been two, and now 3 porche turbo 996s that have run. I know that many of them can get near 500rwhp with only a few mods, some of which are legal. their 3200lbs weight vs the GT3 cup cars with the upgraded engine having weight under 2900lbs and RWHP in the 420 range. 300llbs can be worth near 30hp, and close ratio gear boxes might be worth a few more. The weight however, helps in braking and cornering. These becomes the major factors.
With your comparison of two very different cars, and near 450lbs of weight difference, with only 35hp as a power difference, the turbo would get smoked in every possible way. Even if the power difference was greater, the lighter car would have the advantage in 2/3s of those dependant factors.
Ive spent a good part of the last few years competiting against cars fitting in both ends of the performance catagories. The C5 i race with is 250lbs heavier, but has 90more hp. His bigger tires and more effective downforce, gives him some near same handling, but underbraking, i have a sligth edge. Sure there might be driver differences, but over 100s of laps together , you start to see some of the differences. on the other side, i had an S2000 and a M3 that were much lighter than i was on smaller tires, but were able to spin the same lap times with only 15 less HP. (the S2000 being 300lbs lighter and had 50 lessHP. The point here is that there are a bunch of trade offs.
Back to your turbo, if you can gut it, pull out the FWD and bump up the HP , you could have a real monster on your hands. But, the GT3 with most of its weight already out of the car, might be a better place to start and build from.
mk
ok, so after all the physics talk...lets use a simple car comparison...
996 gt3 with 395 hp and around 2950 lbs VS a 996 turbo at 3400 lbs with 430 hp (so there isnt a HUGE amount in between the two, but noticeable). Assuming that the turbo had enough suspension work, how do you think the scenario would play out at different tracks?
(reason why is I have both currently in the stable...and feel like the gt3 will be faster nearly everywhere...short of MAYBE 160 plus (which is very rare to hit anywhere other than pocono or VIR)...
996 gt3 with 395 hp and around 2950 lbs VS a 996 turbo at 3400 lbs with 430 hp (so there isnt a HUGE amount in between the two, but noticeable). Assuming that the turbo had enough suspension work, how do you think the scenario would play out at different tracks?
(reason why is I have both currently in the stable...and feel like the gt3 will be faster nearly everywhere...short of MAYBE 160 plus (which is very rare to hit anywhere other than pocono or VIR)...
06-10-2008, 02:28 AM
#17
Rennlist Member
I think you are right! In fact, I can remember spending a few nights in the winter pulling out useless street driving based wiring to save 7lbs. I could have sworn it was 20lbs, but the scale doesnt lie. However over the years, 1lb here and there adds up. Then, of course, we all would like that extra 10-15hp if we can add it reliably.
Mk
Mk
OUCH! My head hurts. Make it stop! 
Honestly though, you need to consider 1 hp gain vs 2-4 lbs of weight reduction. Which is cheaper, which does not reduce reliabilty, which has better drivabiltiy characteristics.
If I could shave 100 lbs off my car for nothing, that's what I'd do first. Conversely, if I could gain 10 hp and take 10 lbs off my car at the same time (removing the cat), then that is the best of both worlds.
The answer to you question is easy. Take the free road first. After that is exhausted, do a cost/benefit analysis and go with the answer that offers the greatest benefit for the least amount of money.
There! Thread Closed!
Honestly though, you need to consider 1 hp gain vs 2-4 lbs of weight reduction. Which is cheaper, which does not reduce reliabilty, which has better drivabiltiy characteristics.
If I could shave 100 lbs off my car for nothing, that's what I'd do first. Conversely, if I could gain 10 hp and take 10 lbs off my car at the same time (removing the cat), then that is the best of both worlds.
The answer to you question is easy. Take the free road first. After that is exhausted, do a cost/benefit analysis and go with the answer that offers the greatest benefit for the least amount of money.
There! Thread Closed!
06-10-2008, 04:12 AM
#18
If the power to weight are equal (read the topic), the lighter car will always have the advantage on a road course. Getting 10 mph more acceleration on a couple long straights isn't enough of an advantage to make up where it is losing everwhere else. With equal power to weight, you woudl never see that much of a difference. The larger car will most likely have to brake a longer dstance and to a lower speed due to that extra heft. Corning speeds are lower and peak acceleration between all the shorter corners is less. I suggest you spend less time posting and more time at the track and this will be more obvious. If you had a road course with sufficiently long enough straights to obtain top speed then that may be possible, but there aren't any. Even TWS where the front straight off the roval is 3/4 of a mile, the fastest cars on the straight don't have the fastest lap times. You see the same thing at the races at Rockingham in the UK.
06-10-2008, 10:19 AM
#19
Lifetime Rennlist Member
If the power to weight are equal (read the topic), the lighter car will always have the advantage on a road course. Getting 10 mph more acceleration on a couple long straights isn't enough of an advantage to make up where it is losing everwhere else. With equal power to weight, you woudl never see that much of a difference. The larger car will most likely have to brake a longer dstance and to a lower speed due to that extra heft. Corning speeds are lower and peak acceleration between all the shorter corners is less. I suggest you spend less time posting and more time at the track and this will be more obvious. If you had a road course with sufficiently long enough straights to obtain top speed then that may be possible, but there aren't any. Even TWS where the front straight off the roval is 3/4 of a mile, the fastest cars on the straight don't have the fastest lap times. You see the same thing at the races at Rockingham in the UK.
Comparing different cars on top speed vs. lap time has nothing to do with the original premise of this thread.
06-10-2008, 11:03 AM
#20
Rennlist Member
If the power to weight are equal (read the topic), the lighter car will always have the advantage on a road course. Getting 10 mph more acceleration on a couple long straights isn't enough of an advantage to make up where it is losing everwhere else. With equal power to weight, you woudl never see that much of a difference. The larger car will most likely have to brake a longer dstance and to a lower speed due to that extra heft. Corning speeds are lower and peak acceleration between all the shorter corners is less. I suggest you spend less time posting and more time at the track and this will be more obvious. If you had a road course with sufficiently long enough straights to obtain top speed then that may be possible, but there aren't any. Even TWS where the front straight off the roval is 3/4 of a mile, the fastest cars on the straight don't have the fastest lap times. You see the same thing at the races at Rockingham in the UK.
Coupla points that show--as usual--just how much you are talking out your pooper:
-front straight at TWS is more like 1/2 mile
-same driver at TWS will turn better lap times in a car with higher HP, due primarily to its ability to hit a higher top speed on the long straights, thanks to more HP to overcome wind resistance
-maybe YOU should spend more time on the track, WITH AN INSTRUCTOR, instead of spouting nonsense to the unsuspecting here
-I will compare lap times with you any day, any time, on any track
Have a nice day!
06-10-2008, 02:10 PM
#21
Three Wheelin'
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Dave, coming from that great DE'er with two years of experience, you should listen!!! You know, he even wears his harnesses driving on the street. Now that's a pro.
G.
06-10-2008, 02:24 PM
#22
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And the higher inertia of the heavier car under braking might negate the additional grip there as well.
06-10-2008, 02:24 PM
#23
Rennlist Member
Huh? Let me see if i clearly understand that first comment.
Are you saying that a heavier car can brake and corner as well as a lighter car the same exact shape and size. (that is the discussion by the way, as we are talking about performance differnces due to drag at the higher speeds for two cars the same aero, or same shape and size, but different weights and HP is different to provide same HP/weight ratios)
Basic physics will say, for the same grip, the heavier car will take as much hp difference to stop the same as it would to accelerate the same. In other words, for the heavier car to stop as well, it will need to find some BIG braking hp advantage. in order for it to corner as well, it also will need to find some cornering power advantage. (pop up splitters and wings for example)
I provided a ball park differnce of the HP losses for any speed based on a known drag at speed. Im sure the values are close enough for discussion,
but bascially, we are talking a near 2% loss in power at top speeds for the high powered heavier racer, vs near 10% losses for the lighter racer due to aerodynamic drag. These losses go down with speed, inverse to the square of the speed.
You also have a slight contradiction in your last paragraph regarding the lighter car having a cornering advantage. (you reference downforce) I agree , but keep in mind for a given downforce, there will be drag associated with it as well as rolling friction increases. I guess that would fall in to the comparisons of the aero drag forces with the two racers
mk
Are you saying that a heavier car can brake and corner as well as a lighter car the same exact shape and size. (that is the discussion by the way, as we are talking about performance differnces due to drag at the higher speeds for two cars the same aero, or same shape and size, but different weights and HP is different to provide same HP/weight ratios)
Basic physics will say, for the same grip, the heavier car will take as much hp difference to stop the same as it would to accelerate the same. In other words, for the heavier car to stop as well, it will need to find some BIG braking hp advantage. in order for it to corner as well, it also will need to find some cornering power advantage. (pop up splitters and wings for example
)I provided a ball park differnce of the HP losses for any speed based on a known drag at speed. Im sure the values are close enough for discussion,
but bascially, we are talking a near 2% loss in power at top speeds for the high powered heavier racer, vs near 10% losses for the lighter racer due to aerodynamic drag. These losses go down with speed, inverse to the square of the speed.
You also have a slight contradiction in your last paragraph regarding the lighter car having a cornering advantage. (you reference downforce) I agree , but keep in mind for a given downforce, there will be drag associated with it as well as rolling friction increases. I guess that would fall in to the comparisons of the aero drag forces with the two racers
mk
Huh? All else being equal, there is no reason a lighter car will corner better nor stop in a shorter distance - basic physics tells us that grip is proportional to weight. So unless you are reading more into the question and making assumptions that were not part of the question, there is no difference in cornering nor braking. As I said earlier, if each has the same pounds of downforce then the lighter car wins out on cornering but the higher HP will have the acceleration advantage.
Comparing different cars on top speed vs. lap time has nothing to do with the original premise of this thread.
Comparing different cars on top speed vs. lap time has nothing to do with the original premise of this thread.
06-10-2008, 02:35 PM
#24
Rennlist Member
are you getting into vector forces and they are going to get complicated based on the parameters we are dealing with . same size car, same tires, brakes , aero , but one is heavier than the other. tossing weight in a car, (think spec miata) will hurt not only acceleration (Unless the hp was increased to keep HP /weight ratios the same, AND it would then have an advantage as speeds went up. So then braking and cornering capabilities are less.)
mk
mk
06-10-2008, 03:12 PM
#25
Rennlist Member
Loren, let me draw you a simple picture. I have a friend & fellow instructor who tracks (quite well) an E46 M3. I track an E36 M3. Our power to weight ratios are nearly identical (within a couple of hundredths of a pound/hp). His car is significantly heavier and makes significantly more horsepower. We have identical suspensions, and run essentially the same R compound tires (his are larger and wider). We are also essentially similar drivers, and on any given day would likely be within a couple of tenths of a second/lap in the same car.
At TWS, his car is consistently 1 to 1.5 seconds/lap faster than mine, and it all comes in the latter half of the longer straights (especially 15-1 and 6-7), where his extra HP makes more MPH after dealing with aero drag, while mine runs into an areo wall, especially between 15-1.
I suspect the opposite would be true at MSR, especially on the 3.1.
Again, perhaps you should post nonsense less & ride with advanced instructors more.
Mark, thanks for continuing to baffle us with a barrage of bull****.
Last edited by Veloce Raptor; 06-10-2008 at 03:30 PM.
06-10-2008, 04:25 PM
#26
Rennlist Member
I was about to agree with you, but after your last line, im havng reservations
I have the exact same experience with my e36 racer buddies, because my 928 is almost identical to the M3 e46 racers in weight and power. I generally could have a slight advantage if we would go to some real fast tracks, but because we dont have them here out west, the battles remain in the tenths of seconds of differnce. (due to the points you listed)
getting back the "barrage of BS". what part were you unable to follow or agree with?
mk
I have the exact same experience with my e36 racer buddies, because my 928 is almost identical to the M3 e46 racers in weight and power. I generally could have a slight advantage if we would go to some real fast tracks, but because we dont have them here out west, the battles remain in the tenths of seconds of differnce. (due to the points you listed)
getting back the "barrage of BS". what part were you unable to follow or agree with?
mk
Oh, sorry, I didn't know he had THOSE sorts of mad skillz.
Loren, let me draw you a simple picture. I have a friend & fellow instructor who tracks (quite well) an E46 M3. I track an E36 M3. Our power to weight ratios are nearly identical (within a couple of hundredths of a pound/hp). His car is significantly heavier and makes significantly more horsepower. We have identical suspensions, and run essentially the same R compound tires (his are larger and wider). We are also essentially similar drivers, and on any given day would likely be within a couple of tenths of a second/lap in the same car.
At TWS, his car is consistently 1 to 1.5 seconds/lap faster than mine, and it all comes in the latter half of the longer straights (especially 15-1 and 6-7), where his extra HP makes more MPH after dealing with aero drag, while mine runs into an areo wall, especially between 15-1.
I suspect the opposite would be true at MSR, especially on the 3.1.
Again, perhaps you should post nonsense less & ride with advanced instructors more.
Mark, thanks for continuing to baffle us with a barrage of bull****.
Loren, let me draw you a simple picture. I have a friend & fellow instructor who tracks (quite well) an E46 M3. I track an E36 M3. Our power to weight ratios are nearly identical (within a couple of hundredths of a pound/hp). His car is significantly heavier and makes significantly more horsepower. We have identical suspensions, and run essentially the same R compound tires (his are larger and wider). We are also essentially similar drivers, and on any given day would likely be within a couple of tenths of a second/lap in the same car.
At TWS, his car is consistently 1 to 1.5 seconds/lap faster than mine, and it all comes in the latter half of the longer straights (especially 15-1 and 6-7), where his extra HP makes more MPH after dealing with aero drag, while mine runs into an areo wall, especially between 15-1.
I suspect the opposite would be true at MSR, especially on the 3.1.
Again, perhaps you should post nonsense less & ride with advanced instructors more.
Mark, thanks for continuing to baffle us with a barrage of bull****.
06-10-2008, 04:29 PM
#27
Rennlist Member
Dude, I was just razzing you.
06-10-2008, 04:30 PM
#28
You guys have no idea what you just got yourself into.
Good luck Mark - hopefully see you at a track someday.
Good luck Mark - hopefully see you at a track someday.
06-10-2008, 04:38 PM
#29
Rennlist Member
06-10-2008, 04:41 PM
#30
Rennlist Member