97C2s911

I'm trying to figure out what is the weight and horsepower formula in comparing whether to buy a 2100 lb 310 hp GT car vs a 03 Cup car .
Cups are 2700 lbs with 350 rwhp ?
Where does the formula turn in favor of a GT car ??

thanks

mark kibort

2100/310 = 6.7:1

2700/350= 7.7 :1


but, 2100 has 600lbs less to stop and less to fight centrifugal force with . that is substantial. usualy the cup car will have more technology in suspension geometry and components to help close the gap, but still, absolute weight is still significant. also to note is on long straights, HP/over all drag is a consideration as well.

so, in this example the ligher car has the advantage in HP/weight AND is 600lb lighter. HP to drag on a long straight for two equal Cd cars, will be a slight advantage to the cup car, but not much.

mooty

03 cup published wt is 2550. but most of them, as they come off track at end of race, are around 2600 (no driver and min fuel)

i assure you that cup cars have more than 350hp at rear wheel (of course depends on which dyno). my stock engine, stock exhaust, stock intake (inc oem air filter) street 996gt3 has 350 at the wheel on dypapack dyno. so i sure hope cups are more powerful.

mark kibort

good point.

claykos

I will shamelessly plug my race car for sale which is a 2250 lb GT car with a 996 cup drivetrain :-)

https://rennlist.com/forums/racing-a...1-gt3-cup.html

mark kibort

as a side note to the differences of a GT car vs the cup cars, dont forget the closer gear ratios of the cup car which effectively raises the HP available to the rear wheels over the speed ranges at the track. could effectively raise the Hp near 5-10% depending on the GT gear box spacing and its engine HP curves.

claykos

Mine's got the cup box as well ;-)

mark kibort

I figured as much. thats why I brought it up for you!

97C2s911

How would you show the lap time difference given the 6.7:1 vs 7.7:1 ?

winders

Technically, transmissions multiply torque, not power....the amount of power does not change.

Scott

IcemanG17

My guess is not much difference..... Once you get better than say 10.0lb/HP its serious diminishing returns.....

Assuming equal aero and tires....I'd say maybe 1 sec per lap..if that....

mark kibort

I dont totally agree, especailly with the threashold, but yes, as you go to the lower side, its not as dramatic . BUT, i do beleve this 1 second a lap is near right on. (for this range of improvement.) I saw this, and added another .5 second with brakes and bigger front tires.

Scott, let me know if I respond to you in the most desired way. I said "effectively" I should have clarified that term, as it could be mis understood that the peak HP is increased and you are right, it isnt. But, technically, transmissions do a lot more than just multiply torque. they also alow the engine to apply HP and Maximize HP at any particular speed range. I never said it multiplies HP, but it makes more utilzation the HP that is available. In other words, a close ratio gear gear boxes alows the operation of the engine to be closest to the max hp range, pre and post shift. By allowing this, you maximize rear tire torque.

If I had only one gear, it would be utilizing HP over a very small speed range. (like Tesla's car). but , a simple 2 speed gear box would allow even more of its power utilization i the speeds beyond 80mph, where its HP falls off dramatcially. this proves that gear boxes dont only multiply torque, but optimize HP utilization.

in the example of Claycos' car, with a cup trasmission, its 350rwhp, suddenly gives the effect of more average Hp. certainly would never produce more than 350rwhp, but if the peak hp was 350 and the post shift Hp was 250, the average would be 300 with a normal GT gear box. with a cup gear box, that average could be 25hp higher!

This would be a guess, but an educated one. 1 second would be my bet as well. (Most things being equal)

winders

You wrote:

That is simply an innaccurate characterization. You really should stop writing one thing and then, when you get called on it, writing that you meant to write something else.

Horsepower does not change. An engine makes x amount of horsepower at y RPMs. It doesn't matter what gear the transmission is in. Transmissions multiply torque. They do not raise the horsepower, effectively or otherwise.

Remember, horsepower is work over a period of time. Transmissions deal in torque.

So, if you want to say that better gearing lets you use power more effectively, great. But you can't say that better gearing effectively raises the horsepower.

One more time: a transmission multiplies torque, not power.

Scott

bobt993

A reasonable solution to your question would be to look at the times at the club races. Select the bracket of GT cars running slicks and see where they finish relative to the Cup cars. Very often they run in the group especially in enduros. Keep in mind driver ability is a huge factor as is car setup.

38D

Don't forget the chassis/suspension. A 310hp 914 ain't going to hold a candle to the multi-link suspension of a cup. Then there's also stuff like the brakes, gear ratios and area under the curve (peak power is not everything).