Not common SR VS KA thread. Real life implied

[tvmendoza]

Mods: Please read it first if you still think that this thread should not exist please delete it.

Hello, me and another friends will go to the drag strip of another city(here on Mexico) and the guys from the other city said that they already have a couple of SR's with some mods to race with my car(KA). What i have heard is that they still have stock injectors(370cc). That means that they max power should be around 250 whp probably less.My car is running with 7 psi and made 239 whp at the dyno, so lets suppose those guys have the same power, what should win torque or revs??

Probably i have the advantage of the LSD but i want to get prepared for the date.Thanks for any input

[crzycav86]

this doesn't look like an sr vs kat thread, but it probably doesn't belong in the kat forum either. maybe 240sx gen chat.

[tvmendoza]

It is a KA-T VS SR both with same whp who has more chances to win or who will win,

[240TweakerNewbee]

Torque wins races, hp helps... but its TQ that gets to up to speed and HP keeps you there.

It all depends on the driver too, and the setup. Some setups may show a huge number on the dyno, but is that power actually useable? If someones HP/TQ curve is only above 200 between 4500 and 5500 RPM's;chances are they are going to loose to someone who has TQ/HP above 200 between 3500RPM's and 7000RPM's unless they are an amazing driver, and know that car very well.

Study your dyno and practice driving according to where your power is. The wider your power band the more room for error.

[grimple1]

It's not about rpms. It's about TQ and HP.

[C-Kwik]

Torque wins races, hp helps... but its TQ that gets to up to speed and HP keeps you there.

I am going to shoot the person who first said this. It is about as wrong as it gets. HP is derived from torque and RPM. One isn't any more important than the other. Torque is the actual twisting force seen at the crank. The more torque you have the more force the motor can put out. HP is really a measure of leverage. This becomes particularly significant when you add a transmission to the motor. Since HP is derived from from torque and RPM, it tells you how well the torque can be used at a given wheelspeed.

A transmission is nothing more than a variable torque multiplier. In your lower gears it multiplies the torque of the motor quite a bit. A 03-04 6MT 350Z will see 13.42 times the torque of the motor at the wheels (We'll ignore drivetrain losses for the purposes of this post). With 274 lb-ft of torque at 4800 RPM, that's 3676.15 lb-ft at the wheels but at a wheelspeed of 357 RPM. On the other hand, at it's peak 287 HP of 6200 RPM, it produces 243.12 lb-ft of torque. At the wheels this equated to 3262.67 lb-ft of torque at 461 wheel RPM. It would almost appear more torque is more important.

However, you must consider wheelspeed. Lets compare how the peak torque compares to the peak HP at the same wheelspeed. To do this, we need a different gearset. To acheive 461 wheel RPM at 4800 RPM, you need a gear with 10.41 ratio. So at 461 wheel RPM, you end up with 2852.34. This is less than the torque achieved at peak HP at the same wheel RPM.

We can also do it in reverse and see how the peak HP would fare at 357 Wheel RPM. We would need a gear ratio of 17.37 to get 357 wheel RPM at 6200 engine RPM. This works out to 4222.99 lb-ft! As you can see, even with less torque, the higher RPM provides more leverage. If you wanted maximum accelleration, you could use a Continuously Variable Transmission and have it maintain 6200 RPM while you are accellerating down the 1/4 mile. I guarantee you'll end up with quite a fast 1/4 mile time compared to other cars with the same power to weight ratio using a more traditional gearbox.

But to address my point, it's HP that wins races. But torque is an essential part of HP. HP can not exist without torque. HP also can not exist without RPM. RPM can exist without torque and torque without RPM. But neither can move a car by itself. HP looks at the combined result. You'll find it much easier to predict a car's 1/4 mile accelleration result using HP to weight ratio rather than torque to weight ratio. In fact, the latter would be downright impossible.

Remember, you are still making HP at all RPM's. At 4800 RPM, the Z makes 250 HP. You car maximize your car's speed by adjusting your shiftpoints for each gear by maximizing the HP. The best shiftpoint is where shifting drops you to the same HP level you were at, at the top of the powerband. This won't always happen as gearspacing, especially in lower gears, may not allow, but you want to get as close as possible.

[Jookmasta]

depends on these "mods" that they have..........ultimately tho, driver skill and launch will determine who will win. u could have the slower car and still win if the person doesnt know what they are doing when going down the track................lets also not forget tires.................

[tvmendoza]

That is true, and i am not a good driver hahahah that is why i wanted to know if i have any kind of advantage. I can get a set of 16"s drag radials(235/600/16) but i cant find a set of wheels that will fit them. My 240 is 4 lug , does any one know a car that have 16's with 4 lug that will fit my car???

C-kwik- Thanks for the great info

[crzycav86]

Anyway, if both of you have dyno sheets... a rough way you can calculate who is faster is by finding the average torque each car has in its powerband.

integrating the torque curve(area under curve) from the beginning of the powerband to the end of the power band, and divide it by the total rpm's in the powerband(the rpm at end - rpm at beginning of powerband) will give you the average torque.

The car with the higher average torque should win given a bunch of assumptions such as equal shifting speed, equal launch, and that the cars has the same powerband in each gear.

[GEO]

KA-T will win. Nuff said.

[C-Kwik]

Anyway, if both of you have dyno sheets... a rough way you can calculate who is faster is by finding the average torque each car has in its powerband.

integrating the torque curve(area under curve) from the beginning of the powerband to the end of the power band, and divide it by the total rpm's in the powerband(the rpm at end - rpm at beginning of powerband) will give you the average torque.

The car with the higher average torque should win given a bunch of assumptions such as equal shifting speed, equal launch, and that the cars has the same powerband in each gear.

This is only true given the same RPM range. The SR does have a higher OE redline and if you had similar torque curve area averages, you will not be accounting for the leverage the SR will have due to the higher revs. Using the HP curve is what you will actually want to do. As an example, just consider the S2000. It has a peak torque of 162 lb-ft. I doubt it would end up with a significantly higher area under it's torque curve over a normally aspirated KA, if at all. But it will out accellerate a NA KA on the 240sx or even in the same car for that matter by quite a bit.

You can indeed use torque to calculate this if you wanted, but you'ld have to multiply the curve by the gear ratio, and do this for each gear. It's far easier to use the HP curve.

[TheOne]

everything aside, just take'em to the track, be the best driver and win, and well.....if you loose, well you loose and thats all.

do more than 1 run though, as the more runs the maybe more accurate answer to same setting different engine.

[Florida240sx]

If you have a good launch you will win. If you don't take him on the launch then it's a neck and neck race. 30mph roll I was at 8psi vs a 10psi sr I had him by a car when we went into 3rd....in 3rd he was beside and then at the last rpms 6500 he started to inch away. He wouldn't race me from a stop. If your not ahead by 3rd gear you'll most "likely lose" Also dragstrips are all mainly abotu your launch. I only ran a 14.4 at the track with my car. And I have beaten high 13 second cars. 1st time at the track and had crappy launches. 1st time I bogged and almos stalled. 2nd time I spun until 3rd gear(while passing a volvo)