You also asked originally, "Are you referring to thrust? If so, we have none. Our tranny has toasted synchros in 1st and 2nd. We'll have to start in third and pray for a 200mph tailwind".

Yes, I was talking about Thrust Force AND wheel torque being equal between two cars that have the same tire diameter. If the diameters change, so does the HP relative to speed. As long as two car are traveling at the same speed and exhibit the same HP, they will exhibit the same Thrust Force. (Power=Fv). On a dyno, it doesnt know that the tires are growing, all it knows is how fast the acceleration rate changes.
rate of change of kinetic energy is all the dyno needs to know. (besides the speed of the drums and their size and weight) from that, it can plot HP of the engine vs mph of the wheels, tires or even lack of wheels and tires as when a brake dyno is bolted to the hubs and the force is measured at any rpm, giving HP

So, as far as Thrust, why dont you have any? Again, I'm not clear on your question.

mk

 

By the way, my tests were on a dynapack dyno on my 928 with the older stock engine vs the dynojet. Results were near the same. (within 4-5hp). I was calling it a "mustang dyno" as we usually classify all dynos in 3 groups. dyno jet, brake dyno (mustang or dynapack) and engine dyno. sure, mustang and dynapack are different, but both are still a brake dyno. (one fluild brake, the other eddycurrent brake)
Either way, they measure resistive forces or acceleration rates coupled to rpm values to get HP and thus Toruqe values.
mk

 

So are we both good at knowing that both rylan and I have the same thrust force (total force to accelerate out cars) at any speed where our engines are at 350hp, regarless of engine torque values? (if our cars are at the same weight too )
(Or Torque at the rear wheels through the gear box, IF, the tires are the same diameter)

 

Yes, we are in agreement. One of these days we'll get together and do 9 touge style.

 

Does anybody have dynos (from comparable machines) and gear ratios for the cars in question? This question is very easy to illustrate graphically with thrust vs. speed curves.

 

[QUOTE=jzr,Oct 16 2008, 07:11 AM] Does anybody have dynos (from comparable machines) and gear ratios for the cars in question?

 

Here is my curve. If you look at the torque curve it's pretty self explanatory.

 

That's a start, now we need gear ratios, tire diameter, and all the 928 data.

:edit: Also, race weight with driver...

 

you dont really need the gear ratios, all you need is the MPH shift points at redline.

mine are: 55mph (1st), 80mph( 2nd), 118mph (3rd), 155mph (4th)
my weight is 3000lbs with me in the car and a 1/3 of a tank

If i have a flat hp curve of near 350, then Blackey needs an average of near 330rwhp to be even (HP TO WIEIGHT RATIO), given that he is probaby 200lbs lighter weight. ( think Ry is about 300lbs less if I remember correctly)

For fyi, my tire diameter is 26" and gears are:
8:6, 6.5:1, 4.5:1, 3.2:1 (including my 2.2:1 rear end. Yes, 2.2:1. autobaun rear end to get to 220mph, if i could sport the 800hp needed to do it )

So, what does all this mean? well, with Blackey's HP curve, from 8500rpm to his shift point of 6000rpm (a guess) his aveage HP is 330rwhp. (ie 250 to 407rwhp)
If my average HP is 350, then the HP to weight ratios would be near equal considering im thinking he is 2800lbs with driver.

The subtle differences on the track, is how well the track is suited to the gear ratios. (e.g. are you getting to redline on all of the straights. what speeds are you entering and exiting turns at, etc)

from the video, it looks as though the S2000 with the tire size Ry is running gives the ratios that are almost identical to mine. (if you look at the shift points at laguna, we are shifting at near the same speeds)

do you have the S2000 shift points handy?

I saw from the dyno that 110mph is redline and probably your 4th gear, which is the same as my 3rd gear. I suspect your 3rd is like my 2nd and your 5th is like my 4th. I did notice that Ry would come around turn 11 at laguna in 2nd, which is like my 1st but only stay in it for a short time. I rarely use my 1st there (your 2nd) as it is a cumbersome gear to select with my gear box.

as another note, you guys are using your 4th gear, which is like my 3rd for dynos. when i do 3rd gear runs to 115mph or so on the dyno, i loose about 5-7 more HP.
try a 5th gear run on the Dyapack next time and see what you find.

 

Mark, do you have data for your motor's torque output? A dyno is best, but a to-the-wheels value of tq every 250 or 500rpm from 2000->redline is helpful.

A "flat hp curve" would be a descending torque curve - do you mean to say a flat torque curve of 350?

Does your car have the original internal gearbox ratios of
1st: 4.07
2nd: 2.71
3rd: 1.93
4th: 1.46
5th: 1
?