Weight is 2720 with me in the car full of fuel. Ry is about the same.

Shift points for speed (MPH) from data is as follows:

61 2nd-3rd
83 3rd-4th
108 4th-5th
120+ 5th-6th

Gear ratios
3.13
2.04
1.48
1.16
.942
.763

Rear end ratio is 4.10

 

As i suspected. our gear boxes are very close indeed. Numerically, our gears are one off. meaning, my 1st is your 2nd, 2nd is your 3rd, etc.

S2000
61 2nd-3rd
83 3rd-4th
108 4th-5th
120+ 5th-6th

928S4
55
80
115
155

However, in those gears the s2000 has a slight disadvantage in your 2nd (my 1st and 2nd) i am slightly lower . Where my gear 3rd is to match your 4th you have a slighly lower (more reduction as the redline speed is 115mph vs your 108mph).
anytime you touch 4th, you have an advantage as well for the same speed.
This means you have a very close ratio gear box up top if your redline in 5th is 120mph. (ie 90% drop of rpm) about normal for a street car below that. (about a 73% drop )

 

[QUOTE=jzr,Oct 16 2008, 09:11 AM] Mark, do you have data for your motor's torque output?

 

Bummer about that torque curve! Generally you only see a curve like that in a race motor when you're looking at a turbo motor that has hit its airflow limits.

Based on what you're saying, to make a consistent 350rwhp from 4500-6000, the motor makes 408rwtq @4500rpm, falling to 306rwtq@6000rpm. Is 6000rpm just where you shift, or does the motor go higher? Based on the speeds, gearing, and tire diameter provided, a redline of 6500 seems to fit.

How does the curve look from 2000 to 4500rpm, and from 6000-6500? Based on your car's wide gear spacing, you may find it best (at least from an acceleration perspective, not necessarily a longevity one) to shift at redline.

 

Very good. Right on the money! Actually, after getting the cams timed right, its more like 400 peak torque at 4500rpm and flat before hand from near 3500rpm.

So not so much of a bummer on the torque curve, but yes,if it (torque curve)was more flat, I woudl have 500hp! This is due to the limit of all the stock stuff i have on the engine. Everything is bone stock, even up to the air box. However, i do have a KN filter insert
With slightly bigger valves, and the intake mods that some of the 928 guys are doing, it can get near 500rwhp with no other mods. still the stock ECU and little or no tuning.

Based on a flat Hp curve, it only pays to shift where you maximize the average. because how fast the HP falls past 6000rpm, since it is flat before hand, i would just loose ave HP by shifting higher. However, i can go to 6500. The old engine that was 305hp recently, i would shift at redline almost every shif, especially when i knew the motor was going to come out at the end of this season.

The the interesting thing about more power, is that you then find that you need more brakes! So, i was marginally faster for the increase in HP / torque. (1 second a lap vs prior engine HP. I was hoping for 1.5 to 2 but thats the reality). If i can get some brakes or new pads that dont fade, i might be able to improve that.

mk

 

I have a template that I've found useful many times for these comparisons. Sometimes a graphical explanation is the easiest to understand, forgive me if your graphs weren't doing it for me Mark. Since you didn't provide a dyno I had to make up some numbers to round out your dyno based on your colorful description. The S2000 numbers being from a Dynapack are likely a hair inflated.

The spreadsheet is available here:
http://www.jrho.com/ITE.xlsx

Here's the output of the analysis - basically, the higher the line, the harder the car is accelerating at that speed.


Actual measured acceleration for a data logger will be lower than these theoretical values due to mechanical drag, the percentage difference increasing with speed due to aero drag.

Here's what I see:
Below 25mph it's a tough call, no good data from either car. The 928 has a really tall first gear, and the S2000 has no bottom end.

From 25-40mph the S2000 appears to have a pretty big edge. However, in my experience, production cars on DOT tires set up to turn are generally limited to more like .8-.9 longitudinal G at best, so things are probably a wash there.

From 40-low 50's, the 928 has the edge, and appears geared well for the amount of power available; it should be able to go flat-out in first without spinning the tires too much.

From ~52-~62, the S2000 gains a definite edge, right in the meat of its powerband in its short second gear. The 928 is at its peak torque here, but its tall second gear makes it meaningless, except on slippery tracks, where the S2000 might not be able to use full throttle.

From ~62-~73mph, the 928 regains the edge, still chugging along in second gear, while the S2000 has had to drop to third gear.

From ~73-~85, the S2000 regains the edge, a very healthy and consistent one, pulling through the meat of its third gear powerband, while the 928 is either wheezing to death in second, or in the meaty part of its "merge onto the autobahn" third gear.

From ~85-~94, the 928 has the edge once again, though the edge here is pretty small over the S2000, now in fourth, climbing into its powerband.

From 95+, the S2000 checks out, plain and simple.

Some thoughts on how to make the cars faster:
S2000:
*If speeds below 30 are never encountered, a taller first gear would be good, as it would eliminate the big jump to second, and make the power in gear more usable.

*At tracks where you won't be seeing 145+ sixth could definitely be shortened a fair bit, and fifth, a little.

*If the S2000 could maintain its peak torque value seen near redline from 6000-redline instead (like with a good turbo ), it would be a lot faster, especially above 60mph.

If I were the S2000 on pole, dictating the speed of a rolling start race aginst the 928, I'd want to start at 52mph, or 25mph if I thought I could hook up in first.

928:
*The Porsche could definitely use more upper RPM power to keep up with the S2000. If the motor were opened up so instead of peaking at 350whp and falling, it instead climbed to 400whp, it would make a huge difference.

*With more upper-rpm power, third, fourth, and fifth gears could be shortened a lot.

If I were the 928 on pole, I would aim for a 40mph rolling start, a 62mph start, or maybe a standing start in hopes the S2000 would blow its diff.

Feel free to download the spreadsheet and play around with the gear ratios, engine outputs, or vehicle weight to see how it changes things.

 

my god you guys are geeks...

 

So in summary, Kibort needs his heads ported and Rylan needs a gt3076r.

 

or that turbo S2000 full race dyno i saw on line that put out 440rwhp.

We are geeking out aren't we!

mk

 

[QUOTE=jzr,Oct 16 2008, 03:37 PM] I have a template that I've found useful many times for these comparisons.