RPM/Speed Charts for typical builds

Hi all,

This seems like a bigger deal to me than it probably should but I didn't a car that just felt "off." I also didn't want a car that had a 75 mph cruise of 2600 RPM or an unusable 1st gear or unusable 6th gear. I believe a lot of thought goes into this for a production car to balance all the requirements so I thought making some charts may help me and others know what to expect. The online gear ratio calculators weren't cutting it for me because you could only check one RPM at a time and not see the fluidity that comes with driving a manual throughout the rev/speed range. If anyone has a specific request for a chart, I may field some of those but it does take a little time so the more universally helpful the request, the better. Anyhow, enjoy!

As you can see, the Daytona Coupe would top speed limited (based on 6500 rpm max):

TKX (0.81): 5th Gear - by gearing at 173
TKX (0.63): 5th Gear - by gearing or drag (can theoretically hit 200 mph at 5850 RPM in 5th)
Magnum XL (0.50): 5th Gear - by gearing (at 190 if you could do 6500 RPM) or drag in 6th gear
Magnum XL (0.63): 6th Gear - by drag (could do 175 in 5th gear at redline, shift into 6th and drop to 5100 RPM and accelerate to 200 mph at 5850 RPM)

Overall, it seems the TKX (0.81) probably makes the most sense for a 5 speed street driver since not many people will ever use the true top end of this car (and "only" 175 mph is fine for most). Beware though, highway cruising will be pretty high RPM.

The Magnum XL (0.63) seems to make the most sense as a 6 speed street driver since it allows the full potential of the car while keeping revs manageable for normal use (2050 RPM at 70 mph). It seems to have the widest range with the closest spacing.

The Magnum XL (0.50) version has higher top speeds in every gear (except 4th which is direct drive in both) but that 6th gear is really tall... 1600 rpm at 70 mph.

Lastly, the TKX (0.63) is identical to the (0.81) in the first four gears and then, of course, has the taller 5th gear. The difference at 70 mph is 2050 RPM and 2634 RPM. Hmm...

So... in your real world experience... what are you TKX owners liking, the 0.81 or 0.63? How much of a concern is the highway driving... i.e. do people drive theirs much on the highway? Do 0.63 owners hate the large spacing between 4th and 5th?

Quote:

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Originally Posted by gtrag94

As you can see, the Daytona Coupe would top speed limited (based on 6500 rpm max):

TKX (0.81): 5th Gear - by gearing at 173
TKX (0.63): 5th Gear - by gearing or drag (can theoretically hit 200 mph at 5850 RPM in 5th)
Magnum XL (0.50): 5th Gear - by gearing (at 190 if you could do 6500 RPM) or drag in 6th gear
Magnum XL (0.63): 6th Gear - by drag (could do 175 in 5th gear at redline, shift into 6th and drop to 5100 RPM and accelerate to 200 mph at 5850 RPM)

Overall, it seems the TKX (0.81) probably makes the most sense for a 5 speed street driver since not many people will ever use the true top end of this car (and "only" 175 mph is fine for most). Beware though, highway cruising will be pretty high RPM.

The Magnum XL (0.63) seems to make the most sense as a 6 speed street driver since it allows the full potential of the car while keeping revs manageable for normal use (2050 RPM at 70 mph). It seems to have the widest range with the closest spacing.

The Magnum XL (0.50) version has higher top speeds in every gear (except 4th which is direct drive in both) but that 6th gear is really tall... 1600 rpm at 70 mph.

Lastly, the TKX (0.63) is identical to the (0.81) in the first four gears and then, of course, has the taller 5th gear. The difference at 70 mph is 2050 RPM and 2634 RPM. Hmm...

So... in your real world experience... what are you TKX owners liking, the 0.81 or 0.63? How much of a concern is the highway driving... i.e. do people drive theirs much on the highway? Do 0.63 owners hate the large spacing between 4th and 5th?

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I am not the most experienced person at this issue, but I am an engineer by profession. So here goes my 2 cents (might be worth just that, or less)

Assuming Torque = Acceleration, you want to remain in the maximum torque range when shifting. For a lot of engines this is 4000 - just less than 6500. (If you own the car and are a recreational racer shift just over 6000 rpm)

I live in Houston and plan to track my car at MSR. Watching many videos of others running the circuit my goal is to run sub 2 minutes. To do this I need a max speed of 115 - 120 mph and the min speed would be just above 45 mph. When you run the track clockwise the min speed is immediately after the max.

I began looking at RPM v. MPH plots and discovered that using a 3.55 rear gear I would have to shift to 4th to attain max speed. If I ran a 3.15 rear gear I could have a max speed above 120 in 3rd. This means I can run the course in 2nd & 3rd only to achieve my goal. I would also be at max RPMs going into the tightest turn allowing the engine to help me slow down.

Don't forget the rear gear is a variable too. (I may find out that my acceleration from a red light might be to high, but live and learn.)

As for 4th - 5th gear gap, I would guess that 99% of those owning these cars will never shift from 4th to 5th in anger unless the rear gear is above 3.55. I opted for the TKX 0.68 5th gear as it minimizes the RPMs when cruising on the highway, which is the only time I think I'll use 5th.

Please let me know where my logic is wrong. I'd like to learn.

FracAG1980 (Steve)

Ok, I'll add in.

You might want to consider how much air you're pushing. The roadster is a brick with a CD of a Greyhound bus, takes a lot of power to get speeds over 140. A coupe is much better, pretty amazing actually. Looking at the gearing charts is great fun but and shows how the gearing functions through the non-OD gears, but you'll never use what the OD calculates too.

My previous configuration was 315/335s, 3.27 rear gears and a TKO-600. I've run VIR South Track, Gingerman and Grattan with top speeds in the 140 range, sometimes maxed other times held back a bit. All tracks were run in 3rd and 4th.

I had the .64 OD, worked well when used as a cruising gear on the expressway. Ran cross county multiple times. If all I did was country roads (50-80) the .8 might have been better.

The other consideration is low end torque. Having 400+ at the wheels from 2,500 up does tend the change your outlook.

If choosing the T56 Magnum, not the XL as it's too long, I'd select the 2.66 1st and the .8/.63 ODs. Would be perfect for my motor and 3.31s, if running a 351 or smaller I'd go with 3.55s.

Jim

I wrote Windows program which does a little more than what you show. Here is the link: https://drive.google.com/file/d/1vzy...ew?usp=sharing

There is a README file in the ZIP folder. Do not unzip the file to your desktop! Just thought I would share. I wrote it out of the same frustration you found with other implementations.

Here is the link to the original post, with an image of the output. https://thefactoryfiveforum.com/show...atio-do-I-need

I can run numbers for you because I built a spread sheet for my car.

> At 1,725 RPM I'm scooting down the road at 70 MPH in 6th gear.
> My set up is a 3.73 rear with a ZF 6-Speed that sports a .75 5th gear at .50 6th.
> 125 MPH is 6,000 RPM in 4th which drops to 4,500 in 5th and 3,000 in 6th.
> The only issue is the car feels really, really light in the nose at that speed.

Good Luck & Let Me Know If You Want Me To Run Numbers For You!

Steve

Redbone Roadster:.. https://youtu.be/9WEe6-wdNtA