Gears vs speeds vs RPM.....warning, actual math included

[345s-bspinnin]

Hi everyone,

I am new'ish to the VCA, and felt I should start with a minor contribution.

I have seen numerous poorly answered posts regarding "what's my speed at X rpm, in Y gear, for Z sized tire"? What's the optimal shift point?

My inputs below are based on numerical computations of engine speed (RPM), transmission gearing ratio(s), final/diff axle ratio, and tire size. I added optimal shift points as a bonus.

Speed and Gear Assumptions:
- Tires are sized per actual geometrical dimension (worn tires are smaller, obviously)
- Assumes zero slippage (tires, clutch, twisting axles....you get the idea)

Optimal Shift Points Assumptions:
- Assumption is based on maintaining maximum acceleration
- Acceleration is presented as a percentage on Earth's Gravity (9.8 m/s^2), just because we all can relate to a "G"
- Acceleration is computed for a closed system (drive train only), in other words, it does not include drag force (doesn't influence power produced)
- HP/TQ based on baseline Gen III Dyno, Values below 2000 rpm and above 6500 rpm are linearly extrapolated (this mean's I just made them up)

Yes I am a rocket scientist

Gear, Speed, Rpm, and G CHART:
Find your you speed for any gear, at any rpm. The frequently asked RPM drop off question? Well, take 4th gear to 6100rpm (160.3 mph), shift to 5th, the same speed (159.8) in 5th gear is 4500 rpm.

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Optimal Shift Point:
Displays acceleration at each gear and through its speed range. For example, a 3rd gear's acceleration to anything below its redline (plot shows up to 6100rpm) would be less than optimal. So, shift right before kissing the redline in everygear.

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Again, a big HI to everyone. And yes, I do own a Viper, and plan on joining the VCA.

Pics or it didn't happen? I attached some pics that I snapped with my cell phone (HTC EVO). I do have a "real" camera, but I actually like these cell phone pics

Cheers,

Andres



SRT-10, HRE 545s, ViPAIR OEM Style Hood, ViPAIR Dropped......

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[345s-bspinnin]

I attached a revised chart showing only the old and revised 5th/6th gears.

Sample differences:

RPM after 4-5 shift (160 mph):
- 4500 rpm with "old" 0.74 gear
- 4900 rpm with "new" 0.80 gear

Cruising speed: 70 mph in 6th gear:
- 1350 rpm with "old" 0.5 gear
- 1650 rpm with "new" 0.62 gear

Max Speed in 5th gear at 6100 rpm:
- 216 mph with "old" 0.74 gear
- 200 mph with "new" 0.80 gear


Gear Comparison Chart:

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[FLATOUT]

Smokin' car! Welcome and thanks for the detailed post!

 

[EZ 2B Green]

Good post! I just installed the revised 5th & 6th in my car and your calculations look pretty accurate. One small difference is that 70mph is ~1600rpm in 6th on my car. Two more data points are 1750rpm @ 75mph and 1900rpm @ 80mph. These data values are read from my dash instruments. I love my new close ratio 6 speed!

One more note on the 4th->5th shift at 6100rpm is that the engine is making 50 more horsepower with the new 5th gear at 4900rpm than with the old 5th. That extra power would have been useful at the Nurburgring and could have given the Viper an even faster record setting time.

 

[Black Moon]

I'm changing to a 355. A chart for that would be great if you have the time.

 

[Twister]

good post and welcome

 

[Bigsalgt]

I'm changing to a 355. A chart for that would be great if you have the time.

I would love to see a chart regarding this as well. 3.55 or 3.73 gears are in my near future .

 

[345s-bspinnin]

As requested:

3.55 with old 5th/6th cogs:

You must be registered for see images attach

 

[345s-bspinnin]

3.73 with old 5th/6th cogs:

You must be registered for see images attach

 

[345s-bspinnin]

3.55 with REVISED 5th/6th cogs:

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[345s-bspinnin]

3.73 with REVISED 5th/6th cogs:

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[Proshop]

Welcome and thanks

 

[Black Moon]

Thank you for the information.

 

[345s-bspinnin]

I just threw multiple charts that may cause difficult side-by-side comparison. I have
consolidated speed/gear facts for you those of you deciding if changing the final gear and/or transmission 5th/6th gear ratios are worth the time/money/acceleration:

MAJOR assumption is that acceleration is based on MY DYNO CURVE. The AREA under the curve has major influences on total acceleration. The steeper (numerically higher) final gears will have higher acceleration due to 1) higher mechanical advantage, and 2) typically higher RPM range at a particular speed. However, maximum speed is limited for numerically higher final gears

Acceleration at 40 mph in SECOND gear and different FINAL gears:
Max acceleration (per Laws of Physics), assuming no slipping and no external influences (drag, friction, etc.)

3.08: 0.61 g's (2800 rpm)
3.55: 0.72 g's (3100 rpm)
3.73: 0.78 g's (3300 rpm)


Acceleration at 100 mph in FOURTH gear and different FINAL gears:

3.08: 0.38 g's (3800 rpm)
3.55: 0.45 g's (4400 rpm)
3.73: 0.47 g's (4700 rpm)


Max speed at 6100 RPM in "old" 0.74 FIFTH gear and different FINAL gears:

3.08: 216 mph
3.55: 188 mph
3.73: 179 mph


Max speed at 6100 RPM in "new" 0.80 FIFTH gear and different FINAL gears:

3.08: 200 mph
3.55: 174 mph
3.73: 165 mph

60 - 130 mph Average Acceleration for different FINAL gears:

3.08: 0.54 g's (2nd: 60-90, 3rd: 90-123, 4th: 123-130)
3.55: 0.56 g's (2nd: 60-78, 3rd: 78-107, 4th: 107-130), 3.7% more than with 3.08s
3.73: 0.57 g's (2nd: 60-74, 3rd: 74-102, 4th 102-130), 5.5% more than with 3.08s

 

[Bigsalgt]

Great information! Thank you once again and welcome to the board.

 

[TrackAire]

As requested:

3.55 with old 5th/6th cogs:

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Nice car!!

What does the line in your chart mean with the wording

"Math!!! 0.08092 que Multip"???


Thanks for the charts with the aftermarket ratios, too.

Cheers,
George

 

[vancouver-gts]

345s , could you please post data with 4.10 gears ?

 

[Kala]

Welcome Andres

These charts should be a sticky!


Also that last photo is really nice, post it to the Dupont Registry Sunset Photo contest on Facebook.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

duPont REGISTRY Vote for your favorites by Liking them!

Sunset Photography time! Submit your sunset photos with a Car Theme by posting it on our wall (attach image). This is another chance to showcase the talented individuals we have here. We will accept up to 3 entries per person until October 14th!

Whichever 10 photos get the most likes in the contest gallery(s) will move on to a top 10 Gallery. The most likes in the Top-10 gallery win a prize package and can advertise their website and product here!

No advertisements.
A "Sunset" theme, with the scenery being in focus.
3 entries per person maximum.
Must have an automotive feel.

We will create a gallery with the top 10 vote getters on October 14th, and the Winner will be whichever entry gets the most "Likes" in the Top-10 gallery!

 

[345s-bspinnin]

Nice car!!

What does the line in your chart mean with the wording

"Math!!! 0.08092 que Multip"???


Thanks for the charts with the aftermarket ratios, too.

Cheers,
George

George,

The "Math!!! 0.08092 que Multip"??? Means....the following:

"Math!!!" is just my placeholding note and means nothing. The ".08092" is a conversion of tire diameter that will be used for determining speed:

Equation in that cell: =60*B2*PI()/12/5280, where B2 = tire size in inches.

The "que Multip", is not Spanish for "What Multip". My text didn't fit in the cell, it should read "Torque Multiplier", which is where I compute total mechanical ratio advantage for each gear. For example, in the 3.55 chart, the "7.229" is the result of taking "= 2.66 * 3.55 / 27.2* 12 *2" [= 1st Gear Ratio * Final Drive / tire size * 12 *2]

Hopefully that explanation helped more than confused.

Andres

 

[345s-bspinnin]

345s , could you please post data with 4.10 gears ?

Here you go:

4.10 with old 5th/6th cogs:

You must be registered for see images attach

 

[345s-bspinnin]

345s , could you please post data with 4.10 gears ?

Here you go:

4.10 with REVISED 5th/6th cogs:

You must be registered for see images attach

 

[345s-bspinnin]

Welcome Andres

These charts should be a sticky!


Also that last photo is really nice, post it to the Dupont Registry Sunset Photo contest on Facebook.

Thanks for the compliment Kala, especially since it is a cell phone pic.

I will post it at the Dupont Registry Sunset Photo Contest and see how I fare.

-Andres
345s-bspinnin

 

[SilveRT8]

Thanks for all this info.
If I may ask, could you also post the info for 3.33 gears ?
I have a Gen 4 with 575 RWHP and may go to 600 with a few more mods, I'm afraid even the 3.55 could be too much gear for street traction.

 

[vancouver-gts]

Thanks for the info on 4.10 !

 

[ACRBruce]

Andres,
Thanks for the detailed chart and I wonder if the chart was done in Excel, if so, could you email a copy to me as sometimes I run different sized rear tires than stock.

 

[345s-bspinnin]

Thanks for all this info.
If I may ask, could you also post the info for 3.33 gears ?
I have a Gen 4 with 575 RWHP and may go to 600 with a few more mods, I'm afraid even the 3.55 could be too much gear for street traction.

Here you go SilveRT8:

3.33 with old 5th/6th:

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[345s-bspinnin]

And here they are with revised gears:

3.33s and REVISED 5th/6th Gears:

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[345s-bspinnin]

Andres,
Thanks for the detailed chart and I wonder if the chart was done in Excel, if so, could you email a copy to me as sometimes I run different sized rear tires than stock.

Yes, this was done in Excel 2007. I created the spreadsheet parametrically. It allows you can adjust everything from weight, all gearing, tire size, dyno values, etc.

I will PM you my paypal address so you can send over $75 price for the spreadsheet. I feel its priced right since that how much SCT copy/paste tunes cost.












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j/k.....just PM your email address and I will email you the file.



-Andres
345s-bspinnin

 

[Slithr]

Bspinnin, thanks for the charts this should make gear selection a lot easier . As a rocket scientist do you happen to make your home in the Clear Lake area?

 

[345s-bspinnin]

Bspinnin, thanks for the charts this should make gear selection a lot easier . As a rocket scientist do you happen to make your home in the Clear Lake area?

Home is a bit closer to town up I-45, but I do spend 8-10 hours/day in the Clear Lake area.