GEARING: Let's get the story straight ...

345s-bspinnin

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I have posted the difference in the Gen V new tighter gearing before, but I keep hearing how much its hurting the Gen V. We all need to understand that gears cannot be optimized for all tracks. Any racer will tell that gearing is chose carefully for track specific scenarios. Here are some FACTS regarding gearing selection for the Gen V:


The chart below illustrates the gearing/speed values across Gen III/IV/V. Note that there may be a a minor difference in speed if you use redline vs. fuel cut-off. For this illustration, I am using fuel cut-off; hence the slightly higher numbers when compared to some published data. For the bench racers, notice the large discrepancy in Gen V max speed in my chart verus C&D's deduced value (published C&D article) for 6th gear. While the title states Vmax for each gear, C&D used the mfr's claim top speed claim for 6th gear. My chart shows the theoretical max for each gear, hence the silly 300+mph in 6th gear for some earlier Vipers.


It can be easily seen that the gearing difference is in fact minimal once you consider that the change in final gear is offset by larger cogs (numerically lower) in the lower gears. When compared to previous Gens, the "tighter" gearing is true only for the last three gears. This "tighter" gearing change improves nothing in slower tracks where 4/5/6 are seldom used. However, if we start talking fast tracks (Green Hell???), then perhaps we can understand SRT's true focus in their cog selection.

An alternative rationale for the gearing selection could be inferred by those possessing some mechanical engineering skills. Any regular Joe mechanical engineer could attest that gearing decision could be based on simple mechanics whereby a selection of a mechanically larger cogs (numerically lower) provide better protection against the twisting prowess of the new 8.4L mill. This change allows for reduced strain in the gear box at the expense of increased strain in the final gear. Simply put, torque is multiplied less in the transmission and more in the final gear.



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Steve M

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How accurate is the 6250 fuel cutoff for the Gen IV? I only ask because if you watch this dyno video:

http://youtu.be/oZgn9978shU

You can see the car pull all the way up to about 170 MPH on the dyno in 4th gear - that only makes sense with a 6400 RPM fuel cutoff. 6250 RPM cutoff = 164.4 MPH, 6400 RPM cutoff = 168.3 MPH (which seems about right looking at that video). I've seen both numbers floating around, but which one is accurate?
 

VENOM V

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Great analysis.

Pros and cons to the 4th gear selection. I bet it will bear fruit at Nurburgring as you pointed out. It also illustrates why the Viper beat the ZR1 in acceleration in most categories, but was slower in 0 to 150 MPH. 4th gear top speed is 146, so the Viper had to be shifted to 5th.

I think they made the right choice with the new gearing, benefitting lap times at the faster tracks.
 

ACRucrazy

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Ha, I quickly tossed together a very similar chart myself and was gonna post it, never got around to it.
I mixed up tire size, rear ends, etc between gen 4/5, not as pretty as yours and my tire sizes were a bit diff, but it did the job for me, I just wanted to see the differences.
 

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GTS-R 001

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I guess one big question is...

Can the new car hit the top speed?

It looks like it will have to pull in 6th gear for any speed over 190 mph, will it have the grunt to do that?

I guess it will have more of an advantage (gearing wise) over the Gen 4 or 6th gear top speed runs, but the Gen 4 probably stayed in 5th to do all its top speed (actual) testing
 

ACRucrazy

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I guess one big question is...

Can the new car hit the top speed?

It looks like it will have to pull in 6th gear for any speed over 190 mph, will it have the grunt to do that?

I guess it will have more of an advantage (gearing wise) over the Gen 4 or 6th gear top speed runs, but the Gen 4 probably stayed in 5th to do all its top speed (actual) testing

http://www.youtube.com/watch?v=MQ05clP5tcg
 
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345s-bspinnin

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How accurate is the 6250 fuel cutoff for the Gen IV? I only ask because if you watch this dyno video:

You can see the car pull all the way up to about 170 MPH on the dyno in 4th gear - that only makes sense with a 6400 RPM fuel cutoff. 6250 RPM cutoff = 164.4 MPH, 6400 RPM cutoff = 168.3 MPH (which seems about right looking at that video). I've seen both numbers floating around, but which one is accurate?

The PCM fuel cut-off is accurate. Its the car's tach and speedometer which are off. If you look at the published Edmund's dyno sheet, you will see that they stop at fuel cutoff 6250, or pretty darn close to it.

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345s-bspinnin

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I guess one big question is...

Can the new car hit the top speed?

It looks like it will have to pull in 6th gear for any speed over 190 mph, will it have the grunt to do that?

I guess it will have more of an advantage (gearing wise) over the Gen 4 or 6th gear top speed runs, but the Gen 4 probably stayed in 5th to do all its top speed (actual) testing

You are right Steve. SRT's predicted 206mph Vmax will occur in 6th gear. At that speed, the engine is singing at 5700 rpm.
 
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345s-bspinnin

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I like your video better though..

Thanks. The same point about tach/speedo accuracy can be seen in my video linked above. Take glance at the top of 3rd gear (10-11 secs.), and you will see the tach kiss 6500rpm, and I never actually bumped the actual 6200rpm fuel cutoff!!
 

Paolo Castellano

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I guess one big question is...

Can the new car hit the top speed?

It looks like it will have to pull in 6th gear for any speed over 190 mph, will it have the grunt to do that?

I guess it will have more of an advantage (gearing wise) over the Gen 4 or 6th gear top speed runs, but the Gen 4 probably stayed in 5th to do all its top speed (actual) testing


The old Gen 4 ratios with .74 5th gear with 3.07 = torque multiplication of 3.07 X .74 = 2.2718

The Gen 5 with .63 6th with a 3.55 = 2.2365

2.2365/2.2718 = .98446 = advantage to Gen 4 from 190-220 MPH

640Hp and 600 LBS/Ft X .98446 would be reduced to 630 HP and 590 LBS/Ft

The Gen 4 with the 1.0 4th gear/3.07 has the advantage from 147-160MPH then the Gen 5 .77 5th with 3.55 has the advantage from 160-190, then the Gen 4 again has the advantage from 190-220 MPH with the .74 5th and 3.07

So it has a bit less power/grunt.

The only other draw back is losing momentum against the drag shifting to 6th at 190 instead of being able to stay in 5th until 220 MPH.

I do not think the 3/4 split is favorable.
 
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05Commemorative

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Good to see and educational post on here. So glad not to see any of the "It needs 700hp, wide-body, differentent headlights, my ACR is better, wouldn't sell my gen2 for it" crew chimng in to get us out of the deadly "mediocre" category...

Sorry, couldn't help as my frustration built up after reading so many rediculous posts the past couple weeks.

Seriously, this is a great thread on a subject with real data. I do wish 4th was a bit longer as we have a few tracks around here were we get up to 145-150 on straight and would like not to have to shift to 5th as they usually follow with a turn where you have to get right down to 3rd. Otherwise, looks like great more usable gearing.
 

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