Why no 6 speed love?

[powershift351]

A six speed requires 3.55 gears or better or its a dawg. I wanted the Viper T-56 so bad, but I fell short by 800 dollars. So I got the TKO 2, which is fine, but with the 3.73 gears I have in the back, that 6 speed would rock. Thats the problem you just have to change you gears and the T-56 comes to life

 

[Z28x]

The biggest advantage to the T-56 6 speed is the amount of torque it can handle. 650HP Lingenfelter Vettes use the same tranny guts as a 350HP Vette.

More gears are better but once you reach a certain point The law of deminishing values really comes into play. The jump from 4 speed tranny to 5 speed is a bigger deal than 5 speed to 6.

Interesting fact: Mercedes just came out with a 7 speed automatic. They switch from a 5 speed yeilded 0.3 sec. faster 1/4mi. and 2mpg.

 

[mransr]

Your racing 6-speeds copmparison is not valid. The 6-speeds we are talking about is 2 overdrives, with engine speed below 2000 at 75 MPH+. It takes a lot of torque for that. IF it were a ratio thing to keep engine speed within a narrow torque band, your statement would be true, but we are talking about double overdrive transmissions for the highway, not racing specialties.

well that was exactly my point...with 2 OD gears a 6 speed with a V-8 isn't there for performance reasons at all...

 

[Michael Johnson]

I don't care whether it's a 5 or 6 speed as long as it can handle 500+ rwhp/rwtq.

 

[Rootus]

The 6 speed isn't as upsetting as the IRS though. Whoever pulled this 1000 dollar number out of their butt needs to take a reality check, the cost of an IRS over a live axle is incrementally higher yes, but on a car like the mustang you are talking about 200 dollars more than your live axle set up.

Well, to quote facts, the lead Mustang engineer said the *parts cost* would have been $300 more for the IRS than the live axle. That assumes zero additional development cost. And given that the relationship between parts cost and retail price is fairly well established, $1000 is a very good estimate of what IRS would do to the price of a GT, all else remaining equal.

351CJ: Thank you for posting the 6-speed ratios -- that's a point I've tried to make several times, but people won't listen. If it's a 6-speed, it's definitely better than a 5-speed... just because.

Dave

 

[SVTdriver]

I think the one in the GTR can handle that much power.

 

[04S/CStallion]

Just gonna add some input on what is the point of a 6 speed. I can't beleive that is even a question!!!!!!!!. I know a lot of mustang guys don't wanna hear this but my 2000 Z28 had stock 3:42 gears and ran 11.9 in the 1/4 with only exhaust and 100 shot, with my car doing 75 on the interstate in 6th it ran 1200 rpm and got 31 mpg. Thats the point of a sixth gear!!! And yes it actually takes a motor the has a SAC to push a 6 speed in high gear. 230 rwhp isn't considered a SAC. But the 05 having a base flwhp of 305 can support it, why it doesn't have it is just stupidity or budget cuts.

 

[04S/CStallion]

And I believe the Vettes use a ZF-1 Tranny. The F-body and Vette have not shared a tranny for quite sometime.

 

[SVTdriver]

Just gonna add some input on what is the point of a 6 speed. I can't beleive that is even a question!!!!!!!!. I know a lot of mustang guys don't wanna hear this but my 2000 Z28 had stock 3:42 gears and ran 11.9 in the 1/4 with only exhaust and 100 shot, with my car doing 75 on the interstate in 6th it ran 1200 rpm and got 31 mpg. Thats the point of a sixth gear!!! And yes it actually takes a motor the has a SAC to push a 6 speed in high gear. 230 rwhp isn't considered a SAC. But the 05 having a base flwhp of 305 can support it, why it doesn't have it is just stupidity or budget cuts.

I'm just curious but. If your car got such great mileage and ran so fast in the 1/4. Why did you get rid of it then? To me it seems like you had the perfect car for you.

So how much mpg is saved by the difference in gear ratios between the 5 speed and the 6 speed? I'm betting with the very small difference. Every one keeps talking about how much gas mileage a 6 speed gets. But noone can tell me the difference in speed or mpg between 5th: 0.62 and 6th: .63
If by budget cuts you mean they wanted to keep the cost down. Then you are correct. At least that's what the sources at ford are saying.

 

[04S/CStallion]

I got rid of my car from plain stupidity, I seemed to have thought that I needed/wanted a truck, that was a mistake!!!! The speed difference doing 75 in 5th was around 2400 rpm and 1100-1200 in 6th. I never really ran 5th on the interstate since I had a sixth but I imagine it would give atleast 5mpg difference. I loved the 6 speed because it allowed me to have a higher gear ratio and still be able to run low RPM on the interstate. Oh the six speed in the F-body the car WOULD NOT reach its top speed of 173 mph in sixth, the top speed was acheived in 5th. I think the car quite pulling at about 135-140 in sixth.

 

[SVTdriver]

I got rid of my car from plain stupidity, I seemed to have thought that I needed/wanted a truck, that was a mistake!!!! The speed difference doing 75 in 5th was around 2400 rpm and 1100-1200 in 6th. I never really ran 5th on the interstate since I had a sixth but I imagine it would give atleast 5mpg difference. I loved the 6 speed because it allowed me to have a higher gear ratio and still be able to run low RPM on the interstate. Oh the six speed in the F-body the car WOULD NOT reach its top speed of 173 mph in sixth, the top speed was acheived in 5th. I think the car quite pulling at about 135-140 in sixth.

I was talking about the different transmissions. The ford five speed has a final gear of 0.62. While the 6 speed has a 0.63. That seems to me to be a negligable difference. And as far as reaching the top speed in 5. For a 6 speed that seems kinda sad actually. Cause I still pull really well in 5th (though I have not yet gotten the chance to go top speed)

 

[04S/CStallion]

Ok I am assuming the T56 in the mustangs is the same T56 in the F-body asside the tailshaft and bellhousing. But Im sure that the 5 and 6 are much more different than that for the F-body. So I guess at this point I don't really know what Im talking about.

 

[SVTdriver]

I'm just trying to figure out if the final gear in the 5 speed is so close to the final gear in the 6 speed. What would be the real benefit of having a 6 speed? It just seems the 0.01 gear difference is so small as to be moot. And why switch to a 6? Does anyone have an answer?

 

[Rampant]

Talking from a strictly gear ratio perspective and assuming it is attached to the same engine -- with such similar final gear ratios you are going to see virtually no difference whatsoever in the final gear (from a speed and mpg standpoint). The only difference would be on your way to getting there. By having the tighter gear ratios, you stay higher in the RPM band each shift.

This is why it is less important on a car with a flat, high torque curve such as the Mustang. Cars like the S2000 need the tight ratios so they can keep accelerating. If the RPMs drop too low between shifts, they will loose all torque and acceleration.

The other interesting thing is the comparrison of the first gear. There is a much bigger difference in 1st. Using the stats above (T-3650=3.38, T56=2.66): the 3.38 of the 5 speed would actually be a little quicker off the line since it spins through the RPMS quicker. In a car with a ton of power/torque (i.e. '03 Cobra), it could overpower this and cause you to shift too soon, while also being more difficult to handle tire slip. But, with the GTs engine, I doubt this would be a problem and the increased acceleration would be welcome.

The final thing is from a drivability standpoint. Since the GT is still about getting insane performance while still being friendly on the streets, a 5 spd. means less shifting and greater drivibility around town.

All things considere, it makes sense to me why Ford would stick with the 5 spd. in the GT.

 

[351CJ]

Just gonna add some input on what is the point of a 6 speed. I can't beleive that is even a question!!!!!!!!. I know a lot of mustang guys don't wanna hear this but my 2000 Z28 had stock 3:42 gears and ran 11.9 in the 1/4 with only exhaust and 100 shot, with my car doing 75 on the interstate in 6th it ran 1200 rpm and got 31 mpg. Thats the point of a sixth gear!!.

OK, I'm going to be a real pain in the a$$ once again and present some more facts instead of just using heresay or a vague memory.

First, to answer the question about the T56 in the Mustang Cobra vs. F-Body, the OD ratios are different.

2003 - Cobra: 1st: 2.66, 2nd: 1.78, 3rd: 1.30, 4th: 1.00, 5th: .80, 6th: .63
2000 Z28 SS: 1st: 2.66, 2nd: 1.78, 3rd: 1.30, 4th: 1.00, 5th: .74, 6th: .50

Now comes my pain in the rear point. Your quoted RPM's to do not make sense.

With the stock Z28 P275/40ZR-17 tires @ 75 mph your RPMs would be:

5th: ~ 2450 RPM*
6th: ~ 1650 RPM*

1650 is 50% higher RPM than the 1100 RPM you gave in another post - a HUGE difference.


* I am using the ~ for approximate because I don't have the energy to research the actual rolling circumference for the Z28 tires, so I just used calculated circumference less a typical correction for rolling circumference. In any case the RPMs I gave should be within 50 RPM of actual.

Now one last point. You may be saying WOW! that .50 OD ratio is really tall. I bet it makes a huge difference. Well it does not make any difference compared to a T-3650 5 speed. Here is why:

On the GM T-56, the difference in ratios from 1st to 6th is 5.32:1
On the Ford T-3650 the difference in ratios from 1st to 5th is 5.45:1

In other words, the T-3650 still has a wider ratio spread from 1st - 5th than the GM T56 does from 1st to 6th.

 

[Scot_94GT]

Putting in a 6spd with a 6th gear that has an ultra tall ratio like .50:1 wouldnt be bad. But since the '03 Cobra had a 6th of .62:1, then I don't see the advantage over the 5 spd, since it's 5th was .62:1. Since both the 5 and 6 speed have a 4th of 1:1, why have an extra gear in between 1:1 and .62:1?


I guess having closer ratios past 4th gear would be good if you on a road course with a long straightaway where you might actually redline in 4th and need another gear, but I don't think very many people actaully race Mustangs in real races like that...and if they do, they probbably chagne the engine/transmisson anyway. In stock form, I doubt the Mustang would ever need to shift past 4th in the 1/4 either.

 

[RedGTvert]

The two main reasons for a 6 speed are:

1. To handle to power and tq of somthing like the 03/04 Cobra.

2 For cars that have to wind it out to to acheive thier power, like the S2000.

Sure it would be nice to have a 6-speed, but with the factory power and powerband, it really isn't needed.

 

[65conv50]

The two main reasons for a 6 speed are:

1. To handle to power and tq of somthing like the 03/04 Cobra.

2 For cars that have to wind it out to to acheive thier power, like the S2000.

Sure it would be nice to have a 6-speed, but with the factory power and powerband, it really isn't needed.

So what I'm hearing is that the Mustang 5-speed is missing the 5th gear of the 6-speeds, unlike the Firebird and T-5 Mustang transmissions I am familiar with, which have roughly the first 5 of what I am driving now..

If that is the case, then, you can't use overdrive in slower speed situations, like around town, on urban expressways, etc (the 6th, or in the quoted case, 5th - let's just call it top gear, is useless below 60 MPH - that is fact).

So, I still want a 6-speed. Because with it, I have an overdrive available for urban driving (like 5th I have now), and an even taller overdrive for interstate rural and long distance cruising.

More control of your car is never a bad thing, unless you are an incompetent driver, which I'm sure we don't have on this board.

It really is all about control of your car, which is the main reason for having a manual in the first place. (And also the main reason for rear-wheel-drive.)

 

[65conv50]

I'm just trying to figure out if the final gear in the 5 speed is so close to the final gear in the 6 speed. What would be the real benefit of having a 6 speed? It just seems the 0.01 gear difference is so small as to be moot. And why switch to a 6? Does anyone have an answer?

See my last post for your answer. It's all about control. I thought the 6-speed was one too many until I owned one. Now whenever I drive the Z-3 on the highway, I always want to shift one more time. (Which is a reason to get my sweetie to trade for a Z-4 but we both don't like the styling.)

 

[RedGTvert]

If that is the case, then, you can't use overdrive in slower speed situations, like around town, on urban expressways, etc (the 6th, or in the quoted case, 5th - let's just call it top gear, is useless below 60 MPH - that is fact).

It is not fact. Most people tend to change the rear gear ration. On a car with 3.73's or 4.10's, I had no problem driving around town in 5th.

I am unsure of the point you are trying to make.