2016 shelby gt350 driveshaft

[Grimace427]

Just for clarification engine RPM is irrelevant to driveshaft RPM. Driveshaft RPM is determined by final drive gear, tire diameter, and vehicle speed.

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[ohtobbad]

Once these cars have been in the market for awhile, we will see after market mods
that will be capable. Just give it some time. Aluminium is a possible choice also.

 

[bpracer]

Just for clarification engine RPM is irrelevant to driveshaft RPM. Driveshaft RPM is determined by final drive gear, tire diameter, and vehicle speed.

Huh?

Halfshaft/axle speed is related to final drive, driveshaft speed is related to engine rpm as modified by transmission...

And neither has anything to do with tire diameter. Vehicle speed yes, halfshaft/axle rpm no.

If you are in 1:1 trans gear your driveshaft is spinning the same as engine rpm.

From the link I posted above:
Critical speed is the speed at which a spinning shaft will become unstable. This is one of the single largest factors in driveshaft selection. When the whirling frequency and the natural frequency coincide, any vibrations will be multiplied. So much that the shaft may self destruct. Another way to think of this is that if a shaft naturally vibrates at 130 times a second, and one point on the shaft passes through 0 degrees 130 times a second (7800 RPM) then the shaft has hit a critical speed. There are several ways to raise the critical speed of a driveshaft. You can make it lighter, stiffer, or increase diameter without increasing weight. This is the reason carbon fiber makes a good driveshaft, it is stiff and light and can be made to any diameter or wall thickness. Aluminum, while it has a very good critical speed is not quite as strong as steel. Steel, with good strength characteristics will have a lower critical speed.

 

[PP0001]

The '13-14 GT500 had 3.31 rear gears and taller rear tires both of which reduced driveshaft RPM. The GT350 has 3.73 gears and shorter tires which can cause a one piece driveshaft to exceed its critical RPM limit.

This was explained in the first GT350 press release, IIRC was mentioned by Jamal Hameedi himself.

I certainly appreciate your comments with respect to shorter tires and 3.73:1 gears but my Boss 302 cars has the same final drive ratio gears as the GT350 and suggest that the tire height on my Boss 302 cars may be even shorter than the GT350 cars which means a higher driveshaft RPM.

I am away from home and cannot measure the overall height of the tires on my Boss cars but guess at ~25" and suggest that may be similar or shorter than the upcoming GT350 cars.

Lastly, I have had many conversations with DSS and they assured me that prior to installing the 3 1/4" CF drive shafts in my cars that the drive shafts that I purchased were good for ~1000 HP and up to 10,000 RPM.

Never had any issues shifting my cars many times at 7500 RPM and suggest that Ford opted out because of additional pricing.

:shrug:

 

[10splaya22]

I certainly appreciate your comments with respect to shorter tires and 3.73:1 gears but my Boss 302 cars has the same final drive ratio gears as the GT350 and suggest that the tire height on my Boss 302 cars may be even shorter than the GT350 cars which means a higher driveshaft RPM.

I am away from home and cannot measure the overall height of the tires on my Boss cars but guess at ~25" and suggest that may be similar or shorter than the upcoming GT350 cars.

Lastly, I have had many conversations with DSS and they assured me that prior to installing the 3 1/4" CF drive shafts in my cars that the drive shafts that I purchased were good for ~1000 HP and up to 10,000 RPM.

Never had any issues shifting my cars many times at 7500 RPM and suggest that Ford opted out because of additional pricing.

:shrug:

From Tob with his interview with Jamal Hameedi. I wouldn't say its due to pricing unless you were sitting in the room with the engineers who made the decision. But as far as the decision to go with steel this is the only information I've found. Its a credible source so i'm going to believe it.

I inquired as to why (cost aside) a carbon fiber shaft was not tapped for this application and Jamal repeated a comment he had previously made that a CF shaft simply isn't stiff enough for this application. When I mentioned the critical speed that the CF shafts offer (such that the '13-'14 GT500 could hit over 200mph) Jamal corrected me by stating that it was critical frequency that was the concern. This is where the engineers put the time in to ensure these frequencies were in the range where they needed to be. The two-piece shaft that the GT350 will utilize is not what will limit its top speed.

 

[krt22]

Im with BPracer on this one, Im failing to see how rear end ratio/tire size impacts driveshaft speed. For a given group speed? yes of course..but this will result in a different engine RPM. But the drive shaft and engine are directly coupled via the transmission, cant uncouple that.

 

[PP0001]

From Tob with his interview with Jamal Hameedi. I wouldn't say its due to pricing unless you were sitting in the room with the engineers who made the decision. But as far as the decision to go with steel this is the only information I've found. Its a credible source so i'm going to believe it.

Understand where you are coming from but these are possibly the same engineers that signed off on carbon fiber wheels for the "R" model that became standard equipment and these same engineers can't find a carbon fiber drive shaft that will work for these cars?

After developing a FPC engine for the GT350 coming up with a CF drive shaft should be elementary for this intelligent group of engineers.

Lastly, why the battery was not relocated to the trunk for the "R" model is another question that I have for Ford?

:headbonk::headbonk:

 

[347CobraII]

Everyone and other driveshaft producers have there opinion about single vs 2 piece driveshaft. I call BS on 1 piece driveshaft solving driveline cluck have yet to see anyone prove. I did put 1 piece in my 11 GT because I was chasing vibration. No it didn't solve vibration or any drivetrain back lash. Vibration was caused by pinion got most of it gone using solid spacer and max pre load. Should have went little tighter I think pinion was stretching/ deflecting under load.
Length of driveshaft has biggest effect on how fast you can spin it. People like DSS and etc will say stock is garbage BUT do they do testing that factory does not even close. People talk about old Mustangs like 67-73 or had long driveshafts but they don't turn high rpm either like newer cars. Also GT 350 engine turns above 8k think how fast it's turning in 6th.

I wonder if GT 350 driveshaft has foam rubber inside of it like GT for damping

 

[stanglife]

Im with BPracer on this one, Im failing to see how rear end ratio/tire size impacts driveshaft speed. For a given group speed? yes of course..but this will result in a different engine RPM. But the drive shaft and engine are directly coupled via the transmission, cant uncouple that.

All I can think of is that you guys are saying the same thing, different ways.

To me - I think about the fact that the driveshaft is connected to the tires through the rearend which is a specific ratio and can not change. If you're going 100mph, the driveshaft is spinning at the same speed, no matter what gear the transmission is in. So the driveshaft RPM is directly related to the speed the car is going. I don't see how the transmission has anything to do with it.

Example, one of my first Mustang mods, so many years ago was to change the rear end gears. I changed nothing else. This caused everything to function at a higher RPM, except the rear tires - It ultimately left me stranded by finding a weak spot in my transmission (output shaft bushing was already sloppy and the extra RPM at highway speeds killed it).

So the higher rear end gear ratio you have, the faster your driveshaft spins at a given vehicle speed.

 

[bpracer]

I apologize for my poor explanation. I should not have sneaked a look at work.

I was just trying to say that this engine has a much higher redline and top speed than most cars and other mustangs and that in 5th (1:1 I believe) the engine and the driveshaft are turning the same rpm.

By removing a two piece driveshaft with a one piece you have now lowered the critical speed (natural frequency) of the driveshaft possibly to the point where the rpm and the natural frequency are the same. That can be catastrophic.

If you have a 54"(no idea how long the GT350 shaft is??) driveshaft you have the following max speeds for Mark Williams driveshaft products:


3.0" mild steel 5856rpm
3.5" mild steel 6869rpm
3.5 chromoly 6945rpm
3.5 6061 Alu 6739rpm
4.0" 6061 ALu 7736rpm
3.75" carbon fiber 8973rpm


So a carbon one is the only one that would safely operate at GT350 engine/vehicle speeds, assuming you could top out 5th gear. There aren't many tracks you will sustain those speeds for long, hence my comment about the front straight at Road America. However, I've had friends that have done closed highway events in their Boss 302 where you can run sustained high speeds.

Bigger diameter tubes help as the chart shows, but maybe there isn't that much room. The stock drive shaft does not look like it is very large in diameter. The trans tunnel looks very tight. Also, how close do you want hot exhaust next to a carbon driveshaft? I dunno, but it sounds like maybe Ford looked at one and didn't go for it. Ford probably has a pretty healthy safety margin in their design rules.

When driveshafts go bad, they go real bad...

If somebody, like Mark Williams, makes a drop in one that is really properly engineered, I would be interested.

 

[908ssp]

I was told by one of the GT350 engineers that they fought vibration problems due to the flat plan crank motor. And that was the determining factor in the steel driveshaft. They would have loved to use carbon but it allowed more engine vibration due to the lower weight. He also said that any changes to the drive train could have serious ramification in vibration and that Ford would not cover those issues under warranty so proceed with due caution.

Another example is that silly expensive fly wheel normally only seen on out of balance V6 engines.

 

[TraKWeapon]

I was told by one of the GT350 engineers that they fought vibration problems due to the flat plan crank motor. And that was the determining factor in the steel driveshaft. They would have loved to use carbon but it allowed more engine vibration due to the lower weight. He also said that any changes to the drive train could have serious ramification in vibration and that Ford would not cover those issues under warranty so proceed with due caution.

And don't even think about changing the exhaust either.

 

[347CobraII]

All I can think of is that you guys are saying the same thing, different ways.

To me - I think about the fact that the driveshaft is connected to the tires through the rearend which is a specific ratio and can not change. If you're going 100mph, the driveshaft is spinning at the same speed, no matter what gear the transmission is in. So the driveshaft RPM is directly related to the speed the car is going. I don't see how the transmission has anything to do with it.

.

REALLY driveshaft and tires spinning at same speed as you said if going 100mph both spinning the same ........ 3.73 gear ratio lets see 1 revolution of ring gear and pinion has turned 3.73 revolutions to bring ring gear back to where it started at. Or pinion has to turn 3.73 turns to make ring gear turn 1 full revolution time. Only way that they can turn same speed or rpm if it was 1 to 1 gear ratio. You getting the picture now

[ame] how about 11 million to 1 ratio which mean input has to be turned 11 million times for 1 turn of outer gear aka 11 million to 1. Guess to you they both turn same speed or rpm LOL

 

[NvrFinished]

REALLY driveshaft and tires spinning at same speed as you said if going 100mph both spinning the same ........ 3.73 gear ratio lets see 1 revolution of ring gear and pinion has turned 3.73 revolutions to bring ring gear back to where it started at. Or pinion has to turn 3.73 turns to make ring gear turn 1 full revolution time. Only way that they can turn same speed or rpm if it was 1 to 1 gear ratio. You getting the picture now

how about 11 million to 1 ratio which mean input has to be turned 11 million times for 1 turn of outer gear aka 11 million to 1. Guess to you they both turn same speed or rpm LOL

I believe what people are trying to state about drive shaft speed is this:

If the transmission was in neutral and the car was getting pushed at say 130 MPH by another vehicle, the resulting RPM's of the drive shaft would be greater with 3:73 gears vs 3:31 gears, assuming same size tires.

How fast the engine is turning or what type of transmission the car has is irrespective of the drive shaft RPM for a set speed, with a set gear ratio, and same sized tires.

 

[Trackaholic]

I guess one should say that the driveshaft speed is proportional to the road speed by a factor determined by the rear end ratio and tire diameter.

Of course it is also connected to the engine by the transmission, and so will also be proportional to engine speed, but at a ratio determined by the current gear.

It is therefore more clear to talk about driveshaft speed relative to road speed (rather than engine speed), since the rear end ratio (and tire diameter) is fixed. This is easy to see when watching a large truck with an exposed driveshaft accelerate. You can see the shaft spinning faster and faster and the truck gains speed, even though the engine speed changes with each shift.

So, with that in mind, we can see that the performance of the driveshaft in the GT350 is similar to that of the GTPP at equivalent speeds (the difference being due to variations in tire diameter between the vehicles). However, the GT350 can likely reach 180 MPH in the top of 5th gear, while the GTPP is possibly limited to something lower due to power, which might give the GT350 higher requirements in terms of critical speed.

At 180 MPH the driveshaft in the GT350R (with its 315/30-19 tires, that spin @ 762.76 revs/mile), would be spinning at 180*762.76*3.73/60 = 8535 RPM.

That is getting close to the limit of the single piece carbon fiber driveshaft mentioned above.

The GT500 uses a 3.31 rear end, and a 285/35-20 tire, which spins at 724.06 revs per mile. So, at the 200 MPH top speed of the GT500, the CF driveshaft would be spinning at 200*724.06*3.31/60 = 7989 RPM.

So there was more headroom in the design of the GT500, and the 200 MPH top speed was probably more difficult to reach than the 180 MPH limit in the GT350.

Anyhow, what about a two-piece CF driveshaft?

-T

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