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  #13  
Old 06-26-2015, 10:37 AM
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Re: Pentastar Thoughts

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Originally Posted by padgett View Post
5 speed Merc. Must admit with a torque band essentially flat from 1600 to 6400, and a 2:1 torque converter & lockup I do not really undestand the driver for lotsa gears.

So basically the move to 8 and 9 speed transmissions is because of emissions and mandated fuel economy standards.
Even though the torque curve is fairly flat, once you equate the aerodynamic drag and rolling resistance at a given speed, there will be a small rpm band based on the final drive ratio where you will achieve the highest gas mileage for that given speed.
By having more gears the computer has more options for that final drive ratio when calculating using things like throttle position, RPM, fuel flow (GPH), temperature and so on to decide how to achieve the best possible efficiency.

Those factors can be heavily influenced by temperature, uphill/downhill and also if you are bucking wind or driving with a 20mph tailwind. It is pretty amazing all the factors that the ECM is taking into consideration to decide which gear is best for a given moment.

I dont like how the 9 speed hunts a bit at lower speeds, but otherwise I love it in my wifes Chrysler 200. And the 8 speed in the GC is good.

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  #14  
Old 06-26-2015, 06:28 PM
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Re: Pentastar Thoughts

The 8 speed isn't all that good as it's cracked out to be; the way some go on and on about the big "power difference", there is a tiny difference. It just "feels" more powerful to drive due to 2 reasons:
- it is tuned better, after a shift the rpms are higher up than in the old 5 speed. The 3.6 really is gutless < 1800 rpm.
- all that shifting gives the perception of speed and being busy; "wow, this thing is really flying through the gears, I must be really taking off".

If yout manually "shift" the 5 speed yourself, it is surprising how much better it feels than letting it do it itself.

So it's not the 5 speed, it's not the 3.6, it's the absolutely horrid tuning / computer parameters.
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Old 06-26-2015, 11:22 PM
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Re: Pentastar Thoughts

I dont want to get into an argument about your feelings about the 8 speed transmissions, it really has nothing to do with "power difference" Now with that said most vehicles with a properly tuned 8 speed will accelerate quicker and also average better gas mileage with the same horsepower.

It has been proven with numerous manufacturers including BMW, Volkswagon, Chrysler, GM, Mercedes Benz, Rolls Royce, Audi and others. You wouldn't see 8 and 9 speeds put into 500+ HP BMW's, Corvettes, and into full size trucks if there wasnt a good reason for it.
The ZF 8HP wouldnt still be in production after 7 years if it was garbage a some may say.

Now with that said not all 8 speeds are built equally, but that can be said with any transmission at one point. The old NV3500 I had in a 2001 Ram 1500 was a turd.

The ZF 8HP is one of the best transmissions made today, now remember the GC has two models.
The 8HP70 on the 5.7 & 6.4 Hemi that is manufactured by ZF in the US
The 845RE on the 3.6 Pentastar that is manufactured by Chrysler in the US under license from ZF.

The Chrysler manufactured 845RE seems to have alot more complaints and issues than the 8HP70 manufactured by ZF. That is why a handful of people with the 3.6 v6 are hatin on the transmission.
The real question is why does there seem to be a quality difference between the 8HP45 made by ZF and the 845RE manufactured by Chrysler, they are technically the same transmission. Are the electronics just tuned that poorly or is the Chrysler facility using cheaper materials?
Hard to say.
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  #16  
Old 06-27-2015, 01:32 AM
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Re: Pentastar Thoughts

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Originally Posted by SavageBrewer View Post
I dont want to get into an argument about your feelings about the 8 speed transmissions, it really has nothing to do with "power difference" Now with that said most vehicles with a properly tuned 8 speed will accelerate quicker and also average better gas mileage with the same horsepower.

It has been proven with numerous manufacturers including BMW, Volkswagon, Chrysler, GM, Mercedes Benz, Rolls Royce, Audi and others. You wouldn't see 8 and 9 speeds put into 500+ HP BMW's, Corvettes, and into full size trucks if there wasnt a good reason for it.
The ZF 8HP wouldnt still be in production after 7 years if it was garbage a some may say.

Now with that said not all 8 speeds are built equally, but that can be said with any transmission at one point. The old NV3500 I had in a 2001 Ram 1500 was a turd.

The ZF 8HP is one of the best transmissions made today, now remember the GC has two models.
The 8HP70 on the 5.7 & 6.4 Hemi that is manufactured by ZF in the US
The 845RE on the 3.6 Pentastar that is manufactured by Chrysler in the US under license from ZF.

The Chrysler manufactured 845RE seems to have alot more complaints and issues than the 8HP70 manufactured by ZF. That is why a handful of people with the 3.6 v6 are hatin on the transmission.
The real question is why does there seem to be a quality difference between the 8HP45 made by ZF and the 845RE manufactured by Chrysler, they are technically the same transmission. Are the electronics just tuned that poorly or is the Chrysler facility using cheaper materials?
Hard to say.
Keep in mind 90% of the issues with the 845RE was Tuning/Firmware than the hardware. So it really doesn't matter who built it. There does tend to be some more hardware issues with the 845RE (valve body) now that we are past most firmware/tuning issues. But the bulk of the issues was tuning and Chrysler probably did the tuning for both. It may have been easier to do the V8 or just a different team working on it. The 8HP70 was not without issues as well.

Also keep in mind there is probably 100 V6's for every V8.
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  #17  
Old 06-27-2015, 10:09 AM
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Re: Pentastar Thoughts

Interesting the difference between knee-jerks and reasoned responses. Said I was biased but there is engineering reasoning behind it (may I suggest study of Ricardo and Obert ?)


That said 98-99% of most drivers experiences are on the flats (Denver is where it is because after thousand of miles of staring at the rear end of an ox, the intrepid pioneers took one look at the Rockies and said "we're stopping here."


Also MPG is more driving habits than EPA, my highway MPG is more low 20s because most speed limits here are in the 70s and I usually have the AC going. At least it is 87 PON.


All I can say is my Pentastar/five speed does fine for me pulling a 3500-4000 lb (depending on the tank state) folding camper. And shifts fine.
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  #18  
Old 06-27-2015, 10:33 AM
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Re: Pentastar Thoughts

Quote:
Originally Posted by SavageBrewer View Post

The ZF 8HP is one of the best transmissions made today, now remember the GC has two models.
The 8HP70 on the 5.7 & 6.4 Hemi that is manufactured by ZF in the US
The 845RE on the 3.6 Pentastar that is manufactured by Chrysler in the US under license from ZF.
Is the 8HP70 now being built in the U.S.? My Sept. '13 build was manufactured in Germany.
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  #19  
Old 06-27-2015, 11:03 AM
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Re: Pentastar Thoughts

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Originally Posted by 2014RedHemiGC View Post
Is the 8HP70 now being built in the U.S.? My Sept. '13 build was manufactured in Germany.
Mine was built in Germany by ZF also, the early 8HP70 were. 8HP70 are now built by ZF in South Carolina and the 845RE are built in India by Chrysler. Chrysler also messed with the 845s (probably why they have all the issues)
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Old 06-27-2015, 11:22 AM
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Re: Pentastar Thoughts

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Mine was built in Germany by ZF also, the early 8HP70 were. 8HP70 are now built by ZF in South Carolina and the 845RE are built in India by Chrysler. Chrysler also messed with the 845s (probably why they have all the issues)
I believe you meant Indiana.
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Old 06-27-2015, 11:55 AM
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Re: Pentastar Thoughts

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I believe you meant Indiana.
Yes Kokomo, sorry thanks for the correcting
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  #22  
Old 06-27-2015, 12:03 PM
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Re: Pentastar Thoughts

LOL... poop happens, no problem.
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  #23  
Old 06-27-2015, 12:39 PM
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Re: Pentastar Thoughts

Quote:
Originally Posted by SavageBrewer View Post
I dont want to get into an argument about your feelings about the 8 speed transmissions, it really has nothing to do with "power difference" Now with that said most vehicles with a properly tuned 8 speed will accelerate quicker and also average better gas mileage with the same horsepower.
Right on the first part; adding extra gears does nothing, really, for performance. Half right on the second part; it will only accelerate quickly if the engine has a small spot in the torque curve where it pulls the best, like a diesel 18 wheeler. The 3.6 is strong throughout 2000 - 6000; it doesn't need to shift a million times because it pulls great throughout.

The only benefit of the 8 speed to the 3.6 is mpg, that's it.


Quote:
Originally Posted by SavageBrewer View Post
It has been proven with numerous manufacturers including BMW, Volkswagon, Chrysler, GM, Mercedes Benz, Rolls Royce, Audi and others. You wouldn't see 8 and 9 speeds put into 500+ HP BMW's, Corvettes, and into full size trucks if there wasnt a good reason for it.
The good reason is mpg. My post was addressed to all those going on about the perceived performance benefits of the actual physical transmission. When you shift the 5 speed yourself, and can keep the rpms from dropping below 1900 rpms, the 5 speed is excellent. The 8 speed simply feels quicker because you hear it revving through the gears so quickly.

Yes I would still prefer the 8 for mpg, but I wasn't contesting mpg claims.
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  #24  
Old 06-27-2015, 06:44 PM
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Re: Pentastar Thoughts

Will admit the Hellcat does sound neat through the 1/4 but other than that... The additional mpg for the Pentastar (about 1 mpg -23.6 vs 24.7 - if you look at the raw numbers from the EPA spreadsheet) is more the taller top gear overall ratio in 5th lockup vs 8th.

Am curious: with the 8, first gear looks more like a parade or "grade retard" gear than something useful. Does it normally start in second ?
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