no, it is not a dual dry clutch. it's a conventional automatic transmission with a torque converter.

 

Thanks Funky. Been a long time since I've seen you out on the forums. You helped me out over the years on the LX forums!

 

IIRC, Chrysler says 250 ish millisecond shifts in track mode.

 

That's pretty damn quick!

 

Just curious if the 8 speed automatic transmission is a "dual clutch" type transmission like in the more expensive rides?

FYI, the ZF 8HP transmission used in these cars is widely admired as one of the best autos in the world, regardless of technology. The same model used in the Hellcat (8HP90) is used in the Rolls-Royce Ghost and Bentley Mulsanne. Variants of the transmission that can't handle as much torque are used by BMW, Range Rover and Audi. Lots of very expensive high performance and luxury cars use the ZF 8HP.

There is one difference worth commenting on: while the hardware is shared, each manufacturer does its own shift map programming. So each vendor ends up with cars that shift differently. The way it shifts in a car like the Hellcat will be very different from how it shifts in a Rolls!

 

Very interesting

 

It is 160 ms in track mode. It's a sweet A8 for sure! Pretty compact in size too!

 

I posted this in Sept elsewhere. Drop it here for people interested. Maybe make a wiki entry

Sept 2014 - TIGwelder

I figured since this is new for the Challenger Hellcat, I would dig up some info and we can discuss this new transmission. Here are some informative

links, a video showing the internals and some specs.

An interesting thing is the converter can lock in first gear. Were the older units the same way?
Also it can shift from 8th to 2nd.

Along with a separate chain driven pump and other optimizations it looks like they worked hard to reduce parasitic loss.

Main info:
8HP Automatic Transmissions

Video: fixed link

ZF 8HP90 - Video

Specs:
8HP90_DataSheet.pdf

ZF8 Info at Allpar
845RE / 8R70: ZF 8-Speed Automatic Transmission for Chrysler cars

ZF 8 Speed Automatic Transmission - Equipment and Tool Institute Tech Day - June13 2012
Chrysler PDF Document


==============================================


Let's look at the transmission ratios for the Hellcat

1st -- 4.714
2nd -- 3.143
3rd -- 2.106
4th -- 1.667
5th -- 1.285
6th -- 1.000
7th -- 0.839
8th -- 0.667

That first gear is crazy. I decided to do this because I wanted to know what was up with all the second gear starts I'm seeing. Then I wanted to compare it to other stuff. And then I just went silly with it



Let's compare it to the NAG1 WA850

1st -- 3.588
2nd -- 2.186
3rd -- 1.405
4th -- 1.000
5th -- 0.831

So second is bit taller than first in the NAG1. ( Hellcat 2nd 3.142 vs NAG1 3.588 = 0.445 difference)


Let's check out old school with the 904/727 for reference

1st -- 2.45
2nd -- 1.45
3rd -- 1.00
==============
4th -- 0.69 ( later 4th used with above ratios, even the SRT Ram10 )



=========================================================



Final Drive Ratio
-----------------
For the Hellcat with the 8 speed it's 2.62
Tire: The 275/40R20 Pirelli P Zero is 28.7 inches in overall diameter.


Let's look at gear multiplication, first gear comparisons for several ratios/setups.


Hellcat
( 1st x Final )
4.714 x 2.62 = 12.35068

(2nd x Final )
3.143 x 2.62 = 8.23466 (How I've seen people documenting 1/4 mile passes)


Old NAG1
( 1st x Final )
3.588 x 3.06 = 10.97928


And to show the gearing now to my old school brain, let's compare it to some older stuff.

OLD school 727/904 with various gear ratios

( 1st x final )
2.45 x 4.10 = 10.045
2.45 x 4.56 = 11.172 ( Close to NAG1 )
2.45 x 4.88 = 11.956

4.88s and still not there yet!!

2.45 x 5.13 = 12.5685


Hellcat vs Old School
To compare a 1st gear start - Your final drive ratio would be around 5.04 with a 28" tire ( wow )
To compare a 2nd gear start - Your final drive ratio would be around 3.36 with a 28" tire


================================

So back to the Challenger Hellcat. Let's look at max speed in each gear.

It's basically
MPH = ( RPM x tire dia ) / ( gear ratio x 336 )
or
MPH = ( 6000 x 28.7 ) / ( gear ratio x 336 )
where 'gear ratio' will be ( trans ratio x Final )

or ( 172,200 / (( trans ratio x Final ) x 336 )) @ 6000 RPM
AND ( 177,940 / (( trans ratio x Final ) x 336 )) @ 6200 RPM


1st -- 4.714 x 2.62 = 12.351 ( x 336 = 4,149 ) = 41.5 MPH @ 6000 -- 42.8 MPH @ 6200
2nd -- 3.143 x 2.62 = 8.235 ( x 336 = 2,766 ) = 62.3 MPH @ 6000 -- 64.3 MPH @ 6200
3rd -- 2.106 x 2.62 = 5.518 ( x 336 = 1,854 ) = 92.9 MPH @ 6000 -- 95.9 MPH @ 6200
4th -- 1.667 x 2.62 = 4.368 ( x 336 = 1,467 ) = 117.3 MPH @ 6000 -- 121.29 MPH @ 6200
5th -- 1.285 x 2.62 = 3.367 ( x 336 = 1,131 ) = 152.2 MPH @ 6000 -- 157.32 MPH @ 6200
6th -- 1.000 x 2.62 = 2.620 ( x 336 = 880 ) = 195.6 MPH @ 6000 -- 202.20 MPH @ 6200
7th -- 0.839 x 2.62 = 2.198 ( x 336 = 738 ) = 233.3 MPH @ 6000 -- 241.11 MPH @ 6200 ( we're past the aero limit here )
Then we enter driving in a vacuum land
8th -- 0.667 x 2.62 = 1.748 ( x 336 = 587 ) = 293.3 MPH @ 6000 -- 303.13MPH @ 6200

That's right..let it rip to redline in 8th with zero wind resistance and look at the speed!! haha!


Note: I watched the K&N dyno run, the shift into 6th was around 148MPH, 7th at 191
So my above results are close. There is some rounding in the above numbers.
Also the Tire dia used plays a part ( no resting weight, air pressure, using tire specs, etc ).

==========================

So what did I learn.

- Well, I have to much time for one
- Starting in 2nd has a gearing disadvantage to older NAG1 and gears used before. They have 2nd gear start in valet mode and it would be nice to be able to toggle that feature separately in transmission settings. If 2nd gear start is used then gearing could be changed.
- It's insane how final gearing in first gear is compared to old school cars. 5.04s on a 28" tire, really? Need to stop thinking old school gearing.

Questions:
When does the converter lock? Did I read that it can lock in first gear? ( "The tall first gear allows for early lockup of the torque converter clutch. -- Allpar ). Under what conditions though? When does it lock on launch or hard acceleration?


Maybe somebody will throw in a spreadsheet to play with ratios/tire sizes
Anybody want to tackle the 6M??
Mistakes? :notallthere: Let me know!

Discuss


===============================================
Edited:
v1.02 - Changed/recalculated old NAG1 gearing to 3.06, not 3.09
- Changed "steeper" to "taller"
- Added MPH calcs for 6200 RPM
- Added link for Allpar ZF8 info
- Added converter lockup quote from Allpar ZF8
- Added Chrysler document link

 

Ok I have no clue on where to start to look!
So I think I figured it out !
Press brake put in drive and stomp on gas and pray like hell it stays straight and goes fast!

 

More gears = keeping the engine in its torque band with less revs. Not particularly of interest to HCs, but I am certain it does play a part in the improved mileage for CAFE and other calculations. Nice work, lots of time. Pray for no more CVTs

 

Good info...the 8HP90 handles 737 ft.lbs...some room there to play with...

 

But very little these cars should exceed that number with a tune and CAI

 

Actually, the ZF HP 90 is also used in the BMW M5 and M5 Competition is the same as the Hellcat, but with AWD. They have 675 lb-ft at the wheels.