So its time for me to order a transmission for my Cummins 6.7 swap. Its getting an HE451VE turbo (from an ISX) and EFI Live tuning. I'm shooting for 550-600 HP and 1000-1100 ftlbs at the flywheel.
You think it would be an easy thing to do.
I was all set on the ZF6
except there are a couple issues with it.
1) I'm right on the edge of the power capability of a double disk organic clutch. But Valair has one that should work.
2) DD clutches are known to be a bit noisy. And I'll have regular gear rollover noise too. One of the guys running a DD organic clutch is saying the noise is getting to him.
3) I have to cut the floor pan and/or bend it up because my truck came with an auto and ZF6sd are taller than 5R110s and the floor pans for each are different.
4) The OD
gear ratio of 0.72 sucks.
Its too fast for towing. With 3.73s and 20 inch tires I'm at only 1650 RPM at 60 MPH and 2300 RPM in direct.
Its too slow for efficient cruising. I'll be over 1800 RPM at 70 MPH.
5) I need an adapter plate to go between the trans and the engine. No biggie as I'll make it myself, but its still work.
I started looking at automatic transmission options and the 68RFE caught my eye. I think the 68FRE has the best ratios. 4-5-6 are 1:00, 0.82 and 0.63:1.
At 70 MPH in 6th, I'd be spinning about 1600 RPM, at least 200 RPM slower than with the ZF6
I'd be at 1900 RPM towing in 5th, about 400 RPM higher and dropping down to 4th gear puts me at 2300 RPM and the gear down from that at 50 MPH is 2600 RPM. Perfect.
Another nice thing is that the 68RFE on the 2010s is totally controlled by the Cummins ECM. So wiring it up isn't a problem.
The problem is the 68RFE is that the UD/OD clutches are weak. Actually everything in that transmission is weak, but there appears to be very little you can do with the UD/OD clutches.
So weak in fact that I got a quote for a $4400 custom 68rfe built transmission and the builder said "It's good for up to 550hp however we do not recommend you tow at that level with the 68"
I've looked at the Allison. Its not a strong transmission.
I really don't want a manual transmission for the reasons mentioned above. The 68FRE is junk. I don't want an Allison. So that leaves me with... the 6R140.
It has a stand alone transmission control module that can be reflashed by itself.
Its the only stock transmission that is standing up to any kind of power additions. The 5R110 was good that way too.
The torque converter seems to be good.
It seems like my only logical choice !