My "new" '74 Duster- or why I need a project like a hole in the head
Awesome glad you finally got the 6 speed in. Been following for quite awhile, really enjoy your posts very informative. How much did your gas mileage improve so far? Dustin
Gas mileage? What's that?
Um, around town I haven't really noticed much of a change. I think the "fun factor" of having the 4.30's probably costs me as much fuel around town as I save at cruise on the freeway. I would imagine that on a longer drive, where I spend the entire tank at cruise, I probably picked up a couple of mpg's. But I've pretty much only done mixed driving since I finished the install. And to be honest I don't track my mileage that closely. I have a wideband A/F gauge to monitor my engine tune and as long as my typical commute doesn't suddenly start taking a few extra gallons I probably wouldn't notice.
Stupid question, but what's the benefit of a 6-speed over a 5-speed? I'm assuming it's the added over-overdrive that allows the use of a shorter rear gear? Are they stronger, shorter throws, tighter gear spacing?
An extra gear? :rofl:
Seriously though, I did look at doing a 5 speed conversion. A big part of it was the actual transmission. The TKO 500's and 600's get "ok" reviews IMO. There's quite a few people out there that don't like the feel of the TKO's shifting. It seems like that was the swap to do for awhile with the B/E bodies, it doesn't take a ton of tunnel fabrication on those cars. But I read a lot of lukewarm reviews on that swap. On the flip side, I haven't found anyone that installed a T56 in a Mopar that didn't love it. I mean like
rabidly love it. So that was a really big factor for me.
The next part was the cost and fabrication. After I priced out the 5 speed vs the 6 speed swap, the difference was only about $1k. Which I know is a lot, but if I'm already going to spend $5,600 spending $6,600 isn't a crazy difference. And the fabrication was about the same. Yeah sure, for the TKO's you don't have to do as much tunnel fabrication or quite as much crossmember removal and fabrication. But it's like 80% of the way there. If I already have to cut the tunnel and crossmember, then going a little further isn't as big of a deal. If I could have done it without cutting that might have been different.
And yeah, the gearing is just easier. For the TKO's you get gears of 2.87, 1.89, 1.28, 1.0 with a 5th of either 0.64 or 0.82. For the TKO 500 you get 3.27, 1.98, 1.34, 1.00, 0.68. So the 500 has a big drop from 1st to 2nd. And the 600 either has a big drop to 5th, or only a .82 overdrive gear.
The T56 Magnum I installed has 2.66, 1.78, 1.30, 1.0, 0.80, .063. So the gear splits are all tighter, and with a 4.30 gear I improved my 1st gear drive ratio and still dropped almost 1k off of my rpm at cruise speed compared to the 3.55's which was great. They have a T56 magnum XL now with a 2.97 first gear and the .8 and .63 overdrives, that's the one goldduster318 installed. If that one had been around when I bought mine I could have done like 4.10's or 3.91's instead and lowered my cruise rpm a little. But my 340 doesn't like to pull much below 2,200 anyway. So setting my 70mph cruise at 2,400 was just fine and dandy.
