Quote:
Originally Posted by Tahoe_Hybrid
1971 Firebird has a 2.41 ratio might be able to salvage one from that
should look into a second overdrive gear? 0.5 gear?
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I have considered that very idea, I have two 50s/60s Borg Warner 3 Speeds with over drives.
And I was very close to putting one behind a TH400, using 2nd gear as a under drive with very tall rear end gears, so that when in a city drive I would have a low geared rear end, giving 4 speeds in low, the stock 3 in the auto and the B&W over drive, and then by shifting into third gear (1:1) switch to high and again have four speeds in high. A 8 gears...
BUT it would be a little complicated....I would need a floor shifter between the seats. And complex set up to INSURE I never back up in overdrive, that will rip the overdrive's gears out. And shifting the OD in and out of OD.
The new 6 and 8 speeds give all of that, super low first and second gears at 4.03 and 2.36 for the 6 speeds 6R80, and 4.56 & 2.97 for the 8L90s Both lower gears are BELOW the stock Fords first gear ratio of 2.48 and GMs 4l60E's 2.48 as well. The 6 speed second gear is near the 4's first gear, but the 8 speed both first and second are lower that the 4 speed's first gear.
So there is no need for an under drive...
PLUS these are fully controlled automatics, insuring smooth up shifting and down shifting.
And as I am NOT building a high HP over revving hot rod but a stock motor in the Crown Vic and a Chevy 383 built for LOW RPMs for the Van, totally built to operate around the 2000 RPM range both the motor and drive train will be a match. i figure the 383 should be pulling around 250/300FP of toque at that speed which should be great for cruising.
I have read everywhere that you want your engine to be running near its torque peek for best power and MPG.
So I plan on using a used trans mission, which for the 6R80 can be had now for around $500.00 and the 8L90s running from $700.00 to $1200.00.
Which leaves the problem of controlling them.
One idea is to run dual PCMs, the factory PCM to operate the motor and a Factory PCM for the 6R80, and the same for the 8L90.
OR an aftermarket controller which adds about $1000.00 to the costs.
So for the Crown Vic $500.00 for the 6R80 plus say $100.00 for a factory PCM, or $1000.00 for AM Controller so $600.00 to $1500.00 for the Vic.
And the Van, $800.00 for 8L90, and $100.00 for GM PCM, or $1000.00 so from $900.00 to $1800.00.
I feel and think these will work very well, and not only majorly improve each vehicle's drive-ability with all the extra gears during acceleration plus being to down shift a closer lower gear in traffic a function limited with only four gears.
AND with the tall rear end gears using the top overdrive gears be running both engines below 2000RPMs and at 80MPH..with I think will give me great MPG, even before I do some tweaking to improve MPG.
Like Highway modes, running 16.4 lean at cruse.
Rich