Gear Ratio Recommendation

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DentalDart said:
Lol I want 3.91s but it’s not a great highway gear
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This is true...not at todays speeds..its good for 55-65 mph. I have 2.73s in my Fo body with a 5 speed and that cruises nice but its a 15 second 1/4 mile, where as teh dart with 3.91s doesnt cruise wellbut is faster inthe 1/4. The dart will cruise but with the 4 speed its revving at 70 MPH and above 3.91s are good around town light to light gears...:)
 
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It usually comes down to how perfect can you afford. A simple third member swap could be a great compromise. However the overdrive would be better, but that really ups the scope of the job, and the snowball effect starts……
 
Absolutely! The MoPar OD transmissions have a deeper first gear vs the standard 3spd’s. This can make that 3.91 feel a good bit steeper.

2.45 X 3.91 = 9.57
3.09 X 3.91 = 12.80

A 3.23 difference. 3.91 + 3.23 = Holy S#%€£¥€%% Batman!

:rofl:

Seriously speaking…… 3.55’s with the MP deep first gear is IMO an excellent set up. But the balance in overdrive….. ehhhhh, IDK about a final drive ratio of 2.45. Unless you’re trying to conserve fuel or travel at 165 MPH comfortably.
 
Tremac’s have a nice selection of 5 & 6 speed units.
 
...and that's why I saved up to have a 200-4R OD trans built for my '69 Dart.
It fits in an A-Body without surgery to the tunnel and will let me run 4.30 gears for around town fun and games. The 2.74/1.57/1.00/0.67 gear spread is good and will be like 2.88 rear gears on the freeway.
 
DentalDart said:
Funny thing is I am actually debating a tremec for the new dart. Haven’t been working on it lately as we just got a house and been remodeling
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House first…. Toy car later or at dribs and drabs.
 
DentalDart said:
Funny thing is I am actually debating a tremec for the new dart. Haven’t been working on it lately as we just got a house and been remodeling
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I'm going to put a Tremec T5 in Vixen soon. Along with a custom Ford 9" with 4.11 gears.
 
Mcfarlrm said:
Looking for a better rear end gear ratio for cruising speeds. Current set up is 410 gears, TF 904 with a 2000 stall and 25.5in diameter tires, which screams at 4k rpm around 70 mph. Ideally I would like to be around 2,500 rpm at 70 mph.
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How much cylinder pressure do you have?

With a 3.23/2000TC combo and low pressure, this is gonna be real doggy down low, and again on the 1-2 shift.
Assuming regular TF gear ratios of 2.45-1.45-1.00:
3.23s and 25.5s are gonna get you 5000 rpm at 48 mph. Then on the shift, the Rs will fall back to 59%= 2950, by 55 mph this is 3380, so for passing in Second gear, your engine is gonna need some balls at 3380. If it only makes 135psi pressure, passing is gonna take a whole lotta room.
You can solve some of the take-off woes with a higher stall TC,
But that will hardly put a dent in the 1-2 shift problem, and it
won't begin to touch the passing gear situation.

Now, if you have 165 psi, that's a whole different story...
 
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AJ/FormS said:
How much cylinder pressure do you have?

With a 3.23/2000TC combo and low pressure, this is gonna be real doggy down low, and again on the 1-2 shift.
Assuming regular TF gear ratios of 2.45-1.45-1.00:
3.23s and 25.5s are gonna get you 5000 rpm at 48 mph. Then on the shift, the Rs will fall back to 59%= 2950, by 55 mph this is 3380, so for passing in Second gear, your engine is gonna need some balls at 3380. If it only makes 135psi pressure, passing is gonna take a whole lotta room.
You can solve some of the take-off woes with a higher stall TC,
But that will hardly put a dent in the 1-2 shift problem, and it
won't begin to touch the passing gear situation.

Now, if you have 165 psi, that's a whole different story...
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What information is needed to calculate cylinder pressure?
 
rumblefish360 said:
Thanks for answering AJ’s question. The above I knew.
Why did I ask AJ the question?
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1 yeah yeah i forgot you guys and the banter bs
2 you think its all a bunch of bs
3 ill bow out doesnt really matter
enjoy rumble
 
RustyRatRod said:
I'm going to put a Tremec T5 in Vixen soon. Along with a custom Ford 9" with 4.11 gears.
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I’ve been looking at the TKX, the new dart has 3.23s right now but I think it will get 3.91s. I also think I’m going to redo the motor… right now it’s just feeling lonely in the new shop.

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496 polara said:
3.23 is a great all around gear. 3.55 if you do more around town and less highway.
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YMMV but 3.55's for me was too much gear without an overdrive if you like to drive on freeways unless you're running like 31" tall tires. 3.55's, 27" tires, and a .69 OD of a 42RH was about perfect on my old M body. my duster has an A833OD (.73OD), 3.23's and 25.75" tall tires (215/70R14) and it's ok at 70mph, but I honestly think it would be more comfortable with a 3.08ish rear ratio or going to taller tires.....
 
We are all spoiled by the overdrive automatic transmission. In the old days, (granted, freeway speeds aren't what they are now) 3000-3500 rpm at freeway speed was common. Engines also were worn out in 60k miles.. example: 55 chevy 265, with a powerglide, came with 3.55. Three speed stick was a 3.70. Three speed stick with electric overdrive came with a 4.11. Ford gearing was similar. With the horsepower levels of the time , gearing was necessary to provide any kind of performance.
I commuted to work for years with a 440 roadrunner with a 4.10 dana. 3700rpm at 70mph was common. I wouldnt think of doing that today. I've got three vehicles that I commute from CA to AZ with, one is at 2500 at 70, one is 2100, and the one with the double overdrive is at around 1700.
 
yeah, charger 1.0 was a Toxic Orange 2011 R/T that has the A580 behind a 5.7 hemi, IIRC the stock gear ratio was 2.65:1...with the OEM 28" tall tires, it hit 2000 RPM at like 74 MPH. keep the cruise at 69-70, it would get 30-31mpg on the highway actual calculated. I got t-boned and that car was totaled in 2019. I replaced it with another toxic orange 2011 R/T, charger 2.0 is an R/T road and track, which came with a 3.06 rear. it's turning 2k by around 65 mph, and is around 2200 at 70. that difference is enough that the best calculated mileage I've ever gotten out of it was about 26 mpg. honestly, acceleration between the two ratios felt about the same, granted there was about a 3 month window between driving the 2, never back to back or did a trial side by side
 
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