Benefits of a higher first gear ratio transmission
#1167544
01/29/12 12:50 AM
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ramman5600
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Looking for real world experience with using a trans that has a higer ratio than the stock 727's 2.45? For example the 904 has a slightly higher 2.74 and some of the GM stuff has a 3.06 or the new TCI 6x speed that has a 2.97. FYI - running 3.73 gears, 28" tire, 3800Lb car. Thanks -C
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Re: Benefits of a higher first gear ratio transmission
[Re: OrangeProwler]
#1167547
01/29/12 11:54 AM
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ramman5600
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Quote:
I was told about two tenths in the 1/4 mile. The later 904s I think starting in the very late 70s maybe 1980 started using the lower gears in the transmission. I had a 90 Dakota with the small 3.9 and A500 and that's low first gear got me off the line good especially with 3.55 gears.
So if I had a 727 with a 2.45 first vs another trans option with a 3.09 the second one would definitely have a significant advantage and definitely feel the difference - right? -C
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Re: Benefits of a higher first gear ratio transmission
[Re: ramman5600]
#1167548
01/29/12 04:40 PM
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Pentastar440
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The advantage of having a lower (higher numerically) 1st gear , would be a heavy car with a high geared rear end. A lighter car with a low rear end like 4:10 might not like a low 1st gear and may have excessive tire spin. That low 1st gear is to help a heavy car to get moving.
'65 Belvedere II - 446-Indy,727 transbrake,Dana 4.56
'38 Plymouth 4Dr - 408SixPack, A518, Dana60 4:10
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Re: Benefits of a higher first gear ratio transmission
[Re: Pentastar440]
#1167549
01/29/12 10:01 PM
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Quote:
The advantage of having a lower (higher numerically) 1st gear , would be a heavy car with a high geared rear end. A lighter car with a low rear end like 4:10 might not like a low 1st gear and may have excessive tire spin. That low 1st gear is to help a heavy car to get moving.
So If I were to say have a 67 Belvedere wagon it would probably be a good thing - right
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Re: Benefits of a higher first gear ratio transmission
[Re: Dodgem]
#1167552
01/30/12 04:16 PM
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Quote:
I installed a 274 ist 1.55 second gear set in my 727 (the gear set changes first and second) gained a tenth in the quarter aint cheap. stock gears are 2.45 1st and 1.45 second! definately a boost for heavy cars.
If you swap the 727 for a 277 geared 904 you can gain about 2 10ths.
Would it make a noticeable difference in a mostly street driven car? I see quite a few reply's about the gains in track time. I am actually considering a tranny that has a 3.06 first, 1.65 second, 1.0 third and a .7 O/D
Thanks Chad
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Re: Benefits of a higher first gear ratio transmission
[Re: ramman5600]
#1167553
01/30/12 04:46 PM
01/30/12 04:46 PM
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Rapid340
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Chad, I think you will find the ratios in the OD too far apart for a performance car. Try finding an early trans with a 3.09 1st gear and a 1:1 4th.
1971 Factory Appearing Duster 340 11.000 @ 122 mph
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Re: Benefits of a higher first gear ratio transmission
[Re: Rapid340]
#1167554
01/30/12 04:53 PM
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Quote:
Chad,
I think you will find the ratios in the OD too far apart for a performance car. Try finding an early trans with a 3.09 1st gear and a 1:1 4th.
Heavy wagon and looking for cruising at a comfortable rpm on the highway, so need more O/D than 1:1 as at 70 I would be turning 3300. The car is close to 4000lb and had 3.73 rear gears with 28" tall tires.
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Re: Benefits of a higher first gear ratio transmission
[Re: RapidRobert]
#1167557
01/31/12 12:10 AM
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Quote:
Quote:
Chad,
I think you will find the ratios in the OD too far apart for a performance car.
it's way way off, too wide a spread between the 2 particular gears. it was not right even in a DD grocery getter. Alot of torque at your disposal would help cover the hole a bit but for a serious effort I'd suggest a diff route
Are there any calculators out there that could show the max speed in each gear with particular ratios with different rear gears?
-Chad
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Re: Benefits of a higher first gear ratio transmission
[Re: Dodgem]
#1167559
01/31/12 12:45 AM
01/31/12 12:45 AM
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Seems like a lot of work to get 1 mile to the gallon better fuel mileage on the highway??
What calculation are you using? The o/d will drop rpm with 3.73 rear gear and 28" tire as follows
stock 1:1 = 3133 RPM .78 = 2433 RPM .70 = 2193 RPM
Is that accurate that 700-900 rpm drop would only be 1 MPG?
-C
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Re: Benefits of a higher first gear ratio transmission
[Re: Kern Dog]
#1167561
01/31/12 01:14 AM
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Quote:
Its late and Dodgem likes his beer. The gains would certainly be better than 1 mpg.
I would guess closer to 5-7mpg on the highway. Just based on different cars I have had with various rear gears. I am looking for MPG and also less winding of the engine at cruising speed and less wear over time.
-C
Just can't decide which way to go with my trans decision. Keisler GM O/D or a built 727. I could possibly go the 904 route and get a little better 1st gear ratio, but not sure if they are as tough as the 727. Too many decisions.
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