Gear Ratio Selection
Le Mans Master
Joined: Oct 2007
Posts: 7,453
Likes: 976
From: RI, Now Franklin/Nashville TN
My current 355 L-82 with AFR heads, Howards roller cam, and 10.2:1 compression with 3.70 gears and the 4 speed is built for maximum torque from 2,000-4,500 RPM. In 4th gear 1:1 ratio my engine easily pulls effortlessly from below 2,000 RPM in top gear with no downshift required. If the engine is setup for low end grunt especially any V8, 3.36 gears or even lower would be no problem for my engine and its RPM range, particularly with a 4 speed manual.
I had new a 88 5.0 LX Mustang 5 speed with 2.73 gears and a buddy had the same exact car with I believe 3.23/3.42's and to be honest not a ton of difference in acceleration...noticeable but not like I had a 5.0 V8 and he had a 5.8 Ford V8real feel difference....
I had new a 88 5.0 LX Mustang 5 speed with 2.73 gears and a buddy had the same exact car with I believe 3.23/3.42's and to be honest not a ton of difference in acceleration...noticeable but not like I had a 5.0 V8 and he had a 5.8 Ford V8real feel difference....
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
There is nothing wrong with cruising at 3000 rpms at 70 mph.... These cars have been doing it for 50-60 years and hundreds of thousands of miles....and they still do it... Sure you can get better gas mileage and reduce wear and tear with OD and cruising at 2000 rpms but.... is it REALLY necessary?? That depends on how much you drive I guess.......$5k for an OD trans buys a LOT of gas.....
My car has somehow managed to travel 169k miles in its lifetime with no overdrive..... I have 3.36 gears and I have driven it cross country twice in the last 3 years, running 3000-3100 (70-75) the whole time....
I agree that OD is nice but...its not a necessity, nor is having to cruise highways at 2000 rpms... The public today is just spoiled by new cars and 1500 rpm cruise....
My car has somehow managed to travel 169k miles in its lifetime with no overdrive..... I have 3.36 gears and I have driven it cross country twice in the last 3 years, running 3000-3100 (70-75) the whole time....
I agree that OD is nice but...its not a necessity, nor is having to cruise highways at 2000 rpms... The public today is just spoiled by new cars and 1500 rpm cruise....
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
The ideal cruise rpm depends on the overall build of the engine. The cam is the most important determiner in cruise rpm. An LT1 has a cam that is not going to be very happy at very low rpm.
Mike
Mike
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
There is nothing wrong with cruising at 3000 rpms at 70 mph.... These cars have been doing it for 50-60 years and hundreds of thousands of miles....and they still do it... Sure you can get better gas mileage and reduce wear and tear with OD and cruising at 2000 rpms but.... is it REALLY necessary?? That depends on how much you drive I guess.......$5k for an OD trans buys a LOT of gas.....
My car has somehow managed to travel 169k miles in its lifetime with no overdrive..... I have 3.36 gears and I have driven it cross country twice in the last 3 years, running 3000-3100 (70-75) the whole time....
I agree that OD is nice but...its not a necessity, nor is having to cruise highways at 2000 rpms... The public today is just spoiled by new cars and 1500 rpm cruise....
My car has somehow managed to travel 169k miles in its lifetime with no overdrive..... I have 3.36 gears and I have driven it cross country twice in the last 3 years, running 3000-3100 (70-75) the whole time....
I agree that OD is nice but...its not a necessity, nor is having to cruise highways at 2000 rpms... The public today is just spoiled by new cars and 1500 rpm cruise....
If you have ever done any boating with a Mercruiser V8 like a 260 Mercruiser, you would know cruise speed for these engines are 3500 to 3800 RPM. They are just a mild 350 sbc. They last for years and hundreds of hours doing this.Mike
Last edited by v2racing; May 11, 2018 at 01:56 PM.
Burning Brakes
Joined: Apr 2013
Posts: 1,072
Likes: 61
From: Saint clair shores Michigan
Yeah I have a 383S. But I don't have the engine specs. The guy who I bought it from couldn't find them. He really didn't care. He was a rich guy and just wanted to get rid of the car.
John.
John.
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
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Racer
Joined: Dec 2017
Posts: 355
Likes: 46
From: Chicago Suburbs Illinois
It's funny, because when I bought the car I didn't know it had the 2.73 in it. When I got it home and found out, I was actually disappointed, thinking it had a "grandpa" rear end in it (no offense to grandpas...you know what I mean). Maybe the 500 lb ft of torque will overcome it! (I just bought the car over the winter and have barely driven it.) Right now the tank is down, hence the picture.
Anyone have any experience with a 2.73? I suppose the good thing is that the engine has not worked that hard over its 72,000 miles.
Last edited by ZRXGreen; May 11, 2018 at 10:04 PM.
Racer
Joined: Dec 2017
Posts: 355
Likes: 46
From: Chicago Suburbs Illinois
Burning Brakes
Joined: Apr 2007
Posts: 1,039
Likes: 62
From: Kona Hawaii
What about the T-56 Magnum 6 speed..Pricey for sure but you could keep those 4.11s and have double overdrive with a killer launch....Looks like they have two different ratios..gonna cost you money either way but at least you'll have overdrive with the new trans..Just depends what you want outta your Vette. I installed a Richmond 6 spd trans 10 years ago,never regretted it! I had the opposite problem a 3.08 rear gear,car was a total dog and still screamed over 60mph! Trans changed the whole driving experience ,money well spent..Would do it all over again! Headers not so much ! thats another story...Alohas!
Racer
Joined: Jul 2015
Posts: 396
Likes: 101
From: Lehigh Valley Pennsylvania
I went with the autogear transmission ( a Muncie Knockoff) They have several gear ratios you can choose from. I have about 3 months left to finish the car, so I don't know how it will run. I chose a 3 to 1 first gear and changed the rear ratio to 3.08. This gives me about the same first gear ratio as an M21 with 4.11s, and I still have the 1 to 1 in fourth. The disadvantage is the spacing between gears is much greater.
I have a 454 that I am building for low end and cruising so in hindsight I think I would have been better off with the 2.56 first gear they offer. If I would have known about the 2.73s I would have gone with them.
You can modify your Muncie box by changing the gears and the price should be in the 500 to 700 dollar range. Another option that is probably much cheaper than some of the other considered.
I have a 454 that I am building for low end and cruising so in hindsight I think I would have been better off with the 2.56 first gear they offer. If I would have known about the 2.73s I would have gone with them.
You can modify your Muncie box by changing the gears and the price should be in the 500 to 700 dollar range. Another option that is probably much cheaper than some of the other considered.
Last edited by 2mnyvets; May 13, 2018 at 01:19 PM.
Race Director
Joined: Mar 2016
Posts: 14,402
Likes: 8,209
From: Napa Valley California
This is the first I've heard of a 2.73 rear end gear offered for the C3 Corvettes.
Was it something that was available as a special order?
Is there anyone out there with the 2.73's with a big block and TH-400?
If so, how is the combo working for you regarding all around driving and cruising highway speeds?
Was it something that was available as a special order?
Is there anyone out there with the 2.73's with a big block and TH-400?
If so, how is the combo working for you regarding all around driving and cruising highway speeds?
Le Mans Master
Joined: May 2000
Posts: 8,729
Likes: 1,508
From: Redmond WA
Not the Corvette, but if you got the TH400 and the low-hp 427 in the Impala (the 335hp, single-exhaust setup) you got 2.56 gears.
2.56!
BTW, I think the carrier break on a 12-bolt is 3.73 so that a 3.73 and 4.11 use the same carrier, but I can't swear to it. If this were me, though, I'd stick an overdrive trans in it. You'd wind up with an even steeper first gear and yet you'd net out to a 2.71 on the highway in .67 overdrive. Perfect!
2.56!
BTW, I think the carrier break on a 12-bolt is 3.73 so that a 3.73 and 4.11 use the same carrier, but I can't swear to it. If this were me, though, I'd stick an overdrive trans in it. You'd wind up with an even steeper first gear and yet you'd net out to a 2.71 on the highway in .67 overdrive. Perfect!
Last edited by davepl; May 14, 2018 at 11:51 AM.