Engine and transmission questions
Thread Starter
Instructor
Joined: Mar 2020
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From: Virginia
Engine and transmission questions
I’m looking to buy a c3 corvette (still). I just found a 79’ and the owner put this as the description,“Built 400 sb, close ratio muncie 4 speed, 370 gears. Motor and clutch has 7000 miles, new brakes. Runs and drives great. Alot of fun! T-tops”
Can anyone explain to me what this means in terms of performance or just in general? I don’t have any idea what a close ratio Muncie is, I tried to look it up but not sure what I read. I want a strong/fast C3 but I also want to be able to zip down the highway without the Rpms screaming. Thanks in advance.
Can anyone explain to me what this means in terms of performance or just in general? I don’t have any idea what a close ratio Muncie is, I tried to look it up but not sure what I read. I want a strong/fast C3 but I also want to be able to zip down the highway without the Rpms screaming. Thanks in advance.
Le Mans Master
Joined: May 2002
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From: Lebanon Township New Jersey
The close ratio 4 speed trans has a 2.20 to 1 first gear ratio and a 1 to 1 4th gear. So, with a 3.70 to 1 rear your rpms on the highway will probably be higher than what you're looking for.
Thread Starter
Instructor
Joined: Mar 2020
Posts: 167
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From: Virginia
Is there a way to (online calculator) find out what the rpms would be at various speeds? I had a 6 cylinder Jeep that I changed the gear ratio from 3.73 to 4.10 and I was okay with the rpms at highway.
Last edited by Punkchachi; Aug 7, 2020 at 09:21 AM.
Dr. Detroit
Joined: Mar 2012
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From: New Braunfels Texas
There are several online calcs for determining RPM/MPH....google one up.
I get weary of owners that say "built"....that is pretty Bubba......but the engine having 7000 miles on it means that it is probably in good running condition.
Jebby
Last edited by Jebbysan; Aug 7, 2020 at 09:35 AM.
Had a 1976 L-82, 4-sp
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
It was ok back in the day to scream down the highway at 3500 rpm. Why would anyone worry about it today? These cars are not fuel misers but o/d transmissions can be installed to reduce rpm/gas consumption. If highway driving only accounts for say 10% of use, an o/d transmission would never pay for itself in fuel savings.
Thread Starter
Instructor
Joined: Mar 2020
Posts: 167
Likes: 42
From: Virginia
It was ok back in the day to scream down the highway at 3500 rpm. Why would anyone worry about it today? These cars are not fuel misers but o/d transmissions can be installed to reduce rpm/gas consumption. If highway driving only accounts for say 10% of use, an o/d transmission would never pay for itself in fuel savings.
Racer
Joined: Jan 2020
Posts: 277
Likes: 69
From: Reno, NV
Hi,
There are lots of calculators, and just found this one https://www.strangeengineering.net/g...io-calculator/
Put in your 1:1 4th gear ratio, 3.7 rear ratio and used a 27" tire diameter, and found you will be doing 65 at 3000 rpms. You'll want an accurate measurement of your particular tire.
Did this myself with my project, and had a rear end with a 3.73 and th 400 also with a 1:1 final drive ratio. Wasn't going to work for me on the highways of northern ca where the typical speeds are ~75. So swapped the 3:73 for a 3:36 to make it more cruise-able. BTW.. I will be doing 71 mpg with my 3.36 gear at 3K rpms on the highway.
Good luck.
Cheers,
Brian
There are lots of calculators, and just found this one https://www.strangeengineering.net/g...io-calculator/
Put in your 1:1 4th gear ratio, 3.7 rear ratio and used a 27" tire diameter, and found you will be doing 65 at 3000 rpms. You'll want an accurate measurement of your particular tire.
Did this myself with my project, and had a rear end with a 3.73 and th 400 also with a 1:1 final drive ratio. Wasn't going to work for me on the highways of northern ca where the typical speeds are ~75. So swapped the 3:73 for a 3:36 to make it more cruise-able. BTW.. I will be doing 71 mpg with my 3.36 gear at 3K rpms on the highway.
Good luck.
Cheers,
Brian
Thread Starter
Instructor
Joined: Mar 2020
Posts: 167
Likes: 42
From: Virginia
Hi,
There are lots of calculators, and just found this one https://www.strangeengineering.net/g...io-calculator/
Put in your 1:1 4th gear ratio, 3.7 rear ratio and used a 27" tire diameter, and found you will be doing 65 at 3000 rpms. You'll want an accurate measurement of your particular tire.
Did this myself with my project, and had a rear end with a 3.73 and th 400 also with a 1:1 final drive ratio. Wasn't going to work for me on the highways of northern ca where the typical speeds are ~75. So swapped the 3:73 for a 3:36 to make it more cruise-able. BTW.. I will be doing 71 mpg with my 3.36 gear at 3K rpms on the highway.
Good luck.
Cheers,
Brian
There are lots of calculators, and just found this one https://www.strangeengineering.net/g...io-calculator/
Put in your 1:1 4th gear ratio, 3.7 rear ratio and used a 27" tire diameter, and found you will be doing 65 at 3000 rpms. You'll want an accurate measurement of your particular tire.
Did this myself with my project, and had a rear end with a 3.73 and th 400 also with a 1:1 final drive ratio. Wasn't going to work for me on the highways of northern ca where the typical speeds are ~75. So swapped the 3:73 for a 3:36 to make it more cruise-able. BTW.. I will be doing 71 mpg with my 3.36 gear at 3K rpms on the highway.
Good luck.
Cheers,
Brian
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I had a M20 and m21...first gear makes a difference off the line, but the 400 small block will have similar torque as a 383 so the m21 might be fine. I personally would be fine with the m20. As for the highway your tach and speedo will be almost matched at 80 both pointing straight up...it also brings the heat of the engine up...if you get it for a song, then save for a 5 speed....it will feel like a modern car on the highway
Melting Slicks
Joined: Sep 2004
Posts: 3,227
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From: Northeast
I have a 78 with 3.70 rear and 255/60 tires. At 70 mph @3200 rpm.
FWIW, in 79 a Borg Warner Transmission was installed not a Muncie. 1st gear in a close ratio BW is 2.43. So he swapped it perhaps when he installed another engine. You will find out more about what he did with the engine and where it came from. Good luck.
FWIW, in 79 a Borg Warner Transmission was installed not a Muncie. 1st gear in a close ratio BW is 2.43. So he swapped it perhaps when he installed another engine. You will find out more about what he did with the engine and where it came from. Good luck.
Last edited by BKarol; Aug 7, 2020 at 06:05 PM.
Team Owner
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St. Jude Donor '05
400s make tons of torque, good choice in my opinion
3k on the highway is nothing, had the same gear in a 70 Z28 never felt for a second like it was too high. Not worth a gear change in my opion to go a few mph faster.
3k on the highway is nothing, had the same gear in a 70 Z28 never felt for a second like it was too high. Not worth a gear change in my opion to go a few mph faster.
Had a 1976 L-82, 4-sp
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Just got back from a rare highway cruise. I have a 4.11 and a B-W close ratio and 27" diameter tires. At 70 mph the tach read about 4000 rpm. Talk about screaming, lol. I don't think the primary main jets were even cut in! Anyway, if 4000 rpm is screaming, I love it!!!
Racer
Joined: Jan 2020
Posts: 277
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From: Reno, NV
Interesting conversation, but really depends on what you are looking for in a car. Someone with 10.7 to 1 compression and AFR heads, who likes to hear it scream at 4,000 on the highway, is looking for something different than a person with a milder street cruiser that will rarely see north of 5000 RPM, much less a strip, and wants a comfortable ride on long Sunday trips which includes lots of freeway. No right, no wrong. In fact, both are very cool at different times, which is why many, many, folks on this forum are touting overdrives with manual or automatic transmissions. And spending big $$ to do it.
For me and my 1:1 output in high gear, I knew the 3.36 was going to be softer than a 3.73 in behavior, but then thought about what I would be doing most in my car, which is cruising at high speeds over longer distances.
Cheers,
Brian
For me and my 1:1 output in high gear, I knew the 3.36 was going to be softer than a 3.73 in behavior, but then thought about what I would be doing most in my car, which is cruising at high speeds over longer distances.
Cheers,
Brian
Had a 1976 L-82, 4-sp
Joined: Mar 2011
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
To the OP, the car you speak of was not born with a 400 cid or a Muncie. So a previous owner has swapped out the motor and tranny if the said car's desciption is accurate. Anyway, it does sound like a nice performer. If high performance over the stock slouch is what your after, that maybe the car for you.