mid year overdrive
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Joined: Nov 2006
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From: Western mass
mid year overdrive
Help, I have a 63 and I was thinking about going with a over -drive transmission the car is very nice (matching numbers 250 hp 4 gear 308 rear ) But I would like to drive it not just look at it. Can I do this with out hacking up the car. Any thoughts ? Standard or auto ? How do 308s work on the open road ?
Race Director
Joined: Nov 2000
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From: Beverly Hills (Pine Ridge) Florida
Help, I have a 63 and I was thinking about going with a over -drive transmission the car is very nice (matching numbers 250 hp 4 gear 308 rear ) But I would like to drive it not just look at it. Can I do this with out hacking up the car. Any thoughts ? Standard or auto ? How do 308s work on the open road ?
I have an OD trans with a 3.55 rear gear, but with my smaller dia. rear tires it is effectively a 3.70 rear. OD is .73 for this particular trans, and drops the cruise RPM down from 3400 @ 75 MPH to 2500 RPM. Your rear gear would have the engine turning over @ about 2800 @ 75 MPH. But if you put in the same OD gear/trans, it would drop it to 2066 @ 75.
Depends on how the engine is setup, and what RPM it is most efficient. I like the lower noise level, and less wear on the engine, but with my particular engine, it is not any more fuel efficient (due to the intake, cam, etc. I am running). However, wmf62 with his FI 62 is running the same OD trans with a 3.36 rear gear, and is seeing a significant increase in fuel mileage.
Plasticman
Last edited by Plasticman; Apr 2, 2007 at 07:57 PM.
Melting Slicks
Joined: Feb 2006
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From: Park City to SoCal - according to the map it's all down hill. No bad days in Indian Wells, California
Unless you are planning on tons of highway driving, the 3;08 is already a great cruise rear end.What RPM's are you turning at 60 MPH? Just under 2K would be my dream.
Safety Car
Joined: Feb 2006
Posts: 4,367
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From: FL
I love spreadsheets, they let you do so much so quickly.
If you talk simply gas savings, here is what I did.
Assumptions:
3.08 rear gets 15 mpg ave.
OD gets 22 mpg ave.
Gas prices $2.50
For the 5000 miles many do per year, the 3.08 uses 312.5 gallons and $781.25. The OD would use 227.27 gallons and 4568.18, for a savings of $213.07. At this rate, you need 17 years to save the amount for the swap.
To save the $3500 swap price, you have to drive 83,000 miles for a savings of $3536.93.
Of course, if gas gets higher, you can reach that sooner. For example, if it were $3 per gallon as some have spent, then 5000 miles saves $255.68. At 69,000 miles, you have saved $3528.41 so you are ahead on the swap.
Of course, the real savings is in engine wear, but since a small block is good for 100-150,000 miles easily, and most only drive these cars around 5000 per year, it is going to be 20 years or so until you realize a savings.
If you talk simply gas savings, here is what I did.
Assumptions:
3.08 rear gets 15 mpg ave.
OD gets 22 mpg ave.
Gas prices $2.50
For the 5000 miles many do per year, the 3.08 uses 312.5 gallons and $781.25. The OD would use 227.27 gallons and 4568.18, for a savings of $213.07. At this rate, you need 17 years to save the amount for the swap.
To save the $3500 swap price, you have to drive 83,000 miles for a savings of $3536.93.
Of course, if gas gets higher, you can reach that sooner. For example, if it were $3 per gallon as some have spent, then 5000 miles saves $255.68. At 69,000 miles, you have saved $3528.41 so you are ahead on the swap.
Of course, the real savings is in engine wear, but since a small block is good for 100-150,000 miles easily, and most only drive these cars around 5000 per year, it is going to be 20 years or so until you realize a savings.
Pro
Joined: Aug 2003
Posts: 635
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From: cincinnati oh
agreed prob not worth it
i have the 308 as well and know kinda what you mean. i would love to have another gear to slip into and just cruise at 70 or 75 at around 2k or 2500 rpms. but really not worth it. lots of jack and you are messing with your car. i know the others with higher rear ends are thinking you are nuts, but if everyone is going 75 on the freeway, you gotta keep up, right? or blend in. and for a long haul it gets noisy. specially if you have side pipes or chambered exhaust. so, i would not do it. just accept the old cars for what they are. ie: not really designed for more than about a 4 hour drive. just my .02 worth.
Safety Car
Joined: Feb 2006
Posts: 4,367
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From: FL
What is funny about this is that these cars were designed when 70 mph was a norm on many highways, and people used to boost about doing 800 miles a day on a trip. So they weren't poking along at 50 guys.
We have just become accustomed to long stroke 4 bangers with overdrives pushing our SUVs at 70 with 25 mpg and no noise. If you look, thugh, many of them are really revving not too far off. Ours is running about 2200 at 50 and about 3500 at just over 70. But it is so quiet.....
We have just become accustomed to long stroke 4 bangers with overdrives pushing our SUVs at 70 with 25 mpg and no noise. If you look, thugh, many of them are really revving not too far off. Ours is running about 2200 at 50 and about 3500 at just over 70. But it is so quiet.....
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Race Director
Joined: Nov 2000
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From: Beverly Hills (Pine Ridge) Florida
And yes, we both could of afforded a new 5 speed (Kiesler, etc.), but part of our "fun" is to modify and "hot rod" with some ingenuity (not just purchase a "kit" and install it - although at times that is the smartest way of doing things
).But I agree that for anyone running a 3.08 rear gear, why bother?
Plasticman
Last edited by Plasticman; Apr 4, 2007 at 09:35 AM.
Drifting
Joined: Oct 2002
Posts: 1,818
Likes: 13
From: ar
Overdrive is so much more than just creating a higher final drive, it increases the fun factor plus performance of a vette in many more ways than 1. First, most OD trans have a lower first gear so your launch is much more fun not to mention easier on clutches and easier to drive. Also with OD you can run lower rear end gears which makes the car feel stronger and faster in every gear plus cruise comfortably.
With todays technology that is available and if you want to enjoy driving your old vette upgrade it and make it more fun to drive. If it was all about money the Corvette hobby would not exist.
With todays technology that is available and if you want to enjoy driving your old vette upgrade it and make it more fun to drive. If it was all about money the Corvette hobby would not exist.
Le Mans Master
Joined: Nov 2000
Posts: 7,246
Likes: 21
From: Going too fast over the hill. Iowa
IMO 3.08s work fine on the highway, 19-20 mpg at 70-80mph.
IMO they also work fine in the city if you have a Muncie gearset with a 2.5:1 first gear, which makes the trans feel like a 5 speed that is missing fourth gear. The first three gears are clustered low and fourth gear is a jump to silence and low revs.
IMO they also work fine in the city if you have a Muncie gearset with a 2.5:1 first gear, which makes the trans feel like a 5 speed that is missing fourth gear. The first three gears are clustered low and fourth gear is a jump to silence and low revs.
Melting Slicks
Joined: May 2004
Posts: 2,510
Likes: 531
From: Willowbrook IL
St. Jude Donor '13-'14-'15-'16
Overdrive is so much more than just creating a higher final drive, it increases the fun factor plus performance of a vette in many more ways than 1. First, most OD trans have a lower first gear so your launch is much more fun not to mention easier on clutches and easier to drive. Also with OD you can run lower rear end gears which makes the car feel stronger and faster in every gear plus cruise comfortably.
With todays technology that is available and if you want to enjoy driving your old vette upgrade it and make it more fun to drive. If it was all about money the Corvette hobby would not exist.
With todays technology that is available and if you want to enjoy driving your old vette upgrade it and make it more fun to drive. If it was all about money the Corvette hobby would not exist.
Drifting
Joined: Oct 2002
Posts: 1,818
Likes: 13
From: ar
Magic I tend to agree, I ran a 2.54 first and 3.08 for years cross country and I think it is one of the best combos if you can't do overdrive. But my T5 cost me about 600.00 start to finish and now with a 2.95 first gear and a 3.36 the car is just more rsponsive and in all 4 gears and will cruise at 2000 RPM in OD.
IMHO Jeff
IMHO Jeff
Race Director
Joined: Jun 2006
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From: Inverness FL
St. Jude Donor '07
to quote Plasticman:
"Note that the gears in the MY6 trans are: 3.09 1st, 1.68 2nd, 1:1 3rd, and .73 4th. Also note that this is practically identical to the gearing in the 700R4 GM automatic trans.
With the 3.55 rear end, 3K RPM = 20 mph 1st, 39 = 2nd, 67 = 3rd, & 90 mph in 4th. At 6K RPM 40 = 1st, 79 = 2nd, 135 = 3rd, & 180 mph in 4th. Cruise at 70 mph = 2333 RPM.
With the 4.11 rear end, 3K RPM = 17 mph = 1st, 34 = 2nd, 58 = 3rd, & 78 mph in 4th. At 6K RPM 35 = 1st, 67 = 2nd, 115 = 3rd, & 158 mph in 4th. Cruise at 70 mph = 2702 RPM."
i have a 3.36, so i run in the same rpm range as Jeff, just don't have the extra gear.
Bill
"Note that the gears in the MY6 trans are: 3.09 1st, 1.68 2nd, 1:1 3rd, and .73 4th. Also note that this is practically identical to the gearing in the 700R4 GM automatic trans.
With the 3.55 rear end, 3K RPM = 20 mph 1st, 39 = 2nd, 67 = 3rd, & 90 mph in 4th. At 6K RPM 40 = 1st, 79 = 2nd, 135 = 3rd, & 180 mph in 4th. Cruise at 70 mph = 2333 RPM.
With the 4.11 rear end, 3K RPM = 17 mph = 1st, 34 = 2nd, 58 = 3rd, & 78 mph in 4th. At 6K RPM 35 = 1st, 67 = 2nd, 115 = 3rd, & 158 mph in 4th. Cruise at 70 mph = 2702 RPM."
i have a 3.36, so i run in the same rpm range as Jeff, just don't have the extra gear.
Bill
Drifting
Joined: Oct 2002
Posts: 1,818
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From: ar
Hey Vet2002, you noticed. I put a 100 amp single wire alternator in 4 or 5 years ago and I guess the gauge is designed for the old regulator system, so I have never bothered to change it. The more things that are running the farther over the needle moves to the right.
WMF, I ran a MY6 for a few years, it is a very good alternative and bolts right in. Just a little lacking in gear selection when doing spirited driving in the mountains or autocrossing.
But like you said great launch and good crusing RPMs and it fits.
Jeff
WMF, I ran a MY6 for a few years, it is a very good alternative and bolts right in. Just a little lacking in gear selection when doing spirited driving in the mountains or autocrossing.
But like you said great launch and good crusing RPMs and it fits.
Jeff
Safety Car
Joined: Nov 2001
Posts: 4,424
Likes: 619
From: northern CA
The gear reduction factors between 1st gear (2.56 and 3.08's) and 2nd gear (1.91 and 4.11's) in an early M-20 trans comes out pretty close - 7.85 vs. 7.88 .. With a 4:11 rear in my car starting out in 2nd gear was no problem - fairly simulating a first gear start had the car been equipped with a 3.08 diff. .. The 'test' was to get a feel of what using a different rear gear set for highway cruising might be like.
Going with 3:08's seemed a good way to go. A 3.08 rear diff carrier assembly was acquired to replace the 4:11's in my car when the time comes to do some long distance highway travelling. The higher engine rev's and noise make me rummy after about 200 miles with the 4:11's! ..
The MY6 Muncie conversion sounds intriguing - a true 'Hot Rod' install IMO, too. .. For $500 bucks, or less? .. Nice job Plasticman and wmf62 ..
..
The 5-speed conversions seem the hot ticket these days. Lots of guys going that route, now. What's a guy to do?
Options, options! ..
..
Going with 3:08's seemed a good way to go. A 3.08 rear diff carrier assembly was acquired to replace the 4:11's in my car when the time comes to do some long distance highway travelling. The higher engine rev's and noise make me rummy after about 200 miles with the 4:11's! ..
The MY6 Muncie conversion sounds intriguing - a true 'Hot Rod' install IMO, too. .. For $500 bucks, or less? .. Nice job Plasticman and wmf62 ..
.. The 5-speed conversions seem the hot ticket these days. Lots of guys going that route, now. What's a guy to do?
Options, options! ..
..
Safety Car
Joined: Nov 2001
Posts: 4,424
Likes: 619
From: northern CA
I missed it earlier.
Sounds like another excellent conversion! .. Did you post a thread on the T5 install in your car? .. Archives? .. It would be great to read info on how your experience went. The 'bolt in' part sounds really GOOD ..
..
Drifting
Joined: Oct 2002
Posts: 1,818
Likes: 13
From: ar
I did a little write up in this section but don't know how to find it. I think the title was T5 in a Midyear, maybe you can find it that way. I have had a few other guys want to see it. I did it about a year ago if that helps. I am better with nuts and bolts than computers.
Jeff
Jeff