Your Transmission

[Lugnut]

I have the "pig" C6 transmission...nothing will kill it! Lee, you don't need overdrive, spend some of your hard earned bucks and get a quick change.

Lugnut

[Lee in KC]

I'd love to have a quick-change, Lugs, just one little problem...

[Bob Lemke]

70-75 mph. I may not be remembering the rpm range accurately... could be a little lower, but certainly in the mid-2000s. Anyone know the formula to convert rpm to mph?

Transmission ratio in D = 1:1
Rear end ratio = 3.31
Tire diameter = 31"

Here is a link for you.
http://www.precisionsite.com/auto-x/tools/


RPM First Gear
500 13.9
1000 27.9
1500 41.8
2000 55.7
2500 69.7
3000 83.6
3500 97.5
4000 111.4
4500 125.4
5000 139.3
5500 153.2
6000 167.2
6500 181.1
7000 195.0

[Bob Lemke]

With your rear tires and 3.31 ratio, this is your current TH350 speed in gears

RPM First Gear Second Gear Third Gear
200 2.2 3.7 5.6
400 4.4 7.3 11.1
600 6.6 11.0 16.7
800 8.8 14.7 22.3
1000 11.1 18.3 27.9
1200 13.3 22.0 33.4
1400 15.5 25.7 39.0
1600 17.7 29.3 44.6
1800 19.9 33.0 50.2
2000 22.1 36.7 55.7
2200 24.3 40.3 61.3
2400 26.5 44.0 66.9
2600 28.7 47.7 72.4
2800 31.0 51.3 78.0
3000 33.2 55.0 83.6
3200 35.4 58.7 89.2
3400 37.6 62.3 94.7
3600 39.8 66.0 100.3
3800 42.0 69.7 105.9
4000 44.2 73.3 111.4
4200 46.4 77.0 117.0
4400 48.6 80.7 122.6
4600 50.9 84.3 128.2
4800 53.1 88.0 133.7
5000 55.3 91.7 139.3
5200 57.5 95.3 144.9
5400 59.7 99.0 150.5
5600 61.9 102.7 156.0
5800 64.1 106.3 161.6
6000 66.3 110.0 167.2
6200 68.6 113.6 172.7
6400 70.8 117.3 178.3
6600 73.0 121.0 183.9
6800 75.2 124.6 189.5
7000 77.4 128.3 195.0

[Bob Lemke]

Lee, should you decide on a 700R4 with all else the same 3.31 and 31"


RPM First Gear Second Gear Third Gear Fourth Gear
200 1.8 3.4 5.6 8.0
400 3.6 6.9 11.1 15.9
600 5.5 10.3 16.7 23.9
800 7.3 13.8 22.3 31.8
1000 9.1 17.2 27.9 39.8
1200 10.9 20.6 33.4 47.8
1400 12.7 24.1 39.0 55.7
1600 14.6 27.5 44.6 63.7
1800 16.4 31.0 50.2 71.6
2000 18.2 34.4 55.7 79.6
2200 20.0 37.8 61.3 87.6
2400 21.9 41.3 66.9 95.5
2600 23.7 44.7 72.4 103.5
2800 25.5 48.2 78.0 111.4
3000 27.3 51.6 83.6 119.4
3200 29.1 55.0 89.2 127.4
3400 31.0 58.5 94.7 135.3
3600 32.8 61.9 100.3 143.3
3800 34.6 65.4 105.9 151.3
4000 36.4 68.8 111.4 159.2
4200 38.2 72.2 117.0 167.2
4400 40.1 75.7 122.6 175.1
4600 41.9 79.1 128.2 183.1
4800 43.7 82.6 133.7 191.1
5000 45.5 86.0 139.3 199.0
5200 47.3 89.4 144.9 207.0
5400 49.2 92.9 150.5 214.9
5600 51.0 96.3 156.0 222.9
5800 52.8 99.8 161.6 230.9
6000 54.6 103.2 167.2 238.8
6200 56.5 106.6 172.7 246.8
6400 58.3 110.1 178.3 254.7
6600 60.1 113.5 183.9 262.7
6800 61.9 117.0 189.5 270.7
7000 63.7 120.4 195.0 278.6



As you can see, 1800 rpm will give you 50 mph with your TH350 and 72 mph with the 700R4.

[Lee in KC]

Thanks for the link and the data, Bob. Very useful. I was sooo close to going with a 700R4 when I spec'ed the mounts for my Spirit frame but I was scared off by the cost... almost twice as much as the TH350 for the same HP. Penny wise, rpm foolish!

[Bob Lemke]

Dollars can be a deciding factor. I wouldn't have spent the money for the Tremec TKO 600 to replace the non overdrive Muncie 21 just for the OD. The engine build dictated the upgrade from a transmission rated at 350 lb/ft to one rated at 600 lb/ft.

[Big Bill]

Lee 31" tire - 3.31 rear gear - 1 to 1 trans - 2600 RPM = 72.472 MPH
TO find the Calculator look in tech pages under MATH/ interactive calculators

[Bob Lemke]

Big Bill, your 72.472 mph @ 2600 is real close to my 72.4 mph.

[Big Bill]

Yes Bob, what I was pointing out is the calculators are available in our tech section. Our web site offers a huge amount of information for any car builder. I know the thought pattern that most of us go through when trying to decide about going with a more expensive overdrive transmission because I went through it back in the mid 90s when I switched my T Touring from a 350 to a 700R4. It took me about a year to finally decide to do it, but once I experenced the difference all of my drivers are overdrive. In fact the only non OD I have owned since is my current Bucket and it spends most of its life on a trailer. It wasn't built for long trips. If I had the coin I would like to build a new bucket with 5.3 and a six speed auto with the double OD out of a new Silverdo. I think it would be awesome. But since I am retired that probably won't happen.