Going to a 4speed manual setup in my car. Currently have mild 455 with TH400 good TSP 2800 stall 3.73 rear gear with 28" tire. Worked good but my desire to always have bench seat 4spd car with some good HP is going to happen over the next couple months. Sounds like a (rebuilt) M20 with 2.52 first gear is going in. I am curious to hear from other 4 speed guys what rear gear you like with this similar setup or what are you running for rear gear in your 4 speed car. My motors peak hp448 at 5100rpm and peak trq533 at 3700 rpm per dyno. mainly street car (cam 231/242, gross valve lift 501/527) Mike
If you have a 3.73 rear gear, you might want to consider the M21 with the 2.20 first gear. From the factory, if you had a rear gear that was numerically lower than 3.42, you got an M20. If it was 3.73 or numerically higher- 3.73, 3.90 etc, you got a 21. Conversely, if you put a 21 in front of a set of 3.08s, the car would be doggy in first gear. Then again, my girl has a 3.35 first gear in her Mustang with 3.55s. First gear is good for the first 15 feet. Ive seen alot of brand new M22's for sale on Ebay. For the extra coin, you can permanently remove your radio and just listen to the music from the trans.
Thanks Jason. There is a chance of me getting an M21 with an (Italian) M22 gear set in it that is pretty new (but i was trying to save a few buck for the new shotgun I want but thats a different story). What size tire to you have Jason? I am running 275/60/16 MT ET streets for now. Was picking a M20 or M21 an option that you checked off at the dealer? (My car is not a real GS by the way) I am thinking maybe put in 3.42's if I go with the M20? Mike
The shotgun is already under your hood. :bglasses: I run a G60 which as you know is equivalent to a 245/60-15. I cruise at around 3000-3200 rpm on the highway. Providing my factory tach is correct. The only thing you checked off at the dealer was for a 4 speed. The RPO was M20 regardless if the car came with a 20 or a 21. The decieding factor was the rear gear. 3.42, 3.64 cars got the 21, 3.08, 3.23 cars got the 20. Here's a short clip of the gear whine of an M22. The 55 in Two Lane Blacktop had a 22 in it also. http://www.youtube.com/watch?v=-IkJ7-jbNpM&feature=related
Cool Vid, I like this one too: http://www.youtube.com/watch?v=qV4PjerYj-c&feature=related Is a M22 first gear 2.20 as well?
A freind has an "even milder" build than yours. in a 455 olds. Not sure of the HP since he only wound it up to 4500rpm, but the torque came in at 510. He got the italian gears M22 from Autogear, and loves it. Its a very nice trans. Hes running the "wide" ratio gears, with a 3.08 12 bolt. 265/60/15. He used to have 3.73 as well. The car doesnt seem nearly as torquey as with the 3.73 (but that like comparing getting hit in the face by a green sledge hammer, or a blue one), both hurt, just you feel a lil differnt. The 3.08 are VERY pleasant to cruise with, and the performance aint bad either. 2400rpm on the highway. Its magical.
Yahooo! Go For It! :3gears: :laugh: I set mine up using an M-20 that I thought was getting a good deal on just to get the swap done and car complete and driving. I always planned to $pring for this tranny one day---------> http://www.m-22.com/m22/ which will really compliment my 4.11 rear gear :3gears: The 2.52 first in the M-20 is pretty short with the 4.11's and freeway action is a bit annoying, but, street / strip driving is a rip! Have fun.
i'm going back to 3;55's in mine.had them in years ago.wish i still had the 3;64 rearend!! would it be possible to send me some pics of your bench seat? i'm lookin for one,don't remember what mine looked like.:spank: thanks.
I have a 1965 M20 with 2.56 first gear and a 3.42 rear with 26.1 inch tire. I really like the overall driveablity and interstate cruising RPM is tolerable.
If it's going to see highway use, definitively go with a wide ratio or a 5 speed. Compute the overall first gear ratio: = first gear x rear gear Should be between 8-11 overall ratio. Too low and you are slipping the clutch to get the car moving. Too high and you are shifting into second after moving 10 feet! Above example with 2.56 first and 3.42 rear = 8.75 overall I have a Richmond 5 speed (not OD)in my Special: 3.26 first gear with 2.79 rear = 9.06 overall in first. 1:1 fifth gear is nice on the highway too. Shifter is about 2" further back from the stock one. There is a good article out there on selecting ratios. I'll try to locate it...
Thanks Walt. I really don't want a 5 speed. IMHO I think 4 speed is plenty fun for my car and what I want it for. Yes my main thing is to make usefull all 4 gears and not have too much rear gear for the first gear. I don't mind some revs on the highway. I think some folks worry too much with higher revs on the highway (IMHO) but do understand some want better fuel milage. I am not concerned about fuel milage in a 39yo car with a healthy 455 and my sometimes heavy foot.:Brow:
Try this...drive your car and 'pretend' it has a 4 speed! With your TH400's 2.48 first, and 3.73 rear, you have a 9.25 overall ratio... For that same ratio, A close ratio M-21 would be paired with a 4.20 rear. A wide ratio M20 would be paired with a 3.67 rear. See where your present combo does the 1-2 shift, then decide if you want it to be at a higher or lower mph. Adjust rear gear ratio to suit your preference.:TU:
The car i mentioned before, got the transmission, and had the 3.73 changed out for a 3.08 some time after. So wide ratio + 3.73 the first gear was still VERY unusable. My buddy almost never used it (just for parking the car). Traction in any gear wasnt there after 1/2 throttle. when he did use it, he had to shift at like 10km/h (i think thats 6mph). However with the 3.08 he can finally use 1st again, but the car has lost some of the "umph" it had before between shifts. I think to accomplish what youre looking for you need a compromise between the two. maybe a 3.08 with a close ratio M22 or a wide ratio M22 and a 3.42 would do the trick.
I run 2.73 behind the Super T10 geared with a 3.44 first gear; this gives a first gear final drive of 9.39. I run about 2000 RPM at 80 mph. I have a 118 cam, ported iron heads, 1&7/8" long tube headers; get at least 15 mph on the freeway unless i'm rolling at 150. :laugh:
