That's what I figured. It's funny, I have been installing gears for close to 25 years now and this is the only Tim I have installed lower gear ratios.

 

OK so I wound up with a 3.36:1 gear set and an Eaton Posi Carrier.

Why?

Because my son eventually plans to take out the M22 and put in a 5 speed.

 

The eventual plan of going with an overdrive is all the more reason to go with a lower gear, or keeping the 4.10's you had. 3.36's with your current trans is semi-ok, putting your 60 mph rpm's at 2,509. That's based on having a 27" tall tire, so final numbers can be plus or minus depending on the tires you have. However, with the .68 overdrive of the TKO 500 for instance, your final rpm's will be in the 1,706 range. That's so far below the engine's optimum power band, the engine is going to be lugging at that rpm, and will likely hurt not help gas mileage, not to mention having sluggish response. You're probably going to find yourself toying between 4th and 5th gear when on the highway, especially while going up a slight incline. By comparison, even 4.10 gears with the overdrive would put your 60 mph rpm's at 2,082. Oh the power of overdrive, gives you the best of both worlds when you gear the rear right.

 

I'll have to check, I believe the tire diameter was 26 and we ran the estimate at 60 MPH Highway Speed. That put the RPM at 2600 for the 3.36 with the 1.00 Muncie Transmission ratio.

 

I put the 3:08s in mine last Friday and I am running a 245/60r15 tire my rpm at 60 mph is 2400. I am running a m22 4sp trans . Much better than th 2900-3000 at 60 mph before.

 

On a t-350, 400, Muncie, or Saginaw, the final ratio out of the trans is 1:1. 3:08 is a great all around gear for a typical 300 hp engine. The higher your rear gear ratio is, the faster the engine needs to turn to go 60, 70, 80 mph. Unless you have a race car or an overdrive transmission, be realistic as to how you want to use your car. 4:10's are useless on a street car. You would never be able to go anywhere far on the highway without winding out your engine. In general, high rpms equal high heat and high wear.

 

I have 308 in the rear of my 67 convertible and it's a very nice highway cruising gear. Your certainly not going to pull the front wheels off the ground, but that's not my thing, I like to cruise.

 

All, Have 68 with SB 350 400Hp, 308 rear. Shopping for Auto Trans... Any suggestions ?

Thx

 

Just a thought, you could keep the 4.11 and install a 5 or 6 speed over drive transmission.

 

Thanks all. I think I will stick with 3:08 rear for some mileage and go with 700R4 found at FB trans. out of NY state. They have a good rep and stand behind there work. Little more pricey than some others but my buddy got one from them and he's pushing 900hp and hasnt broke it...yet.