3.70 Gears w/ 3 speed???

[classic_man]

I could use some advice or opinions on this topic. I've got a 79 Malibu. Its my city cruiser but I plan to run it at the track from time to time. Just curious what my cruising speed would be and what my top speed would be? Its got a ford 9" non posi...I'm going to put limited slip with 3.70 gears on 15 in rims. Probably 255x15x60 tires in the rear or similar. I'm also running a 3 speed TH350 and pushing about 300hp. I"m open to putting in overdrive down the road but Id be running a 3 speed at least for the time being. Just want to cruise around town...do a burn out now and again and run a respectable 1/4 mile drag time.

Any input would be appreciated. Thanks

 

[olds307 and 403]

I get 2765 on the calculator I use. Mine is right on showing 1813 but that is with the converter locked up. Expect around 3000 rpm at 60 mph.

 

[King_V]

I get close to the same calculation - 2846 RPM @ 60MPH assuming zero torque converter slip.

So, figure 3000 with torque coverter slip, and say you're trying to cruise at 75MPH, that puts you at 3750 RPM.

 

[pontiacgp]

Since you have a ford 9" why not get another 3rd member set up with higher gears to use for daily driving. It doesn't take long to switch out the 3rd member

 

[classic_man]

OK...Thanks. I'm open to getting an additional 3rd member but right now I'll be running these gears for a while. I think I'm gonna move forward on the 3.70. I think its gonna be a big difference from what ever is in there now..which is either a 2.89 or 3.08.

 

[pontiacgp]

what about using the posi for the 3rd member for street use and using a spool for the 3rd member for the track. You can get a spool for under $100.00 which is alot cheaper than a posi

 

[classic_man]

Also curious what anyone thinks of 3.55 vs 3.70. How much low end are you gaining with 3.70?

 

[classic_man]

I put the 3.70 in with a yukon duragrip locker...I'm very happy with the decision I run roughly 2600 to 2800 on the free way going 55mph on 14s. Pulls a lot harder. I was at 2.75.

Just wanted to give an update.

 

[King_V]

Yep, a jump in gearing like that will definitely give it a satisfying amount of extra kick.

Me, personally, I'd be unhappy with the RPMs at highway cruising, but I'm fussy about that sort of thing.

 

[-83MONTESS-]

I have a TH400 with 3.73s and dont mind it a bit. Its a 30 year old car with a 40 year old v8 that is gonna get bad fuel mileage anyway and I prefer the sound. Maybe thats just because im around race cars all day so im used to it :lol: