Some 350/700R4 Questions

[84BlueCJ7]

I have had my CJ7 for about three years now. It's a loooooong story.

I purchased it this way but have spent time and $$$ fixing problems as the arise. I am still having power issues at 55mph and I do not know the best option. I will throw out the numbers and see if it makes since to you guys.

1984 CJ7
Chevy 350 (LM1 Block# 10066036)
Heads (993?) (casting 33417369)
Pertronix (Pertronix Chevy Flame-Thrower Distributor - Speedway Motors, America's Oldest Speed Shop
Looks stock except for a cam, unknown make and info
Stock TH700R4 "K" case with manual lock up switch
AMC20 rear with one piece axils (3:54 gears)

Performance - runs like a scalded dog at high rpms
Daily Driver - sucks at 55mph, fine at 65-70mph

At 55 mph the rpm is about 1,200. Good gas mileage at about 13mpg but absolutely no power. At 65 mph it's 1,800rpm and better power.

The closer to 2,000 rpm, much better power response for going up hills etc. Passing cars is not problem at all when you downshift...and fun.

I want better drive ability as a daily driver at 50-55mph.

Question - Should I swap to an RV cam or replace the gears? Whichever can you give details and part numbers?

 

[Old Dog]

sounds like you need to regear, what size tires are you running?

 

[84BlueCJ7]

sounds like you need to regear, what size tires are you running?

Thats what I figured! I have 32's right now. Speedo is correct. If I do need to regear I have no idea what to get. 3:73, 4:10s. You guys are gonna hate me but I don't do any off-roading. Can't afford to break anything any more.

Oh, I can cruise with the lock up dis-engaged but then I over heat in the summer. Transmission cooler sits in front of the radiator. Winter is no problem. 1,700-2,000 rpm seems to be key in performance and power. I don't want to gear too low.

 

[Old Dog]

Heres a link to help you out. Gear Ratio Calculator

 

[Old Dog]

You should measure your tires as most are not as tall as they say. This will affect the results that you calculate.

 

[84BlueCJ7]

You should measure your tires as most are not as tall as they say. This will affect the results that you calculate.

Thanks Dog!!!

 

[derf]

The power you're getting suggests you're running closer to a race cam than an RV cam.

Now, I'd say that 1,200 RPM is low for 55 MPH and you should probably regear to get it in a better range. And that's what I'd do first.

But I'd also look at doing a cam swap to an RV style. You really should be able to get good power out of that engine down in the 1,200 RPM range.

 

[planoboatguy]

You can also just leave it out of Overdrive if your only running uder 60mph, then switch it into 4th gear on the interstate. It will not hurt the transmition to drive in third gear, and it is recomended if you are towing. You may even find that the fuel economy goes up because the engine isn't working and lugging so much at 55 mph.

 

[84BlueCJ7]

You can also just leave it out of Overdrive if your only running uder 60mph, then switch it into 4th gear on the interstate. It will not hurt the transmition to drive in third gear, and it is recomended if you are towing. You may even find that the fuel economy goes up because the engine isn't working and lugging so much at 55 mph.

Thanks boatguy. I can do this in the winter. I have a manual switch. In the summer time it overheats. Gas mileage is actually worse but thats ok.

 

[84BlueCJ7]

What all do I need for a gear change? Is there a complete kit?

 

[derf]

What all do I need for a gear change? Is there a complete kit?

You can usually get a master install kit where you buy your gears. You need some special tools to do the swap but it's not brain surgery. You really want to make sure you get the parts installed exactly right or they'll wear prematurely and you'll have to do it all over again.

 

[albatros 3]

You are definitely lugging the motor. My '82 has 2.73 gears with the TF999 on 31" tires and that's barely liveable. Sure I am at 2k at 70 MPH, which gets me 20 mpg, but after the lock-up kicks in at 40 mph, 40-55 is sluggish and bad mpg. If you're not going to off-road your Jeep, I would look into 4.10 gears. 4.27s are also an option, depending on availability. 4.56s are too much if you're not going to really off-road and 3.73s are not much gain. The 4.10 will give a good bump driveability in stop-n-go driving.