CJ I6 question

We need to know your Differential ratios. Your T-5 will be direct, one to one in fourth gear. And your tire will be 27.7 inches in diameter for the other number to plug in at:

Bless America, =DFill O|||||||Omailto: snipped-for-privacy@aol.com

True I forgot to ask for axle ratio. But, I'm not looking to put my info into a calculator. I want to know what RPM the engine was

*designed* to run at while driving at a particular speed.

As an aside, I'd also like to see the factory torque/horsepower curve for a stock 258. Which reminds me, I should have specified the 258 in the original post.

What year? Many older Jeep engines are designed to run efficiently around three grand. Choked SMOG engines down around two. Of course, that it will vary with carburation size in Cubic Feet per Minute, Camshaft cross flow duration, compression ratio, and headers God Bless America, =DFill O|||||||O mailto: snipped-for-privacy@aol.com

I have a 258, T-5 with 3.31 gears turning 33x9.5" BFG muds (no metric equivalent for the bigger off road sizes that I know) and at 65 mph in

4th I spin 2300 rpm. If I use 5th it drops to 1750 and my gas mileage drops radically as well.

That 2300 rpm seems to be a nice 'sweet spot' for my engine with the best mileage (23 mpg) and tons of punch if needed. It will hold it up any highway hill I have hit.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Clap Trap wrote:

Thanks Mike. Mine has the 258, T-5, and 31x10.50s on it, also with 3.31 gears. Mine runs about the same as yours. But, mileage stinks in either. RPMs in 4th are too high, 5th too low. I am getting ready for another round of upgrades and was thinking about regearing the axles since I really don't need bigger tires or a lift.

Any idea what the factory RPM was supposed to be in 5th at 55 or 60?

The CJ7 came with 31's for some versions and 31's fit any stock one like the TJ so you are 'really' close.

I get a sweet 23 mpg on the highway fully loaded running at 65 mph. If I run at 75-80 I drop to 18 or 19 mpg, if I run at 50-55 on secondary roads I get 25+ mpg. I have a 200 mile regular route to check it on.

I don't use 5th.

I was told the engine has the advance full around 2300 and I run an Accel SuperCoil for a hot spark with the engine set up manually. I killed the computer.

When I killed the computer, my top end went from a 3500 rpm bog to a fast 4400 rpm which will pull me quick up to 50 mph in 2nd gear!!!!

My friends and they are folks from the group say they got 10 mph per gear with the computer sleeping.

I also went up 100 miles per tank for gas mileage when I use 92 octane.

I still pass emissions and so do a bunch of friends who have also killed the computers.

Manually the 258 can be tuned up to run sweet and just purr at idle, though a bit of a lean rumble at idle is better for the emissions sniffer.

Here is a link the the best boost you can give it and it is free!

I add two new wires rather than mess in the harness like the author does.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Factory gearing was typically the 3.07 axle ratio which will give you about 1700 rpm at 60 mph in 5th. A real DOG!!!!

I'm with Mike, around 2300 is a good spot > Mike Roma>

Impressive! I'm lucky to get 17 unloaded, downhill, with a tailwind. Mostly, I get about 14.

No computer on mine either. I also did a TFI conversion and noticed an improvement. I don't have to worry about emissions testing so all that is gone as well.

Mine is all done manually (except for the electric choke on the Weber). It runs great. Plenty of power, unJeeplike smooth idle. But mileage just stinks. And it smells like it is running a bit rich. But I've leaned it as far as the carb will go and it still smells rich.

Your tagline says you run 33s on your glass bodied Jeep. How much lift does it have? Did it have 33s and that same lift pre-glass?

The first thing I would check on yours is the accuracy of the speedometer. For some reason my speedometer was about 7 mph off with

31" tires and became exactly right when I put the 33's on???

I think someone needlessly changed the speedo gear when they installed the 31's not knowing the stock gear was right for them or the t-case is used with a different gear, who knows. This is GPS verified speed.

Meanwhile, the 7 mph difference affects the 'perceived' gas mileage big time.

I had 31's on with the stock suspension and steel body. I put YJ shackles on for a 1/2" lift and got a 2.5" spring lift. I have tons of clearance.

You could have issues with that Weber carb running rich. It is too big for the engine by rights so can have too rich a jet in it stock if you aren't running headers and a high flow exhaust. You might need to rejet it.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's