5-speed trans conversion

I was wondering if anybody has converted their jeep to a 5-speed trans. I am currently running the stock T-14/Dana 18 combo behind a soon to be turbo charged 225. I plan on running 34inch tires, with the factory 3.73 gear ratio. I would like to keep the rpm's down around 1800-2000 for fuel ecomony, as it will be a daily driver more than an off road jeep. With the current combo, i was told i would be somewhere betwen 2200-2500rpms.
Any information would be greatly appreciated.
Thanks in advance,
Matthew Haver

 

I am hoping to try and get the mid teens for fuel mileage. the closer to 20 the better, but not holding my breath. I thought an overdrive unit, but hard to shell out the 1000 dollars for a new one, and have been unsucssessfull trying to find a good used one.
Essentially, i am looking for the cheapest and easiest route to an overdrive, whether it is a unit or different transmission.
Thanks for any info
Matthew Haver

 

Having never used an overdrive unit in a jeep, do you use them like you would a Gear Vendors or a split shift truck. Or do you pick overdrive and keep it there?
Example
1st, 1st od, 2nd, 2nd od, 3rd, 3rd od,
or
1st, 2nd, 3rd, od.

 

There aren't a lot of types of overdrive transmissions available. You could probably make the T-5 work, but you would have to adapt it at both the engine and transfer case end. Plus, it's not a very strong transmission. http://www.jeeptech.com/trans/t5.html The more desirable 5-speeds are the NV3550 and NV4500, but both of those are overly long for the CJ-5. The short wheelbase limits the number of transmissions you can easily swap in.

The overdrive is your best option - it's a lot to plunk down all at once, but I doubt you could do an overdrive transmission swap for much less. Plus an overdrive will increase the value of your Jeep to a knowledgeable buyer, or you can remove it and easily sell it if you choose not to sell it with your Jeep.

There are a few overdrive 4-sped transmissions - Herm sells one of them, but it's no less than the overdrive http://www.hermtheoverdriveguy.com/id41.htm

What are your axle gears now?

There have been plenty of threads here about fuel economy. There's no guarantee that your mileage will go up if you slow down the engine. The aerodynamics of the Jeep are very limiting - it takes a certain amount of power to move at that speed, regardless of how efficient the engine is. "You can't squeeze blood from a stone."

 

I kept the factory 3.73, just added front and rear Lock-rites. After doing more research, i like the idea of the od unit, hardly any fab work, plus it's like having a 6-speed.
Other than mileage, my other concern was keeping the shifts short to keep the turbo spooled up. When i was given the jeep, it was nowhere near road worhty, and there was 4 ft of snow, (2 years ago january) so i never really got to drive it around and shift through the gears.
I also found some of the posts dealing with mileage, and found it interesting that alot of people were getting high teens, since a jeep has the areodynamics of a box.
Thank you for all the info, i am going to try and find an overdrive unit and hopefully it will be on the road come spring.

 

email herm and see if he has any rebuilt units for sale.

I get around 18mpg with my 4.27's, OD and 32" AT's.

 

Dan has a good point - the Borg-Warner 3-speeds are not fast shifting transmissions. At the least you will wear out the blocking rings quickly. At worst, you'll miss a shift at WOT and break a gear.

More opinion if I may - you are mixing your objectives. Keeping the turbo spun up and good mileage are clearly contradictory. Remember that the objective of the turbo is to pack more air/FUEL mixture into the cylinders on each cycle, thus making more power. Power is always equal to the amount of fuel consumed. You can improve efficiency by metering the fuel to the need more precisely, but power out will always be directly proportional to fuel in. (Sorry if this sounds like a lecture - occupational hazard for me).

So you need to decide what you want, and how much you are wiling to spend to get it. Another opinion - I would delete the turbo and focus more on gearing.

 

I'm not looking to race the jeep, just looking for a little more power. The turbo setup i have is off a 79 buick riviera with a 231. having driven bothe a v-8 powered riv and a turbo v-6, i was impressed how much quicker the turbo car was. i figured it was a good idea for my jeep. plus, i plan on keeping the stock setup, which was around 7-9 lbs of boost. Hence i wanted the power to be there when i wanted it, but not there all the time like a built motor.
Guess i'll have to ponder the turbo idea some more, but i am definatly going with an overdrive unit.

Is there anybody running the stock drivetrain, 225, T-14, Dana 18 with 3.73 gears and 33's. i was wondering what kind of mileage you were getting and if you were happy with the setup or if you would regear.

 

with 34s, an OD, and 3.73s I doubt very much you'll be running 2500 RPM down the road at highway speed.
I think you'll be 2000 or way under that....maybe lugging it a little....if they are a true 34" tire.

 

I personally thought it was high, but i was using one of those online calculators for crusing speed. it was the only one i found for crusing speeds, the rest were crawl ratio clcs, and i lost my formulas from a teacher to do the calcs myself.

 

the turbo sounds like a cool idea. Should add some good power without hurting milage too much. But youll probrobly need to run higher octane fuel so that needs to be considered aswell

 

I might, but the original car the setup came off of, (79 Buick Riveara) the owners manual recommended 87 octaine. i might however have to run a higher octaine fuel with a lead additive, because it is the original motor from 1971, unless i rebuild the heads and use hardened valve seats.
We shall see, i have the setup and everything works great, and i bought a couple of DIY turbo books from Gator Turbos. the conversion would be simple, since the setup is a draw through style, so you don't have to spend lots of money on special carbs or special carb rebuild kits. Plus it came of of a 3.8 liter motor, so i know it is the right size. Just need to find the type of Q-jet used. somebody beat me to it and grabbed it already.

 

Naturally aspirated 231's were about 8 1/2-1 going from memory. I want to say the turbo'd V-6's were lower than that.

 

If I understand the research reading I've done on turbo charging, It's always on boost at any thing over idle. As long as you are not lead footing it and ease on and off the gas your gas mileage should increase. Maybe only 1 or 2 percent, maybe more, but any increase is better than none.

However if you are going to race from the stop lights, that all goes out the window.
With the higher compression engine (the 225 at 9:1) you will probably find that you want less boost to keep from blowing seals or even making the blower exit from the top. 3 or 4 lbs will be more like it.

Most Turbo or Blower engines are running at 7:1 compression ratio.

I have no idea how turbo-charging will work off road, though. Don't know any one that's tried it yet. Let us know, ok?