Should My CJ7 Be Able to Go Faster?

[LongHorn]

Any NV3550 or AX15 swappers out there? - Page 2 - International Full Size Jeep Association
Yeah one guy here went with the ax-15 and another the 3550 and there are two other members on the forum that have gone with AW-4 Automatics as well as one other member who had installed a 5.3l Vortec in his Cherokee and ran the GM version the NV3500 with 35s and I think 4.1 gears?

It probably wouldn't hold up to hard core offroading but if you were going hardcore I would think an OD tranny wouldn't even be on your to do list. For a DD rig with the occasional Offroad adventure should be a good choice.

IMHO is not wise to use a Transmission that's not rated for the power of the engine your bolting it to. Then there's the extra money you have to spend to alter the drive shaft buy adapters. When I do a swap or modification to my rig it's always to make it stronger & more reliable not less.

 

[IOPort51]

I guess you have to give up something to have the Overdrive . and then again there is the nv4500, I hear thats a bear.

 

[ThisGuyUKnow]

IMHO is not wise to use a Transmission that's not rated for the power of the engine your bolting it to. Then there's the extra money you have to spend to alter the drive shaft buy adapters. When I do a swap or modification to my rig it's always to make it stronger & more reliable not less.

Well I think we are getting off the main topic. As far as the 3550 goes according to Novak it is as strong as the AX-15 and both the AX-15 and 3550 are suitable for service behind a v8, plus there are a hand handful of Members on IFSJA who have installed them behind mild 360s and have not had failures on or off the road

 

[IOPort51]

quite possible. back on track!!
Does anybody have a close guess on the torque of a AMC 258 i6 / 4.2l at "cruising speed"
maybe 2000 RPM?? should be fairly proportional to the gear ratio back to the final drive. 4th gear is 1:1 and 5th is .75:1 What is the vehicle weight?? I would think you could compare pounds of force at the outside radius of the tire and compare that to the weight of the machine . I would say factoring in the % angle would be reliant too. this of course disregards rolling resistance, wind drag and mechanical efficiency through the drive line. But it may give a clue to the answer to your question. If you end up with a 1 pound of force to 1 pound of weight on a 10% incline you should start to prepare to roll backwards!

Well I think we are getting off the main topic. As far as the 3550 goes according to Novak it is as strong as the AX-15 and both the AX-15 and 3550 are suitable for service behind a v8, plus there are a hand handful of Members on IFSJA who have installed them behind mild 360s and have not had failures on or off the road

 

[IOPort51]

please understand that to most of us the thought of building anything that won't climb a tree or to make a change for the sake of fuel economy especially at the cost of off road performance is totally foreign.
I drive a J-10 every day , AMC 258 i6 / 4.2l with a T-176 4 speed and 2.73 rear end and although it will never race at Indy I can accelerate up hill , pulling a trailer with a small ford Diesel tractor on it.
Do the math , let me know what you find.

Well I think we are getting off the main topic. As far as the 3550 goes according to Novak it is as strong as the AX-15 and both the AX-15 and 3550 are suitable for service behind a v8, plus there are a hand handful of Members on IFSJA who have installed them behind mild 360s and have not had failures on or off the road

 

[ThisGuyUKnow]

quite possible. back on track!!
Does anybody have a close guess on the torque of a AMC 258 i6 / 4.2l at "cruising speed"
maybe 2000 RPM?? should be fairly proportional to the gear ratio back to the final drive. 4th gear is 1:1 and 5th is .75:1 What is the vehicle weight?? I would think you could compare pounds of force at the outside radius of the tire and compare that to the weight of the machine . I would say factoring in the % angle would be reliant too. this of course disregards rolling resistance, wind drag and mechanical efficiency through the drive line. But it may give a clue to the answer to your question. If you end up with a 1 pound of force to 1 pound of weight on a 10% incline you should start to prepare to roll backwards!

I think the fact that the front of a CJ7 looks like a giant peice of toast is a huge factor in this whole mess When I get back from the middle east and I have a chance to check out all the issues that have been suggested in this thread I want to try to do the 4.0head and eventually junkyard MPI swap to see if I can't get some improvement out of the AMC 258 i6 / 4.2l .

 

[IOPort51]

Do the TFI ignition up grade, the most bangs for your Peso. cost is about what you would spend on a tune up wires cap and rotor and throw in a new coil . and the best part is you get to keep your distributer.

I think the fact that the front of a CJ7 looks like a giant peice of toast is a huge factor in this whole mess When I get back from the middle east and I have a chance to check out all the issues that have been suggested in this thread I want to try to do the 4.0head and eventually junkyard MPI swap to see if I can't get some improvement out of the AMC 258 i6 / 4.2l .

 

[ThisGuyUKnow]

Not sure because the T-5 went out while the GF was driving it after I left back for Iraq, but when she took it to her mechanic the dizzy was not at the right setting and the vacuum advance line had come loose on the engine side. I feel really dumb for not noticing the vacuum advance line but in my defense I was looking at the dizzy side of the engine and the hose runs to the carb side where it connects and I only had a day or two left in the country so I didn't mess with it. Hopefully when I get the AX-15 I picked up to replace the T-5 the problem will be corrected.

 

[Titan907]

Why would you want to go any faster? Jeeps are all the thrill and excitement at 1/3 the speed...;-)

 

[ConceptCustoms]

Maybe this is where I am getting lost here. I don't think I fully grasp the concepts behind gearing. Assuming that the axle ratio is 2.73(I have no reason to beleive it has been changed from stock) then according to the calculator on Novak-adapt at 80 MPH the RPMs would 2035.77 and 100mph would be 2544.71. So I see how the the gearing would not be Ideal.

So what I am gathering aside from the gearing is that I should:
-Check the exhaust for blockages
-confirm that the timing is correct on the dizzy
and
-Possibly make sure the Carb is correctly tuned

Has anyone here with a T-5 had a similar issue I dont want the Cj to go 100mph but I would like to beable to hit 80 on the interstate at the least.

I know, this is an old thread, but I have customers ask about this very problem ALL the time! Most of the Jeeps here come with 3.31 ratios, and work well with about stock tires...

I certainly have to agree with tuning, but say, the gearing is absolutely what is killing the speed and MPG's. Even a badly tuned engine can run circles around a perfectly tuned rig with bad gearing. A note on the carb tuning peice, how do you suppose the inside of a carb thats tends to see LOW vaccum numbers (when an engine is heavily loaded) looks after 20K miles vs. a carb the sees a consistant higher vacuum?? Do you suppose internal contaminant build ups may differ?

As a general rule, 6 and 8 cyl engines should have cruise RPMs from 2000-2400 at 65-70 MPH, and at around 80, that should be almost 2800 RPM.

Using 2.73 gears at 70MPH (as mentioned earlier) with 31" tires (again, I think this was the tire mentioned earlier), and using T-5 Transmission ratios, you should have right at 1781 RPM in 5th gear (0.86 Overdrive ) - at least 400 RPM lower than ideal midrange, and realistically not much above idle speed.. Even on flat land, the motor is almost 100% loaded in 4th gear (2000 RPM.)

Another way to think about this, the stock Jeep CJ's came with something like (about) 28" tire. To change this to a 31" tire is and effective change in torque reduction of about 10%, and probably closer to 15-18% due to rolling friction and rotational efficiency.

If you do much towing (or live in someplace like CO with lots of hills) we would tend to use at least a 3.73, and very commonly a 4.10 ratio with a 31" tire. 3.73 will increase effective torque by 36% (approx.) and you could likely see an average increase in MPG by 15-25% due to reduced engine load - based on original tire size, or about 18% torque / 12% MPG, based on current tire size. BTW, 3.73 gears will still get you up to 120.8 MPH in 5th gear (by the math anyhow.) Put in some 4.10 gears, and you could easily outrun a lot of cars off the line with an old 80K-120K mile I-6 (not that this is what a Jeep is made for.) Check out my website, the I-6 stroker shown there is installed in an '86 with 4.10's and 33's is making enough torque to smoke a GMC Syclone at Bandimere.

On a last note, the T-5 is a lightweight "car" Transmission that AMC used because of GVW of CJ's. We all put bigger tires on, and the bottom line, the Transmission can't hold up to the added torque stress of those larger tires. If a guy want's to keep the T-5 , correct gearing is critical, and the same really applies to any Transmission , although some tend to be more forgiving.

Anyway, I know I'm new here, but thats my 2 cents...