[Cannonball]

I have two general questions:

1) does anyone have suggestions, use or have done a stroker of any kind on a 2003-2006 TJ with a 42RLE automatic transmission (this would be the Rubicon package with the auto trans)?

2) does any one have a drivability history on the stroker engine and trans combination above?

I have a 2004 Rubicon with the 42RLE automatic transmission running 35"s and 4:56 gears as my daily driver. I am running out of power on the highway between 65-75mph @ about 1950-2300 rpm and or in the sand/dunes. swapping a 5.7 hemi is not the answer but the one I get the most often. I drive this every day and dont want a tempermental build nor do I want one that wont run at all in winter. My wife gets in it and drives it too and dont want her to worry either. Reliability and drivability are key for me, I read people are getting mixed issues on reliability which I feel is mostly either due to wrong part selection or improper build or break in. But I dont get the feed back I am looking for with the drivability concerns.

The trans seems to be pretty much a computer controlled unit which by all comments cant be changed. It was designed to an engine with more HP than the 4.0 can produce and thus the curent problems not holding overdrive and or highway speeds. I get the impressions from other forums that had the 4.0 had 50 more HP and more torque the trans issues would go away. Perfect for a Stroker in my thinking. I do have a transgo kit in it already.

I see people building the strokers for XJ's and early TJ's and lots of older units but the newer TJ rubicon and this trans combination have me looking for more answers and sugggestions and or guidance than I have been able to read in any posts all winter. I believe adding 50-75HP to the engine power and torque will help greatly. Nitrous would too but its hard to use every day.

I am going to start with a junk yard engine from a 2003-2004 TJ so I know everything will swap in / bolt up correctly when its done. I cant lay this up for ever so once the engine build is done it gets installed and back out on the street in under a week (taking a weeks vacation to do it). I will have one shot to get this right or Ill prolly loose my job if I cant get to work and my wife if I spend the money and it all goes south with issues.

I dont need a high RPM engine just one that pulls harder and will still retain some fuel economics. Im thinking if it pulls harder and breathes better making more power I wont have my foot on the floor board wasting fuel as much either. Yes there is always a trade off so this is why I am here looking to all or you for input as to the correct way to do this once.

I do appreciate any and ALL responses and thank everyone of you for my ignorance. Ill ask a question once and learn from the answers maybe ask a related question but Ill never ask the same thing twice, Promise!

CB

PS I push a snow plow here in Wisconsin winters just to get to the main road and I tow a small utility trailer hnting / camping sometimes loaded weight is under 1000 lbs.

[biffgnar]

While a stroker is always an interesting option, you are significantly undergeared. With the 42RLE, even running 4.88 with 33s is marginal. Bigger tires and higher gears you are running not a good match. Your Rubicon axles will go deeper than that. Get that right before taking on engine swap.

[Cannonball]

Thus another paradox, I have a 2003 Rubicon running 33's and stock 4:10 gears with a manual trans 5 speed. No issues and typically on the street start in 2nd gear.

Doing the math the 2004 calls for 4.56 gears. going to 4.88's would raise my engine rpms approximately 250-300 rpm over stock rpms with correct and corrected gearing. going any deeper I might as well give up the over drive and keep what I have? Does the 42RLS suck up that much horsepower? I can only believe the Auto and Std trans have the same final drive ratio if they both come from the factory with the same axle gear ratios?

This is where I am getting frustrated..... if the 42RLS comes with a factory 4.10 gear and 31" tires every gear calculator I go to comes back with 4:56 as the corrected ratio. I drive on the highway and fuel economy is a concern. If I go to 4.88's it may help but I cannot see needing to go to 5.13's or Ill be just screaming as well. But I believe you are on part of my problem. Taking into consideration just the gearing factor 4:56's were correct but add into this rolling resistance, additional horsepower to turn them etc More gear would allow me to run a little higher RPM breathing easier for the engine and perhaps get it into a better power band ( I dont know whare the power band actually is on a 4.0)

Does any one have a 42RLE equipped Jeep rubicon 4.0 with 35" tires and what ratios and RPMS are you running @ say 65MPH.

Thanks


CB

[Offshoredrillin]

I have an 03 Rubi with a 4.6 stroker from Golen, I absolutely love it.I am putting the Derale TJ trans cooler and 4:88's in next week. My trans guy is loving the fact that I'm not cheaping out and doing the budget job. I have 168K on it and love it. mostly hiway driving for me though, 30K per year.

[RubiconRazorbac]

You're trying to maintain "stock" RPMs on a non-stock vehicle. More weight, rolling resistance, higher aerodynamic profile, etc are all factors that are ignored by online calculators. You need to be higher in the power band to both accelerate & maintain speed.

FWIW, being under-geared will kill your MPGs just as much as anything else. Lower RPMs do NOT equate to better mileage in every system. If you're under-geared & running 2200 RPM but the engine is lugging to keep it there, that's much less efficient than running 2800 RPM in a well-balanced system.

[RubiconRazorbac]

Originally Posted by Cannonball

I can only believe the Auto and Std trans have the same final drive ratio if they both come from the factory with the same axle gear ratios?

No.

[Tamatacan]

NV3500 has a .73 od ratio. The 42RLE has a .69. With 4.10s that means a 2.99 final drive. With the 42RLE that would give a 2.83. Not a lot but at 65 mph with a 33 tire the stick shows 2000 rpm. The auto is about 1925. With a 35's and 4.56 with the .69 OD you would have 3.14 final drive. That would show 1975 rpm at 65mph. The factory 4.10's with the .69 od equal 2.83 final drive. With a 31 tire that shows right at 2000 rpm at 65. This is from an Isky Dream wheel. I can do exact but this is really close.
Bob
Just read the above. Bigger wider tire plus lift means way more wind and rolling resistance. Wind being the worst of the 2 at that speed.

[RubiconRazorbac]

Originally Posted by Tamatacan

NV3500 has a .73 od ratio. The 42RLE has a .69.

TJ specs show NV3500 OD @ 0.78

0.78-vs-0.69 is significant

[Tamatacan]

Might be I got my spec off Wiki.

[Tamatacan]

4.10x.78 = 3.20 x 31 tire = 2250@65

[cunnart]

As the others have said online calculators do not account for many variables and only the very good ones let you put in your transmission or trans gear ratio's. I don't trust the online calculators for squat.

[driggity]

Another thing to keep in mind is that the stock Rubicon tires weren't actually 31s. They're not much smaller but they are smaller. Honestly my stock Rubicon with the 42RLE feels underpowered at highway speeds with stock size tires. And that is in flat, low-altitude Texas. I imagine that in an area with real terrain it would spend a lot of time in third gear.

[Danno6102]

I am running 35's, 42RLE & 4.88's. I really wish I could go to 5.13 or higher with my current axles...

I'm turning about 2100 at 65 mph. I'm getting ~16 mpg. Mostly 2 lane, very little stop & go.

[Tamatacan]

Here try one of these, If you can't find what you want then let me know.
http://www.wallaceracing.com/Calculators.htm
By the way use the chalk method to get your circumference. Exact circumference will give you exact distance traveled per 1 rotation.

[TheBoogieman]

It's not hard to push the OD button off.My under-geared 42rle with 3.73 gears and 35's got much better gas mileage than my over-geared 32rh with 4.56's and 32's.