First off, the build is for a 2006 LJ Rubicon, transmission is the original 6-spd manual. The Jeep is lifted 4” and runs 34” tires, as well as what seems like several hundred extra pounds of weight in the form of armor plating, a cage, a heavy winch up front and a heavy bumper/spare on the rear. 2006 is the last year Chrysler used the 4.0, and there are some oddities with the 2005 and 2006 engines that I had to account for during this build. I wish to thank Russ Pottenger for not just providing all the parts for this build, but for spending hours of his time on the phone with myself and my mechanic to explain just what it is we got ourselves into when we embarked on this effort.
The stroker recipe is roughly what Dino documents as the 4.7L Medium Buck Stroker. Russ specced out a Scat 3.895” stroke crank, Scat 6.125” rods, .060 bored pistons, comp. height 1.385 with 22cc dish. (Russ, if you’re reading this feel free to correct me on the exact specs.) The cam is a Comp Cam 68-0005 206/214 and the head was sourced from Clearwater and had the full Russ Pottenger Treatment done to it with Chevy LS1 valves and a full porting and polishing. The ’05 and ’06 4.0 engines used an oddball throttle body that had to be custom opened up to 62mm. I couldn’t use an earlier TB on this engine as there are a couple of additional electronic sensors on it that the computer needs in order to figure everything out and not blow any codes through the OBD2 in doing so. I know, I tried. Another thing that appears to be unique to the ’05 and ’06 engines are the fuel injectors, in my case more Chevy LS1 parts under the hood.
Aside from a supplier issue with the connecting rods, this engine swap has taken far more time than I ever thought it would when I started this project. For the most part time has been taken by a lot of associated support parts that also got swapped / upgraded over the course of this effort. With the increased displacement of the 4.7, and the fact that the original cooling system was 10 years and 91K miles old, I thought it best to replace the radiator during the swap with a heavier duty two row unit. Also decided on a full 2 1/2 inch exhaust, that on my particular Wrangler needed to be bent special to clear my suspension at full travel and full rest. Might as well put in a new clutch while I’m at it, you get the picture. Also after getting the engine in we discovered (the hard way) that the Camshaft Position Sensor had failed and needed replacement. The check engine light finally went off after replacing that sensor.
My first impression after starting it up is that throttle response is very touchy - a quick blip of the gas pedal spins the engine up to 2K RPM almost instantaneously. This is undoubtedly the result of the balancing of all the internal components plus the 62mm Throttle Body upgrade, the old 4.0 *never* reacted to throttle inputs this fast.
So yesterday I was finally able to take it out and drive it on the street. The first thing I noticed is the sound of the exhaust - yeah, I knew what I was getting when I replaced everything from the head on back with high flow performance stuff, so the days of silent rock crawling appear to be over. I never went beyond 3K RPM - I’m breaking it in - but one can only imagine what it will sound like north of 4.5K. I am getting used to it though, the low rumble at idle is starting to sound… good.
The second thing I noticed is the massive amount of torque right after idle. To compensate for the old 4.0 I replaced the gears long ago with 4.56’s so first gear is already quite short, I’m thinking now that as the engine gets broken in I may be starting off from rest in second gear. The power develops quickly and I’m in sixth gear no sooner than 40 MPH. The thing is, the power is usable right across the RPM range, from right off idle to over 3K. It’s like driving my son’s Mustang GT - there’s usable power to move this thing in any gear, the only question is what RPM do I desire to use in doing so? A couple short freeway runs at 65 MPH pointed out that downshifting is no longer needed for a quick sprint to get around a semi and back into the right lane before my next exit, you just roll into the throttle and the engine responds, even in 6th gear.
Driving in heavy traffic on a hot day (high 90’s) yesterday afternoon with the A/C on I briefly saw 227 degrees on the digital temp display. We put a 195 degree thermostat in and the whole cooling system is new so this didn’t make sense, so I kept my eye on it. This was with only about 4 to 6 miles on the new engine so I started to think it might have to do with break-in. After coming home and shutting it down I swapped out the digital display with a new one (this was a planned upgrade anyway) and added a bit of water to the radiator. After that I started to see temps no higher than 211, mostly 209 and in this morning’s heavy traffic and low morning temp (71 degrees) I never saw anything higher than 205. I’m thinking that as the engine breaks in there might be less friction thus less heat? Does that make sense?
Other than that, the all knowing and all seeing engine control computer on the late model 2006 seems to have adjusted to the new parts and displacement quite well. The engine idles at about 700 RPM and no codes and no check engine light have been thrown. The engine seems to run smooth with no odd vibrations at any RPM range.
Joe
