Turbo Jeep Cherokee XJ-R Build

A few people have contacted us through our facebook page (facebook.com/JeepXJR) asking if we had a build thread on any Jeep forums. Since our project was built for the Grassroots Motorsports Challenge we had it up on their forum then never really got around to posting it anywhere else. Our project started back in 2008 mainly as a joke but we have been continuously working on and improving the Jeep as time goes on.

I mainly copied Jeff’s post from GRM but I should be able to answer any additional questions and hopeful add more to it later since we made a lot of changes for 2012

PART 1: We started the project with a difficult search of finding a two door, two wheel drive Jeep Cherokee. As it turns out one was recently brought up to New Hampshire from Mississippi for us! Talked the dealer down to $600. Let’s face it; no one in New England wants a 2WD Jeep. Good news for us.

Windshield cracked no title, 243k miles, chunky brown coolant, but running great, no real rust and fairly straight body. The only bad part is that we couldn’t find a manual transmission XJ. The automatic transmission (AW4) is bulletproof though so it isn’t all bad news.

We started the build with finding our starting weight. Not terribly heavy at all, only 2,865 lbs, and began removing the roof rack, rear seats and other unnecessary items like a/c and heater accessories, wiper motors (front and rear) and radio and speakers. We also gutted the hood and installed pins. Final racing weight in Gainesville was a very respectable 2,677 lbs.

Second step was to find a suitable rear axle. Since they are plentiful, strong, come with disk brakes, limited slip, and have better gearing (3.73 vs. 3.55) the Ford 8.8 out of an Explorer was the perfect solution. $100 for a nasty looking one at a junk yard was the easy part. We then cut the spring perches and re-welded them at the proper width for a Jeep Cherokee but flipped them to the bottom so we could convert to a spring-under layout achieving the rear suspension drop of about 4.5". Used U-Bolts attached the stock Jeep leaf springs to the Ford Axle. A $25 adapter from Spicer made the job of attaching the Ford axle to the stock Jeep drive shaft a breeze.

To increase spring rate we used a second pair of junk sagged stock Cherokee springs and doubled up most of the leaves with the original pack. It gave us more spring rate without increasing ride height.

Finding shocks for a lowered Jeep Cherokee proved to be difficult but after a lot of research on shock lengths and specs, craigslist got us a pair of new Rancho 5000 shocks for a Ford F150 for the front and a pair of used Bilstein shocks off a Toyota Tacoma TRD in the rear. They are both compressed a lot but should do the trick. We may have to look into ways to get more travel out of the system if its purpose expands from just autocross as they would bottom out too quickly for rally-cross duty.

The front axle was much more involved. Since the solid tube front axle could hit the oil pan under full compression we decided to cut and notch it. Having had lifted jeeps in the past we knew the big problems that can arise from changing the angles of the control arms so we needed to address that. The upper and lower control arm brackets on the axle were shortened and lengthened respectively to compensate for the drop in the front. Additionally we made a drop bracket off the axle to use a stock length track rod that still centered the axle after all the changes.

Since offset front ball joints are way to rich for the budget and we were cutting the front axle anyway we decided to notch and bend the front axle for additional camber. After researching more about the front axle modifications the Archer brothers used successfully racing the Jeep Comanche in the SCCA Truck Challenge series we found that they actually bent the front axle. Since we don’t have the facilities to accurately bend it whole, we cut a pie out of the middle leaving a small portion at the bottom intact and stood on it until we ultimately achieved -2.5 degrees static camber on each side.

A great deal on poly front control arm bushings firmed up the axle control and a few sections of steel plate were welded onto the stock control arms to box them in for strength. The new axle modifications clear the oil pan with room to spare and the control arms retain their stock angles.



The driveline was firmed up with poly motor mounts found on eBay for $0.99! They were for a Jeep Wrangler (TJ) so they had to be cut approximately 1” to fit an XJ. We couldn’t find a steal like that on a transmission mount so we injected some polyurethane into the voids in the stock sagged rubber mount and let it cure. What a difference!

Used crusty Addco anti-sway bars were taken off a parted out Jeep and installed front and rear. They’re 1-1/8" front and 7/8" rear. The rear links are poly bushings with washers and a long bolt and we had to fabricate and weld a mounting location onto the rear axle. The stock front links were cut shorter and rewelded to fit the much lower suspension. The combination of cut springs, stiffer shocks and sway bars results in a very stiff vehicle

PART 2 Now the front and rear disc brakes were given some love. New rear hard brake lines were bent up and the stock Jeep rubber hose was attached to the Ford brakes. In the rear the stock rotors were wire wheeled clean and Kool-Vue $7 pads were installed. The front got throw-away rotors and used Duralast Gold pads. The brake lines were bled and everything works well enough. Very surprisingly, and likely the first time ever on a Cherokee, Alan McCrispin described them as 'awesome'... I’m thinking the tire diameter/weight advantage over stock was the largest factor.

Next up was pulling the engine for a good cleaning. Some degreaser and a pressure washer helped get years of oil leak accumulation off the engine and transmission. A badly leaking valve cover gasket was replaced and the engine was ready to go back in. We also removed the engine bay wiring harness for later and relocated it under the dash to de-ugly the engine bay. Only essential interior wiring was retained and everything was run on the driver’s side along the door sill. Huge holes left in the firewall from the removed blower motor, wiring harness, and HVAC lines were patched and painted.

Next step took us well through the winter: Gutting the stock engine harness and patching in Megasquirt.

There is very little information on wiring Megasquirt into a Jeep so we were mostly on our own here. A factory service manual and many hours later allowed us to cut the wiring harness in half and in theory have Megasquirt running ignition and fuel using the stock distributor's internal hall effect switch with a Ford V6 6-window trigger wheel. After many, many hours of troubleshooting a no-rpm signal issue we removed all jumpers and modifications to Megasquirt only to find that my very first jumper installed was in the wrong hole on one end. Soldered back correctly and viola! With the wiring harness back in the Jeep it came to life on the first try! It ran amazingly well with the baseline tune (modified 1.6L miata turbo tune...) and runs pretty well with more time.

Running gear is a take-off set of 275/35/15 Hoosiers from a local autocrosser that we mounted on 15x10 steel wheels front and rear. The front wheels have a 5" backspace and the rear backspace is 4" as the ford axle is narrower than the original so the front and rear track width and the bulging tire look is roughly equal.

The Jeep needed to look a little more like a proper race car. We decided on a front and rear bumper tuck. The rear bumper is a basic tuck. Caps were welded on the ends and the bumper painted white to match the body.

The front bumper was more involved. We discussed blending the bumper to the existing body work and Dave took that idea and created a really nice contoured bumper. We also cleaned up the stock lower valence and riveted on a strip of aluminum to the back to straighten the wavy piece and add rigity.

The interior also needed a lot of attention. A plastic racing seat was bolted to the stock slider bracket. The stock steering wheel center ring was cut out and a cheap eBay steering wheel was mounted.

Once the interior was gutted we realized that it wasn’t too bad. The basics were clean but since there was some rust on the flood it needed a clean coat of $0.97 Home Depot white spray paint and some truck bed lining in the rear. We also cut up a 4'x8' sheet of gray PVC to cover the holes left by the interior panels.

PART 3 Finally last but not least was the turbo. This proved to be the most “interesting” part of the project. A junked Renix (1988) exhaust manifold was cut and re-welded to hang a bit higher. Then a piece of old square basketball hoop pole was cut and used as a spacer to mount the turbo flange too. Then a simple piece of 90 degree bend was welded to the internal waste gate housing to create the down pipe.

In reality we ran out of time to install the turbo before the event. So we packed up the pieces and headed off the Gainesville Florida. Once we were there the rumors started swirling that we might try to install the turbo down there. We decided as a team that it had to be done. Once we got back from a full day of autocrossing and concourse judging it was time to…drink. Then flash forward a few hours and NOW it was time to start installing the turbo. So at around 11 PM we all gathered in the parking lot and started pulling the stock parts off the Jeep and mocking up the turbo parts.

The install lasted into the next day and the 15.5 second ¼ mile run didn’t impress many, but it was all worth it. To be able to install that turbo with my friends under pressure was a blast.

Dave and I want to thank everyone who helped make this a build I will remember for a long time. I especially want to thank Greg, Pat, Tony, and Rob. Without them there is no way this all gets done. Last but not least I need to thank my wife Lindsay for putting up with me and Dave working on the Jeep so many hours and for not complaining about all the spare parts in the basement and race cars in the driveway.

Hopefully we can bring the Jeep back next year with more power.

Re: Turbo Jeep Cheorkee XJ-R Build

When we built the rear leaf packs for the $2010 Challenge we took almost two entire stock leaf packs and combined them into one rusty and very stiff pack. One of the packs came off an old XJ that had seen many winters up here so there was a thick coating of rust on each leaf. This resulted in a leaf pack that wouldn't move much. Once we started pitching the XJ-R into corners we realized it was lifting the inside rear tire right off the ground. This combined with a weak LSD resulted in loss of time out of each corner.

At the Challenge Alan McCrispin suggested we rebuild the packs so that they can move freely and not bind. We listened.

Cleaning up old leaf springs:


Before and after



Repacking:


Greased and reassembled:


Custom Andy Nelson leaf spring plate / shock mount:



Wrapped to keep the grease in and dirt out (yes, in duct tape…?!)


We also took the time to rebuild the limited slip in the Ford 8.8 since we were one wheel peeling on the unknown junk yard axle. We restacked the friction packs for more bite and shimmed it as tight as possible while still being able to install the Z-spring. It was a little tight but we got it. Here is a DIY:

Step 1:



Step 2:


Step 3:



Back out on the AutoX course:



Results:
Much better spring movement throughout the entire travel. The XJ-R felt much more planted in the corners and, now that the limited slip actually works, we were able to power out of the corners. The Jeep is dancing between cones with vigor!

Re: Turbo Jeep Cheorkee XJ-R Build

Sorry for the huge pictures, I'll see if I can fix them later.

Also can someone fix my stupid typo in the title?

Awesome! This is so cool.

Re: Turbo Jeep Cheorkee XJ-R Build

Pic's are fine for anyone not running 800x600.

Awesome build, that thing is sexy!

Re: Turbo Jeep Cheorkee XJ-R Build

One of the coolest Jeeps ever. Have you guys ever looked into some aluminum rims? I know the price increase would be huge, but the reduction in unsprung weight would make a pretty big difference in performance.

I love it! Great build!

So how does your turbo work? How much boost? Any CEL's?
Where is your MAP sensor located? No air filter?
What are you doing for extra fuel under boost? Timing retard under boost?

PseudoSport said:

Click to expand...

what is parked in front of that k car in the background? vw beetle?

It looks like a BMW Isetta body on ?VW? pan/frame. Idk. Definitely a Isetta body though.

-bpas328xi

thats what i thought, but i figured those were a bit too rare for that.

CobraMarty said:

So how does your turbo work? How much boost? Any CEL's?
Where is your MAP sensor located? No air filter?
What are you doing for extra fuel under boost? Timing retard under boost?

Click to expand...

They're running a megasquirt ecu instead of the factory one.

supertubesocks said:

They're running a megasquirt ecu instead of the factory one.

Click to expand...

Thanks, that's right. That changes things a bit.

Yes, we are running MS1 with the 3.0 board. Its a complete stand alone computer controlling fuel and spark for under $200. Currently we are running around 7 psi but have had it up to 12-13 psi with the new intercooler. As far as power we did rush to try and get it on a dyno last year but found we had a big boost leak. We were hit 6 psi then tapered down to 4 by redline. Even so we made 201hp/263tq at the wheels. Another issue we had on the dyno is we could only do WOT pulls after 3000 RPMs or the trans would kick down a gear. We have since sorted out a few issues so hopefully this spring when the snow melts off the XJ-R we'll get it back on the dyno.

Incase anyone wants to megasquirt a 91-95 Cherokee I came up with this pinout. This is for use with a 91-93 distributor and a 6 vane shutter wheel:



The k-car in the back ground is now known as the Scaries and actually came in first last year. Pat and the guys have done an amazing job wit the car and you should see it now. If you have time check out their build thread.

http://www.turbo-mopar.com/forums/showthread.php?51514-Pat-s-GRM-ScAries!

The BMW Isetta has custom control arms mounted to the factory suspension points and a mazda rotory engine in the passenger seat. It defiantly bent the rules a little but I love seeing stuff like that show up as long as its within budget.

Oh and the red Miata in the background is mine. It was a challenge car from 2009-2011 and has placed as high as 4th over all. I miss that car.

PseudoSport said:

Another issue we had on the dyno is we could only do WOT pulls after 3000 RPMs or the trans would kick down a gear.

Click to expand...

That's the same issue we had. I am sure that there is more TQ below 3000rpm. Getting RAdesign shifting and switches to lock it in 2nd for the dyno pull.

With the 50 trim T3/T4 we are starting to build boost as low as 1700. I think next time we might try to disconnect the kickdown cable and see if that works. Also during the drags at the challenge we were having some shifting problems. During the burn out if we hit the rev limiter the Jeep would want to start in 2nd gear. If you left it in "D" it would short shift 2nd and third. We could hold it in "1-2" then shift to 3rd manually but without a tach or shift light that made it harder. We are still using the factory shift computer but would love an RAdesign shifter.

You don't need the $100 RADesign shifter if you don't want to spend the money.
You only need 3 switches.
1-DPDT on-on to switch between 'auto' and 'manual/switch' shifting
1-SPDT on-on to switch on or off 12v to solenoid #1
1-SPDT on-on to switch on or off 12v to solenoid #2
Then it follows just like the switches described by RADesigns.
1st gear-switch for sol#1 ON and switch for solenoid #2 OFF
2nd gear-switch for sol#1 ON and switch for solenoid #2 ON
3rd gear-switch for sol#1 OFF and switch for solenoid #2 ON
4th gear-switch for sol#1 OFF and switch for solenoid #2 OFF

To dyno it- just put it in D, flip the 'auto/manual' switch to manual, flip both switches ON. You will be in second gear. Nail it 1000-5000rpm.

To drag it- just put it in D, flip the 'auto/manual' switch to manual,
then 1st switch ON, 2nd OFF and foot on the brake- you are in first gear, Hammer it!
Flip the 2nd switch ON and you shift into second gear,
Flip the 1st switch OFF and you shift into third gear,
Flip the 2nd switch OFF and you shift into fourth gear and cross the finish line.
Now flip the 'auto/manual' switch to auto and drive back to the pits just like the usual auto works under the TCU control.

Most of 2011 was spent doing this:



We had removed the turbo set up since we didn't have the time to sort it out and autocrossed it the rest of 2011 NA. We had to skip the challenge that year since one of our teammates was getting married the same weekend.

Last year we decided to sort out the turbo set up we pieced together in a hotel parking lot Here are some pictures of whats going on under the intake manifold as we fix and clean up a few things.




Oil feed line



After spending a lot of time trying to get a front mount intercooler to fit we came up with this instead:



Its an old DSM intercooler welded to some small aluminum tubing off a turbo Saab. This is by no means efficient but it did cut 90 degrees off our intake temps. I wanted to add water injection too but we ran out of time and budget.

Another small change we made for last year was finishing the rear bumper caps


old end link = exhaust hanger


In 48 hours this needed to be painted and on the trailer. It felt like we were on some crappy TV restoration show


We stripped off all the panels we could and and turned Jeff's shed into a paint booth. With all the plastic it looked I kill room from the show from Dexter. after day one we had almost everything in primer and a few things painted red



Since we were running out of time we built a paint booth inside a paint booth so we could spray 2 colors at the same time



With less 12 hours left everything was painted but we still had to put everything together. At this point we called it a night and decided to assemble it as we loaded it on the trailer.



Ok, so we left an hour or 2 late but about 90% of it was done.



Stickers and engine bay paint were done in the hotel parking lot. Much easier then building a turbo set up.