Mud racing with a stroker?

[jonb8]

Little update, She ran the Wirt Co fair and placed third. The LSD 8.8 pooped out and she was open diff again and with the 34/10.50 TSL's she didn't hook up and bounce off the limiter the whole way. We ran coolville also and she took 3rd, another xj on 33 12/50 boggers won and a big block ford took second. She didn't hook up there either, so this week I pulled the axles and put the stock axles back in and started looking for a 2dr to build. I was worried about the 12 BW crank would be too heavy so thanks for the input, I've found several 12 BW motors and no 4's.
My plan is too build a 2dr xj with as little lift as possible, 35/10.50 boggers, 410 D30 and 8.8 with a spool. So what's the downfall of just using the 258 crank and rods in a 4.0 block with stock pistons? I worry about a cam because I have to pull stock vacuum. I just hate to put tons of money in the motor and put it in the mud. I can run racing fuel in it, if the added compression helps with HP. I only need about 20hp to gain the 3 or 4 tenths She's getting beat by.

[amcinstaller]

with using 4.2 crank and rods, and sstock 4.0 pistons, the piston is too far down in the hole at top dead center. so the quench sucks and you get a crappy burn or hot spots. someone else will chime in im sure and explain it more/better

[lafrad]

If you are allowed to run race gas, i would go with the KB pistons.

Get the 4.2 crank, run it with the 4.0 rods and the KB pistons that are built for high compression (if you can get them to give you flat-top pistons, even better)

Race fuel (or even AVGas from your local airport) LOVES compression... LOTS AND LOTS of compression. a flattop with a 4.2 crank would give a bit over 11.5: CR. there is 20-25 HP more just in compresison alone. Add to the fact that you get decent geometry from the long rods and more displacement from the crank, it would be a HUGE upgrade over what you got now.

[amcinstaller]

wasnt there a thread a while back where someone wanted to run aviaton fuel but the lead content destroyed the catalytic converter? im sure i read that here.

[lafrad]

yeap, race gas and AVGas will be not good for a Cat and will reduce the life of Oxygen sensors to under 25,000 miles.

But honestly, if you are mud-racing a truck with Cats and are expecting to rack up over 25,000 miles of racing... I would question your motives

[Bodo]

VP sells a high octane, unleaded fuel. VP100 and MS109. I have a customer with a modified saab that needs this stuff. $$$

[amcinstaller]

yeap, race gas and AVGas will be not good for a Cat and will reduce the life of Oxygen sensors to under 25,000 miles.

But honestly, if you are mud-racing a truck with Cats and are expecting to rack up over 25,000 miles of racing... I would question your motives

this is true. good call

[jonb8]

Little update, I've finally found a 91 2dr with to build the mud racer out of. I was thinking of just stroking her trail jeep that she races now but it's getting so heavy with the bumpers, rock rails and stuff like CB and onboard air. To take advantage of the stroker I thought I'd better just start with a stripped 2dr and the fun of building this new jeep has got me pumped....My biggest problem now is finding a HO head, all my good heads are OBD2 and don't have the temp sensor in the back of the head. Any way around this problem from you guy's running 97+ heads on HO motors?

[yuppiexj]

My biggest problem now is finding a HO head, all my good heads are OBD2 and don't have the temp sensor in the back of the head. Any way around this problem from you guy's running 97+ heads on HO motors?

I have a 2001 engine in a 94 XJ and run one of these http://www.hesco.us/shop.asp?action=det ... catId=7969 (actually my home brewed knock off version)
It's a standard t-stat housing with an extra 1/8 NPT hole for the sensor that would go in the head.
You could just drill and tap the hole in the later model head (the pad for it is still there in the casting), but it would be an expensive mistake if it got screwed up.
I did the t-stat housing, because they're was a bunch of extras in my parts pile and wouldn't be out anything other than 5 minutes of work.

The gauge reads 5-10 degrees F higher with the lengthened sensor wire, and the sensor location at the front of the head instead of the rear.
You will break the temp sender if you toss the serp belt, so stock up on an extra sender or 2.

[jonb8]

Thanks, that helps alot. I really wanted to use the 98 motor I already have.

[jonb8]

Thought I would stop by and update alittle. I have a 1980 258 for the stroker build but I haven't got it started yet, I have been working on her mud racer though and almost have it done. I ended up with a renix 89 2dr and transplanted everything out of rustbucket 96xj I had into the 2dr. I'm running 410's, with a spool in rear and 33/10.50 boggers. I have removed every bolt in this jeep I could and still get it to start, it's very light. I plan on starting the stroker soon and have it in by fair season, but for now I'm running stock again. Here's a few pics of the build.

[jonb8]

[gradon]

I love 2drs w/o roof racks.

[racing89]

Gonna run the aw4?

[jonb8]

Yes I'm running the aw4, I like the way it shifts on the limiter as long as the TPS reads WOT. Takes the guess work out of it for my wife.