Performance mods for a rock buggy? BACK FROM THE DEAD!

[Jeep-hauler]

I need some help from my fellow first genners. I've read through lots of power recipe threads, but thought this was a little different than a heavy truck designed to tow trailers or pull sleds. Hopefully this fits in this section.

I'm building a tube chassis truggy around '51 Power Wagon sheet metal. My donor engine is a stock VE-pumped 12 valve out of a 92'. I will be running a NV4500 behind it. It will be relatively light(for Cummins power) at around 4500-5000 pounds trail ready. I would like 350 HP, and from what I've read should be reliable. I want as little turbo lag as possible. Twins are out of the question due to packaging. I won't be towing or pulling with it, just play time in the rocks, and occasionally street driven. I do not have a blingtanium budget.


With all that in mind:

What fueling mods would you suggest, including lift pump?

What turbo would you suggest (I have the stock HIC and giant 21cm housing)?

I ran a Southbend Con-O in my old truck, but I guess a CON-OFE might be a better choice for higher power levels. Are they grabby? I need a clutch I can slip a little bit, then lock up. Any suggestions?

Here's a mock-up picture of the project. I've already started on the chassis, but its not in the picture. It will be about 7" taller at ride height.

[oldestof11]

I have thought about this in-depth for when I have extra (HA!) money to sink into a 2nd truck...

My setup would be as follows:

DDP 2's or 5x12's
HE351CW or VE if you want some better tuneability
4k rpm spring
110 lbs valve springs
Walbro 392 with a 2nd Gen piston lift pump (I like redundancy for going off-road)
Holley 4307M regulator set at 16psi for safety
Timing advance spacer
Con-FE for some slipping (grabby but it helps hold the power)

All this is good for 350hp and high revving that you are going to need.

Now the HE351VE (variable vane) would be the hot ticket if you can get it to work just right.

Most use a small air cylinder to control the vanes so they open up with more boost or drive pressure. Now this is great for a street truck. Also some have put a spring in the linkage for an electric solenoid that is activated by the brake pedal to shut the vanes closed for an exhaust brake. My idea would combine these 2 and add a 3rd element. Another solenoid that closes it so at 1500rpms, there is about 2-5psi of boost. The button for this would be in the shifter. I would press and it would close the vanes thus making the need to rev skyhigh or load the engine for boost null and void. Hold button, push gas, let out clutch, get moving, drop clutch, drop the hammer, instant boost, let go of button so engine can breathe, 4k rpms here I come!

Just a thought.

[Jeep-hauler]

I have thought about this in-depth for when I have extra (HA!) money to sink into a 2nd truck...

My setup would be as follows:

DDP 2's or 5x12's
HE351CW or VE if you want some better tuneability
4k rpm spring
110 lbs valve springs
Walbro 392 with a 2nd Gen piston lift pump (I like redundancy for going off-road)
Holley 4307M regulator set at 16psi for safety
Timing advance spacer
Con-FE for some slipping (grabby but it helps hold the power)

All this is good for 350hp and high revving that you are going to need.

Now the HE351VE (variable vane) would be the hot ticket if you can get it to work just right.

Good stuff. I was already thinking a HE351CW would work good, but I'm not sure I want to deal with the complexity of the VE. I hadn't thought about a 4k spring and valve springs. The extra rpm sure would be nice.

Is this doable with stock head bolts? Sorry for the newbish questions, but I need to learn this stuff.

I forgot to add in the first post that I already have a PS intercooler for it.

[Tacoclaw]

Yeah, port out the wastegate hole and set the 'gate for 30 or so psi. You're gonna have a tough time making a ported 351(or HX) creep.

My list would be a bit cheaper, as I'd just use a 12cm 'gated HX35 and a LPLP with big inlet lines. The top-end stuff is good insurance, since you're going to be begging for RPMs in an offroader. I'd also consider higher gears than what most people run in their trucks. 4.56s work good with a big block that can wind up to 7k, but ~4000 will be your max.

You're also going to be working with a lot more inertia and torque than most have, with the diesel and heavy flywheel it uses. Just a thought, considering how unforgiving a clutch like a Con FE can be. Could equal up to a lot of busted stuff if you're not quick on the clutch, however, that depends more on the rest of your drivetrain I guess.

I know my Con O-FE is grabby, it'll make my truck shudder if I take off too slow.

[Deathrod]

I would just put a smaller housing on your stock turbo and spend the money where it counts.....axles and a doubler. That motor has plenty of torque the way it sits...get your crawl ratio down low and you wouldn't even notice 100 extra hp...just break more $hit. A buddy and I are building a crawler too with an RV 440/727 trans, 205/203 doubler...and are waiting on $ for knuckles,cromo shafts...etc to make the D60 attempt to stand a chance. I hate being stuck on the side of the trail when a Toyota crawls passed you because your heavy foot got you into trouble!

[Deathrod]

Oooh ya I forgot...that thing is gonna be badass!!

[Jeep-hauler]

I would just put a smaller housing on your stock turbo and spend the money where it counts.....axles and a doubler. That motor has plenty of torque the way it sits...get your crawl ratio down low and you wouldn't even notice 100 extra hp...just break more $hit. A buddy and I are building a crawler too with an RV 440/727 trans, 205/203 doubler...and are waiting on $ for knuckles,cromo shafts...etc to make the D60 attempt to stand a chance. I hate being stuck on the side of the trail when a Toyota crawls passed you because your heavy foot got you into trouble!

Maybe a lower powered build to get it working is a better idea. At least until the chassis/drive train bugs are worked out.

A 3.8 Atlas is on the way with 300m input and comp gears, so the T-case is handled. I have a high pinion 60 for the front, and a 14 bolt for the rear. They will have alloys, but the Atlas just emptied my account. I was already planning on running higher gears because of the increased torque and limited rpm.

[Jeep-hauler]

Oooh ya I forgot...that thing is gonna be badass!!

Thanks. I'm stoked to get it together, but in reality it probably won't be running until next year

I rescued the truck from property in the back woods of the Cascade foothills. Originally I was planning on restoring it with my son, but when I got it home I realized it was too far gone, although it did run. There wasn't a straight panel on it, and the cab floor was basically gone, so I don't want people to think I'm cutting up a restorable classic.



Short clip after I got it running at home. Check out the custom "fuel cell".

[oldestof11]

I would just put a smaller housing on your stock turbo and spend the money where it counts.....axles and a doubler. That motor has plenty of torque the way it sits...get your crawl ratio down low and you wouldn't even notice 100 extra hp...just break more $hit. A buddy and I are building a crawler too with an RV 440/727 trans, 205/203 doubler...and are waiting on $ for knuckles,cromo shafts...etc to make the D60 attempt to stand a chance. I hate being stuck on the side of the trail when a Toyota crawls passed you because your heavy foot got you into trouble!

The torque is fine but you need the HP and RPM's for a rock crawler. HP gets those RPM's up quicker.

I wouldn't do a air-to-air cooler as it needs lots of moving air to cool efficiently. I would do a water-to-air setup with glycol (antifreeze) and water with a big radiator set up behind the cab and its own set of fans. Also you don't have as big of a package to find a place for.

Also, to move the torque around, play with the timing and when the wastegate opens. If it opens sooner with less boost, and timing is pretty far advanced, the torque pre-2000 rpms would be significantly less making the drivetrain last slightly longer.

[Tacoclaw]

I don't know that I'd IC it at all. It doesn't hurt, but considering that crawling won't be pushing that engine anywhere near it's limits I don't see an IC being needed. I figure air-to-water is too complicated, but if you've got room and find yourself looking for something to do it's nice to have.

I'd port the head and have a baby turbo and a free-flowing intake and exhaust. A ported head and cam gave my truck a noticeable increase in off-idle power. Sometimes you need that instant bit of power to bump up over stuff. You just don't always have time to get the turbo spooled.

[dazedandconfused]

Id personally run a auto with a manual valve body.

[Jeep-hauler]

The radiator will be behind the cab because there's no other place for it. The PowerStroke IC will be mounted up front with its own electric fan. So even at low speed it should be effective.

Also, to move the torque around, play with the timing and when the wastegate opens. If it opens sooner with less boost, and timing is pretty far advanced, the torque pre-2000 rpms would be significantly less making the drivetrain last slightly longer.

That's the kind of thinking I was looking for.

Id personally run a auto with a manual valve body.

Most dedicated buggies are automatics because it easier to drive on rocks and easier on the rest of the drivetrain. If I had a choice I might go that route, but I've already got the 5 speed, and I like to row gears

[dazedandconfused]

Ive wheeled both and clutching all the time in a bigger vehicle on the trails sucks. My brother has a Joyner thats a 5 speed and its fun but when i wheeled bob tailed trucks it sucked.

[Deathrod]

Ive wheeled both and clutching all the time in a bigger vehicle on the trails sucks. My brother has a Joyner thats a 5 speed and its fun but when i wheeled bob tailed trucks it sucked.

Ditto about the clutch....gets old real fast...I'm sure there's about 1000 guys out there that would swap their auto for your 5 speed....but it's your rig so do what ever you like

[Jeep-hauler]

Ive wheeled both and clutching all the time in a bigger vehicle on the trails sucks. My brother has a Joyner thats a 5 speed and its fun but when i wheeled bob tailed trucks it sucked.

Ditto about the clutch....gets old real fast...I'm sure there's about 1000 guys out there that would swap their auto for your 5 speed

Yeah, I get it. I've wheeled jeeps with manuals and autos for years. Yes, autos are better in almost every aspect for rock crawling/racing. Using a 6bt in a rock crawler is a bad idea too, but I'm doing it.

....but it's your rig so do what ever you like

Egg-zackly. Your car is turning out very nice, by the way.


Back to engine stuff:

Do I need head studs if I'm shooting for 300-350 hp and high RPM's(4100)? Any head mods will need to be done before its in the chassis because the last two cylinders are under the cab.

Definitely leaning towards a HE351cw and mild injectors.