HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

[kcstudly]

Glad I caught up w/ you Dave. We've missed you out in the print world.

Jeff Smith (you know him) said that the Vortec head on an HT383 "would create excessive static compression ratio with a flat top piston", but he didn't say how high "excessive" was. (I think he meant with 8 flat top pistons, but that's another discussion.) Humor me and consider propane fuel for a minute.

As a car guy (always have been, '66 & '67 big block SS Chevelles), a hot rodder/classic trucker (chopped and lowered '72 Chevy Super C10), corner carver ('89 Chrysler Conquest TSi), and 4x4 enthusiast (Jeep TJ Wrangler) I think there may be something for us crossover gear heads here.

The SBC in a Jeep is an old trick for cost effective power gains, and propane fuel is a great alternative for off roaders (we're all just gearheads, right?). With propane's higher octane rating and lower power content, a mild mannered high torque high compression solution may be just the ticket for a good rock crawler.

Anyone have any thoughts or insight on this setup?

[Scott Liggett]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

A 383 with flat tops and 64 cc heads give you about 11.32:1 compression which makes running gas, at least Cali gas, near impossible with iron heads.

You will be better off with 76 cc chambered heads to give you 9.91 compression.

[Freiburger]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

To me, lower compression and the cheapest possible gas is the best for a rockcrawler. I want to be able to buy dog-water gas ANYWHERE and not need to find propane when I'm in the middle of nowhere. My Jeep runs a crate 350 with like 8.5:1 and it runs on anything and lugs down to 300 rpm loaded.

I don't really know anything about propane.

[JoeyG]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

I don't really know anything about propane.

It's a gas..gas..gas

I don't have any experience with rock crawlers. But mud runners and buggie trucks usually will go best like Dave said. Hell I've seen some trucks suck water like a hoover vac and keep chugging through because of the low compression and cam profiles (mainly bleed-off). I think Rebel is right though, with the Cali gas try and build a more econo friendly setupmaximized for torque. The propane injection (carb) setups seem to work fairly effieiciently. Its just the need to swap between carb/propane setups if the used fuels are having compatibility (quality) issues.

[JeffMcKC]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

The guys around here switch them to EFI, so no matter what angle it at it runs fine.

[Freiburger]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

My QuadraJet runs at any angle.

[dieselgeek]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

My QuadraJet runs at any angle.

I've done more EFI jobs for serious four wheelers than racers. They tell me that carbs don't work at extreme angles. What's the fix for this?

[JoeyG]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

My QuadraJet runs at any angle.

I've done more EFI jobs for serious four wheelers than racers. They tell me that carbs don't work at extreme angles. What's the fix for this?

27" of engine vacuum :D

[JeffMcKC]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

The air is different out West ;D Everything is anti gravity, Boobs, Gas you name it, in the Midwest we call it California bolt on you buy it and just bolt it,,,,, on after weeks of work. I prefer EFI as long as you can keep, the sump covered.

[smallblockjay]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

EFI is popular for off roading. Some carbs, like Q-jets and AFB's can work decent. For whatever reason, I have seen propane used on crawlers. I always assumed it was for the same reason, extreme angles. If money allows, I think I'd go with EFI and cheap gas.

[dieselgeek]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

I've done a lot of simple TBI swaps. There's no need for multipoint EFI on a straight six jeep or formerly TBI 350 Chevy.

A TBI can be grabbed out of the junkyard nearly free. Make sure it has injectors, and was from a similar displacement engine (i.e., 4.3 Chevy v6 is great on a 258 jeep six). A "rebuild kit" for a basic TBI is about $25 and it includes a new diaphragm and spring for the built-in fuel pressure regulator (another nice feature of a TBI). The pumps for TBI injection, which requires much lower pressure than multipoint EFI (9-15psi), are about $35 at a parts store. A megasquirt makes a heluva brain and is EASY to tune on a TBI (most of us recommend TBI tuning with Megasquirt first, as it's a great way to learn cheaply and it's simple to do). You can leave the ignition in place, or have the MS control ignition later on if you want. A pre0-built MS-1 is about $350 or assemble it yourself (it's easier than painting by numbers) for $180ish.

$30 in wire, hoseclamps, butt crimp connectors, and an afternoon of fun - and it's on!

[TheSilverBuick]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

(it's easier than painting by numbers)

It's true!

[kcstudly]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

yeah, I was in on the megasquirt early in the second version, way back when it was just taking off (wish I had more time to keep tabs on everything some guys were just getting the EDIS setups to run back then). Still have that for my turbo Conquest.

I can see the advantage of low compression on stink butt gas (o-lean, that is..panther piss) out in those wide open deserts when you're three days from home, but out here on the east coast in New England where we have much smaller areas to play in (lots of trees and mud, by the way) I don't have to worry so much about how far I would have to go to get a refill. From what I gather the big bottles are good for 8 - 10 hours of wheeling and cost less than a tank of 87 tane. Maybe I'm all wet, but if you tip the thing over at least it's dry.

So what you guys are suggesting is that I should take the 70's vintage 455 Buick I have out of moth balls and do a quickie low compression, Squirted deal on that for a dedicated buggie? Maybe a fabricated MPI manifold w/ 17 inch runners w/ trumpets in a nice tight plenum, and some long tube headers?

[JoeyG]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

That would take the "budget minded" out of it though :D

[HoosierGTA]

Re: HT383 w/ Vortec Heads Flat Top Pistons on Propane for a Rock Buggy

I agree with Joey G and Dave When your in the middle of now where nothing like a carb for simplicity and the Q jet can be made into an extreme angle wheeler. If I did EFI a wheeler it would be t.b.i. since it's the next simlest and doesn't require a lot of preasure the run ,like 12-15 And similar to a carb if you have juice to the distrib. you could rig a 2-liter coke bottle and hose to get out to civilization if need be!