Ok guys, given the cost of benzene is outta control and that were getting royally fleeced at the bowser here in Oz, Im looking to convert to LPG. Propane gas here is cheap, plentiful and widely available at the pump and the Feds rebate you for the install so here's the plan.... Im looking into building a nice 383 (maybe a 400) sbc for use on propane only. Pre-requisites? Need real good TQ off idle to 5K max only, stock convertor, mild duration @ .050" cam but reasonable lift for breathing and NON Vortec heads for a vintage look to the whole deal. A TH 700 will fit in and be modded to the factory column shift for the stock look. Good efficiency is important here. To facilitate the period look, I will run the early (57 Chevy) air cleaner converted to modern element, front fill intake, Cal Custom finned or early 60s Vette valve covers without breathers, hidden PCV, hidden propane convertor, hidden propane filler valve in the rear fin where the existing fuel tank filler is I already have an early EB Torker intake with the oil fill tube at the front, an Impco 425 lpg carb that will be covered with the Bel Air air cleaner as mentioned. A modded Delco early dist to electronic will provide the fire.... Im looking along the lines of a 383 combo, adding MY SP intake, around 10-10.2:1 CR for the propanes higher octane. In a 383, that will mean a zero deck Hypereutectic piston with 5cc of valve clearance, a 4.030 bore, 3.75" stroke, a cleaned up 76cc head to give 75cc and a shim head gasket of .022 crushed which will yield around 10.2:1 CR. A juice cam with about 205-210 int and 210-220 exh duration @ .050" is what I have in mind here. Can you guys recommend a cyl head that is non Vortec, has straight valve cover mounting holes, around 74-75cc of chamber (milled), and has decent flow characteristics? Has anyone built something similar for their combo - what parts did they end up using?
First off - your piston to head clearance is way too tight, and the piston will be contacting the head. Pistons rock in the bore slightly. With a hyper piston, you will be quickly getting a new engine when the pistons fall apart if you tried to run that combo. The tightest I would run is about 0.032" on a engine with a real tight piston/bore clearance to keep the piston from rocking. The impco 425 only flows 425cfm, so you will be out of breath pretty quickly with a 383 or 400. You can run a pair however on a dual quad intake. Propane as an octane rating of around 108, so you can crank up the compression quite a bit - usually propane only engines are 11-12:1 compression. A flattop piston and a 64cc chamber at zero deck and 0.038" composite gasket is the easiest way to get there - about 11:1 compression. That cam would work well but is a bit small for all those cubes. Get something like the 214/224@50 cam ground on a tighter 106 or 108 lobe seperation angle, and run it with 4 degrees advance. It will have a little rumble at idle but a ton of midrange torque. I would run iron heads with this combo with a smallish intake port. Dart Iron Eagle platinum 180's would be my first choice. For a nostaligic head, the old fuelie heads would work well here with some hard seats inserted. Pay special attention to exhaust valve clearance and open it up to the maximum reccomended. I like stainless exhaust valves for propane because propane really puts a lot of heat into the exhaust valves. For an engine that is going to be seriously worked like towing or in a heavily loaded truck - open up the exhaust guides to 3/8" and run the stainless sodium filled valves. Carbide seats are needed for extreme heat conditions like this as iron seats will erode. I did these mods for my endurance racing turbo smallblock. It was eating seats and valves before this. Same issue, too much heat in the exhaust valve.
I agree with rick for the most part. Impco rates the 425 at something like 460 cfm, though a guy I've talked to with lot's of dyno experience with them says he sees about 570. (you wouldn't think it to look at them) I think it depends on the throttlebody used. Impco is based on a 2bbl design and this guy uses the holley 750 4bbl base plate. I plan to run two on a 1:1 linkage since they are a constant velocity design. Being vac operated, you won't run the risk of over carbing. I'm going with the vortec heads, though, because they are more lpg ready out of the box. There are aftermarket versions available with early valve cover and intake patterns for about $600 a pair. They have a much better chamber and port design than anything before. As you raise the compression, that's a bonus. I need to confirm my pistons, but my engine shop originally built the motor for another customer as a 10.5:1 motor for nitrous. They are about .040 down in the hole. I may see 11:1 if I deck the block and choose the right gasket. Your cam choice sound reasonable, though I plan on something in the 250* range at .050 with about .550 lift on 106-108* centers. I want it kinda nasty and will be using a 4 speed.
Hey great info Rick and Scotty. For the most part this engine will be in a street 57...NO racing, not even on the street. I have fitted a Holley 725cfm vac sec baseplate to the 425 so as mentioned, it should flow well for my needs. The trusth is that this mill prob wont see more than 4K, hence the cam specs I suggested to keep the low/midrange TQ high and move the wagons bulk easily and to allow a stock convertor. Racer I think you may have misunderstood me. I didint mean a piston to head clearance of .005" I was referring to a zero decked picton with a 5cc valve relief lol. I wont run a quench any tighter than .030" with a steel rod...I don't feel theres a need for it. Tight quench is good but even .035" to .040" is sufficient for this engine as it won't be knock snsitive with 10-110 RON. And I agree with you re the duration @ .050" specs...I already have a juice cam with 214/224 @ .050" can but not sure of the lobe sep - Ill check it out. The s/s valves and hardened inserts should be sufficient - I wont be towing (rarely anyways) . BTW, any reason why you recommend the 180cc Dart iron Platinum heads? Would 180cc out fo thebox be ok or would 200cc better? Curious about these heads? Scotty, tell em a bit more about these Vortec heads with the early valve cover/intake design? Where do I get em - is there a site where I could scope em out ? BTT and thanx for the input ! Rat
I added you on MSN, have a few links regarding and would like to discuss them with you. Best Regards Andy
Not to hijack but I am looking for the same info for a Ford 300 build. I want to build it specifically to run on propane with a pair of small turbos and possible an intercooler.
Your above combo listed has a zero deck pistons with a 0.022" shim head gasket for a total piston to head clearance of 0.022". The 383 and 400 SBC's are undervalved and the tighter LSA has proven to give healthy gains in mid range torque. Most cams of that duration are ground on 112 LSA so they idle nice, with about 5 degrees advance ground in. The dart 180's are the smallest of the Iron Eagle Platinum series. You want the smallest runner that flow well for torque because of their superior velocity. These heads also have a very good exhaust port.
Thanx for the feedback Rick...a Felpro would give me .039" with quench built into the gasket if I end up with a zero deck. Sorry for the confucion mate. I since checked out the Dart I ron Eagle 180's and it makes sense to keep up in take/port velocity to maximise TQ....hi rpm power here is not the goal so the 180s should be OK. In your opinion what size/length/collector size header would work best to maiximise the exh flow for the propane as well? 1 5/8" or 1 3/4" OD ? Once again thanx for the input guys ! Rat
These guys offer a vortec head specifically for early intakes and valve covers. Not sure about their pricing, but should be competitive. http://www.aaeq.net/Enginequest/Home
Thanx for the link Scotty, but the cyl head page won't work. Their online catalog aint working properly. Thanx Any comments from the Aussies? Rat
A set of vortec heads would work well also, if you can find those that take the old style intake and valve covers.
download their pdf catalog and look for the vortec heads on page 4. There's one for old tin and manifolds.
We've run propane on cars with great results, as was said we found the single mixers weren't good for top end power, more mixers were the answer for us!
How about propane injection ? Check http://tinyurl.com/2wuky4 Prins is coming out with electrical heated converters so you don't need coolant hoses anymore which makes it a lot easier to hide them. Also check this forum for good info regarding running on propane : http://tinyurl.com/6cjnwm Rik
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