392 propane build up questions

[Rusty Escandell]

I am building a 71 800b with a 392 cid, propane, Borg Warner 3spd auto, d300, SOA, d44/d60 (3.73 now soon 4.88), 40" or 44" tires. Its intended use will be for some street use but mostly sand/mud/rock. The stock 392 engine is apart and I'm going to reassemble soon, so here are the questions before I do, I’ve read many threads on engine building, but none with propane for fuel.

1) What cam, if you would replace?
2) What piston rings and from where?
3) Because of the propane what gasket set? The set I have is FEL-PRO KS2702

Any information or direction would be very much appreciated
Thanks
Rusty

[pete wolla]

propane has high octane can benafit from more compression.not a problem where you are but up north propane vaporazation in cold weather can cause problems

[Paul "Misterfixit" Schulz]

Down here i would venture to say that 95% of all commercial 345's and 392's are on propane/LPG, most scouts that are driven any great distance are on it too, alot of these vehicles are converted to a dual fuel setup so they can run both, most with absolutly no engine modifications, all that is really needed is a good mix of 50/50 etheylene glycol and water in the cooling system and a decent coolant supply to the convertor, i have read here that there is special intake gaskets but in saying that most of the ones here in the commercial use were converted from near new. set your mixtures at 2% CO at idle and 0.5% at cruise revs, use composite intake gaskets and if possible get the OEM style steel shim head gasket to keep up the compression.

[Blackdog]

You need about 9:1 compression and hardened valve seats. I'm not a propane expert but I am in the process of converting my 196.

[pete wolla]

it was years ago when i saw the article in HOT ROD mag but i seem to remember octaine was about 110 this would support much higher than 9to 1 seems like they were running 11to1. dual conversions are used up here cause the propane wont vaporize properly at -40f i'm not recomending you run 11to 1 but more pressure = more power it will run at stock compression just fine but seems a waste of all that octaine

[bmacguyver]

what 392 are you using ic or non-ic? if non-ic you can use 345 heads which if memory is correct wil yield about 10:1 compression. if im wrong im sure someone wil correct me. with propane and stock compression forced induction would be very fun.

hth

mac

[Rusty Escandell]

Thanks for everyone's input so far.
The 392 is Improved cooling (IC). I don't really want to replace pistons, since the motor specs out great, head swap is out of the question, beacause this motor is IC type.
I am willing to replace cam if, there is a tried and true cam for propane.

Accelerated Motion cams shows cams for propane engines see http://www.amotion.com/amcams.html#00000
Thanks
Rusty

[canaminal]

Northern auto has propane rings listed on their E-bay store.

I have 240,000 on 345's and 392's on propane only. I have modified the dist to limit mech advance. thats all thats ness to run hard on propane @ 14 degrees static adv.(14 + 8 at dist = 30 at crank) I had issues with open throttle detonation (melted pistons till I reduced the mech adv.) or gutless and backfiring with less static advance.

I have milled .08 and .1 off compression surfaces and .065 and .055 off intake surface to get my C/R up . to some advantage

A OHG 450 mixer will bolt to the holley square throttle plate (adapter to Q-jet for spread bore)

I also mounted shutoff and reg/evap on fender as a propane installer suggested w/1" hose ($80) 3/4 Mnpt ends to keep torque and vibs from affecting reg. operation . This works fkin good in rough ugly zone!
Use what youv'e got and have fun. I do

[canaminal]

Thanks for the cam link I will call them as they are 10 miles from me and I'm getting my .03 over 392 I/C back from Mach shop in 2 days.

I may opt for a 200/200 cam just because. 2 weeks to let you know effect.

Iv'e had no issues with stock cam and most will probly agree that fuel bill /range will be an issue running a 392 . I often tow 2-4 dirt bikes in steep
mountainous terain or a 345 would be lots.

In the exhaust ports there are unnessisary bumps (cast for air pump) limiting flow. THEY MUST GO

OK I just pushed th F**K It button. Cam regrind to .480/.480 256/256
For $110 Cdn 1 week turn over. Full torque output!!

I'll let you know in 2 weeks how well it runs

[Rusty Escandell]

Update, I decided to go with the stock cam for now, ordered my rings, main and rod bearing from Northern Auto http://www.northernautoparts.com/Pro...ctModelId=1311

OK I just pushed th F**K It button. Cam regrind to .480/.480 256/256
For $110 Cdn 1 week turn over. Full torque output!!

Hi Canaminal
Glad I could be of help. (boy do I love Google search results, that’s how I found them). Thanks for your input, please do post your results. I’m sure many of us will be interested.

A

OHG 450 mixer will bolt to the holley square throttle plate

Roy from http://www.propaneguy.com/www.propaneguy.com/Index.html said

425(392 cfm) entre level kit would work , i would use the 450 kit (500
cfm)with new mixer with adjustable fuel rods for $450.00, power valve $50.00
adapter to holley throttle plate $50.00
...shipping ground now is $30.00...roy..then you need service hose and a
propane tank..cheaper in usa..roy

Did you bolt your OHG 450 with out an adapter?

Thanks
Rusty