alright...yall double check me

im trying to calculate compression ratio for my motor, and ive tried 3 calculators and keep coming out around 13.16:1 10.952:1 dynamic comp ratio

its a 8 cyl
3.85" stroke
4.42"bore
75cc comb. chamber
.040" head gasket compressed
4.5" head gasket bore size
12.1cc dome on piston
.025" piston deck clearance
43* IVC (ABDC)


im too lazy to cc the heads myself, but everywhere i look says 75 cc for dove-a's

who thinks this will be too much for a 472 on propane? supposedly it has a 105+ octane rating?

I hope its alright because i already have 4 slugs in the motor

with my head flow #'s and my lunati custom grind solid lifter cam and approx 550 cfm(thats what propane guy said the x-450 mixer flows)

it says 457 hp@5000 569 ft lbs @ 3500.

it shows over 530 ft lbs from 2000-4500

cam is 264 272 advertised 232 238 @.050 .542 .559 lift

114 lobe seperation

I found a gasket i could exchange tomorrow at summit racing with bore of 4.54" and .0595 thick

changes it to 12.39:1s and 10.32:1d.....maybe that woudl be more workable?

do i need to be running copper gaskets with this compression?

i talked to "gotpropane guy"(cary) and he said hes heard of 12.5 or so successfully but couldnt remeber if he has ever heard of 13:1 being done? lunati cams tech guy said go for it???


are there any other dangers of running 13:1 on a trail motor??

what do you all think??? Tear my idea apart

 

i have no experience with propane other than my grill.on the head gasket front,i know there are guys over on 460ford running the 1018 fel pro's in the 14-15-1 range with no probs.are these what you had?darrin1999 has some experience with propane in a truck.he'll chime in when he sees this.

 

yep im here anyways, if you get hd-5 propane (motor grade) its a more strictly controlled mixture than the just general grill gas, and would be what youd need for a high compression engine. hd-5 is 97 motor 112 research octane, or about 105 "pump" octane. are you polishing the chamber? youll need to. youll also need a 160 thermostat and make sure you have a good cooling system to keep it there, otherwise your evaporator will gum up with crud, and so will the vapor line. the harder you work that engine the higher your octane requirement, and the dome pistons could screw with the fuel distribution and create hot spots. a good flat top would be better for detonation resistance, but you wouldnt get as much compression. i usually err on the side of caution for compression and use the motor octane rating if going low speeds or towing (which trail riding would qualify for). the ohg mixer is a good choice. running the rpm range you would with a cam like that it should run a little lean, which is what you want. unlike gasoline a lean propane mixture runs cooler and has less chance of detonation. you may want to swap that head gasket out for the thicker one for detonation resistance, as quench doesnt mean much to propane. if you had aluminum 75 cc heads i wouldnt be as worried, but with cast iron youre really testing the limits. oh, and make sure you block off the heat risers, and polish the intake and exhaust along with the chamber for better flow, a cooler intake charge, and less settling.

 

i will polish the chambers and ports...the heads already have some porting, bowl blending and 2.19 176 valves....whats the purpose of the 160 stat??? does a propane engine just need to run cooler???


i appreciate the advice.....best advice ive gotten yet!! wheres a good place to get the tools to polish the chambers etc...and also do you think i should run the 12.4 comp ratio or the 13:1?

thanks!!

 

12.4 comp... if you had aluminum heads id say go for the 13.1, but with iron even 12.4 is pushing it
yep propane engines need to run cool, because if you dont the evaporator and vapor lines get clogged with crud and wont run worth crap after awhile, then you have to rebuild the evaporator and lockoff and replace the vapor line. putting a low temp thermostat slows the deposit formation. another reason youll want the 160 is the lower your engine temp the less prone to detonation it is- and youll need all the help you can get.
as for polishing the chambers and runners- do you have a dremel? if not, pick one up and a set of bits. my mom got me a nice 61 piece set for christmas, i think she paid 20 dollars for it. it may take a little longer with a dremel than a die grinder but id rather it take a little longer than risk screwing anything up. just polish everything from the top of the intake through the heads and exhaust ports. being a gaseous fuel you dont need to worry about wet flow, so anything you can do to smooth the intake and exhaust out will increase port velocity and torque good luck and have fun
p.s. being a trail vehicle are you using a forklift tank, or are you getting the proper tank from sleegers mfg or manchester tank? theyre the only 2 companies that make approved road tanks.
oh and one more thing, you should have your distributor recurved for propane. theres a forum supporter here that specializes in distributors. id get the recurved duraspark

 

Hate to change the subject, but out of curiosity, does the propane still run through the carb or do you have to change over to an injection system. I have never run propane on anything. This is just a curiosity question, I have already sunk to much money and time in my tunnel ram and 2 4s.

 

it uses its own "carb" called a mixer. if you use an impco 300 mixer then you can do a dual fuel setup, otherwise if its a dedicated setup you could run impco 425's or ohg 450's or if you really need alot of flow and have a few bucks, you can get a technocarb mixer (700-800 cfm rated depending on internals) for a dual quad setup id do probably impco 425's

 

Thanks, as I stated that was a curiosity question only I am not planning on doing any changes any time soon.

 

i appreciate your help! i have a dremel but i need to get that set of bits your talking about...i will get the heads polished up this week....might even do a little more porting to the exhaust side of things

I have two 8 gallon aluminum forklift tanks and two forklift brackets and they will be mounted right behind the cab where my fuel tank is now.....about 95% of the trail vehicles i see with propane are running the aluminum forklift tanks

I cant wait to get this thing going ....one more question about propane....ive heard from some people to make the spark plug gap smaller? is this necesary??? also does propane produce alot of carbon buildup like a gas engine??

 

thats one of the best parts of propane- 0 carbon buildup- oil stays as clear as the day you put it in, its just the additives that wear out- so you can easily double your oil change interval. anything thats lubricated by motor oil will last 2-3 times as long- its just hard on valves... youll have to have the heads rebuilt about every 80-100,000 miles. youll need good stainless steel one piece valves and good hardened valve seats, also any seal that would normally be lubricated by gas will dry out, so you should put some vaseline on the gaskets that come in contact with propane to keep them from drying out, but youll never have to be into the shortblock also yes its definitely recommended to shrink the plug gap to around .025-.030 because its a vapor, not a bunch of droplets like gas, so it doesnt need as hot of a spark, and in doing so your plugs will last about twice as long
the reason i asked about what tank youre using is that forklift tanks are not legal for road use, you have to have a special tank and there are only 2 companies that make them.

 

thanks! this vehicle does not see the road, its trailer only....so i dont think i have to worry about the legal issues

any more tips that you can think of???

 

i dont know how assembled the engine is or how much of it is ordered but youll definitely want standard tension oil rings for oil control... on the cam youd want a slow close on the exhaust to be easy on the valves and seats, and id have gone hydraulic for the cam because i dont want to have to be adjusting valves all the time, or solid roller because if i do have to adjust valves i want a power benefit instead of just an rpm benefit, but thats me

other than that i cant think of anything. if you have any more questions you can think of, just either post here or pm me

 

darrin...where would i find a blue thunder dual quad dual plane intake???

 

best place to find one is either www.ford-y-block.com or www.survivalmotorsports.com
i think survival motorspors is an fte sponsor and is where ill be getting mine,
but theyre 500 dollars.
best place to get propane parts and supplies: www.propaneguy.com
you can get a full dual quad propane kit from him for 600 dollars- all you need is service line and a tank.

 

just curious where did you get the 550-575 cfm number for the ohg????

ive looked everywhere and cary at got propane said about 550 but was unsure