Propane stroker?

[sass]

How much power could I get out of a 4.7 stroker with 11-1 compression running on propane. Propane is roughly 108 octane and Got propane.com has a kit that retrofits 4.0 jeep engines on propane with no computer or sensors.
It would stand to reason that a lot of power could be made without the paramaters and constraints of the computer.

Just food for thought
SASS

 

[bajacalal]

I've thought about doing this as well (for years now actually). The higher compression of a 4.x stroker would be well suited to propane. LPG (propane) and dual fuel conversion kits for the Cherokee 4.0 are common in some foriegn countries but are rare here in the USA.

 

[sass]

Go to gotpropane.com . They have a kit for around $800

sass

 

[old_man]

Historically, an equivelently configured gas vs propane/butane engine, the gas engine gets 3-5% more horsepower. If you can't run the gas engine at the the higher compression ratio, I guess my analogy no longer applies.

We ran butane on the farm for years.

 

[sass]

I was thinking that running an engine on propane and removing the computer and sensors from the picture, it would open up new ways of thinking in the way of compression,piston choice,cam, ect.
Most propane engine conversions lost power becuase propane has less btu's than gasoline. But that was on engines designed to run on gasoline. Build a motor with much higher compression and a radical cam profile and see what happens!

 

[Vince]

I have a European propane conversion on my 4.0L XJ which is six years old now. During wide open throttle acceleration it automatically switches from propane to gasoline because the liquid propane cannot change to gaseous state fast enough to meet the engine's demand. Modern direct propane injection systems that inject through the gasoline injector do not have this problem. If you are planning to use an older style venturi plate system this may be a problem for you.

 

[sass]

I saw a video of a 600 hp drag car on propane. I belive your conversion changes fuel because it is a dual system intended to run on both gasoline and propane.In an engine intended to run on gasoline,you get more " passing power" running gasoline. I doubt the reason it changes over to gas is that it can't convert it to gaseous form fast enough.

 

[Israel]

Coincidentally, I have been looking into the same thing over the past few weeks. I PM'ed Dino (Dr. Dyno) since he seems to be 's stroker guru to see how I could get compression in the 12:1 range for propane. What we came up with is to use .040" overbore Silvolite 2229 pistons which have a dish of 11.5cc, shave .030" from the deck to get a zero deck clearance, shave .030" from the head to reduce the chamber volume and use a Mopar or Victor headgasket. All this shaving from the block and head will require a rocker arm shim kit from Crane, part number 99179-1.

This should yeild a 11:1 CR which is about as close as your going to get on a shoestring budget. If you can afford custom pistons, then I guess its not that helpful.

 

[sass]

Great minds think alike!

Custom pistons would be nice,but I think I would go your route first to see how everything worked together before investing in custom pistons.

What would the weak link be? The rods?

I belive there would great potential for power with this set up.

SASS

 

[Dr. Dyno]

What would the weak link be? The rods?

The 4.2 rods with ARP 112-6001 rod bolts will get the job done very nicely. Just make sure they're all balanced to the same weight.

 

[lilredwagn]

Just out of curiosity for the folks looking at the conversion - are you doing it for performance, out of environmental concern, concern about near-future quality/availability of gasoline, for economic reasons, or something else?

 

[Israel]

I can't speak for everyone, but I am looking to do it for both economical reasons as well as environmental reasons. As of last week when I called around for propane prices, it varied from 2.49 per gallon to 1.89 per gallon. Gas is 2.79 per gallon for the cheap stuff. 2.79 divided by 17mpg is 16.4 cents per mile. 1.89 divided by 15mpg (assuming I lose some power with the propane which I don't think I will since I'm building the motor specifically for propane) is 12.6 cents per mile. I drive about 750 miles per month in my XJ so on gas I spend about 125.00 per month. When I change to propane, I'll spend about 95.00 per month. If I can get 20 mpg out of my propane motor with an exhaust, intake and ignition upgrades, then I'll be at about 75.00 per month. That propane conversion and stoker motor could pay for themselves in a little over a year.

I'm not saying propane is best for everyone or that it doesn't have disadvantages, but it is really looking like a good move for me. More power, less money spent on fuel.

 

[Chancer]

OK, you guys have pricked my interest. Like Vince I have a propane XJ, and I've thinking about stroking it for a while. Can anyone do the science bit and suggest the optimal compression ratios for a DD propane stroker, or is 11:1 about right?

Personally I run propane because it's clean and cheap, and more power is always nice!

 

[Israel]

There really is not optimal compression ratio for all engines running propane. I believe propane's CCR (Critical Combustion Ratio) is near to 12.5:1, but with variables like camshaft profiles, the purity of the propane being used, intake air temperature and others, a safe compression ratio can vary both above and below the 12.5:1 mark. I was hoping to get close to 12:1 compression with engine support mods that would help prevent pinging and detonation, but being on a shoestring budget, the 11:1 combination listed in my first post will still do a great job. I have heard that higher compression ratios also increase emissions when running propane so maybe 11:1 is best anyway. Here are some links to my favorite propane pages so far.

http://franzh.home.texas.net/engine.html
http://www.propaneguy.com/www.propaneguy.com/parts.htm
http://www.gotpropane.com/p4.html#JEEP
http://www.patooyee.com/propane/propane_1.htm
http://www.pirate4x4.com/forum/showthread.php?t=409353&highlight=propane+efi

 

[mylt1]

didnt think lpg could be used on road in the US? also, how are you gonna switch over to a carb? this may be an upgrade just waiting to go on my xj.

 

[Maximus]

I also assume the wear on the engine would be less if I am not mistaken, this is something I started thinking about after visiting Key West FL. Most of the vehicles there I beleive are required to run propane.

 

[MudDawg]

Propane and dual fuel vehicles are very common here in the agricultural community. (despite all the growth Florida still produces a significant portion of the world's citrus fruit). There are a few things to know...while the octane value is high (useful combating detonation), the BTU per pound is lower than gasoline...the lower fuel to air rato results in decreased miles per gallon compared to gasoline...so the ultimate cost per mile for fuel may well stay with the same range as gasoline....another issue is the transportation of the fuel...D.O.T. regs prohibit transport of a flammable gas inside the passenger compartment..so the tank(s) must be outside the vehicle...not a problem on a pickup...but a problem on a XJ...you would have to fab a ventilated enclosure or mount the tank(s) under the rig or other location....benefits...high octane...the crankcase, sump, and other lubricated areas will have far less sludge (Typically a propane motor looks as clean as new after many K miles) Easy to get in most locations...the rig will stay running even upside down, so off camber problems are non-existant. Possible problem areas...you need hardened valve seats and stellite valve facing due to the complete lack of lubricating properties of the gas...advice...have a professional with the proper gas analysis equipment set up the mixture.

 

[Israel]

the BTU per pound is lower than gasoline...the lower fuel to air rato results in decreased miles per gallon compared to gasoline...so the ultimate cost per mile for fuel may well stay with the same range as gasoline

This is true when converting a motor directly to propane. But building a motor specifically for propane use with higher compression and advanced base timing would minimize a loss in miles per gallon. Also, at a bulk propane dealer like Suburban Propane or Freeway Propane, you can often find propane at least 50 cents cheaper than gas. Shopping around definately pays off with propane.

Possible problem areas...you need hardened valve seats and stellite valve facing due to the complete lack of lubricating properties of the gas

I was under the impression that the vast majority of motors nowadays use hardened seats for the use of unleaded fuel. If converting an older motor, then yes, this would be an issue to take care of first.

have a professional with the proper gas analysis equipment set up the mixture.

Great point! A couple miles per gallon can be had through a proper tune by a shop experienced in propane conversions.

 

[sass]

Great points Israel. I belive that it would be possible to get better mileage than gasoline with a properly built and tuned engine as well as better power.

Right now I have a '94 xj with 260 k on vehicle and about 40 k on reman engine. I have never been happy with this new engine. Not nearly the power of the original.

Now I'm having the problem of every sensor , injector, and harness plug getting old and causing problems.

I'm thinking of building a high compression stroker with a fairly agressive cam and converting to propane. This would solve many of my problems as well as giving me great power.

Other than the standard stroker build info, what else should be done to run a high compression propane stroker. What cam should I run? I would want as much hp as as I can safely get. Mileage is not that important.

 

[Dr. Dyno]

I'm thinking of building a high compression stroker with a fairly agressive cam and converting to propane. This would solve many of my problems as well as giving me great power.

Other than the standard stroker build info, what else should be done to run a high compression propane stroker. What cam should I run? I would want as much hp as as I can safely get. Mileage is not that important.

You could copy my stroker using the same cam but with different pistons (Silvolite 2229) and 0.030" shaved from both the head and from the block deck (total 0.060"). This would bring the CR up from the 9.25:1 of my stroker to 11.0:1. You'd have almost identical HP/TQ outputs from propane with an 11.0:1 CR as you would from regular gasoline with a 9.25:1 CR. No worries about detonation either since propane has a 104 octane rating and burns a lot slower than gasoline.