Propane engine builds (tech, questions, advice)

I've read a bunch of discussion about propane engines, cams, etc in some of the other threads about efi vs. propane.

Has anyone did a build, or compiled the info about building engines for propane?

Here are some things I've picked up: (feel free to add or correct me)

- propane is higher octane and can handle higher compression to pick up some lost power from the energy per volume of 'pane.
? How much compression is too much? from a starting/reliablity

- decent vacuum at idle (less duration/overlap) helps with starting/idling (starting without having to prime the evap)
? Do most people just pick a cam from the catalog, or the cam manufacturers have "propane" specific type cams?

-a single mixer/evap setup will only support <400 (maybe 350?) hp.
? what is the commonly accepted HP limit of a single system? rpm per cubic inch limit?
- I assume you can run a single mixer on a larger cubic inch motor if you don't intend to spin it fast, or vice versa (small engine/high rpm)



I'm considering building a 351w for propane. I figure with the limitations of a single mixer system, there is no sense in building a stroker.

Here is my experience with propane, I run a Ford 460 BB.

I bought it from http://www.flitelineenginesupply.com/. When talking with them before the purchase, they told me because I was going to run propane, it would have to be built with hardened rings, valves and seats. In addition to that it has a hotter CAM but it's not been on a Dyno so I don't have any real numbers. Flightline said it's around 350 HP and seat of the pants tells me the torque number is massive.

Anyway, it cost me $2,300 for the motor and another $1,200 - $1,500 for the intake, propane system and accessories so, $3,500 - 3,800 and I feel I got a really STRONG motor with zero time on it at a decent price.

I too would like details on propane systems, CAM's, single/dual mixer/evap setup and other parts but I would really like to know if it would be possible to get 600 HP out of propane and what I'd have to run to get it (if it's possible).

For a while I ran a 427 big block chevy. L72 ,11 1/2 to 1 pistons, 600 lift solid cam, rect. Port heads, made about 520 hp on gas with a 850 carb. Took it out of my 69 camero because of to much compression for pump gas . Installed it in my jeep and put it in pane because of it's higher octane rating. Ran pretty good but did not have the power it had on gas. Called comp cams and told the tech dept what I was doing and they ground me a cam that would build more cylinder pressure. My old cam had so much overlap that more propane was going out the header pipes unburned than was being burned. This cam gave me at least 50 hp. Than I put two mixers with two throttle bodies on a duel plane single four barrel intake, hooked upon progressive linkage. Ran on one to 1/3 throttle and than kicked ass when opened up. Got all my hp back and gat a lot better milage to boot. Propane goes inas a gas and displaces a lot of oxygen. Needs a defferent cam to build better pressure, but with this pressure is more heat which is harder on valves and seats. Won't hurt rock crawlers but would hurt school busses and such. That's about all I know!

I got a magazine last month that had an article about a car with a supercharged injected motor on propane that was over 800 horse, it had 2 direct port injectors per cylinder. I think I have it in my tool box at my shop I will look for it tomorrow, it would be worth reading if your on propane

Elliott said:

I got a magazine last month that had an article about a car with a supercharged injected motor on propane that was over 800 horse, it had 2 direct port injectors per cylinder. I think I have it in my tool box at my shop I will look for it tomorrow, it would be worth reading if your on propane

Click to expand...

Was it running solely on propane? or using it as additional fuel for high boost?

I'd be interested in seeing the magazine article, thanx!

We just pulled an 8.1 liter Vortec engine from a medium duty truck that was out fitted with true propane injection. It had aftermarket injectors for the propane setup and it used liquid propane injected directly into the intake. This is a new setup to me and we are going to take it off and use stock injectors due to our lack of knowledge of this system. It may be an option worth exploring. I also have a 406 sbc that I built for my jeep. Used a cam with moderate lift and not too much duration so not much overlap to provide better vacuum. That thing is awesome! Running a single 425 mixer and the cam runs out before the mixer starves, I turn it about 6000. I believe it was a .460 lift with a 242 duration @ .050, hydraulic flat tappet. Just my .02

I will be running my 460 on propane. What I did was mill the heads down to raise the compression. I had hardened seats installed on the exhaust side. Which was a good time to go with a cobrajet size valve (1.76). The valves I got are stainless. The intake side is a stock valve as I was told that only the exhaust needs to have the hardened seat. I then called Scott Johnson at RHP and told him what I was doing. He custom ground a cam for my setup. I will be initially running a single mixer but will add a second on at some point. Will be running a set of Scorpion roller rockers also. I also got a recurved distributor that will bring in the timing quicker because of the higher octane. I dont have the truck together yet but Scott estimated it to have around 400 HP and 500 TQ and it should all come in by 3500 rpm.

jayphizzle said:

I also have a 406 sbc that I built for my jeep. Used a cam with moderate lift and not too much duration so not much overlap to provide better vacuum. That thing is awesome! Running a single 425 mixer and the cam runs out before the mixer starves, I turn it about 6000. I believe it was a .460 lift with a 242 duration @ .050, hydraulic flat tappet. Just my .02

Click to expand...

That's probablay about what I will put together, good to know it runs good,

I'm thinking 351w (89 non-roller block), small chamber (for compression) aluminum heads from RHS or ?, and a "bigger" hydraulic flat tappet cam. Should be good for 375+? hp and run pretty much forever

Something like this cam:
http://www.summitracing.com/parts/cca-35-243-4/overview/make/ford
and these? heads:
http://www.summitracing.com/parts/rhs-35011-01/overview/make/ford


Of course, I've considered the "easy way out" and getting one of these edelbrock top end kits: Edelbrock claims 400hp/420ftlbs
http://www.summitracing.com/parts/edl-2092/overview/make/ford

I figure if I can get 400hp engine, the propane kit, and ignition for ~$4000, then I'll be pretty happy with it.



I keep reading that the IMPCO 425 is only 450-470cfm, and that it will only support ~325-350 hp. It "seems" like lots of people are running some stout motors on one mixer, but if the 325hp figure is correct, then it almost seems like a waste to build a motor capable of 400+hp unless you are going to run dual mixers.... ???

According to the calculator, 460cfm will allow 351 cu/in to turn 5500rpm, so that might just work out. I've seen a LOT of 350 Chevys with aftermarket heads/cams/intakes on single mixers that seemed to "go" pretty good.



I should probably get a junkyard LQ4 and a TH400 :****:, but I've already got the 351w, a built C6, and some Superduty axles.

The imco 425 mixer that everyone uses flows about 460 cfm, which is enough air for about 325 hp. More than that and it won't necessarily not run, but it will be an airflow (horsepower) bottleneck. Propane has less energy than gasoline so it will cost you 10-20% of your power just switching a gas motor over. You can get some of that back using higher compression and advancing the timing. Propane is around 105 octane. I ran a 496 bbc for awhile on two mixers (dual quad intake). It was 10.7:1 and timing was locked out at 40*. It ran fine and was strong but used a lot of propane. Switched to efi for that reason. Just too hard to carry enough fuel for all day. I'd run propane again on a smaller motor though. For cranking, I'd just start it cranking before I flipped the ignition on; it would crank easy that way.

I have a 383 stroker with vortec heads 12 to 1 comp. With a edelbrock c26 dual quad intake with 2 425 mixers. I got about 2k in the build. It has a small comp cam 454 lift. It seems to have alot of power but it seems to burn alot of propane i need to have it tuned any ideas?

I looked this morning then got into something pretty deep and forgot to grab that magazine when I left but I'm almost certain it was the last issue of hot rod. It had a 69 Camaro and a zl1 on the cover. The motor I was talking about was strictly on pane. But I've built a 350 with 11.5:1 with a 274 crane cam with only one mixer that runs like a raped ape and starts fine, couldn't tell any power loss when swaped from gas. The trick seems to be a cam about that size and as much compression as you can get and about a 2400 stall and I think you will be happy.

Jamie needs to chime in on the 22r he built that's in my truck. I don't know all the specs to a T like he does. It's no high hp v8, but it's built high compresison and runs solely on propane.....peppy little bastard for a 4 banger and runs like a top.

this is what we did to my old truck engine which jd owns now, 22r with got propane kit
my son in law built the motor for us.
ricky had his machine shop in hazelgreen al bore the block 30 over, decked the block and head
balanced the crank, rods and pistons. we went with 10.5 to 1 pistons. probably looking at 11.5 to 1 or even 12 to 1
compression after the decking of block and head. ported and polishid the head, put bigger valves and springs
in the head. comp cams built a cam for us that the rpm range was 2,000 to 6,000 on propane.
put a header on it. motor does pretty good from what i could tell.

we took our new motor to ricky a couple weeks ago to build for my sons rig
it will be the same except more compression and screw in studs for the crank and head, bigger valves and more porting.

Great info. More than I've seen in place in years. :afro:

You have several good questions. I have been in the propane conversion business for over 21 years. We have engines with as much as 13-1 compression running propane. The info about having a cam with reduced overlap is great for building torque as well as useable hp. You need to make sure you have an adequate cooling system to handle the extra heat created by using propane vs gasoline. Gasoline tends to cool components down before being vaporized in the cylinder under compression where propane is already a vapor so you lose that cooling effect. The heads we have built use hardened seats and stainless steel valves on intake and exhaust. The intakes are usually the valves that deteriorate quicker because they are not made from a heat resistant material like the exhaust valves in standard engines.

A single mixer setup is good for about 325 hp@5200 rpm and on a 355 small block. The bigger the engine the lower the rpm. The photo is of one of our dual mixer setups on a 383 stroker that dynoed at 565 hp on propane. It had a flat torque curve of over 500 ft lbs starting at 1800 rpm and going up over 6500 rpm. The dynamic compression worked out to about 11.7 to 1 on this engine.

If I can help out give me a call.
Buddy Gamel
Precision Sales & Service, Inc.
451 64th Place South
Birmingham, Ala. 35212

877-403-7827
205-591-2266
205-591-2267, fax

[email protected]
[email protected]
www.alternatefuel.com
www.workhorseservice.com

So, say on an engine dyno chart such as below, where it's making 375 HP at 5000 rpm, would this be possible with a single mixer propane setup? Basically chop the chart off at 5200rpm

(this is edelbrocks graph for their power pack on a 351w with 9.5:1 compression)

I assume on a propane setup, you'd want different pistons or smaller chamber heads to up the compression to 11-12:1

A single mixer is good to about 325 horse

Fire Freak said:

A single mixer is good to about 325 horse

Click to expand...

I've seen that quoted time and time again,

the CFM of a mixer is only an air flow restriction (an engine is just an air pump).

Horsepower is simply a calculation of power (rate that work is done)

HP = Torque * RPM / 5252

So, a "325HP" engine at 5200RPM would only be making 328 ft-lb of torque.

There are TONS of engines that make WAY more torque than that at 5200 rpm.


Saying that the 425 mixer (flowing 450CFM) will limit the RPM of an engine is accurate, saying that it limits the HP is inaccurate.

Like the old saying, "TORQUE IS WHAT MOVES VEHICLES, HORSEPOWER IS WHAT SELLS 'EM"


I say :flipper: horsepower, build for TORQUE (high compression, high cylinder pressures, good flow/high intake velocity, high scavenging effect) and let the HP fall where it is.




No disrespect to Buddy, or anyone that is in the propane business, but the math doesnt' support the "325HP" quote.

(hell, it may even help sell a few more single mixer simple kits if people knew they could get 400HP from it with a proper built engine)

Discuss

I agree with you TBItoy. I hade an engine built for my rig and my engine builder said it would do 600 hp 625 tq on gas with a 750 cfm fast throttle bodie.I was concerned if 750 was big enough, he said cfm had nothing to do with hp it was rpms that need cfms. He said he built a 355 for circle track that was going to turn 9500 rpms and the math said it only needed a 750 cfm carb. I think if your motor can make big power down low, it will make it but won't make any more up high than the cfms will allow. My .02