I heard about aluminum heads having issues in boats to do with heat generated from the high rpm use, and was told that it somewhat applies to propane.(heat not high rpm) The issue came up when I was looking at Edelbrock heads, I just wish I could remember what the issue was. Also, I didn't know the technocarb was computer controlled, suppose it proble can be same as the 425 though, I was told (propaneguy.com) that a Vialle Model D converter with a technocarb would work fairly well on my truck, still have yet to swap that though.

 

The technocarb mixer is a 700 CFM unit and can be used without a computer. I am referring to the system. There is a brochure for 87 and earlier rigs. The mixer has been updated and has a throttle body incorporated into it.

I have a pic of the newer mixer that was sent to me by Technocarb. I need to upload it.

 

I have an older one based on the quadrapuke- so will adapt it- after I rebuild the base plate- got it for $50 or so on ebay. I think they are the best that I've found- it's the off road version.

 

Roy the PropaneGuy.com sells them new for $500. That was a good grab!

 

seems like there a number of unkowns dealing with propane at the higher compression ratios and creating heat/burning heads etc.. For what it is worth this text is directly from the propane guys website:

These propane cams are modified to cool. The exhaust valves. These cams run more overlap, to stop wear on exhaust valve plus seat the exhaust lobe. Has a slow descend and a soft seating

Any Questions contact -

Jeff at http://www.coltcams.com



Seems to confirm that heat can be an issue for the exhaust valves. Anyone bothered to contact coltcams?
On a side note how many years of propane supply we have here in N. America?

Look forward to this thread continuing to sort out the practical side of building a dedicated high comp propane engine. Devil's in the details.

 

The Technocarb 4bb carb is quite pricey, espeically if you compare it with a bare Impco CA425 mixer. However, it is a complete feedback fuel system that comes in 4 power levels ranging from stock small block to modified big block. To convert an open-loop Impco or OHG system to feedback operation, you would also need a feedback controller such as Impco's ADP or Dual Curve's PN 5952. The Technocarb 4bbl carb kit would look a lot like this:



Since I haven't built very many engines, I can't offer very much advice about picking the best cylinder head for propane operation. However, I believe a better head is better no matter which fuel you're using. If I were trying to pick which head to run, I would choose the head that gives a CR of around 11:1 with a minimum amount of piston dome. Take that advice with a dollar and buy yourself a cup of coffee with it.

Although propane mixes well with air in a mixer, the fact that propane is 1.5 times heavier than air makes the possible for the fuel to separate from the air under the right conditions. Fuel-injection intake manifolds were designed to carry only air and certain fuel injection manifolds like GM's TPI intake are prone to poor fuel-mixture distribution and do not make good candidates for mixer-stye conversions.

Generally, any intake manifold that works well with gasoline will work well with propane. Dual plane manifolds are better at low RPMs because they minimize low RPM reversion effects, which results in a better part-throttle response and a smoother idle. The generally smaller cross-section of a dual plane's intake passages also result in improved cylinder filling at low RPMs. Popular Hot Rodding has a lot of great tech information and they have an excellent article about intake manifolds. Franz Hofmann has some great current information about building propane engines but his site is quite busy and often exceeds its bandwidth by the end of the month. He'll be publishing a propane book later on this year

Propaneguy explains that his propane cams are designed to cool the exhaust valves. I do not believe that exhaust valve cooling is an issue if the engine was properly prepared for propane operation in the first place. As a propane conversion is usually a significant investment, the engine should be in freshly-built condition. That is, the exhaust valve seats, faces, and guides must be in good condition. Either the valve seats must be either induction hardened (as is the practice for unleaded fuel) or hardened valve seats must be installed. The cooling system must be clean and scale-free. Finally, the fuel mixture must be correct. If you run a standard or lean gas valve and set the full-throttle full mixture to produce 3.0% exhaust CO, the fuel mixture should never become over-rich.

BTW, I'm not sure why you would not want to run cast iron heads and high CRs with propane.

Also, propane has been a motor fuel in North America for several decades already. Propane motor fuel has been available for over 50 years and HD-5 has been around for over 30 years.

Frank

 

Thanks for the input Frank. Remember that the Technocarb mixer is a 700 cfm unit and if anythinf over 500 cfm is needed, dual Impco 425s would be needed.

I believe that if I run my World Senior Heads on a 393 or 408W at 10.5 or 11:1 CR with Propane, I'll be o.k. I just haven't seen anything regarding propane and heads which is odd.

I agree with you that a fresh build specifically for propane is the way to go and I also think a good RV cam may be better under the circumstances than a Colt propane cam. I'm just trying to verify this theory.

Roy the propaneguy told me my stealth intake would not do well with propane. Its a 302 manifold though. I was considering a 302 originally for the propane project. Its still a possibility but I wouldn't use the World Heads I have on it because it would put the power band up too high unless I stroked it to 347 and it would still likely be too high.

 

Never mind can't show the pic.

 

The 393 CID would reach the rated flow of the 425 mixer (460 CFM) at around 4760 RPM while the 408 would reach it at around 4585 RPM. If your transmission shift points are less than these RPMs, then a single 425 mixer should work fine.

There is nothing that would stop you from running at a higher RPM with a single 425 mixer even though the air/gas valve reaches the limit of its travel at 460 CFM. This just means that higher air flows would not recieve progressively more fuel and so the fuel mixture would become leaner with higher RPM. Leaner fuel mixtures do not harm the engine unless it becomes so lean that the engine has a lean backfire. Your power will just drop off past the rated flow of the mixer.

A pair of Impco CA225 mixers (329 CFM each) would probably work better than a pair of CA425s. Staging them progressively would give your great throttle response at low RPMs but this would be a bit more complicated to achieve.

I'm not sure of the 700 CFM rating of the Technocarb mixer. That information isn't on their brochure and I don't think they have an official flow rating for it yet.

 

The 700 cfm I saw on the Propaneguy.com site. There is a twin feed option for the Technocarb for engines rated over 400 bhp according to their Brochure.

 

There's an Australian outfit that makes some high performance propane components, I'll see if I can find the address (computer crashed and lost my favorites).

 

I did a ton of research before putting the components of my build together and found a guy who is a regional/national expert and was responsible for a lot of conversions for corps/govt as well as designing propane engines for big generator types of projects- lost his name, email etc when my last computer puked. He had a lot of scientific background in his answers and was concerned about dynamic compression ie if you are building a rv type build and dropping...say a point and a half of static compression you would not want to be much over 10:1 static to yield 8.5 dynamic. Race engines seldom go over 9.2:1- 9.5-1 (in short lived race motors) due to heat and while propane does burn differently- heat can be more of an issue so if you want an engine to last a long time 8.5:1 - 9:1 is a decent range or compromise. Without real good quench a 91 octane engine would be around 8.0:1 dynamic so 8.5 is impressive.

Folks talk about static compression like it's the end of all design and that is really dangerous. You can build a 9.1:1 and turn it into a major dog if you have a performance cam that drains 2pts of compression and you end up with 7:1 dynamic. But then if you want to run forced induction that is what you need yada yada. If your building yourself take the time to figure that stuff out and if your having a shop build it they typically look at the cam and it's recommended range only but if you have the $$ to experiment with 11.1 static and 9.5 dynamic with propane...go for it...other wise expect to run a cam that will drain yur static compression down to 8.5:1 or so if you want to be safe with an engine that should last. Then again this could all be hyperbole.

Also- stainless exhaust seats and valves period. Open chamber heads or dome are thought to be better for the way propane burns (over closed chamber- high compression heads) but the guy wasn't sure- it was speculation. Some recommend that you insert stainless seats into intake as well and since I already have a grand into my heads i might as well.

Having a cam specific for propane that increases duration could also be to drain a bit of compression to get those high staic numbers down into range. Nascar engines, from what I understand, run up to 16:1 but with their wild, unstreatable cams, they run about 9:1- 9:3 dynamic compression. Someday I'm going to research this some more...it's fun.

 

You wanna be a little careful with cams and how much overlap you run,which will cut down your dynamic compression. Engine vacuum is what pulls the vaporized propane into the engine since propane carbs have no accelerator pump. Running less overlap and higher LSA's on you cam will keep your air velocity up high at low rpms which will keep your torque numbers up if this is a 4x4 or street engine. My 302 ford that I built for my '64 runs a 114 lsa cam that I designed and I'm very happy with it. Its 11.1:1 with aluminum heads, with a nice mild idle.

 

To be a bit more precise, engine vacuum draws air into the engine and vacuum in the mixer draws propane into the airstream.

The only reason that a gasoline carburetor needs an accelerator pump is that gasoline flow doesn't instantaneously match air flow when the throttle is suddenly opened. Since the propane mixer is a gas mixing device, there is never a sudden lean-out of the fuel mixture and therefore no need for an accelerator pump.

If you're running a lean fuel mixture and want a richer mixture under load, the Vacuum Power Valve (PN VPV) may be added to the converter. The VPV enriches the fuel mixture when when manifold vacuum drops to 3" Hg. Otherwise, the shape of the cone in the gas valve controls the AFR.

 

I was running a Marvel Mystery Oil inverse oiler for a while. Have lost the reservoir cap and haven't had it hooked up for quite awhile. Not sure if they are available anymore. I bought mine 25 or 30 years ago. They were very popular before that.