Hi all,

I'm getting a bit closer to starting my propane motor build, and wanted to see what others thought about this question...

Since a turbo motor essentially runs as a naturally-aspirated motor at low RPMs, until the turbo spools up, would the FT heads with their smaller, high-velocity intake ports, be a better match for a turbocharger?

This won't be a high-RPM build, just very durable (basing my build on a 391, so will have the FT heads, if I decide to go that route.) It will probably rarely ever see 5K, and less likely 5500RPM, but needs to have grunt all the way to the top.

Will the turbo help to overcome the severe limitations to mid-range power built into the FT heads? And will the turbo/FT combination breathe up to about 5500RPM?

Thanks,

--Silly

 

Don't recall enough about the project to pull it outa my scruff. However, I'd ask a few question based on just what's in this thread If your planning on these heads are you planning on the FT intake as well ?

From the start I dunno why you want to take a extremely low compression engine and use it as base for a propane powered engine. To run propane it's my understanding the CR has to be WTF up there. 12+/1 or ?? CRS sorry... and then propane has other issues (oiling comes to mind), hardened seats for the temps etc.. This is all hearsay as I actually know jack squat about running propane but very interested as to where this thread will go..

 

To make propane work, you need either high static compression, or artificially high compression (like putting a hair dryer to work.)

I figured that with the right set of pistons, maybe some forged flat-top 390 car slugs, compression of about 9.5:1, when you figure in a Victor Reinz head gasket, a large-chamber head, etc., could be reached. Use a closed chamber head and a steel shim gasket to get to around 10.5:1. Neither of which is terribly good for propane. But add a turbo, and things get kind of interesting.

I've not decided on anything, except that the 391 block and steel crank seem to be a good way to start building a motor that should grunt for ages. I know I'll either have to turn down the snout of the steel crank, and maybe get it internally balanced, or run the FT accessories and whatnot... Maybe get the block sonic checked and punch it out to a 406, while I'm at it... wonder if anyone makes cross-bolted main caps that could be put in and the block's cap registers drilled...

So, I'm kinda stuck. Either I get a hair dryer for the motor, or I have to figure out how to jack the compression through the roof, and I've not seen a good way to do that present itself while I've been reading here yet.

 

Oh, I figured on hardened seats and stainless valves (at least on the exhaust) anyway... propane being a dry gas, it'll be a bit rougher on those parts. Need an EGT gauge and probe, too, I suppose.

 

Running propane at 5500 wont "require" a forged crank anymore than it will cross bolted mains. Just the same, American Made - American Proud: Pro-Gram Engineering Corp - Manufacturer of Race Engine Parts - Products Catalog here are the caps, knock yourself out.. A girl I worked with a while back had a **** buddy who sold propane and a 73 F250 he ran on both gas and propane. Never asked the guy about it as the truck ran like a POS on either one lol, although it never broke down in the 2 years I knew them LOL... what can you say.

 

Yeah, I know I won't "require" the steel crank, nor the H-Beam rods, nor the cross-bolted mains (those probably least of all...) but hey... I'll have the motor apart anyway, and it might see some severe duty because of the possibility of putting a turbo on it, and ... all the good excuses I can think of to be able to light the motor up righteously if I want to, and still make it palateable to the wife to spend some extra cash on the build.

I'm thinking a set of D2's will probably be adequate, given a little bit of love. That's another thing about the turbo, though... suddenly, the way the heads are ported doesn't mean quite as much as it would with a pure naturally-aspirated motor. Don't need a huge cam, don't need fancy heads, etc., just a bullet-proof bottom end.

But, it makes me wonder, is there a way to get the compression ratio of a 390 up over 12.5:1 or so?
That ratio, with a moderately small cam, should provide some ridiculous cylinder pressures. Maybe I'll leave off the bore to 4.13"...

--Silly

 

Wow... just got some info... NA propane wants to run somewhere between 14:1 and 15.5:1 compression. Forced induction to about 15psi and you can run propane all the way to 12.5:1. Sheesh... given the higher mechanical efficiency of those compression ratios, I can't see how the 10% reduction in energy via propane can't be overcome, where power's concerned. No worries about fuel puddling or falling out of suspension... hmm...

 

I would doubt the FT heads would flow well enough to reach 5000, much less 5500.

 

With the small-port FT heads, you'd see an artificially high boost pressure, which would cause a lot of temp increase in the intake charge.

If you really want low-end power, two small turbos with FE heads would be a better way to go, I'd think.

Not that I've done much work with turbos, just theoretically... I've done a lot of research to put twin turbos on my V10 and keep low-end torque as high as possible. Caveat Emptor

 

Why Propane? or is it actually LP? They run ALOT of stuff on LP with no issues. We have two towmotors that are bi-fuel and I'm pretty sure that ol '69 Slant 6 is NOT 15:1 compression!

I'm with Art, if you want low end torque and turbo's put two small ones and skip the FT heads.

 

Yeah, what I'm looking at is LP, which gets vaporized and fed to a mixer to go into the motor. Liquified Petroleum == Propane, more or less.

The whole reason for doing a build this way, is that LP (Propane) is about $2.15/ga.-equiv. here in CA, while the dishwater they call gasoline nowadays is $4.50 here. With the energy disparity between gasoline and propane (propane = approx. 90% gasoline) the motor needs to be built to run propane, to get the best efficiency. The nice thing about it is that propane runs about 104 octane equivalent, so tighter compression (and greater cylinder pressures) bring the mechanical efficiency of the motor back to where a propane engine, properly built, can produce as much or more power per gallon equivalent as a gasoline engine, built with the limitations of gasoline in mind.

All of this is because the 360 in the truck is tired, and will need to be replaced soon, and it makes no sense to me to build a motor for gasoline, when it is twice and more the price of propane, when the propane motor could be built for roughly the same price. I tend to overbuild everything, anyway, so I'd be doing a gas motor with H-beam rods, steel crank, forged slugs, and all that... Plus, the truck won't likely run out of area that much, and the guy at the station close to my house said he'd be as happy as a pig in ***** to fill my truck with propane instead of gasoline.

Just trying to figure out the best way to go about it. High compression seems to be kind of a bear to attain with an FE, unless you go with popup pistons, which can still impede the travel of the flame front inside the cylinder and ruin combustion efficiency.

The idea of twin turbos had crossed my mind, but I'd thought that might be gilding the lily a bit. Maybe not, though, if I ran them staged. I don't want to overrun a very small turbo and turn it into a grenade, so I imagine I'd need a wastegate for it after a certain manifold pressure had been attained... about the time the larger turbo was kicking in, if done right?

Easier than turbos would be a good way to make a high compression NA motor, but how do we do that with an FE?

(With a Pontiac, I could slap a set of closed-chamber 389 heads on a 455 and run ridiculous compression... and I'm a Pontiac nut, more than anything... teeheehee... wonder how much trouble I'd get in for building up a 455 for the truck...)

 

360 bored 30 over, hard seats/good valves, any FE head probably, 3.98 crank(428/410), L2291P pistons (forged), deck the block, shave the heads and pistons. Should be able to find a happy medium in there LOL...


COAE 6090D heads would give you 58/63cc ? chambers but you'll pay out the **** most likely

 

kinda figured that was what you were doing.

 

Silly, we just built an FE with one of the 4.250 cranks and flattops with something like 13 & 1/2 to one, it is going to run on the local 105 octane E85. If you built an 390 with H395Ps ( 360 piston ) and decked the block to zero with milled D2s and shim gaskets you can easily get over 11....would 11&1/2 be enough ? DF, on JR's 'puter today

 

Try to buy an out of production copy of Jay Storer "Propane Fuel Conversions" book. Written in 1977, but alot really has not changed. Several FE propaned vehicles in there, along with turbos and propane, ignitions, compression ratios, water injections, etc. The info. is all there. I was lucky to find on eBay for $65 in very good condition. I've seen one sell for $165 there. It pays to shop & snipe!

You DO NOT want high compression and a Turbo, with or without Propane. If you want naturally aspirated and Propane, go for the high compression.

I plan on running stock 390 truck compression ratios (what ? 7 to 8:1 ?), a single Rajay 301E turbo (that I have), and Propane. At 5-7 psi of boost, it'll make plenty of dependable power.

I was fortunate enough to speak to people at Ak Millers shop, before Ak died. I got my turbo FE exhaust manifold from them. They said my turbo would work great on a 390, on the street, and towing, etc.

I'm not saying that you cannot run high compression, a turbo(s) and propane. The cost of the electronics and EFI system to make it live long would make it very prohibitive for most working people.

Hope I helped you some.

Oh, I haul Propane, and the company I work for also does installs of all kinds. It's very interesting, and I have asked those that know, alot of questions.