Has anybody successfully tried yet?
What problems would there be, other than the usual propane related issues?
How would someone go about correctly timing a turbo propane engine?
Can it be done reliabily?
With an octane rating of 110, would propane make a good fuel to compress?
Since mixers rely on vacuum, how would you regulate the flow of LPG?
This is the story i've heard from my friend... His brother tried a twin turbo propane setup on a 1991 chevy 350. The turbo setup was homemade, simply flipping the manifolds and welding flanges to fit two chrysler 2.2l turbos. The mixer was an impco 450cfm, but shimmed out to 600cfm and modified to run with boost. How?, I don't know. The engine ran comfortably on 8lbs of boost for one week, but then the boost was run up to 18lbs and the connecting rod bearings let go. (motor had over 200,000kms on stock bottom end). I've heard from a few people the truck had tonnes of power, even at 8lbs of boost. The only downside was the burning eyes you would get from standing beside the tailpipe.
So anyways... I am interested in trying a single turbo setup on a rebuilt 351w and tuning it on the dyno at my school. I'm interested to find what kind of numbers I can obtain with LPG and if it can be done reliably.
Also... I'm just curious to how much boost a 351w block can handle
Blow-through turbocharged propane systems are fairly common and quite simple to do from the propane fuel system point-of-view. The Impco mixer supplies fuel based on air flow not vacuum and the fuel mixture is controlled by the shape of the gas valve. I'm not sure how your friend "shimmed it out to 600 CFM" but it sounds to me like he changed the rate at which the gas valve opens. Regardless of what he did, the exhaust should not make your eyes water. If it does, it could be that the fuel mixture is extremely rich which reduces power and burns exhaust valves.
To allow the mixer to run properly in blow-through mode, you need to install a balance line between the mixer and the converter. This ensures that the mixer supplies the correct fuel mixture regardless of the pressure. Also, the octane rating of propane motor fuel is 104 rather than 110 and a safe CR for mildly cammed, naturally aspirated propane engines is around 10:1 to 11:1.
When you ask about problems other than the usual propane-related issues, there are very few. The main problem is that people don't properly build and maintain the engine and then blame the fuel when something goes wrong. Use propane motor fuel (HD-5) rather than commercial heating propane to minimize residuals in the converter and set the mixer for the correct full throttle fuel mixture.
A completely stock, fresh EFI 351W can handle 8-9psi to 5000 RPM without a problem, assuming you're running 92 or 93 octane. Less boost if you're running lower octane because the compression ratio obviously is fixed.
Some people have done a little higher than 8-9psi, others got close to it and couldn't quite reach it without serious pinging.
If the engine is old, worn out, and in need of a rebuild, adding boost will just hammer the already loose bearings and knock it to death.
What it can do on propane, I'm not sure, never tried. I believe you would get better results with a higher compression ratio than with gasoline.
I got a diesel snowblower engine to run on propane, and that's something like 15:1 or 16:1 I think...
Wow... thanks fraso for the link!, and yes people do tend to blame the propane for poor performance, not the setup.
Oh, sorry the mixer my friend used was built by OHG, not impco. Apparantly, by using .055" washers, he spaced out the top cap on the mixer, just for the purpose of allowing more air to flow through. And yes, he adjusted the mixer to run very rich. For what reason, I don't know.
For this project, I plan to go start at 5lbs of boost and if all goes well, mabey 9-10lbs maximum. I haven't decided on the turbo yet, probably a garrett gt35r running through a stock SD intercooler.
My 351w features...
Eagle forged 4340 crank
Eagle "ESP" H beam rods
KB forged flat top pistons
Stock, ported heads
Performer RPM air gap intake
MSD box, yada yada... the bottom end is built and that's whats important.
Again, thanks guys... pictures and updates will follow throughout this project.
I run 8psi in a propane supercharged 'suck through' setup. I had it on a 351c with base comp at 9.4:1 and after 3 months it took a lobe off the camshaft.
engine now rebuilt to 8.5:1 and stroked to 408ci, at 8psi again. no trouble yet!
UPDATE: I just recieved my garrett gt35r turbo i bought off ebay and GOD it looks good. And now i'm in the planning stages as to how I will run the turbo piping. I'm still on the lookout for an intercooler for cheap, possibly steal one from a stock Superduty and trim it to the correct volume. Currently I am up to my a** in bookwork and have very little time to accomplish anything on the project.