I have recently obtained a 429.
I have been rolling around the idea of building a propane engine...

So with that being said. I want to rebuild the 429 and get more power out of it... I also will need to boost the compression to about 14:1.

I would like to hear ya'lls opinions and suggestions. Im open to anything right now, im pretty set on the propane part of it though as gas is getting redicoulous, so the engine will be built to run purely on propane...

 

Well, my guess would be you'd need some high buck pistons and or heads to get 14:1 CR...IIRC the D0VE heads we used on our 460 have like 75cc chambers...if we swapped to just a 4-valve relief flatop piston, we could have gotten 11 or so :1 CR...so, you either have to raise the dome in the piston, or get smaller CC heads, both might offest the cost of fuel for the next 10 years

But...all things being equal...can you run propane at that high of a CR? Seems you're venturing into deisel range.

 

since propane is a higher octane fuel... Usually about 104, there fore requireing a higher compression engine... Through my research ive heard that 14:1 is the ideal compression ratio.

 

thanks for the info by the way.

 

Even back in the "day" as a kid in the late 70's when we could easily get leaded 101...12.5 was about the most anyone could run with iron heads (Al heads were not even a thought to us)...101 with lead will cool the CC's much better than 101 unleaded...hence allowing you to run more CR.

I honestly don't think you'll be in good shape running 14:1 with propane. but again, it might have different charachteristics that you can't get with gas?

FWIW, I'm a propane fan...the only forklift I keep running is the one I have on propane, oil stays cleaner/etc.

Draw back (as I'd see it) is my 6 gallon propane tank weighs about 30-35 pounds empty...curios what weight a 25-20 galong tank would weight?

Also...as a must (I'm sure you know and is pretty common these days) you have to run a harden intake and exhaust seat in the heads, most propane rebuilds also use a different exhaust valve...I think the material is called "stellite"...can't recall, but is neeed for longevity.

It's an undertaking for the swap to be sure, just recheck your facts on CR and such...also...what's the intended use of he engine?

I/e, if you're looking for a driver/work truck and you run 14:1 CR, you'll need one big-azz cam to bleed cylinder pressure off with, just to get it to start...bigger cam/etc, all leads to a higher RPM engine and is that what you want?

Just a conversion with propane in a mild/stock engine for fuel cost benefits, and 7 or 8 to 1 CR is fine.

 

you could also look at turbos for that motor also with propane.

might be an interseting alternative to 14:1 pistons and such.

just another option for you to ponder.

Rgds
Mike

 

I too am considering a rebuild for propane. I am running a stock bore 429 D0VE block with factory "flat tops" they do have the valve reliefs, it used to have the C9 heads with port work(rated at 11-1 cr.) until the exhaust valves were ate up. I now am using a set of stock D3's(around 9-1 cr.) and what a major power loss-and mileage-even tho it runs better and doesn't stall out because the old valves were shot and weak springs.
My next build I want a 10.5-1 to 11-1 cr. 460, windage tray, maybe some 2.19"/1.72" valves, decent 4x4 cam straight up, with a weind 8012 intake. I am also setting up to run 2- 425 impco mixers on one baseplate-for some cfm. One will work, but it runs out of breath and doesn't make much power past 3500rpm on my 429.
I run straight propane btw.
14-1 sounds high, it might work but propane can still detonate.
From what I learned, for heavy use 9.5-1, or 10-1 is ok. Performance use can be 11-1, even 12-1.
A good friend of mine built up a 400 sbc, with 11.5-1 cr. He spent alot of time "matching" parts for power, and said it had way more torque than the lame stock 454 it replaced, in a big 2wd suburban.
Some knock sensors, with easy adjustable timing would be nice-for most engines.
Of course a turbo or two would be trick-but thats a whole different game.

 

Propane conversions on FT powered trucks generally work well and engines seem to last twice as long. Pick-ups are a little harder to convert in that you loose valuable cargo space in the process. For the RV'ers out there this poses no hardship, but everyone else converting to propane effectively turns their 8' pick-up into a short box.

 

i dont know about this 14:1 thing i have a 350 chev(i know i was young)and it was a stock 85 motor and it ran great on pro even started at -40 without being pluged in

 

14:1 with a 429 and early-style iron heads will require a custom 18cc domed piston, probably $1100-$1200 in pistons.

Use a 460 crank in place of the 429 crank and then you can use the Speed-Pro L2443NF030, a 460 shelf piston, $435 per set, and get 13.5:1 with a zero-decked block.

Paul

 

Ross custom dome pistons run you $1154 whatever compression ratio you want. arias has some dome on the shelf run you about $92/hole, or a custom is 120/hole plus pin fitting.. nice way off tacking on 20 per piston. i just priced out pistons yesterday.. still fresh in my mind. its not cheap at any rate. engines still run with lower compression on propane. neighbor had a 75 f 100 with a 360 on propane.. runs fine....lacking power though.