I am building a 429 for my 79 Bronco and am planning on running propane. This will not be a daily driver, but I want it to be streetable, with off road (Sand and Rocks) in mind. I also want to keep relatively good economy, as I will be driving this to the trails I am running.

I currently have an edlebrock performer 460 intake.

The propane carburetor I am looking at (IMPCO 425) ($300) is only rated at 500CFM. That is only good up to about 4000 RPMs. I would like to still have power through 5000 RPMs. There are basically three different options for getting more carburation:
1. Spend more money on a different carb Technocarb ($1000)
2. Get a two into one manifold with two IMPCO 425s ($1000)
3. Get a dual quad intake (Blue Thunder) ($435) with two IMPCO 425s ($600).

As you can see all three options are about the same cost, so here are my questions.

First, with a cam with off road and economy in mind, is it really possible to still develope good torque through 5000 RPMs?

Second, will my current intake support options 1 and 2 through the higher RPMs?

Third, is the BT intake a good option for off road, low end torque applications? I really like the idea of this option for the bling factor, but bling isn't one of the more important factors on my wish list.

Any input would be appreciated.

Jonny

 

JonnyBronco---

I don't have any experience on "high performance" propane----but have run a number of trucks and tractors on propane. I currently have a 89 F700 with a factory propane 429 engine (equipped with the 425 carb).

My past experience has been that the 425 will deliver a lot of gas----but no more than is delivered to it by the vaporizer. To do what you are planning---I would think that you would alson need a "big" vaporizer. You might be able to pick up on some information from Impco's tech department.

You probably are already aware of it----but the factory propane engines ran higher compression ratios than the conventional gasoline engines. So if you are building the engine up---I would recommend taking this in to account.

Hope somebody with performance experience steps in with some good information for you. Uh-----with multiple 425's on a 429, I wouldn't know where the meaning of "economical" would fit in.LOL My F-700 has lots of power----gets approximately 3.5 miles/gallon (loaded or empty).

Used to have an 84 model Bronco with a 351---the big Bronco was a great truck. Good luck---

Delta Dirt
Avon, Ms 38723

 

Delta,

Yes, I plan on about an 11:1 compression ratio to maximize the octane rating of the propane. Is there a vaporizer that is bigger than the IMPCO Model E? Or could I just run two vaporizers into one mixer?

As far as economy, I know I won't be getting much over 10 MPG. I would be extatic with 12 MPG but extremely dissapointed with 6 MPG. The "PropaneGuy" indicated that the systems with two carbs actually got better mileage than the ones with only one carb. Do the systems run more efficient at lower air flow?

Thanks for the input, keep it coming.

Jonny

 

JohnnyBronc---

11:1 sounds about right----I am thinking that is close to what the factory specs are on a factory propane engine based on info I picked up when I bought the '89 F700 about a year ago. It was originally a propane delivery truck. With the higher compression ratio---the factory propane engine supposedly closely matches up with the gasoline version in power rating.

Have no idea on increasing mileage with multi mixers. I think the model E is one of the larger vaporizers "generally" available for the automotive and tractor industry, but larger vaporizers are surely available for some of the higher horsepower "industrial" engines that have been operated on propane. I would think Imperial (Impco) would be a good source of information.

My gut feeling is that you would be happy with the Bronco and the 429 set up with one 425 and one model E vaporizer. That 429 is a lot of engine----you may outrun your drive line with much more. I have run a number of farm trucks in the past----and am highly impressed with the 429 in the F700. I would be sorta hard to compare it to the performance of the Bronco due to totaly different weights, axle ratios, and intended use. My dad had a '73 station wagon with a 429----and it would really move on down the road (and I had a '73 Chevy wagon with a 350 which was not even in the race). My 84 Bronco had a 351 with a 4 barrell Holley----would pass just about anything but a gas station.LOL

Just depends on how much power you want and how much you are willing to spend---you might want to try it on the single set up and see what you think. You might be surprised. Good luck---

Delta Dirt
Avon, Ms 38723

 

jonny...I'm running a '78 460 w/10.5:1 forged SpeedPro pistons with a 450 OHG mixer and an Impco "L" vaporizer. I had the truck on my buddy's chassis dyno and it's making in excess of 425 ft/lbs. of torque at the wheels. I would think that would be enough to motivate your Bronco pretty good! :-)

 

AerostarDad,


That's some great information. 425 ft/lbs is pretty good, what RPM was that at? At what RPM did it start starving for fuel, or did it ever starve? My 429 would probably have lower torque, but should get higher RPMs.
I have also considered the OHG450, but they are typically more expensive and I haven't seen any good side by side comparson of it and the IMPCO425, does it flow more than the IMPCO? Isn't the Model L even smaller than the model E vaporizer? If so, why did you choose it? From what Delta Dirt said it sounds like the vaporizer is the limiting factor in fuel delivery.
In any case it seems that you are happy with your setup, is there anything you would have done differently?

Thanks

Jonny

 

From what I have gathered in info, the "E" and "L" flow about the same. The "E" works better in colder climates due to its different design in the heating/coolant passages. I have seen a 700 cfm propane "carb" on a website from a west coast Canada propane parts dealer that uses 2 vaporizers that flow into one carb (basically 2-2 barrel carb's back-to-back). That carb is around $500 by itself,then you need to plumb in the extra vaporizer and fuel lock. Mine does run out of flow at about 4000rpm,but,in a truck,my engine never sees that rpm anyway,so I'm happy with what I have now,especially with propane at 48 cents per liter!