460 conversion confusion
 

i will be converting my (1979 f150 4x4) 460 to propane. i had a truck before that had a propane 460 and i liked it.

i have a few options. (a big box of propane parts)

an ohg x450 and x1 cnverter (was on a chev small block)
an impco 425 and model E (a couple of each dont remember what i got em off of)
or (if i can get it back from the friend i sold it to)
a dual 425 mixer setup on a proform 950 holly throttle plate, with 2 model e regulator vaporisers.

so what would you guys use.
and what would you recomend for dizzy re curve specs/kit

If its stock 460 the 425/model E would be a good setup if its "souped up" go with the twin 425 and at least one Model E

If you are going straight LP 28-32 degrees total advance with about 18 initial. If dual fuel you are going to half to wing it. Snice dual curve doesnt exist anymore and if you set it for lp it will be over advnced for gasoline. You can play with this to see what works best for you.

Regards

ill be going with straight lpg. what rpm would be best to have the advance all in by? i wanna try the dual mixers (i plan to rev this thing well past 4000 rpm)

when i had this dual mixer setup on the last engine, one mixer would open at a different rate. are there different diaphram springs available for the 425?

i want to get all the settings of both mixers back to "stock" is there a manual in.pdf available?

should i connect the ballence ports of both mixers and both vaporiser/regulators together (you said one should feed the engine?)
sorry for all the questions ive been away from lpg for a few years and only ever knew enough to be "dangerous" lol

A rule of thumb for setting up advance on a propane engine is 14-14-14. That is, 14° initial, 28° total centrifugal (all in by 2250-2500 RPM), and 14° vacuum advance. Each engine is different but this is a good starting point. The goal is to find the advance curve that gives the best torque and the best fuel economy. See Vacuum Advance.

The Model 425 is not meant to be staged with the opening rate of the gas valve. The slower mixer will actually be supplying a leaner fuel mixture so they should ideally operate in unison. If you want a manual, see Franz Hofmann's Diagnostic Guide. Adjusting the mixer has been covered in detail in the Fuels Forum. See 425 Adjustments. The balance port on the mixer should be connected to the vent port of its converter.

The Model 425 mixer reaches its nominal 460 CFM flow rating at about 4066 RPM on a 460. The mixer will work above this flow but the power will gradually drop off. As much as you think you plan to be revving above 4000 RPM, I think you'll actually be spending very little time do so. A single Model 425 will work fine in your application.

For your dual mixer setup, do you have the (now obsolete) Impco dual mixer air cleaner? If not, you will have to use individual air filters, which require a lot more hood clearance.

The OHG X450 operates both like a air valve mixer and a venturi mixer. It should have a slightly higher flow capability but is more complex to properly set up, which is explained in the Diagnostic Guide.

im going to dissasemble the mixers and make sure they both have the same gas valve in them. what would you guys recomend for a start point for the idle screws? and i assume the best way to synchronise the big screw would be to measure the ammount protruding from the mixer body?

should i try feeding them with a single vapouriser? and tie all the ballance ports to a common header, or leave them vented to air?

The idle and power screws should be turned out the same number of turns. Impco recommends to set up the power adjustment on a chassis dyno so that exhaust CO is about 2% at full load. See Impco Fuel Mixtures and Ideal O2 Levels.

You could try to feed 2 mixers from a single converter. If it's not enough, the converter will frost-up if it supplies more fuel than its rated capacity (about 325 Hp) but it can supply higher amounts for short bursts.

The balance line is to ensure that that the converter (aka vaporizer) is "seeing" the same pressure as the mixer. If you leave the converter's port open and the air filter becomes dirty, the fuel mixture will become richer. Similarly, if you've got a cold air system on the mixer, the balance line will keep the fuel mixture from becoming leaner. As I mentioned earlier, the balance port on the mixer goes to the vent port on the converter that is supplying it with fuel. If you have the dual mixer setup's single air cleaner assembly (instead to 2 individual filters) and only one converter, you only need connect the balance port of one mixer to the vent port of the converter.

Will a 425 impco mixer be enough for a healthy 428cj with 10:5:1 compression? Have a setup I'd like to use to convert it.

If its stock 460 the 425/model E would be a good setup if its "souped up" go with the twin 425 and at least one Model E

If you are going straight LP 28-32 degrees total advance with about 18 initial. If dual fuel you are going to half to wing it. Snice dual curve doesnt exist anymore and if you set it for lp it will be over advnced for gasoline. You can play with this to see what works best for you.


I would recomend two

Otherwise you might be lean and short on power

Regards