equivelant flow from carb to mixer

[socalfurnow]

Any rules-of-thumb for swapping from gas to Propane regarding the size of the propane mixer? Standard sizes for small blocks and big blocks? I might assume I'd want something with a larger flow capacity than my existing carb or does propane flow more rapidly? Do spread bore propane delivery sytems make as much of an impact as with gas? Same difference for 1 barrel vs 2barrel vs. 4? Any help is much appreciated.

[brown79]

my 460 has an impco model 425 mixer and it runs fairly well. if you want bigger there is a company called technocarb that makes a 750 cfm mixer the kit sells for $1750.00 canadian and comes with a mixer converter and an electronic fuel controller. www.propanecarbs.com has lots of good info and links.

[socalfurnow]

thanks for the reply. I will definitely check the links.

[351M]

The technocarb is only 750? I thought it was like 900-1000 CFM. The Impco 425 is right around 425 CFM and can seriously chock a large engine or a modded one that is built to take advantage of propane's octane rating. For the spreadbore are you talking a Thermoquad or Quadrajet type? tiny primaries and huge secondaries? Because that will make a difference over the holley style, it will use less fuel till you actually get into the 4 barrels.

[socalfurnow]

I have 2 engines - a 460 with mild rv cam and a stock injected 351.

The 460 is currently running off of an alum edel intake and 650 edel carb. I cannot lean it out enough to get anything better than cocoa colored exhaust pipes. The 460 (in a 77 350) is my first priority for getting onto something cheaper than regular gas. The valves would benefit from a refresh soon so I could tie milled heads in with the propane conversion to increase compresion.

Can you remove injectors and bolt up a propane kit? Need to make sure the tranny isn't computer controlled and ties in with fuel injection data? Soooo glad FTE started this forum.

P.S. Anyone here recently converted and if so howz it goin'?

[351M]

You can also get propane systems that are controlled by the stock computer, they, some also have injectors that replace the stock gas ones.

[socalfurnow]

learn something new every day - I'd never heard of propane injectors. Awesome. Suppose if I'd thought of it the modern duel-fuel vehicles must have them, right? And next thing yer going to tell me is that they'll have a comp chip that they can switch over to if they change fuels? Modern technology is frikin' awesome.

[351M]

So far all I know is that when you convert to LPG and dump gas you have that option, most vehicles still use the standard Impco and Vialle systems though. I have never gotten a look at the LPG FI systems and have heard that they are expensive.