Propane Mixer Requirements 1

[ktbundy]

I am currently building a turbocharged Ford 2.3 engine for racing. I'm hoping to manage 350-400hp and plan on using my readily available Impco parts. My dilemma is that I seem to be on the borderline of using one 425 mixer. Should I just fabricate my intake to accept two mixers? Or is it possible to overcarburate with mixers? In theory they should both only open according to the engine's needs and boost. Or is my theory all wrong?
Tom

 

[shabba]

Are you based in Australia? If so there is a company that can supply you a high performance gas setup...

 

[ktbundy]

I live in Canada, about as far away as you could get. I have a wack of Impco parts, but I seem to be caught in between one mixer or two.
Tom

 

[franzh]

The Impco 425 is the only one that will accomodate your airflow/bhp requirements (yes, I know that there are larger ones, but the 425 is the only one with reasonable size and it has a low speed/idle provision larger mixers do not).

The 425 is vastly over carbureted for this engine in normal aspirated mode (read as non-boost and low speed) but will work at higher airflow rates. You could stage two 225's in progressive mode, one opening first, then the other.

I would also plan on two model E vaporizers too.

Franz

 

[pbloore]

I don't know about the availability in the US, but if you're looking to develop an engine for racing you might be better looking at an injection system. It avoids the need for a venturi which restricts the airflow.

I think Impco have a tie up with an Italien company BRC who make injection equipment.

 

[ktbundy]

Franz are you suggesting either one 425 or two 225's? I was a little leary of one 425 at 350+hp. Can't say that I have ever seem anyone blow through a 225, but that's an interesting idea.
Being as though I have access to lots of Impco parts(but very little others)I plan to make this a budget project. Injection would be nice, but there still seem to be so many unknown factors(and costs)involved.
Tom

 

[franzh]

The 225 will blow through, just the same as the 425. Just compensate the vaporizer. I have seen more than one 425 in blow through at well over 350 bhp, but I am concerned about low speed performance and off throttle tip in with a mixer this size and an engine that small, before boost.

Setting up an injection system for performance is possible but it requires special injectors (not gasoline units!) and other proprietary stuff. Also, the injection tables will have to be generated from scratch as the gasoline tables will not work. Impco will not sell any injection stuff to the consumer/installer, and there is no off the shelf Impco LPG injection equipment available. They are in R&D only.

Franz

 

[slickoo1]

hi guys iv just found your site and hope you can help me as well. i have a 1978 460ci ford on propane with imco and i just put electronic ignition in and was wondering if you could tell me what to set the timming and plugs at. i am also wondering how to set the propane chamber on the back of the propane carb. is it four and a half turns for a 460 thanks for your input slick

 

[franzh]

This should be either on a seperate thread, or another forum, its a little off topic.

For starters, set initial timing 5 degrees more advanced than with gasoline. If, and only if, you are familiar with the built in recurving properties of the Ford distributor (thats not the function of this website) recurve the total timing to about 35 deg BTDC at 3000 rpm.

Not sure what you mean by a propane chamber, the Impco doesnt have one. If you have the 425, there are two adjusting screws, the smaller one for idle mixtures, the larger for max gas flow, also called the power valve, although it will not give more power, only less by gas restriction.

To set the idle, use a gas analyzer and adjust for approx 1% CO. For the larger screw, its best to usually leave it alone unless you have access to a chassis dyno and gas analyzer, then set for 1% at full throttle load.

Franz

 

[rubberducky360]

I have a few questoins about what propane mixers i should use. i sucked a butterfly valuve off my old impco mixer in to my 350 small block chevy, and i am replacing the engine with a 454, basically stock, with a rv cam, and harder seats in the heads, but i dont know what mixer i should use, or what intake i should use

 

[Lou Scannon]

ktbundy, for the power level you're seeking I assume you've got a large intercooler in mind. Given that, you really don't want to be thinking about draw-through. For one, transient mixture control will suck, due to the long transport delay between the carburetor and engine. Second, an intercooler and charge air system full of pressurized stoichiometrically mixed gas and air is a pretty good approximation of a bomb, which is what you will have the first time it backfires through the intake.
When you apply a carburetor in blow through mode, the sizing gets factored in inverse proportion to the density ratio you are targeting with the turbo-intercooler system. So a carburetor that is good for 200 hp at ambient conditions will be good for 400 (on the air side, anyway) if density is doubled. You will have to develop the gas delivery side of the system to deliver the peak required gas flow, but in principle that shouldn't be a problem if the gas regulator is pressure compensated from the mixer. I agree with franzh that one Model E would be marginal to inadequate at 350-400 hp so you better go with two. There are some things you can do with the primary and secondary springs to optimize the regulator for a specific pressure, but the passages inside are the limiting feature. Impco has developed some higher flow E's for certain customers but I don't know if they are available aftermarket.
You will also be hard pressed to find a high pressure regulator to deliver the flow you want when your tank pressure is depleted below 1000 psi (I know the HPR 3600 isn't capable), but if you plan to keep the tank topped up that may not concern you.
I know many have taken the Ford 2.3T past 400 hp on gasoline, but that's with the benefit of internal cooling via enrichment. You better figure on a decent water injection system to keep exhaust temperatures down and keep from detonating.

 

[franzh]

Hemi, I believe the 'duckey may be talking about LPG, not CNG, he did not state which. That does make a big difference on what equipment he should use. Also, Impco is not the only game in town. The model E is for propane, the PE or the PEV is for CNG.
Otherwise, you are right on target.
Franz

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[Lou Scannon]

Good points franzh.
I'm kinda sloppy in my terminology for the Impco regulators, i.e. when I think Model E, I don't distinguish between the LPG and CNG variants, at least until the fuel is specified. They all say 'Model E' on the cover.
I guess another reason I lump them together is all the heavy duty CNG applications I did with those regulators, I used the propane vaporizor base with the CNG regulator assembly (does that make it a PEV?), to reheat the CNG after it was cooled from the Joule Thompson effect in the high pressure regulator. We did not want sub-freezing gas flowing through the fuel system potentially creating problems with fuel metering. This was a concern in heavy duty applications where sustained flows above 100#/hr are commonplace.

 

[franzh]

The E regulators from CNG were also positive pressure, while the LPG units were negative pressure. The secondary levers had the spring on top for CNG, on the bottom for LPG. Physically, almost all of the parts interchange with the center section, allowing for customized applications. Heating CNG has never been popular since it results in a decrease in power due to its lower density. Cooling the CNG has a better benefit, as long as it is consistent.
The "P" means pressure. The "E" is the series, while the "V" means vacuum, even though the units would flow as soon as fuel was supplied (the PE and PEV CNG units.)
Sorry to get off of topic.
Franz

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[Lou Scannon]

Thanks for the refresher. The applications I did were boosted, so power wasn't an issue. Robustness/reliability was, hence reheating the fuel to a relatively constant, above freezing temperature. As I alluded before, customers like DDC had their own version of Model E CNG regulator; these had the heat exchanger section, I assume because they had the same concerns. My apologies too for the hijack - back to our regularly scheduled thread.

 

[ktbundy]

The fuel in question for me is LPG, and yes I do have a large intercooler up front. I am going to be using two model E's with two Impco 225 mixers. Pretty much everything under the mixers has to be custom, so I have my work cut out for me. Are you the same Hemi from turboford.org? If so I have learned much from your previous posts about the 2.3T.

 

[benn73]

I have a related question for franzh. I am planning on building a turbo SBC (350 or 383 cubes) running on propane pushing around 600-650hp. Would you recommend 2x impco 425's and E convertors for this type of application?
Will they be too big when running off boost, and should the linkages be staged to reduce this problem, should it exist?

I have built n/a small blocks in the past running single 425's, but never anything boosted, or anything that required 2 x mixers/vapourisers.
Ben.

 

[franzh]

The topic of the original post is a little off topic as to the requirement of engineering content. Here is some homework: do a web search for me and contact me directly and I will make some recommendations. The reason for posting my e-mail address should be obvious.

The Eng-Tips forum is for engineers to discuss engineering topics, not really to discuss personal projects, even though that seems to be the thread!

Note to anyone else: I am not re-directing posters for any services, this is information only.
Franz

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Lou Scannon]

Yes, I am Hemi from Turboford. Thanks for the kind words.