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To inject or not to inject


tonyslongez
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I was out in may garage the other day looking at my 13b standing by for it's intake manifold when it dawned on me. " Why am I killing myself making this intake manifold when there is allready one available for a carburetor"?:irked: so rather than haveing 30psi of fuel preasure all I need is 5 or 8psi that would eliminate other issues less wiring for sure. All I would need is a solid ignition system maybe make an adapter plate for the Marvel shebler carb so I can adjust my mixture does this seem like viable option to anyone? I think I've been blinded by the F/I issue. I understand the fuel burn is only about .5 difference in favor of F/I but who cares? look what I don't have to do to make it run. I really could've had my motor running months ago if I wasn't injecting, I think:rolleyes: So before you post any wisdom please understand I'm not looking for "YOU CANT"S" I don't care what Tracy has I know what he has. What I want to know is what am I missing is it going to be easier than injection? and I would like to start a list if we could to figure out the Pros and Cons of the two. If I can't make this thing simpler I'm going with a Lycoming..

 

thanks for everyones help.

 

Tony

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Tony,

Sorry for quoting the obvious, but thought I would try and get the ball rolling.

 

F/I pro's

No carb heat

No Carb iceing.

less baffeling (???)

Depending on F/I unit, self leaning (less controls)

 

Carb pro's

No power required to run (redundant system, all elecs could fail but still have fuel and spark as long as ignition is mechanical).

Simple (means cheap)

Easy to re-build

 

Tony this is just an outside looking in point of view as I am still in the planning to build stage but sometimes being totally new to an area can help.

 

I have to stop with the cliche' stuff.

 

Jamie

"An upsidedown Australian that wants to build an aircraft that flys backwards"

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AP

 

thanks for the post I really enjoy reading posts that don't start with "YOU CAN'T" Yes the ice thing could be an issue but plumbing carb heat can't be as hard as the complete F/I system. I'm now looking at two revmaster carbs these look like they may be the cool setup. I'll have to do some 3D rendering in autocad to see how this is going to play out, but at this point I'm leaning heavely to the Carb side just for ease of installation. for about $1000 I can have my entire fuel delivery done, manifold, plenum, and carbs :) now all I'll need is a good ignition system.

 

Tony

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Tony,

Several people have and are using carbs. The natural progression is to go to injection. For efficiency and performance. Also some of the FI electronic controls control the ignition also. In a carb rotary, several people started with distributors for the ignition, which created a problem with cowls as they protruded. Tracy started with the motorcycle carbs and then built the EC2 which we use today. If you can handle the ignition and want to experiment with carbs then I would say why not.

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Man! it just seems like a whole latta work to setup this F/I:sad: We have rotaries that are failing now with F/I so how good is it? maybe the injectors themselves might not be failing but certainly other subsystems of the F/I are so what is better/easier to deal with? There inlies the RUB:rolleyes: I guess. Is it just a matter of setup and nothing more with the carb and F/I systems? Or is it something more cynister like fuel line plumbing and 35psi fuel pumps? look at the old Chevy's, 4 barrels and ignition that was it. Yeah the mileage sucked but man they would'nt quit for anything unless it was catostrophic.

 

Maybe I'm overthinking it.

 

Tony

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Tony,

 

I remember reading an article (car related) on basic performance mods on the cheap for the RX-7 13b, eg twin carbs rather than F/I.

 

I will see if it is floating around somewhere and scan a copy for you. (Might have been thrown out with one of my moves).

 

The way I look at it is, How many certified aircraft out there have carbs? Answer Lots and to be honest most of us probably did most if not all our flight training in a carb'd engine powered aircraft. Who is to say this is not the option for you. Is that not what "Experimental" is all about.

 

All aircraft are a compromise. You cannot get without giving in a certain area.

Take the Canards, we get great cruise performance and economy but we trade it for short/unprepeared field landing capabilities. In your exmple you are looking at Carb's rather than F/I, I guess for expense and complexity you are trading efficiency and performance (all be it a small part if your data is correct). In the end it is "Am I happy with this compromise"? and if it has not been done before for your configuration "Am I happy with the risk"?

 

Myself I am looking at using to the most part a stock subie engine (F/I) but I have not even started yet so things could change an infinite number of times before I make a decision.

 

Is there anyone that has done an Auto Convesion 13b with a Carb/s?

 

Jamie

"An upsidedown Australian that wants to build an aircraft that flys backwards"

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AP

 

Well I know tracy started with carbs. I agree with your post about our flight training fact is, I just recently started flying injected 172's and I hate starting them. (good lord give me a carb:irked: ) Don't get me wrong it runs well enough and the no carb ice issue is cool (no pun inteneded);) but have you seen under the hood of an injected 172 holy cow! there is alot going on in there. there has to be a better more reliable way. does anyone know any other brand of Carb that has adjustable mixture? So far its a stock Lyc carb or a revmaster. I'll be honest I'm not pro carb or pro F/I just looking for the easiest safest setup. (Aren't we all:rolleyes: )

 

Thanks BTW for looking for that article would definitely like to see it, if you still have it.

 

The other thing is no O2 censor which I know we don't use anyway but that is because of the 100LL otherwise it would be there. While I sand on my canard I start thinking alot about this motor. Right now I don't feel like our peripherals to make this engine run are even up to automotive standards now I may be way out of line saying that but look at what Tracy is selling, good stuff, no doubt. But there are still problems with MAP readings, that people are having partly because of no O2 censor I think, wiring issues, flooding.... I probably don't know what I'm talking about:rolleyes: but that is my perception as I read through all these web sites that airplanes have rotaries. Frankly! I think if your going to go F/I there has to be a way to use the stock mazda computer to run it, that would make me feel all warm and fuzzy. Better yet- Put two together and have a back up. But now we get right back to the O2 censor:irked: . (damn you O2 damn yoooouuuu) If I'm going to F/I, I really feel like if we could get closer to what Mistral has, which looks more like an aircraft engine and so far seems to be performing like one. I think it would speak volumes for this engine. Only, we can do without the $31000.00 price tag. (Probably why it looks so good.)

 

 

Frustrated, Tony

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Tony,

 

Could not find article, from memory it was dealing with 2 stock RX7 carbs.

From little reading I have done and what issues some friends of mine had with some twin SU's on a Mini, A twin carb set up can be a pain in the pants to tune.

 

I have no experience in this area.

 

Jamie

"An upsidedown Australian that wants to build an aircraft that flys backwards"

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