air draw through the carb

[pflaming]

While working on the truck with the engine running I put my had over the carb to see how much draw it had!!!!!!!!!!!!!!!!!! What a surprise. I will NEVER have a dirty filter on an engine again. I had no idea that much air was moved and the engine was idleing!!!!! With that much going in, a clear exhaust system then is equally important. Don't catalytic converters, etc choke down an engine?

[TodFitch]

Yep. If they aren't restricted by the choke plate, throttle plate, manifolds, valves and exhaust system then a four stroke Otto cycle engine will be trying to draw 1/2 half of its displacement every rotation of the crank. A 218 cu.in. engine will try to draw 109 cu. in. per rev and you are turning over at least 500 rpm at idle (seems like people are used to higher idle speeds now, so make that 750 rpm). So 750 x 109 = 81750 cu. in./min or about 47 cu. ft./min.

Thats on the intake side. The exhaust side carries more because of the expansion of the burned mixture.

That's the reason that people spend so much time on things that will make the flow better: Dual carburetors, split exhaust, headers, porting and polishing, etc.

[ggdad1951]

catalytic converters definitley affect the exhaust flow....when mine went good bye on on my old Sunbird and I straight piped it, I suddenly had a bit more power!

[pflaming]

When I was a kid in the late '40's they used to put a potato in the exhaust pipe of the 'just married' couple's car. When the car started that potato FLEW. Considering the cu. in. of air going into that exaust pipe, wasn't that a bit dangerous for the wedding party?

[ggdad1951]

When I was a kid in the late '40's they used to put a potato in the exhaust pipe of the 'just married' couple's car. When the car started that potato FLEW. Considering the cu. in. of air going into that exaust pipe, wasn't that a bit dangerous for the wedding party?

well the poor guy just got married, maybe they were trying to save him some pain?

[Plymouthy Adams]

the ideal was for the potato to stay in the pipe and as such restrict the motor from running..old old trick..thisis een more effective on a two stroke engine..a partical plugged muffler on a two stroke will give you all kinds of low performance issues that would suggest anything but exhaust problem..

[Young Ed]

Oh boy does it ever Tim. One time a plymouth club tour Dads 39 just wouldn't pull. No power strange behaviors etc. At the lunch stop we discovered he had backed a tad too far into the garage and bent the tailpipe over. Quick fix with a tire iron and permanent fix when we got home by sawing off the extra length that stuck out too far.

[pflaming]

Ed, I didn't know you were Jewish!:D:D

Seriously, I have an extra set of manifolds. Now I am going to clean the inside as best I can, then put on a second exhaust port, and then have someone put a Y on the existing exhaust header pipe so that the two feed into one tail pipe. That should give me a better exhaust system.

Comments welcome.

Edited July 11, 2012 by pflaming

[Rusty O'Toole]

Ed, I didn't know you were Jewish!:D:D

Seriously, I have an extra set of manifolds. Now I am going to clean the inside as best I can, then put on a second exhaust port, and then have someone put a Y on the existing exhaust header pipe so that the two feed into one tail pipe. That should give me a better exhaust system.

Comments welcome.

Old hot rod trick known as splitting the exhaust manifold. For best performance use 2 pipes, separate all the way to the back of the car. Leave a passage between the 2 sections of the manifold for a mellow sound.

[pflaming]

Got tired of working on the floor so picked up the air cleaner again to see how it works. The air is drawn down the sides then up through the large cavity then down into the throat of the carb. The air never really comes in contact with the oil.

I am surmising that the flow is like a cyclone on grain grinder in that the air circulates and the debri (dust) bugs, etc then drop out into the oil. There are screens in the center to catch 'whatever'. For a totally good air flow, the connection to the carb would best be TIGHT, I would think.

I'm going to use this AS IS. I like it.

[wallytoo]

that isn't the way the oil bath works. the oil level should be high enough to force air to pass through it. if there's space between the top of the oil and the passage to the carb, you'll get virtually no air filtering.

the oil is also "lifted" up into the wire mesh by the air flow, helping to trap particles, which then drip back into the pan, and the trapped particles settle out.

[pflaming]

Wally, so then there is a 'filter' in the inner chamber of the air cleaner. Mine only has screens and the upper inner is as good as gone. A metal screen would not be sufficient would it? Maybe use a coffee filter in there?

I would guess many people use / used this air cleaner incorrectly and unknowingly did not get any benefit from it. I certainly would have. Thank you.

[wallytoo]

the filter mesh is steel curls/twists. similar to what's in the oil filler cap.

at least now you can feel better about modifying the one you have to accept a paper element, since it is missing the filter mesh.

[pflaming]

What it means to 'choke' the carb.

It just occured to me that the carb is drawing "1,000 psi" of air. When the butterfly is closed or a hand is placed over the carb's throat, the carb's throat seeks out air but the only other source of anything is the gas line, so it SUCKS GAS! So when I had a 3/16" fuel source, it could NOT supply enough for the demand, thus a 5/16" is required to provide that sudden need for ______.

The same holds true for accelerating, when the foot pedal is depressed, the butterfly closes the throat, more gas is drawn and more power is the result. Very interesting. I didn't understand this before tonight.

Hence the need for a clean air cleaner: air flow / available gas is power!!!!

[pflaming]

I've heard that to clean a carb, one 'boils' it out. What does that involve? Will soaking the carb in gas or diesel work? I've noticed that brake fluid is not friendly to certain finishes, is brake fluid a "cleaner"?