crx warm air intake
my carbureted crx has a 1 3/8" hose going to the exhaust manifold . it is vacuum operated to open when the engine is cold. I am considering fixing it where it is open all the time. the problem is, it raises a flap that closes off the main air tube, which is 2" diameter. I could remove the flap , allowing it to get air from both sources, or partially block the 2" tube, allowing it to draw air from both. any suggestions?
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I removed the flap so it can now draw both cold and hot air. the cold air has no hose on it, so it is getting warm air from inside the engine compartment. the 2" tube should be drawing warm air, and the smaller tube can also supply hot air all the time now.
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That flap is thermostatically controlled, so whatever you do, make sure that the air going in to the carburetor is kept at 100F, otherwise your engine is going to run to lean if the air is to cool.
That bit of ducting is the same size of course as the 1.5L engines used in the 4 wheel drive, 4 door wagovan, so I wouldn't worry to much about it in your CRX's 1.3L engines intake, you could look up what size is the ideal size for air intake tubing for your size of engine, but I suspect it will be pretty close to what you have as the intake on my civic vx is pretty close to that size as well with nearly twice the peak HP. |
I have an upper grill block, so the under the hood temps should be plenty warm. if I have to, I'll route the 2" intake closer to the exhaust.
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Over time it's pretty easy to tell if your engine is running excessively lean... of course you already have a lean burn engine so running even leaner is risky, but if you find that you are burning and bending valves or burning holes in your pistons then you are running to lean, with your engine design your spark plugs are getting a rich charge so it will still start and run ok, other pattern I've noticed with people who've removed the warm air intake thermostat controlled flap is head gaskets don't hold up either, not sure if it's connected, but engines that are running lean tend to burn hotter then designed.
Did you find any charts to see what your ideal intake size is? to large of an intake and you loss momentum and loss efficiency. |
I very rarely run it over 2,000 rpm. so I doubt I will have a problem running too lean. I could always choke down the 2" intake to match the 1 3/8" heated pipe. I would guess those having head gasket problems are running much harder than I drive.
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I know I've seen calculators before for figuring ideal intake size but I can't find one at this hour, but that 1 3/8" heated air duct is the same size as the Honda Accord used to supply air to their 1.8L engine of the same vintage as your car, so I really doubt that it's causing a lack of HP or MPG for your 1.3L engine running at 2,000 RPM, I just would hate to see you damage your engine because you ran it lean by disconnecting some of the controls on the carburetor. On the other hand it might just keep the choke on if the air is not up to temp, so you might be safe from engine damage but would also be wasting gas and reducing the performance of your engine by having the carburetor keep the choke on. |
I appreciate your concern. by removing the little flap, I am allowing it to draw hot air from the manifold continually. I might go ahead and block off the main inlet ,and just feed it with the 1 3/8" hot air tube. I seldom, if ever rev it over 3000 rpm, so the loss of the 2" inlet tube probably won't hurt mpg. I could also run a hose down to the exhaust manifold, and have 2 warm air intakes.
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I guess I'm at a bit of a loss now as to what you are trying to do, from what I've seen people tend to find their peek mileage when their intake air is around 100F to 120F and your car has a very clever way that keeps the intake air exactly in that temp range.
I would also guess that if you wanted, you could use a chunk of a larger size of garden hose to supply the warm air and not notice a change in performance or gas mileage up until near full throttle. |
I thought the warmer the air, the better the mpg. are you saying that anything over 120 degrees will hurt mpg? one thing I have done is make sure that I didn't damage anything, so I could put it back if I had to. I will watch my mpg as the weather warms up and see if it gets better or worse.
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http://ecomodder.com/forum/showthrea...akes-1755.html
and http://ecomodder.com/forum/showthrea...a-21038-3.html They all seemed to say that they saw a drop off if the air got to hot and others have said the same thing as they get above 130F or so and that is even with fuel injection which is going to be able to lean back the fuel to air ratio as the air gets warmer, your carburetor is not designed to cut back the amount of fuel it's feeding in if the air temp is to high so at some point your engine is going to start running to rich if you feed it to hot of air. Either way, if you read some of those threads you will see that a number of people are trying to build more or less the same warm air intake that your car had new from the factory because a non regulated warm air intake just didn't cut it. Also, gasoline can start to boil at 100F altho the boiling point is 100F to 400F... one of the few things that they don't give a exact boiling point for, so do run the risk of vapor lock if you get the carburetor to hot as well. |
I blocked the main intake, and tried just running the 1 3/8" manifold heat tube. temp outside 85 degrees. car stumbled anything over 1500 rpm. unplugged the main intake tube, now running both tubes full time . car runs fine. got 56 mpg in 310 miles. 150 of those miles on freeway at 65- 70 mph. passenger window open.wife needed air.
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That is some quality info, Mike...thanks! :thumbup:
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