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Old 06-27-2008, 07:59 AM   #11 (permalink)
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Quote:
Originally Posted by justpassntime View Post
You don't want warm air always being sucked into the carb, it lowers the horsepower.
You're new here, aren't you?



LOL, just kidding. Lowering the horsepower isn't really a concern to most ecomodders. Efficiency is the holy grail we're chasing.

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Old 06-27-2008, 08:56 AM   #12 (permalink)
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Quote:
Originally Posted by justpassntime View Post
You don't want warm air always being sucked into the carb, it lowers the horsepower... Yeah those under the hood air intakes look cool but they don't help mpgs.
When just tooling down the road, you don't need much horsepower. Most vehicles can easily keep a good cruising speed with less than 20hp, but to get that out of an engine designed to deliver as much as ten times that, we have to strangle them down to a much reduced capacity.

The warm air intake delivers less air mass to the cylinder while permitting a wider throttle setting. That makes for better pumping efficiency since the cylinder isn't trying to pull as hard a vacuum behind the throttle plate. It can be good for mpgs, but like always, YMMV.
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Old 06-27-2008, 11:03 AM   #13 (permalink)
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My crx and my current cvcc civic have stock warm air intakes from the factory and hae plenty of power, had the cvcc civic on the highway today and it has alot of pep and plenty of power while full of people, the reason cold days are good for racing is that it's kind of like a turbo, you get more air going in to the engine so you can get enough power to beat speed records, when you are going for good gas mileage you normally don't try to win races at the same time.
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Old 06-27-2008, 02:05 PM   #14 (permalink)
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Yeah I never even come close to even opening the secondary butterflu on my crx.. been debating disabling it totally.. HP means nothing in the FE game.. Really i think if my CRX motor was 20hp vs 50 i could cruise along and accelerate just fine .. i never get above 2500 rpm and barely touch the throttle even when accelerating.
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Old 06-28-2008, 01:57 PM   #15 (permalink)
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Ideal would be a WAI that could be switched in and out. Switch to cold when you need the power. (it's called carb heat on an airplane).

I highly doubt that not exceeding 2500 rpm is maximizing your FE - the engine is most efficient at outputs higher than that. Try accelerating a little faster.
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Old 06-28-2008, 04:08 PM   #16 (permalink)
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Quote:
Yeah I never even come close to even opening the secondary butterflu on my crx.. been debating disabling it totally.
Well I think that the secondary is there to keep the mixture correct as the engine air flow increases (among other reasons). The mixture might move rich or lean (i don't know) if the airflow thru the primary becomes very fast. The carb is an analog computer after all, I am amazed they work at all. If you disable part of the "equation solver" you might get an unwanted result.
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Old 06-28-2008, 04:19 PM   #17 (permalink)
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Quote:
Originally Posted by jonr View Post
I highly doubt that not exceeding 2500 rpm is maximizing your FE - the engine is most efficient at outputs higher than that. Try accelerating a little faster.
No, staying below 2500 is a good thing. Efficiency drops off above that, peak is usually closer to 2000 at about 70% of peak torque and drops off in any direction from that.
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Old 06-28-2008, 04:56 PM   #18 (permalink)
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most efficient engine speed is often near peek torque, and on a crx hf that is at 2,500 rpm, so on that car you really don't want to go past 2,500rpm.


Quote:
Originally Posted by jonr View Post
Ideal would be a WAI that could be switched in and out. Switch to cold when you need the power. (it's called carb heat on an airplane).

I highly doubt that not exceeding 2500 rpm is maximizing your FE - the engine is most efficient at outputs higher than that. Try accelerating a little faster.
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Old 06-29-2008, 12:16 AM   #19 (permalink)
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Ok, if best BSFC is at 2500 rpm and 70% peak torque, then you want to average around that number when accelerating - lets call it the 2000-3000 rpm range. Fairly different than "less than 2500 rpm" and "barely touch the throttle" (which suggests low loads).

The BSFC graph would show the right answer. A Metro should be accelerated in the 2500 to 3500 rpm, 70% range.

Slow acceleration does not lead to best fuel economy.
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Old 06-29-2008, 05:08 AM   #20 (permalink)
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I allways thought warm air into a carb was to combat carb icing,when warm air is selected on a light aircraft the idle rpm drops by 100 or so.I would have thought if you lived in a dry warm area warm air would not be needed. I experimented on a 1988 ford
and fitted manual cold/warm air selected by a switch in the car.The situation may be different on a more modern car where it may be designed to compensate for differing air temps.

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