Question about Throttle

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stickicivi
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Question about Throttle

Post by stickicivi »

I notice that the difference between pressing the throttle like 1/3 and flooring it is about the same. Say i'm already moving in 2nd gear, pushing moderately on the gas gets me going fast, but then if I were to start at the same speed and gear and suddenly floor it, It actually seems more sluggish.

Is this a result of the computer limiting gas injection or does it have to do with pumping more gas than can be burned with the available air?

In a way i'm wondering whether in a manual car like my Honda Civic, is the gas pedal directly connected to the throttle or does it go through the computer first which might put a limit on things. I'm not like super knowledgeable on how engines work so go easy on me.

This isn't really a matter of racing or anything, it's more something I noticed and am curious about.
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Shadow
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Re: Question about Throttle

Post by Shadow »

Assuming that your 2003 Civic is drive-by-wire, I'd say what you're describing is pretty much normal. Most manufacturers are tuning their throttle opening to be more aggressive in the earlier part of the pedal travel. But I'm not 100% sure that you car is DBW or not....but I'm guessing that it is.

If you pop your hood and take a look at the throttle body, you should easily be able to see if there's a cable or not.
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Re: Question about Throttle

Post by theholycow »

stickicivi wrote:Is this a result of the computer limiting gas injection or does it have to do with pumping more gas than can be burned with the available air?
The throttle controls air, not fuel. When you step on it you're not pumping fuel*. The computer measures air and injects fuel to match however much air enters. Low RPM and/or closed throttle both can limit air intake. At low RPM there is often no difference between 30% and 100% open throttle, except maybe a little bit of pumping loss (an effect used by those looking for fuel economy as well as those looking to go faster).

What is the RPM you're experiencing this at?

Google tells me that the Civic didn't have DBW until 2006. Cable throttle systems can't stop you from opening the throttle but some can reduce power other ways, a function mostly used in traction control systems to reduce wheel spin. (Side note: Some can also open the throttle.) Regardless, cable throttle systems tend to behave more predictably.

*: Well, with a carburetor and maybe some primitive fuel injection systems like TBI, there actually is an accelerator pump that squirts when you move the throttle, but once the throttle is held steady (even wide open) that pump does not operate. Even a carburetor depends on the amount of air to determine the amount of fuel.
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stickicivi
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Re: Question about Throttle

Post by stickicivi »

I haven't really tried at higher rpms so it could definitely be that. Funny that they call it the gas pedal if it doesn't pump gas.
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Re: Question about Throttle

Post by theholycow »

Agreed. For that reason, I mostly avoid calling it "gas pedal". I usually call it the accelerator or "go pedal", since "throttle" isn't always accurate either...with DBW it's an acceleration request device, not a throttle lever, and with diesels there's not even a throttle to control.
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six
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Re: Question about Throttle

Post by six »

theholycow wrote:...with DBW it's an acceleration request device, not a throttle lever...
:lol:

"Press R2 to accelerate"
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stickicivi
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Re: Question about Throttle

Post by stickicivi »

DBW is like

"Request to accelerate"
"Request granted"
"Preparing to accelerate, acceleration ready!"
"Ok, go!"
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Re: Question about Throttle

Post by theholycow »

:lol:
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bk7794
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Re: Question about Throttle

Post by bk7794 »

maybe its the computer adjusting the air/fuel mixture. The drastic change.

I sort of get that, but I think its also psychological..possibly. If I understand what your saying.
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kamesama980
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Re: Question about Throttle

Post by kamesama980 »

It's not psychological. Very simple if you get into the physics of the engine. The throttle is sized for where you have peak power (where you have max airflow)...in a honda, probably 5.5 or 6k at least. Airflow is volume x rpm (minus inefficiency) hence you need a lot more airflow (and bigger intake/exhaust openings) at high rpm. at low rpm, the engine is already pumping all the air it can at 30% throttle. If you get a vacuum gauge or look at MAP reading via OBD2 live data you can see it happen. you'll hit atmospheric pressure at very little throttle at low rpm, but at 5k you have to hold it 3/4 open just to maintain the same speed, much less accelerate. almost all cars are like this. The exceptions are the ones like my mom's buicks with the chevy 3100 and 3800...very small throttle body relative to engine size but both have a lot of low end torque and very little top end.

To elaborate on the A/F thing: unless you have a lean burn ECU (a few of the early 90s civics, a few of the newer cars just coming out) the A/F ratio might vary but on everything else, it never does except to go slightly rich at WOT. (those cars ran very lean for economy but had to have elaborate schemes to control NOx emissions which is why it's uncommon)
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Re: Question about Throttle

Post by Roger »

It would be the RPM you're at, if you're out of the powerband then flooring doesn't make it go much faster. Eg if I 1/4 throttle at 2000RPM, I would accelerate the same as if I went full throttle at 200RPM. Whereas if I was at 5000RPM, 1/4 throttle would only lightly accelerate, if I floor it it'll go hard.
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