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Guest Message by DevFuse
 

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Driving wide open throttle


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9 replies to this topic

#1 JaySmurff

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Posted 23 November 2006 - 04:26 AM

I rarely drive with the accelerator fully pressed, just have some weird feeling that I am getting worse gas mileage and wearing the engine more. I have read that at WOT your engine is at its maximum intake for air/fuel so I can figure that more fuel = less gas mileage, also with the added acceleration I'm guessing that would hurt mileage a bit as well, but with this is there any added engine wear or is it all in my head?

(no I'm not drag racing, I just like to have a comfortable level of acceleration in my 137hp ej22)

#2 Storm

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Posted 23 November 2006 - 05:24 AM

I don't think there's nearly as much wear on the motor at WOT when compared to short stop and go cycles, lots of starting the car and no warmup before harder use. How and when you load the drivetrain is probably going to effect wear more.

Keep fresh oil in it...Milage will be less if you're using WOT naturally. I usually don't need to go beyond 30-40% throttle when playing nicely on the road but I will go to WOT on occasion just to keep things cleared out.


Jay

#3 Setright

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Posted 23 November 2006 - 07:15 AM

Let's see...EJ22, with regular oil change intervals between 10-12000km or once a year, it will take you around 400,000km to wear that engine down :)


So, WOT for fun, and if you stick to legal speeds, you won't hurt your mileage that much.

#4 The Dude

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Posted 23 November 2006 - 08:37 AM

Are you talking about WOT after gradually attaining speed? Or are you talking about a "jack rabbit" start from a traffic light? Because, without question, excessively hard acceleration from a stop is very, very hard on a car. The engine, drive train, and suspension will probably have greatly shortened life spans.

#5 Virrdog

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Posted 23 November 2006 - 02:33 PM

Going WOT at low engine revs is not as horrible as you think it would be. The pumping losses for the engine are at a minimum and there is very little air flow under 2500 rpm or so. So less pumping losses and very little air (aka very little fuel) would be your friend in this case.

That all goes out the window if you have a turbo, though.

And I don't see how the act of going WOT would "hurt" the engine. The only things related to that would be over-revving the engine at the wrong time (ex: cold, low oil). The actual cause of hurt to the engine is usually something else like a problem with the oil, not the actual go pedal.

#6 porcupine73

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Posted 23 November 2006 - 02:41 PM

I wouldn't worry about going WOT. Sure, there's additional force on the bearings and stuff, but as long as you have a good oil with good AW characteristics and stuff it will handle it. I don't know if you have AT or MT, but I would try to avoid lugging the engine.

#7 newsance

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Posted 24 November 2006 - 10:45 AM

The horsepower an torque of an EJ22 aren't enough to really cause wear issues. Its just not that much power where you run into issues like pounded out main bearings.

The other piece that makes these so reliable is that the redline is low. High rpm operation is anothing item that causes increased wear, but the Subaru's redline is pretty low.

Fuel use is another item. Your engine will get notably worse fuel economy if it is accelerated at wide open or near wide open throttle.

This is because at part and mid throttle, the engine management computer will work to keep the AF at a 14.7:1 ratio, to run as cleanly as possible. Very light/no throttle will be much leaner.

However, the engine management switches to "open loop" mode when it approached full throttle. It ignores the 02 sensor (which is inaccurate unless the AF is close to 14.7) and instead runs of a preprogrammed map at around 12:1 for maximum power.

So, at full throttle, not only is your engine injecting the maximum amount of air and fuel, it is also getting proportionally more fuel than it would get at half throttle.

#8 JaySmurff

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Posted 26 November 2006 - 01:41 PM

Good info guys, Yeah I defiantly avoid "jack-rabbiting" the thing. To the guy that asked I do drive a manual. Basically I just wanted to know if it was okay to WOT it if I was already moving at a normal clip i.e. 40 mph to get onto the highway onramp or w/e. But from what I read I’ve concluded that it’s no real problem just get regular oil changes and don’t expect amazing gas mileage. ;)

#9 zyewdall

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Posted 26 November 2006 - 11:51 PM

The other piece that makes these so reliable is that the redline is low. High rpm operation is anothing item that causes increased wear, but the Subaru's redline is pretty low.


Compared to what? My EA82 is redlined at 6,500 (I try to keep it below 4,500), and I regularly have it at 3,800 while cruising, to get a semblance of power. That seems pretty darned high to me (though everything else I regularly drive is either a diesel, or an old V8, so I don't know what the little four cylinder gas engines in hondas, etc, usually operate at)

#10 newsance

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Posted 27 November 2006 - 12:07 PM

Compared to what? My EA82 is redlined at 6,500 (I try to keep it below 4,500), and I regularly have it at 3,800 while cruising, to get a semblance of power. That seems pretty darned high to me (though everything else I regularly drive is either a diesel, or an old V8, so I don't know what the little four cylinder gas engines in hondas, etc, usually operate at)


Compared to many other 4 cylinder engines on the market.




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