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Auto Transmission : Engine Braking Vs Brakes


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#181
tpl

Posted 18 April 2011 - 07:32 AM

tpl

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QUOTE (vr2turbo @ Apr 17 2011, 09:17 PM) <{POST_SNAPBACK}>
Oh, then forget about it until you make a trip there........ smile_tongue.gif

easter family coming so c whether they wan to go o not...
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#182
vr2turbo

Posted 18 April 2011 - 05:53 PM

vr2turbo

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QUOTE (tpl @ Apr 18 2011, 07:32 AM) <{POST_SNAPBACK}>
easter family coming so c whether they wan to go o not...

ok, wait for your result if you go..... smile_tongue.gif

#183
tpl

Posted 18 April 2011 - 06:53 PM

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QUOTE (vr2turbo @ Apr 18 2011, 05:53 PM) <{POST_SNAPBACK}>
ok, wait for your result if you go..... smile_tongue.gif

smile_approve.gif
2012 NMT President

#184
jonlsl

Posted 14 June 2012 - 03:56 PM

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QUOTE (nofear1979 @ Jan 25 2011, 10:23 AM) <{POST_SNAPBACK}>
i think i can TRY to do a test..

we have a fuel consumption meter..

Can test this when doing down hill... i'll reset the meter... and look at the reading..


Some cars will have a fuel cut mode some cars will not have a fuel cut mode. Not all cars automatically will go into a fuel cut mode when the throttle is shut. E.g. like my company camry. Only when certain conditions are met will the car go into fuel cut. Like my cefiro it has no fuel cut but my civic has.

When I used to tune the HKS V-Pro ecu for my customers I always use fuel cut to save fuel as soon as the throttle is shut and if the throttle remains shut the reactivation point when fuel starts to spray again in fully closed throttle would be 1500rpm with A/C on and 1200rpm with A/C off.

For racing you can program no fuel cut for better on-off throttle response or tune to spray fuel and retard the timing on zero or close to zero (1%-5%) throttle to have engine overrun to reduce turbo lag as the fuel is being burned in the exhaust, this puts alot of extra stress on the exhaust manifold and in a turbo system the turbine exhaust can get really hot. This is what they normally call "anti lag" system which is widely used in WRC to help with turbo lag during off throttle. Same principal was used in 2011 F1 engines where some teams was using hot overrun to blow their blown diffusers. There is cold overrun as well. But cold overrun can only be done with e-throttle or hydraulic actuated throttles only, not practical (still can be done) on cable operated throttles (as a system has to be made to cut fuel and still allow you to open the throttle). This is because during off throttle. The ecu will automatically open the throttle and cut the fuel, then the air being pumped by the pistons will just flow out the exhaust rather than the throttle being shut and creating a vacuum in the engine thus cold blowing the diffuser. This will in turn cool the valves of the engine as well. This was the argument that Renault used to have the "throttle open" when the acceleration pedal is at zero position or off throttle. That is why when the FIA said NO throttle angle to be open Renault said cannot, that will affect the reliability of the engines. So then the FIA said ok lah I allow a little bit to open only.

#185
vr2turbo

Posted 18 June 2012 - 05:25 PM

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My wife's Chery SUV, when going down steep gradient will slow down by itself, considered fuel cut? smile_question.gif

#186
jonlsl

Posted 19 June 2012 - 08:58 AM

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QUOTE (vr2turbo @ Jun 18 2012, 05:25 PM) <{POST_SNAPBACK}>
My wife's Chery SUV, when going down steep gradient will slow down by itself, considered fuel cut? smile_question.gif


Hard to say. You can try going down the steep gradient either hold 2nd or 3rd gear make sure A/C comp. is off. Then look at the engine rpm. If it has fuel cut, when you shut the throttle above 2.5k rpm, then rpm will drop, then let it drop by itself until 1000rpm. If any where in between you need the needle jump up the fuel has come back on you mighht feel a slight nudge forward. If its smooth all the way to 1000rpm it has no fuel cut.

Usually they will cut fuel until 1200rpm (a/c off) with a/c on it will cut fuel until 1500rpm. So in either situation when the needle drops to 1200 rpm it will shoot up to 1300-1400rpm again.

But if you don't find fuel cut in you auto don't worry, not a very common feature in autos but some of them do have it. They usually don't have fuel cut in auto because they want to smoothen the drive and most of the time people leave it in "D" and the car will upshift to the higher gear when you off the throttle and cruise which usually drops the rpm to a range which is not always suitable for fuel cut and if it does, its for such a short time that hey don't bother.

This feature is best for manuals and if you know how to make full use of it, other wise you're not gonna save much.

#187
vr2turbo

Posted 19 June 2012 - 02:07 PM

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Next time must try out..... smile_wink.gif