Question about the SRM

IDZRVIT · 05-31-2013, 09:51 AM

Quote:

Originally Posted by theDreamer

It will do something if you are slightly under the RPM range it has calculated for what it thinks you are going to do.
Remember if you are cruising in say 4th and go clutch in, the systems will know 2 things. You are either going up or down so it holds or slightly bumps the RPM to prepare itself. If you go down it can quickly rev up and if you shift up it drops them off.

I don't pussy foot around when I shift so the shift is completed in say a 1/4 - 1/2 second. The computer doesn't have time to do anything because the the digital data its presuming, as you note, then collecting actual data, now has to be processed and then work the mechanics of the engine. That will take more than a 1/4 second to complete those steps because nothing in this world is instantaneous. So, if someone is slow to shift, then one might notice an increase in rpm as you and others have noted before the shift is completed but for me I just complete the shift and move on. If I had the time to prove this I would just video the tach on an upshift and see if it moves up i.e. several hundred rpm because thats what it takes to become "noticeable", but its not important enough to me to do so as I'm in the process of putting my retro fit roller motor back into my 'vette.

Maybe you or someone else could do this to prove the point? Be sure to complete shifts within say 1/2 second. Anything more is granny shifting.

theDreamer · 05-31-2013, 09:59 AM

Quote:

Originally Posted by IDZRVIT

I don't pussy foot around when I shift so the shift is completed in say a 1/4 - 1/2 second. The computer doesn't have time to do anything because the the digital data its presuming, as you note, then collecting actual data, now has to be processed and then work the mechanics of the engine. That will take more than a 1/4 second to complete those steps because nothing in this world is instantaneous. So, if someone is slow to shift, then one might notice an increase in rpm as you and others have noted before the shift is completed but for me I just complete the shift and move on. If I had the time to prove this I would just video the tach on an upshift and see if it moves up i.e. several hundred rpm because thats what it takes to become "noticeable", but its not important enough to me to do so as I'm in the process of putting my retro fit roller motor back into my 'vette.

Maybe you or someone else could do this to prove the point? Be sure to complete shifts within say 1/2 second. Anything more is granny shifting.

You do know electrons, which is the basis for computation, travel at a much faster rate of speed and are beating you in your shifts. What is probably happening with you is that on your upshifts you are above its 'increase' limit meaning it sees no reason to raise the RPM when you upshift. Different shifting style.

IDZRVIT · 05-31-2013, 10:26 AM

Quote:

Originally Posted by theDreamer

You do know electrons, which is the basis for computation, travel at a much faster rate of speed and are beating you in your shifts. What is probably happening with you is that on your upshifts you are above its 'increase' limit meaning it sees no reason to raise the RPM when you upshift. Different shifting style.

And you also realize that those elctrons are sent through wires to a fuel injector (after the computer has determined the TPS opening and compared that parameter with a few others in order to produce the corect voltage signal to that injector) that has to open and introduce fuel into the cylinder on a compression stroke (gotta wait for the right stroke and there are four of them), fuel then is compressed, more electrons sent to the ignition to fire a plug which then needs to create the spark at a precise moment as the piston moves up the cylinder, and this will will ignite the air/fuel mixture to start the combustion process which will expand as it burns (fuel doesn't explode as some do believe) and force the piston back down the cylinder under load which will then rotate the crankshaft and the crank sensor will send electrons back through the wiring to the tach sensor which will then be converted to a mechanical force to rotate the needle in the tach. Yes, it happens fast but not as fast as you are trying to make this out. Probably best measured in 1/100 ths of a second or even 1/10 ths but not in a couple of nano-seconds.

Edit: There is a process which has to be completed from the time you move that shifter out of gear to the time you visually see the result at the tach.

SS_Firehawk · 05-31-2013, 11:51 AM

Quote:

Originally Posted by theDreamer

You do know electrons, which is the basis for computation, travel at a much faster rate of speed and are beating you in your shifts. What is probably happening with you is that on your upshifts you are above its 'increase' limit meaning it sees no reason to raise the RPM when you upshift. Different shifting style.

Dreamer, you are my hero, I thought the same thing... but you were sooooo much nicer about it than what was in my mind

theDreamer · 05-31-2013, 01:23 PM

Quote:

Originally Posted by IDZRVIT

This can turn out to be a good discussion on how SRM works. Yes, I can see where the computer could be programmed to add fuel (increase in engine speed) if left in neutral for a small period of time during the upshift process or anticipating such but is that true? I know the purpose of SRM is to eliminate heel-toe for downshifts but you don't heel-toe for upshifts. There is no reason to. If I'm already at say 3500 rpm and for ready to upshift and the computer detects this as I move the shifter into the next higher gear, why would it want to increase the rpm? If the revs drop several hundred rpm (foot off gas, clutch in.....) and the shift is completed at say 3100 rpm without SRM, why would the computer want to increase the revs to say 3900 rpm if I wasn't planning on accellerating any more because I've reached my cruising speed? To me, that would cause a slight unwanted surge in speed. If that is what this discussion is about and I have explained this scenario correctly for SRM interaction in an upshift, then this would be a safety issue, no?

Yes, it is true that the system will increase RPM on a shift up. I am trying to locate a few articles but it was discussed with Nissan and they said the Revmatch works on both up & down shifts to help 'smooth out' shifts.
Now the questions we would have to look at is how it determines this smoothness factor and what issues it could cause on an upshift.
I would presume the upshift rev is more of a safety net for the transmission. Meaning that it keeps the parameters inline with what it wants to be around so if you are off by 100 it will do a slight bump to bring it up for you but this could cause the driver to have some jutter if not prepared or ready.

This would be a fantastic test on a bone stock car.
Do some slow 1-2 shifts and 3-4 and record the RPM gauge and OBD2 readings/logs and then some faster higher RPM shifts and do some data comparisons. The shift speed factor can come into play and can be controlled a bit but will just need a driver who is steady.

Quote:

Originally Posted by SS_Firehawk

Dreamer, you are my hero, I thought the same thing... but you were sooooo much nicer about it than what was in my mind

I seem to be the nice guy on the forum.

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