Clarification on rev match K24

[sacklunch]

Hey all,

I’m considering buying the G4x for a K24a2 in an 01 MR2. I’m running a usdm ep3 5 speed trans which does not have a speed sensor (speedo runs off wheel speed). How easy is it to add rev matching using the G4x? I know I will need to buy a dbw throttle body and pedal assembly and possibly the hardware add on for the ecu. Is that it? How exactly does it know which gear I’m in? And how smooth is it? I tried searching for videos of folks installing this feature but couldn’t find anything. Thank you!

[superstockneo]

I've posted one here, it's been discussed but being a 5speed H pattern trans with now way of indicating to the ecu what gear you are in, it is a bit tricky.

 

[dx4picco]

you can calibrate your speed and gears if you have a vehicle speed sensor, even with H pattern gearbox

[Electredge]

maybe someone smarter will chime in but you could blip for up and down shifts, then rev match would work 

[Adamw]

For a true "rev match" you would have to use the motorsport gear shift function which is over the top for what you want I think.  

To use the gear shift function to achieve a rev match it would be done something like this:

In road car with an H pattern shift and no strain gauge or similar on the lever then really the only thing you have to indicate to the ecu that you want to initiate a gear shift is a switch on the clutch pedal.  But that alone doesnt tell the ecu whether you want to do an upshift or downshift.  So you use a GP output to asses a whole lot of conditions that you think would be present for a down shift but not an upshift.  This, for example, could be something like Throttle pedal is not pressed, clutch and brake pedal are both pressed and the speed is above 30kmh.  Whenever the ecu see's all of those conditions true then it will initiate a downshift sequence.   

Next, for the ecu to be able to rev match, it needs to know what gear you are in and the ratio of the current gear and the ratio of the next gear that you want to engage.  Since you dont have a gear position sensor, you will need a working speed sensor so the ecu can then determine which gear you are in by using speed, RPM and gear ratios. 

With all of that the ecu would then have enough info to generate an RPM target that it needs to hit with the blip based to achieve matched input and output shaft speeds during the shift.  This RPM target can be met in 3 different ways.  1). You can use a speed match limiter - this is where the ecu blips the throttle a little more than is required and introduces a rev limiter to control the RPM at the desired target.  This is the most accurate and fastest blip. But you dont really want to be bouncing on a limiter on every shift when driving around town etc. 2). You can use what we call an RPM target blip. This is where the ecu performs a blip then removes the blip once the target RPM is reached. Since the throttle doesnt close until you are already at target you will get quite a bit of overshoot with this method.  3). A predictive blip, this is where the ecu looks at the rate the engine is accelerating during the blip to predict how long it will take to reach the correct RPM, it can then close the throttle early so you dont get as much overshoot as method 2.  

Having said all that, it is rare to do a proper RPM match for a road car with a synchro gearbox, the normal technique is just to switch to a 2nd e-throttle target table when your downshift conditions are met.  That table can have RPM Vs gear or Speed Vs gear on it so you can command more blip for high speed gear changes and less or none for low RPM/speed shifts.