Rev Jump When Upshifting under Hard Acceleration

[egxflash]

FInally stretching my DE5's legs after break-in and noticed something peculiar under hard acceleration.

When upshifting 1 ->2 and 2 -> 3 , I noticed the revs jump ~500 rpm in between shifts. I thought maybe I was a little late to take my foot off the throttle but even after being mindful of that, it still jumps up a bit.

I'm finding I have to shift around that so as not to bang on the rev limiter. I been reading around and I've seen mention of rev matching but that doesn't make much sense to me. Also, this phenomenon happens even as I have the rev match feature off.

Is this rev hang? Is it just me? I'm not very familiar with it and never had this experience in any other manual car I've had. Granted, all my other cars have been N/A.

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[frenzal]

Same thing for me. I hate it when the car does that! Looks like if I'm not able to shift correctly! Very anoying!

 

[PointByPatrol]

I believe this has a lot to do with the clutch delay valve in the slave cylinder. The clutch disengagement is delayed by this valve, and could henceforth allow the engine to continue it's revs from centrifugal force until the delay valve gets its act together and disengages the clutch. I've not removed my delay valve yet, but plan to soon, and was planning on reporting back afterwards.

 

[egxflash]

I believe this has a lot to do with the clutch delay valve in the slave cylinder. The clutch disengagement is delayed by this valve, and could henceforth allow the engine to continue it's revs from centrifugal force until the delay valve gets its act together and disengages the clutch. I've not removed my delay valve yet, but plan to soon, and was planning on reporting back afterwards.

I'm not familiar with this - any detriment to the mechanics of the car by deleting it?

 

[Gansan]

I believe this has a lot to do with the clutch delay valve in the slave cylinder. The clutch disengagement is delayed by this valve, and could henceforth allow the engine to continue it's revs from centrifugal force until the delay valve gets its act together and disengages the clutch. I've not removed my delay valve yet, but plan to soon, and was planning on reporting back afterwards.

This doesn't quite make sense. The clutch delay valve delays *engagement* when you let go of the pedal, not disengagement. It keeps a high revving engine from suddenly connecting with and stressing out the drive train. It doesn't work in both directions.

When you remove the CDV, you'll find that engagement becomes more abrupt when you let the clutch out quickly. Pushing the clutch down will be the same.

I suspect the drive by wire throttle isn't responding fast enough to close the throttle. When you push the clutch down, there's still some throttle opening, causing the revs to jump. This is like rev hang but a mild version of it.

 

[PointByPatrol]

This doesn't quite make sense. The clutch delay valve delays *engagement* when you let go of the pedal, not disengagement. It keeps a high revving engine from suddenly connecting with and stressing out the drive train. It doesn't work in both directions.

When you remove the CDV, you'll find that engagement becomes more abrupt when you let the clutch out quickly. Pushing the clutch down will be the same.

Thoughts on what you think it could be? It doesn't have anything to do with rev hang. I found this out after having the last car tuned, and it still did the same thing. New car does the same thing too. Judging by where the valve is located inside of the slave, I'm still suspicious that this might play a factor in this.

 

[Gansan]

Thoughts on what you think it could be? It doesn't have anything to do with rev hang. I found this out after having the last car tuned, and it still did the same thing. New car does the same thing too. Judging by where the valve is located inside of the slave, I'm still suspicious that this might play a factor in this.

Whoops sorry I was editing my post while you were replying! See above.

 

[Gansan]

Thoughts on what you think it could be? It doesn't have anything to do with rev hang. I found this out after having the last car tuned, and it still did the same thing. New car does the same thing too. Judging by where the valve is located inside of the slave, I'm still suspicious that this might play a factor in this.

The reason it can't be delaying clutch disengagement is from the way hydraulics work. When you press the clutch pedal and pushing the master cylinder piston, you're displacing fluid down the tubing through the CDV and pressing the piston in the slave cylinder, right? Suppose the CDV stops the clutch from receiving this fluid pressure. That means it's blocking the fluid from moving. Fluid is incompressible, meaning if it doesn't move down the tube, the master cylinder won't move, and the clutch pedal will be blocked from moving. You would 100% feel the pedal refusing to go down if it really did block disengagement. Think about the brake pedal. When the pads contact the disc, your foot is blocked from pressing the pedal further because the brake fluid stops you.

For engagement, the spring in the clutch is pushing back on the slave cylinder, and the CDV is restricting the flow of fluid to slow it down. The fluid is still incompressible, so the clutch is feeling the resistance through the slave cylinder and that resistance results in slowing the engagement of the clutch.

 

[Icehawk]

It's rev hang although not how I am used to seeing it, I'd call this "rev flare" personally. Can't stand it.

 

[PointByPatrol]

It's rev hang although not how I am used to seeing it, I'd call this "rev flare" personally. Can't stand it.

Yea dude, me neither.... Even with the hondata tunes making the throttle more responsive...it still does it just as bad.

 

[Icehawk]

wait this isn't cured by tunes???

 

[PointByPatrol]

wait this isn't cured by tunes???

It wasn't on my last car when it was tuned.

 

[egxflash]

It wasn't on my last car when it was tuned.

Which tune did you have?

 

[PointByPatrol]

Which tune did you have?

Custom tune from @Jester04

 

[MooMoo]

yep, it sucks that it does this.

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