Skipping Gears with SRM

MJM33067

I've been driving manuals most of my life and frequently skip gears when downshifting. For example if I'm coasting towards a red light I might downshift from 4th straight to 2nd to brake. Was wondering if this practice could be dangerous with the SRM turned on.

spearfish25

Nope, SRM can rev match any downshift as long as you don't shift an extreme that would go past the redline (SRM will still attempt rev matching and you'll risk engine damage).

09370z

Actually it will engage the rev limiter and therefore will not damage the engine at all...

JoeD

I was just about to say. I'm pretty sure SRM revving would be bound electronically by the rev-limiter as opposed to a mechanical over-rev.

It's not like I will ever try it, but has anyone (either by accident or some stretch of curiosity) attempted a shift into a gear too low for their relative speed with SRM on without releasing the clutch? Will it pin the rev-limited or does the computer sense impending doom and act otherwise?

travisjb

I think I've done this one the track a few times and well... I think spearfish is right - I remember landing above redline ! ouch ! i should be able to verify once I can figure out how to get my darn RPM wire working on my traqmate

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davidyan

Actually your car could still go way past the limiter and blow the engine. The rev limiter is essentially a fuel cut. When upshifting, it can prevent an engine from being damaged but not on a downshift. Think about it this way, lets say you're going 7000 RPM in 3rd and drop it to 2nd. Even though the rev limiter kicks in cutting the fuel, your clutch is still engaged to the engine and due to the mechanical force will pull the engine way past the redline. This can only be stopped by immediately pushing the clutch back in to disengage the engine/tranny. It would be so instantaneous, it would be hard to do though and I don't recommend it.

AK370Z

I drive with SRM on most of the time. I downshift from 6-4 all the time. I also upshift 2-4 and 4-6 as well. SRM works flawlessly. Even though spearfish and travisjb are correct, you don't have worry about it costing to redlight (i.e. normal driving). If you're tracking or driving very aggressively at higher speed, then downshifting with skipping gear may overrev your engine.

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JoeD

Again though...how would this over-rev situation be any different if SRM was off?

If you improperly downshift into 2nd at say 80 MPH and release the clutch, the engine will over-rev mechanically as it would with any car. However, I don't think the actions of SRM itself (pretend you put it in 2nd at 80 MPH but catch yourself before you let out the clutch) will cause an over-rev because there is no mechanical force driving the engine beyond its capabilities.

spearfish25

You're absolutely right, but if you engage the clutch on an SRM downshift you're still forcing the engine speed to match the transmission (over-rev). I suppose if you catch yourself in a bad shift before engaging the clutch, you may not go past redline. However, bouncing off the rev-limiter isn't a great idea. The 'problem' with an over-rev downshift exists with or without SRM. The OP was just asking originally if SRM will allow gear-skipping downshifts. It absolutely does...I just enjoyed a flawless SRM-assisted 6-3 downshift on the highway today and sucked the doors off a guy going slow in the left lane .

travisjb

Good point Joe and Chris, downshifting into too high an RPM will have the same result with or without SRM... BUT... SRM makes it SOOOO easy to downshift into higher RPMs that for me at least I tend to push the limits and end up downshifting at too high speeds for the gear

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2009 370Z #104
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