jakeclkdude

Can anyone tell me what is meant by "rev matching"? I was discussing with a tuner the pros and cons of engine breaking using touch shift and the guy mentioned that if I do it I should rev match. Not wanting to sound any dumber than I am, I played along acting like I followed him. Nevertheless, it sounds like something I should know.

Turbo2

Rev-matching can simply be described as when you are down shifting, to rev the engine to the approximate RPM's the engine should be at for the gear you are going to be placing the vehicle in. Therefore, not having the RPM's at idle, then downshifting and having the engine have to play catch up with the transmission. The engine is already prepared for the RPM's that the gear will be delivering.

Rev-matching is better for both the engine and transmission but doesnt have the same affect on engine slow down as if you were to non-revmatch.

Kind of hard to explain and understand, do you understand?

Dave OH

Turbo2 explained it pretty well. Jake, rev matching is a technique that isn't really feasible with an automatic transmission. It is used in a manual transmission car in between the point where you have disengaged one gear and before you engage another. As Turbo said it it used in downshifting because when you downshift the RPM of the engine will be higher than it was. The tuner you were talking to didn't know exactly what he was talking about when suggesting you "rev match" with your auto car. In fact, you transmission effectively "rev matches" for you when you tap the lever left for a down shift. What you've been doing is fine, though its better to put the everyday wear on the brake pads/rotors as opposed to tranny components.

Turbo2

Dave-
I was going to comment on the automatic tranny and downshifting, but I havent gotten a chance to drive any of the newer cars with "tiptronic" so I wasnt sure exactly how it worked. However the idea of rev-matching an auto. just sounded a little bizarre.

jakeclkdude

Thanks for the replies. One more question. With touch shift, couldn't I screw up by down-shifting to 3 instead of 4 when I'm moving at excess speed? I've done this a couple of times (I also had my engine replaced recently with only 45,000 miles) and of course the engine redlined and shut down.

Turbo2

Once again, I have not had much experience with the tiptronic transmissions, but I assume that the computer would cut in and place the car in the correct gear. If not, I assume you could do a poor job of rev-matching with an automatic tranny. Did MB pay for the replacement of the engine?

jakeclkdude

Turbo2, as to your first point, the only built in protection is the rev limiter. Once you hit redline the engine shuts down until the RPMs drop below the limit. As for the engine, MBZ replaced it free of charge, as it was still under warranty. My rep told me it would have cost nearly 9 grand otherwise. Thank God for warranties!!

Turbo2

Jake-
Why was your engine replaced, was it because you downshifted to much and therefore destroyed the engine, or was it something else? If you did downshift too much, which in turn caused your engine to fail, it seems as if by MB replacing the engine they are stating that there tiptronic needs to have some sort of safeguard from preventing the user from dropping down too many gears.

jakeclkdude

Turbo2, perhaps I misled you. There may have been no connection between my downshifting and the engine's demise. I added that comment about my engine because aggressive downshifting was about the only thing that I did which one could consider abusive to the engine. Leading up to the engine replacement, I was consuming too much oil (3 quarts in about 1 month). When MB looked into the problem they found that one of my pistons or cylinders was scored. For the three years that I owned the car, I had taken car of it like a baby, following all the scheduled maintenance, etc. Thus, the only thing that I can surmise that damaged the engine were the 2 or 3 times that I did a bad job with the touch shift feature.

Turbo2

Jake-
I see what your saying now, those 2-3 times when you didnt downshift properly, did each time the engine redline and then shut down, or just get towards the upper stretch of the RPM's but not shut down?

jakeclkdude

it shut down each time, but I'm sure only after the engine speed exceeded it's threshold (if only for a second).

nukblazi

I might be a little late on this one, but momentum will push you past the rev limiter with the manual, does the auto upshift automatically to protect the motor?

jakeclkdude

Not from my experience. The only protection is the rev limiter.

Noredline

No, the Porsche tiptronics do though. I had mine in third going up, and accidentally had it shut down before I could upshift to 4th. An override of some sort might be useful. I just wanted to see where my truck shifted best between 3rd and 4th, about 90-95 max.

nukblazi

Yeah, my '00 325xi had that as a safety feature. If you got close, not even to the redline, it upshifted for you.

Pretty neat feature.