DaveK

Over the past 6 months or so I've thought that my rev limiter didn't seem to be cutting in. I fairly regularly change up at the red line and a few times when I'd left it slightly late I was surprised the rev limiter hadn't cut the power.

Last night, I floored it in first and changed up way too late - I saw the tacho get just past 7400rpm. Happily, my valves didn't meet my pistons so no harm done - but it has convinced me the rev limiter isn't working.

The car is chipped - but this was done over 2 years ago and I've hit the limiter many times since then so I know that isn't the cause.

Does anyone know what could stop the limiter working? I'm confused because I know the limit is stored in the DME (must be, because some chips raise the limit), and I assume that the DME must perform the limiting - and all it needs to know to do that is the engine speed. It gets that from the flywheel sensor - and it that wasn't working I somehow doubt I would be able to reach the red line because the car wouldn't run!

joey bagadonuts

Why don't you pop in your old chip to confirm that the new one is not the problem? This is kind of a stumper since, as you pointed out, the DME controls the rev limit.

DaveK

Don't have the old one (bit of an oversight when I got it chipped). But I can't see how it can be that - I've hit the limiter many many times since it was done.

I must confess that one day when I find spare money in my account I want to go back to stock chip anyway. I don't think I really got any power gain and I'd be happier these days with stock chip and O2 sensor.

DaveK

Well - I decided to hold my breath and try opening it up in 2nd and seeing what happened......

The rev limiter is cutting in - just over 7K rpm. Not sure why it didn't when it got to 7400 in 1st yesterday - maybe it wasn't really revving that high and it was just that the needle carried on as I changed up.

Obviously this is still a bit high - but although I've hit it many times before I suspect it has been this high since it's been chipped. Another reason to return to the stock chip at some point I think.

Cupcar

I would bet the chip had the rev limit changed all along and you just now noticed the increase.....

Steve Weiner-Rennsport Systems

Dave:

If I might offer a few thoughts,....


1) Porsche tachometers have lots of hysteresis; needle bounce. As such they are not that accurate in assessing RPM excursions. We use an Autometer recording tach to really see peak RPM's.

2) Any chip that raises the rev limiter is seriously detrimental to your pocketbook unless your engine has upgraded rod bolts, valve springs & retainers.

I would suggest that you install a chip (performance or stock) that retains the stock rev limit at 6750 RPM. FWIW....one can certainly feel a properly made performance chip.

Cupcar

I would bet how much one feels a chip is dependent on where one lives, given that we have different octane ratings available from state to state.

It was with extreme jealousy I refilled my rental car after Rennsport Reunion II at Daytona Beach Florida last weekend and noted 93 R+M/2 octane was available at the pump....our maximum in California is 91 R+M/2.

My car's RS chip pings slightly on 92 before the knock sensors dial back the timing, I have not even run 91 preferring to mix in race gas to get 93 since our change in California to 91.

Steve Weiner-Rennsport Systems

Cupcar:

True words.

Almost all performance chips offer the greatest gains when used with 93 octane or better.

The factory chip in your RS is happiest with 98 RON which is 94 R+M/2. You are doing the right thing by mixing race gas with your 91 pump fuel to get 93 or more.

There is a matrix chart on my website showing the result of mixing various quantities of 100 octane unleaded race gas with 91 pump premium.

Cupcar#12

I had the same problem with my chip of course - i ended up with a second DME and a detuned chip for Washington and an "Race Gas" DME with the RS DME and the Andial Cup Chip.
back on topic....
i would definitly check the Chip first since the DME controls it.