Akrapovic exhaust - speed limit bonus...

[Gazzerthegreat]

Had the Akrapovic system fitted to my 2014 F10 and she sounds sweet.

Last week on a dry sunny (rare for UK) Sunday morning heading to Brands Hatch for the BTCC event (it was early 7am, although in the UK the clocks had just moved forward an hour for summertime, so 6am in old time!) a favourite dual carriageway was fast approaching. The road was dead straight, level, a mile or so long, no joining roads and no other cars or police around (health warning - don't do this if other cars are around on publics roads)

I thought the car was limited to 155mph (250kph), but thought I would check it out and have some fun to get me in the mood for the day ahead.

Well, what an added bonus it turned out to be and not sure why or how as I hit 166mph (267kph) Has anyone else experienced a similar added performance above the factory limiter setting as a result of an after-market exhaust system? Can someone explain how the limiter is meant to work, as I expected the throttle to stop once the speedo read 155mph? Just interested only - no intention of getting the dealer to correct the 'error'

[Ex_Stig]

Your speedo is probably not accurate. There is no way that an exhaust change would impact a computer imposed limiter.

If I remember correctly, the BMW tolerance for speedo accuracy is 10% + 2.5mph. So, at 155mph your speedo could indicate as high as 173mph.

If you really want to test it you should get a separate GPS and bring it in the car.

[v3n0m]

This is true. The speedo is optimistic by about 10%

[Palmnuts]

OP - I would be cautious about the phrasing of your post on a public forum....maybe tweak it a touch

As for the speed, I've had an indicated 170mph from my M6 whilst on the autobahn in Germany and I'd suggest that most of the incremental 15mph above the limiter (at least 10 of it) is just speedo over-read.

Its such a shame that BMW UK don't offer the M Drivers Pack with the 190mph limit - I for one genuinely do travel to Germany a few times annually so would definitely benefit from it given the car smacks into an indicated 170mph limiter so easily. And thats exactly what it does - the car is still accelerating quite strongly and when it hits c.170mph it's like it hits some massive resistance and the thrust just stops....it's most unnatural!

However, I am in talks with BMW Aachen (through AC Schnitzer, who's HQ is based at that dealer) who believe they can do an official retrofit the genuine M-Drivers pack (including providing the track day tuition that comas as part of the option). I should find out on Monday if this is all go - if so, I'm off to Germany the following week so will be having it fitted. With the expected speedo over-read, it should show an indicated 200 after that's done


P.S. I was also at the Brands BTCC event last week too...I was in one of BMW's hospitality suites.

[bimmer-boy]

Yeah speedo is defo not accurate...

Congrats on the akra they sound awesome

[mstmng]

all M cars in UK limited to 170mph, other bmw's limited to 155

[Palmnuts]

Not quite - my M135i clears 160mph on the speedo.....just. But it does prove theres a difference between M, all of which do seem to do c.170mph indicated, and non M-BMW's which.....don't.

However, although 170mph is likely to be close to a 'real' 155mph, I highly doubt BMW actually go to the trouble of limiting to a correctly calibrated speed for the M's and not other cars. I also guess it means non-M's that hit the limiter at c.155-160mph don't even make 155! Not that any of this matters one jot to my everyday commute

[Mbdurham17]

The speedo is definitely off. The speed on my passport max (GPS) and an iPhone speedo app (also gps) always show faster than my speedo by a few mph and the difference increases with speed. I am not sure of the ratio but this has been discussed at length many times here

[JOHNBMWM5]

Originally Posted by GNALUZU

Your speedo is probably not accurate. There is no way that an exhaust change would impact a computer imposed limiter.

If I remember correctly, the BMW tolerance for speedo accuracy is 10% + 2.5mph. So, at 155mph your speedo could indicate as high as 173mph.

If you really want to test it you should get a separate GPS and bring it in the car.

My LCI is accurate too 3 MPH @ 100 MPH using GPS Rider.
Using my winters 275/35/20 rears it's Spot on.

[msi200]

This is normal, the speed limiter is roughly at 270km/h.

[Gazzerthegreat]

Thanks guys for the info. I'm use to things being what they say, so disappointed that these days Manufacturers can't calibrate a speedo correctly! I'm sure there are other ways to avoid 'culpability' issues and besides we are all responsible for our own actions - no one loses their license for just being over the speed limit by 10%.

Palmnuts - I was in the BMW hospitality suit - 2nd floor in the window on the right! Now those BTCC cars are loud - small world

[Palmnuts]

Originally Posted by Gazzerthegreat

Palmnuts - I was in the BMW hospitality suit - 2nd floor in the window on the right! Now those BTCC cars are loud - small world

It certainly is a small world - I was there on the 2nd floor, sat back with my other half on the left. In fact, did I sit next to you and your other half during the last race and then see you again as I was driving out of the car park?

[Ex_Stig]

Originally Posted by Gazzerthegreat

Thanks guys for the info. I'm use to things being what they say, so disappointed that these days Manufacturers can't calibrate a speedo correctly! I'm sure there are other ways to avoid 'culpability' issues and besides we are all responsible for our own actions - no one loses their license for just being over the speed limit by 10%.

Palmnuts - I was in the BMW hospitality suit - 2nd floor in the window on the right! Now those BTCC cars are loud - small world

Pretty sure this margin of error had been in place for a very long time. Also, it is only a one sided margin. There is no allowable tolerance if your speedo reads slower than you are actually going. If that were ever the case BMW would fix the car immediately.

I guess I just don't see what is really worth getting worked up over this.

[avlnch]

I am sure there is some sort of solid legal reason for now our speedo's work (my AMG's are the same way).

If you notice when you drive past a speed sign, they read around 3mph slower than your driving. Now sure how those speed signs are calibrated though.

[alvinabed]

I don't think that there's correlation between you changing the exhaust and speed limit. I just had my exhaust changed to akrapovic evolution, just feel like the car is faster due to the exhaust sound.

[shahano]

The limiter outside the US is 172 MPH which is 270 kph... So its totally normal.. Now how do we get rid of that as well?

[Gazzerthegreat]

Sorry Palmnuts,

I meant to say on was on the left as well, not right. So it was me you sat next to on last race.

Until the next freebie