Hexhead Performance questions and clarifications (torque dip anyone?)

[DutchBMW]

Hi Everyone,

I've been a happy ('06) GS owner for over a year now, but i do have some questions about the performance that need some clarification.
I've noticed that the GS has a VERY annoying torque dip at around 5000 rpm and i see that every hexhead suffers from this (SOHC or DOHC).
A lot of people say this is due to emission restrictions (extreme leanness), but i think i have to debunk this:
Every GS i've seen online (remapped, PCIII, PCV or nothing) has this dip.

I've read somewhere (can't remember correctly where i found it though..) that the boxer engine doesn't breathe really well at this rpm and (lean or not) the dip will always be there..
I just think it's very annoying to fully accelerate from 3000 to redline and i really notice the dip quite well (engine also vibrates a tiny bit more) and engine sound just isn't as throaty.
The engine is very strong from 3-4000 and above 5000 to redline.

In the meantine i've fitted Lennie's rocket sprockets and these made a very good improvement in how the bike performed (especially at low rpm's), however the dip is unaffected.
I fitted a catless header and the higher rpm's were better (sound also a bit better), but the dip is unaffected.
I fitted a Remus muffler and sound is alot better, however the dip is unaffected (DB-killer in or out).
I've also fitted a set of AF-XIED's and the whole rev range is better due to enrichment of the mixture, however the dip is unaffected (feels a bit better, but definitely there)!

I've ridden a friends RT and it has the same.
Reading the online dyno's of the HP2 Megamoto and Sport, they both have this dip.

And yes, i've done a valve adjustment, throttle body sync, air filter change, spark plug change (all 4), fuel injector cleaner, but nothing changed the dip.
Has anyone ever fixed this annoying dip???

Regards,
Otto

 

[Santa-2512]

Hi Everyone,

In the meantine i've fitted Lennie's rocket sprockets and these made a very good improvement in how the bike performed (especially at low rpm's), however the dip is unaffected.

Regards,
Otto

Well apart from being as much use as a chocolate teapot, id be asking for my money back.

Where did you fit the sprockets ?

Did you preset the front combobulator? and lift the anti unicorn shim to its top setting?

Hint - GS1200 is shaft drive!

 

[DutchBMW]

Well apart from being as much use as a chocolate teapot, id be asking for my money back.

Where did you fit the sprockets ?

Did you preset the front combobulator? and lift the anti unicorn shim to its top setting?

Hint - GS1200 is shaft drive!

Do you know what these sprockets do?
They're cam sprockets, they have nothing to do with the driveshaft!

 

[Santa-2512]

Do you know what these sprockets do?
They're cam sprockets, they have nothing to do with the driveshaft!

Ah a little bit more information - Always helpfull -

Never noticed a dip - i just ride the dam thing

 

[Pukmeister]

They alter cam timing relative to crank. This is not the same as fitting a performance camshaft with higher lift and/or longer duration.

 

[Slipperyeel]

I don't know the cause of the dip you're describing. But this bit gave me a laugh

Do you know what these sprockets do?
They're cam sprockets, they have nothing to do with the driveshaft!

Sent from my SM-N910F using Tapatalk

 

[papasquelch]

Oh, no, not another post touting for business from you know who...

 

[Lord Snooty]

Mine no longer has the dip since I had it remapped.

 

[DutchBMW]

Mine no longer has the dip since I had it remapped.

Do you have a dyno sheet available or have you seen it on a chart?
I'm wondering because more people have said this after a remap, but i've never seen 1 (!) chart where the dip was actually gone..
The power is sufficient, but the dip just annoys me and i'm willing to remap just to get it removed.
I've also taken a look at charts with the AFR's and it doesn't show a lean spike or anything, so there's only so much you can do with AFR tuning.

I'm at around 4500 rpm on the highway, so whenever i need to overtake quickly, it always starts in the dip :-(

 

[Pukmeister]

I think the dip is an inherent characteristic of the boxer twin design, you can reduce it markedly but not remove it entirely.

A remap filled in the hole in the midrange, added a bit more at top end and pushed the entire bhp curve upwards slightly. Whilst its no litre sportsbike, its no slouch either and the mid range dip is now negligible. Its also a lot snappier and cleaner off a closed throttle and from part throttle whereas it was hesitant before.

 

[Bendy toy]

The Power Commander V on my bike pretty much removed the 4000 revs power dip so I see no reason why a remap would not do the same. The dip is caused by weak fuelling after all.
The PCV did nothing for the vibration at the same rev range which seems to be an engine characteristic.
Funnily enough the Yamaha Diversion 900 suffered a similar rough patch but being carb fed had no fuelling dips.

 

[jjones]

I also have this dip at 4-5k (2005 GS) and it is annoying. I do not want to remap as at 55k i do not want to put extra strain on the drivetrain and the cost would be a significant percentage of the bikes value.

 

[Bendy toy]

I also have this dip at 4-5k (2005 GS) and it is annoying. I do not want to remap as at 55k i do not want to put extra strain on the drivetrain and the cost would be a significant percentage of the bikes value.

The bike will be more than up to the "strain" of making more power and you don't have to wring its neck everywhere you go.

More importunely, the remap improves the weak fuel mixture so exhaust valves are under less stress and an engine running smoothly puts less stress on the drive train. Everyone's a winner when the engine is running as it's designers intended.

 

[Pukmeister]

As I recall, the 2005 bikes were the worst for lean running. A mate had a yellow one which dropped a right hand exhaust valve, luckily for him as he was riding it to Bahnstormer to P/ex it, they took it as promised and repaired it.

A remap is the best way to richen the fuelling where it is needed and reduce the risk of valve heads snapping off due to a hot lean mixture.