It depends more on your requirement than on the differences between these two beemer options.

R80 runns ok/well with a road-weight(?) of 350-400kg. 450kg is ok as well, but hitting 500kg... it does get sluggish...
It is a smooth running, sweat and soft engine, especially in the version that you are asking about (8.2:1 50hp).
You will however find that raising the compression by swapping pistons to the 9.2:1 55hp pistons will be a -good- investment. The engine becomes a little "raw" though, and a triffle "nervous".

R100 - far more power. Better milage. Runns cooler. Raw. Brutal. Not to my liking (though I do use them).
The light-weight tune-up kit from Germany is however a very neat tuning; the engine will not be as brutal and raw. It will be more rev-willing.

In either case, both models benefits from oil-cooler...

As for cutting costs...
50hp... vs 67(ish)hp
50(ish)Nm... vs 75(ish)Nm...
...that -is- a huge difference...
You will/may spend a bit on fixing the power-less 800cc engine I guess...
55hp and 56Nm is ok though... and that will set you back about 3-400USD (if prices have not risen since I checked), if you can swap the pistons yourself i.e.

As for tuning options:
www.motoren-israel.de

The 800 cc engine benefits hugely from T-shaped high-flow valves, e.g. Buggpack 44mm. That would require new seats though, so less you plane to change seats 42mm high-flow-valves would be your option. Bugpack valves costs about 50-60USD each, needs to be shortened and new collet groves swiveld and lasp-caps added. The power increase is modest, but pushing the power just over the sluggish limit; the engine will get that little extra that makes it ok to drive.

Dual-plugging is a tuning that I recommed, but it is costly. (I wrote about it in 2008; "ITU gone bust" I think I called the string).

__________________
Drive Safely,
Albert

Hello,

This will be my first ADV bike so I am looking for any recommendations or advice. I have been riding sports bike for the past 20 years and its time to transition to different bike with more capabilities. I have some experience with dirt bikes but not a expert. I am thinking between 2013 KTM 990 ADV Baja Limited Edition or F800GS. Looking forward to your feed back.

KC

You might be better off posting a new question in the which bike section rather than on a thread about completely different bikes to the ones you are interested in.

I love googling something and finding a post from the HUBB.

FROM TWENTY YEARS AGO.

And it's just as relevant today as it was then.


Suck that Facebook.

__________________
Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.

one further piece of information that may be relevant to some in regard to the above is that the electrical output is less (around 280 I think for the above bikes) than many later model motorcycles such as the 1000cc Africa Twin. If you need to run additional lights and say various pieces of heated clothing plus GPS etc, then you may need to consider this aspect, although some clever people may figure a way around this issue.

There are indeed upgrade kits for the anemic airhead electrics. Stock is 240 watts, and struggles unless you keep the revs up. EARLY airhead R75 owners in the US complained of major electrical issues, dead batteries etc. Germany didn't understand why, until they discovered the average North American rider rode around under 4000 rpm, not wanting to "stress" the engine, or perhaps used to slow revving Harleys, and old English bikes. The airheads didn't START to charge until 4000! Changes were made, but barely adequate. If you knew to rev it they were fine.
An excellent kit available: https://www.bmwmoa.org/blogpost/1239...e-for-Airheads
I have an early version, I think 450 watts, in my R80G/S and it works fine, nice simple bolt in upgrade and extremely reliable. I can run two electric vests, electric gloves and a 100 watt headlight without issue.

Another is: https://www.euromotoelectrics.com/product-p/edl4.htm

__________________
Grant Johnson
Seek, and ye shall find.
------------------------
Inspiring, Informing and Connecting travellers since 1997!
www.HorizonsUnlimited.com

We rode around the world two up with a stock (plus dual plugging and oil cooler) R80G/S, and the power was fine. Not great on the Autobahn, but generally adequate everywhere and more than enough most of the time.

Returning home, and then in the UK, I upgraded to 1000cc with a complete R100 top end with 40 mm carbs. FAR better power, MORE vibration, WORSE fuel mileage. For NA and Europe, a better choice. But the R80 engine is VERY nice, sweet, low vibes, pleasant to ride. The R100 is as noted above, more RAW - which you might like . No surprise to me, as I'd had a couple of R100S's before.

Given a choice, I'd go for the R100GS paralever version, despite the flaws. Overall better. Tubeless, longer wheelbase, much bigger battery, stronger forks (I put R100GS forks on my R80G/S), better front brake.

__________________
Grant Johnson
Seek, and ye shall find.
------------------------
Inspiring, Informing and Connecting travellers since 1997!
www.HorizonsUnlimited.com

I just wanna thank everyone for the information in this thread really useful I'd been weighing up r80's vs r100gs's to sit alongside my 1150 so a big help