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KTM 640 Duke LE

  •  KTM 640 Duke LE Original
  •  KTM 640 Duke Black Edition
  •  KTM 640 Duke Black Edition
  •  KTM 640 Duke Spiegler
  •  KTM 640 Duke Akrapovic
  •  KTM 640 Duke Akrapovic
  •  KTM 640 Duke Akrapovic
  •  KTM 640 Duke K&N
  •  KTM 640 Duke K&N
  •  KTM 640 Duke Gearing

Januari 1998

My First KTM!

I always loved the design of the original Duke. A classic and the first production 'motard' type of bike. Also KTMs first street oriented bike. The 1998 Duke 640 Last Edition had the same colors als the first model from 1993. I just had to have it.

It was a different galaxy coming straight from a Triumph Speed Triple. It took me weeks to get a little used to the total absence of weight and bulk. The superfast handling and the short geared, short of breath but punchy LC4 single. But then madness took over. This bike turned you into a mouth-foaming nutcase the moment you pushed the starter button. The city becomes an MX circuit and B-roads a racetrack. I've dented more ego's of fellow (Sports)bikers and had more fun with this bike than with any other so far. Brilliant. I even rode it to the South of France and back. During the 3.5 years I had the Duke it was tweaked, tuned and modded to pieces.

After 2 years  I swapped the bodywork for all black from the 1995 model, the best looking IMO.

660 Factory Rally engine

With help from my dealer and a bit of luck I was able to get my hands on a original 660 Rally engine. This engine really finished 8th overall in Dakar 2000 and even second in the last leg to Dakar in the hands of Dutch rider Henk Knuiman. It was completely checked & rebuild by the factory and Dutch KTM Importer Brouwer Motors. Thanx Eddie!

Took me a day to get rid of the "genuine rally look". I swapped the clutch and alternator cover for new ones and used 3 old toothbrushes and a gallon of WD40 to remove the desert dust from all tiny corners etc. But then it was as fresh as a baby again.
With a near street legal SXC Enduro exhaust from KTM and stock opened up airbox the power increase is some 4/5 HP reaching 54 to 55 HP at the rear wheel. That figure alone isn't earth-shaking but the difference in feel and character of a 660 is. Rally engines are not tuned for top-end power alone. Torque, midrange power and reliability are more important when grinding through the desert. The much higher torque and longer stroke gives a 660 engine a misleading easy and 'lazy' feel. The power output is effortless and strange enough smoother with less vibration than a 620 or 640. Very good.
    Some specs:
  • Factory (hand)build
  • Bore & stroke 102 x 80  654cc
  • Forged piston
  • Gas flowed head
  • Higher compression ratio
  • Reinforced rocker-arm mountings
  • Reinforced crank & big-end
  • (Very) Reinforced clutch... auch!...


Akrapovic full Ti race exhaust

This Akrapovic system is a work of art. I've never seen such a beautifully made exhaust and, as it turned out later, never seen such a good exhaust performance-wise either.

This system is a replica of the exhaust build for the KTM factory SM bikes. In fact, it's identical apart from the headerpipe(s) to make it suitable for e-Starter engines. Besides the short stainless steel headers it's completely made from titanium and as light as air. Picking it up makes your jaw drop in disbelief. The extremely low weight made me even a bit worried to break it while putting it on my bike. Unnecessary as it's probably stronger than the original steel KTM items. It saves a good 4 KG over a stock system with SXC silencer.
The entire system is conical. From the mounting-flanges in the cylinder head right up to the end-cap of the silencer. At the the silencer the pipe-diameter is a whopping 60mm (pictured). That's almost 15mm more than the stock pipe which looks like a drinking straw by comparison...

Don't be fooled by the big silencer though. This system is LOUD !! And I mean VERY LOUD. It's really offensive but the tone is so beautiful... A very low, deep hollow bark. Just like Kini's bike! :-)

After a test-ride and a run on the dyno you'll have a tough time being civilized and remove it again. I had to fit a main jet 3 sizes smaller (!!) than with the KTM SXC exhaust. The flow of this system is that good. The engine is transformed. Even the idling is better from the first beat on. No less than 6 HP power increase to 61 HP and 67 Nm torque at the rear wheel. The 660 engine revs out really fast and holds on to max power for almost 1500 rpm. When the power gradually starts to drop between 8000 and 8500 RPM the gain over the stock pipe with SXC silencer is a mind-blowing 12 HP. Nuff said...

K&N airfilter

Ever had any doubts about the small airbox & filter on Duke I e-start models? Well, they are valid. When the KTM Factory SM team was in Venray Holland for a race in the European SM Championship we had a close look at the factory bikes. They run K&N filters straight on the carbs without an airbox in sight. My suspicion towards the little asthmatic stock airbox was confirmed. I just had to have such a filter on my bike too.

With the help of the pictures we were allowed to take, a special alloy mounting bracket was made with a BIG alloy pipe to fit the K&N filter and bridge the distance over the upper mounting point of the shock to the carb. Just like on the factory bikes. Next up where some hours on the K&N Website to figure out what was the biggest filter that would fit and clear all the surrounding parts like the battery etc.

Done! Works great and looks clean & tidy too. Carb setup was a bit difficult but after some fiddling on the dyno it's spot on. Throttle response is much better and a general power increase throughout the rev range of 1 to 3 HP and 2 to 5 Nm torque. And you never have to change or clean the filter again. There are downsides too. K&N filters are not suitable for real dirt bikes and you get A LOT of intake noise! But it's a nice kinda sound. BRRROOOAAAAHH !!....

Spiegler full floating cast iron disk

"What's wrong with the stock front brake and gorgeous looking stock disk on a Duke?" you might wonder. Well, not that much actually but things can always be better as this item proves. The stock setup has plenty of power, especially with pads from Carbon Lorraine but it suffers from two problems:
1. Most Duke front ends screech & squeak. Mine always did, regardless the pads used. Very annoying.
2. The initial bite is good, bordering on to much with CL pads but in the end it lacks feel and progression.

This good looking piece of German quality engineering from Spiegler works really good and is a big improvement on the stock setup. A "kit" consists of a disk with selected Ferrodo pads. The inner carrier is a feather-light alloy CNC job and the outer ring is Cast Iron (the stuff that rusts in one night). It's fully floating and makes nice 'n cozy ringing noises when the bike is idling at traffic lights etc. Just look at the pedestrians passing by... :-)

The braking characteristics and stability at different temperatures of Cast Iron is far superior to stainless steel. The first bite is much softer than stock and the braking power progresses linear with the lever-pressure gradually building to a power level the stock setup can only dream of. The clear feel in the lever from gently whipping of speed to brute eyeball popping anchoring is in a different league. Temperature doesn't seem to play any role. From stone cold to red hot the brake behaves exactly the same. And all this takes place with a gentle "hissss" without any screech or squeak. Very impressive.

A no brainer upgrade IMO. A big thumbs up!

Last modified: 15-09-2009