8th July 2019 at 10:25 pm #25186
thank you !
I’ve startet just 1,5 years ago, ok, close to 2 years now, to race on a track. Most instances were training, only a few races until now.
As an experienced motorbike rider I said, that I can find the ideal line on the track myself and will learn proper riding by watching and copying other riders. Both is wrong. I would highly recommend an instructor training. That is a lot of fun, learning and it can be quite fast 😉12th July 2019 at 5:58 pm #25200
As I am working on an engine upgrade with 906 ccm and didn’t finished it since 5 years now, a lucky moment happened at the “Built not bought”. The seller of my big-bore-kit was present and offered me his engine with 906 ccm, a lot of modifications and at least 2000 km used on the road !
Adjustable camshaft sprockets, EX-cam as IN-cam, larger inlet and exhaust valves, 906 ccm, dual spark plugs per cylinder, Ignitech ignition, balanced crankshaft, centrifugal force powered self-boosting clutch, modified crankcase ventilation and the beautiful Keihin CR carbs with funnels.
With these modifications the measured values are 68 HP at 6.800 rpm and 82 Nm at 4.900 rpm. Measured and available at the rear wheel !
Delivery service by my uncle Hubertus, thanks to him !
Mounted the engine right away into my Dirtbike to complete the installation and doing initial running tests. Ok, still preparing for the first run 😉
Finally this engine shall work in the “Vienna” by end of September, ready to race at the Spreewaldring 3rd and 4th of October 2019.
Need to complete the electrical installation, incl. positioning of two dual ignition coils and related ignition cables. Need to modify upper engine holders to fit the two coils under the tank.
Oil supply line outside of the engine are good to avoid untight head gaskets but they doesn’t allow to mount the existing high tube exhaust. Will fiddle with new exhaust, puh.
Peter will help me with that. Will be a 2-into-1-system. Two downtubes slim to the middle, left and right of the oil drain plug and an under-engine silencer, maybe an additional silencer right hand side.
Easy to operate Keihin CR Special with 37mm Venturi.
Intake and inlet valves are matching them 😉
Outlet valves are larger as well.
Cheers, Michael6th October 2019 at 11:37 pm #25285
Well, I didn’t manage to fit the tuning engine into my racetwin by now, so I will do it this winter.
Had the last track days last week and besides the GPZ 305 I rode my “Vienna”:
There will be some work to do during this winter and the race season starts again in April 2020!
Cheers, Michael3rd December 2019 at 5:12 am #25362
Wow, great build!
So many questions as I am in the process of doing my own 906cc engine! Sorry if it seems overwhelming but its cool to see someone else hot rodding these engines.
The “dry block” – because you are bypassing the oil jets between the cylinder and the head how do you increase oil pressure after the crankcase to the head?
Have you run into cooling issues with the bigger bore?
What is the static compression / cranking compression?
what size exhaust valve? custom valve or custom guide?
What size exhaust tube primary?
Did you port and polish?
you mentioned frame modifications but I think the photos got removed. what did you do there?
Love the look and and track action!4th December 2019 at 10:20 pm #25374
thank you for your interest in the engine tuning.
Well, let me sort some of your questions:
The major frame mod at the “Vienna” is to cut the rear frame off and also the rear cross-tube out of the frame. The cross-tube was in the place where the silencer is now. To gain stability of the frame again, I’ve welded angled cross-tube out of an 125ccm Aprilia rear frame (very cheap part over here at ebay) into the Kawa frame, one is above and one is below the silencer:
The ideal inner tube diameter is 40mm while the length of the downpipe is 66cm (incl. exhaust port depth down to the valve). The collector should have a length of approx 15cm, not just a conjunction of two downtubes.
The silencer is an absorption style damper with 60mm inner diameter. I have to use a dB-Eater in it to have 96dB at about half rpm in half a meter distance of the microphone. Without the dB-Eater it is still well sounding at 98 dB, but to loud for my favourite race track.
I am using the Mikuni TM34-120 with K+N single pods, an electronic Sachse ignition (german manufacturer) with 9 preset ignition curves to select by potentiometer. Max. enhanced firing at 38° BTDC, but 36° BTDC is fine as well. Rev limiter set to 7.800 rpm.
Major change is the exhaust camshaft modified to use as intake camshaft. The engine is eager to turn with high rpms.
This still stock 750ccm engine doesn’t even has other pistons, higher compression ratio nor larger valves or ported in- or outlet ducts.
I am using still 4 liters of 20W-50 mineral engine oil. No overheating even at 35°C in summer.
Rich jet setting may add some cooling to the engine. Just added two air-guide-tubes unter the fuel tank to route fresh air to the air filters.
Ok, next engine, a 906ccm, since years on my workbench. It has the same piston and barrel set as the tuning engine I’ve shown above (sister engines). I struggle to put it together as I want to create a small series of modified balancer chain guides, but that takes it time as well.
Used “play dough” (clay for children?) to determine the gap between piston, valves and head an to find where to reshape the combustion chamber:
This head was ported and when the mechanic should drill a hole and thread for a second spark plug per cylinder the milling maschine cut away other essential parts and this head is dead, to bad !
Ok, the 906ccm tuning engine that I’ve bought. Not well documented but everything is touched.
I will fit it this winter into the “Vienna” and will tell about it after first race event end of April 2020 😉 Not sure about the exhaust routing, the external oil line do not allow to use the existing exhaust as it is. Had Peter to make me new downtubes routed under the engine and I have to add a silencer, but that would distort the look of the Vienna. Better to have a distorted look and a powerful engine than other way round 😉 That’s racing !
The oil lines are routed in tubes outside of the barrel / cylinder block and head. You can see in one picture far above, that there is an orifice used in the oil line. It has the same inner diameter as the orifice used in the stock engine betwwen cylinder block and head.
Next tuning engine is the one that is still mounted in a Twin that I have bought recently from Manfred. 950 ccm ! A real beast, very powerful !
You can find pics and detailed information here:
Ok, so much for now 😉
Cheers, Michael22nd December 2019 at 12:37 pm #25384
To upgrade our transport and camping capabilities I’ve bought a Ford Transit.
Diesel, 100 HP, air conditioning, auxilliary heating, an Airline rail system in the floor and an integrated wheelchair ramp !
After some modification we can transport three racebikes easily now.
Big advantage is that we don’t have a general speed limit anymore as it is existing for trailers in Germany. With trailer only 80km/h are allowed, special trailers (with brakes and approval) may run 100 km/h and some parts of the motorway have a ban on passing when pulling a trailer.
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