December 2, 2013 at 8:19 am #16890
Hi looking for some help going to have a play with a rotax max engine for fun not race use ive got a good spare bottom end & standard cylinder and a spare DD2 cylinder Ive heard that dd2/supermax cyl is not to good with low end power can you carry out any mods to change this? or do I stick with standard cyl, get a good porting job done vforce reeds programable cdi unit theres a company in germany Krauss Max getting 39bhp out of a RM!!!!
December 2, 2013 at 10:19 am #16927
Thanks for your input James ive found this ignition system that removes rev limit
December 2, 2013 at 10:26 am #16929
Would like to keep it on gas looking for about 35bhp would you think thats realistic??
December 2, 2013 at 10:42 am #16933
If you pop over to the UAS\Open board on 4cycle.com you will likely find someone thats’ Max’ed a Max. Keep in mind though, most of these guys run ovals with fancy clutches ergo narrower powerbands, so when asking for advice make it clear that you are running “sprint asphalt” as they call it.
Unless you can bag yourself one of these: http://www.karting1.com/continuously-variable-transmission-for-karts-test.htm
Then alky it up to 65HP and call it a track smoker!
December 3, 2013 at 1:08 pm #17014Peter De SaegherParticipant
Hello Lee, for more than 2 years I have been working on 4 cilinders to found some HP. For the moment I have 33,8 hp on the wheels and a engine with a width power band. Engine has now 15 houres , no problem at all. It’s a real pleasure driving it.
First of all ==> writing about HP is much easier than having them realy on a testbench. Believe me it’s a lot of trail and error. Bigger ports doesn’t always mean more power guys, it’s not that simple. I had more power with a smaller exhaust port than a bigger….. you don’t want to have all your fresh gases going without burning into your exhaust pipe and cool it down….
The Krauss max doesn’t have a reliable image in europe and not very popular.
The Polini kit has the same problem ( mine had 3h and boemmmmm :-(
The DD2 cilinder or supermax only has high rpm output , I was not impressed because of the lack of bottom and middle power.
What I have done :
I have the ignition you have mentionned but directly from the OEM without rev limiter.
Modified cilinder ( additional booster ports, modified A, B, C ports )
Other cil head & piston
Handmade exhaust & muffler.
I will try to post some pictures to make it more visuel.
just a question : what’s the price of a Rotax max cilinder in your country ?
December 2, 2013 at 9:04 am #16913
What’s your budget and what are your goals exactly? You could probably make 45HP+ on gas, even more on alky from it but the powerband would make it slower than molasses over a lap on a typical kart track without an oil clutch or CVT to keep the engine “on the pipe”.
If you want to go full on you could punch it out a few MM, make it drink alky, get some buller dual carbs on there, widen the exhaust port and so on. Tal-Ko in the UK make bigger pistons that may work. You could stroke it too.. a few folk got cought doing that with “sealed” motor LOL.
I don’t think I’d be too keen to change the port heights unless you plan removing the rev limiter somehow. Width have at it, but the powerband is kinda narrow already so I don’t think I’d want to raise the exhaust much.
For a quick pep up, take some volume out of the head. Adjust ignition timing and fuel octane as needed. At least with the head its dead easy to go back to stock. You might need to start using an external starter however. I’m sure you could get some trick reeds on there too. If you are running it on a sprint track, I’d be inclined to scrap the stock carb and move to something in the 30mm territory to get some better low end response. Something from KF1, or the VHSH30 that’s used on ICC/KZ motors. Maybe the new tillotson slated for Max use? Thats available in 27mm and 30mm venturi.
There might be gains with the pipe, either with modification or someone with specific knowledge on the Rotax setup might be able to tell you.
**disclaimer, I’m not a professional engine builder… more of a tinkerer and observer.
December 2, 2013 at 10:36 am #16932
It’s a single geared kart, HP don’t really matter when it comes down to it. You could tune for nearly 50HP on gas on a dyno, put it on the track and it would be absolutely pathetic. Think of how a shifter pulls (well, doesn’t) when it’s in too low of a gear. With a single gear its how much area you can create under the curve. Actually thats true for gearboxes too but I digress.
Hmm, at $400+ to remove the rev limit. I think I’d spend the 400 looking for ways to make the motor pull better throughout the range. Smaller carb, maybe a little powervalve trickery, reeds widened exhaust ports. More ignition advance (with correct fuel), shaved head.
No idea where you would end up in peak HP, but the times would drop.
December 4, 2013 at 12:45 pm #17156
Hi Peter thanks for your reply ive been looking at your posts and its clear you have spent alot of time perfecting your RM, new cylinders are £280 in UK but ive got one dd2 cyl & access to some good used standard cylinders I will take your advice and stay with standard cyl how did you modify yours, you say extra booster ports so is that similar to dd2 just positioned better?? did you do the work yourself other head are you using VHM what make conrod ive seen youe exhaust youve had made have you tested it was there much perfomance gain
if you could help me with best place to get parts is that ignition system worth getting or could you tell me of a better one and where to get it
The plan for my first build ported cylinder vhm head new ignition system vforce reed block & tag carb upgrade or new tillotson
have you seen the new tilloton carb upgrade for rotax could be good upgrade for you
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