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Hello all, I went out for my first track day yesterday and I can't believe how fun it was. But I was left with some ways to improve performance of my 96 m900. I currently have the 41 flat slides on and my gearing is 15/41. When fully tucked in I was only able to get 117-120 for top speed. There was a guy with a 750ie who was able to top out at about 125 and seemed to have the same pull as I had. His gearing is stock 15/39 I think. I loved the torque thru the corners it was awsome but the top speed was hard to deal with, people on the big liter bikes had 40-50 mph on me, I was able to gain on braking and cornering (couldn't pass in the corners) but they would blast away or past me in the straights. My question is what is the best way to get more power from the engine, 944 kit, high compression pistions, st2 cams? If anyone has any input I would really appreciate it.
 

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I've looked into this a bit, and basically the answers I've gotten are basically that if you want to get a big bang, you've got to spend big bucks.

It seems like if you want to stay out of the bottom end, you can go for ported heads, short intakes, high comps and /or overbore, and a larger diameter full exhaust system.

If you want to crack the cases, there are all kinds of options.

Of course, if you're just looking to get the top end back, you could gear up a bit on the rear sprocket and then compensate on the bottom by letting it spin up faster with a light flywheel/clutch and light wheels.

I kinda like the last option first, because you're always going to be fighting an uphill battle trying to get an air-cooled two-valve to be even remotely competative with any modern Japanese I-4 sportbike. With lightening all those spinning things, you improve handling with performance. Once you're running it for all it's worth, then you can look at head work or maybe even a 4v bike.
 

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The thing that strikes me though is your comment that a 750ie beat you on top end. As you suggest, you have to consider the gearing, but I've gotta wonder if you could do with some breathing exercises!

Top speed is HP. You certainly have torque over a 750. If you don't have HP over the guy, then you're not breathing as well.

Do you know anything about his intake/exhaust compared to yours?

As Fillmore said, don't worry about what the liter bike guys did. That's on a whole different plane of existence!
 
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Thanks for the feedback, Man I know there is no way I can compete w/liter bikes, I am just trying to minimise the advantage they have. As far as breathing issues I have a 2-1 full exhaust system, I am not sure if it is the best for the bike, any info? I think I need to take it into the dyno shop and see where I'm at, check compression, valves and work my way up from there. I now have all winter till next track season, so hopefully by then I will get some things worked out. Thanks again guys for the info, its a big help.
 

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Do you have the Sil-Motor 2-1 system? That's supposed to be a top end pipe, but I've heard that you really need ported heads and a hotter cam to take advantage of it.

Actually, I've heard that about the Arrow 2-1 also...

Don's right about the 750i.e. issue, it sounds like your bike is running out of breath before it's generating the RPMs to take advantage of your displacement advantage. The 41mm FCRs should be more than enough, so either the front side (airbox, etc) is too restricted, or the heads are at their limit for flow.

Hi-comps would probably be a good way (and not too expensive) to get some more power down lower in the band before you run out of air, as well as take the best advantage of what you have at the top.

Oh Yeah, I stuck the link in my first post that I had originally forgot... D'oh!

--Fillmore
 
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I have 15/45 gearing on my 900SSie, which is much more realistic for a track day than anything taller.

What are you doing with your FCRs? Are they connected to the airbox? Is the top on the airbox? Do you have the stock intake runners? All of those things conspire to decrease the ability of the motor to breath at high rpm. Empirical evidence: http://www.meccanicacorse.net/images/dyno_charts/manifolds.htm

As far as compression, displacement and cams: yes! They're all ways to get better power. Do not forget head work. Good (not just pretty) porting is important to get the bike to really move some air. It's all expensive.

Your lap times will probably drop faster with an investment in suspension and more track time. At least that's been my experience.

Good luck,
tim
 
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As far as airbox mods, I have no airbox and am using Uni foam pods. The bike is still running a bit lean so I will take it in and have the exhaust checked. My friend at the local shop was telling me about a guy who put the hopped up cams in and he swears it pulls as hard as any of the superbikes. I will try to locate that guy and get some info from him.
 
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