2012 Vetter Challenger Build ( 1981 Yamaha SR185 streamliner)

[sendler]

What does the intake of your engine look like? Is there any kind of runner like my Honda has or is there any room to add one?
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[offalot]

Originally Posted by sendler

What does the intake of your engine look like? Is there any kind of runner like my Honda has or is there any room to add one?

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Between the carb and the head? There is like a 2" runner.

Why? i thought you wanted your carb as close to the head as possible.

[sendler]

Originally Posted by offalot

Between the carb and the head? There is like a 2" runner.

Why? i thought you wanted your carb as close to the head as possible.

Before the carb. I see there is a runner there already. The length of which, along with the cam timing, will determine the torque peak.

[renault_megane_dci]

Originally Posted by offalot

Why? i thought you wanted your carb as close to the head as possible.

Max power => short inlet track

Max torque => long inlet track

BUT the lenght is always matched with the cam and so on like said before.

[bschloop]

Max power => short inlet track

Max torque => long inlet track

BUT the lenght is always matched with the cam and so on like said before.

How would I go about tuning it for max torque? I don't have a lot of experience changing things inside of engines, so it would have to be a fairly simple process. I could make an intake tract fairly easily, though.

[sendler]

Originally Posted by bschloop

How would I go about tuning it for max torque? I don't have a lot of experience changing things inside of engines, so it would have to be a fairly simple process. I could make an intake tract fairly easily, though.

It would be tough to know if you were improving anything without a dyno. There are calculators for intake length but any of the ones I have played with didn't seem to be making sense. You would try to make the first edge of the torque peak coincide with your average cruise rpm. Which it might do already. Do you have a generic dyno of the same model bike? Here is mine for the CBR250R.
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With the stock exhaust, my bike probably has the best BSFC at 5,500 rpm and it does have a long snorkel leading to the throttle plate.

[bschloop]

I don't know if anyone has ever put one of these little bikes on a dyno, I am going to look, but I don't think I'll be taking it apart anyway. I'll just finish out the aero, and see if I can gear it taller for next year. I won't have much money again, since I had to buy a vehicle ahead of schedule, but I still hope to clean up the fairing and tail as well as bringing the weight down some more.

[renault_megane_dci]

Don't bother trying to improve on Yamaha's design, it would be a waste of time.

[beatr911]

With the 185 you'll be looking for pretty small gains. Yeah a dyno will be the best way to find them.

With my Concours there is a guy that spent significant time playing with cam timing and the size of the opening of the airbox to fresh air. It resulted in advancing the exhaust cam 7 degrees and closing, not opening up, the airbox inlet to about half the original dimension. This also required rejetting because it made it rich. All told, a noticeable low and midrange boost was found with no loss of top end as found on his dyno. I think the restricting of the airbox inlet allowed the airbox to resonate with more strength as only a well sealed airbox will work. Kind of like a leaky musical instrument will sound really bad.

"Simply" advancing cams is a common way to get more lower end but dyno time and/or trial and error is the only way to optimize it. I advanced the cam in my truck 9 degrees for much better pull in 1st going up my steep driveway when fully loaded. You may be able to find an offset camshaft woodruff key for your 185 which would be a really cheap way to advance the cam. It's the origination of the Yamaha TW200, xt200/225 series so parts are common, still available new and may share camshaft dimensions, though there are a few different grinds over the years. Don't advance the cam one tooth, it's way, way too much.

[redyaris]

If you are looking for better FE performance, then you would be better off getting an O2 sencer/fuel air guage, then adjust your carb jetting to get the optimum fuel air ratio, in the range of speed in the contest.

Very good advise once given to me by beatr911...