mikstr

I just got back from having my DJ kit installed and having the bike dynoed. The final (peak) results are 68.8 lbs/ft torque at 7K and 105.5 hp at 8800 rpm. My set-up includes Micron slips ons, DJ kit, stock airfilter (modded with ridge removed), two long intake runners and stock TPS setting (@821 ohms). The torque curve is very very flat with just a very slight dip at 5K (maybe 2 lbs/ft, over 60 lbs/ft from 3600 rpm to 9200). It is the flattest one I have seen to date for the VTR. Throttle response feels good and the dyno operator commented that it pulled nicely for a VTR (and they have done lots of them). Incidentally, the bike has 65,000 kms on it so it isn't new by any means.

I was expecting a bit more hp but going to the two long intake runners likely robbed me of a couple on top. Going to two short ones would likely get me very close to 110 hp (going from one long/one short to two short is said to be worth @ 2 hp on top so I would think that going from two long to two short would be @ 4 hp) but I do most of my riding in the mids and the long runners work nicely here. Also, I noticed the bike is a bit smoother at my typical freeway cruising speed (4500 rpm).

that is it for the mods for this year. I will likely address the forks next year with Racetech springs.

Bye for now.

P.S. I will attempt to have the dyno results scanned and post them.

cheers

icebud

Pretty cool, congratulation!!

That seem to be very nice, even if your final HP is lower than your expectation, this is nevertheless very good 105HP, as compare, Brian Law from Dynamohumm got "only" 103 with his!

I think the most important thing is that you are happy of your set-up and especially on how your VTR ride!

Is it cost you exactly what was expected?

Cheers

NOrrTH

Was there any farting around with jet sizes or needle clips?

What did you end up with?

mikstr

Hi NOrrTH

I am not sure what the mechanic ended up putting in it (I dropped the bike off, ran some errands and came back just in time to catch the last dyno run).

All I can say is that the graphs are really smooth and linear with no spikes or valleys (except for the very small torque dip at 5K). I am very happy.

How is your running? Did you ever get rid of the flat spot you had (if I remember correctly)?

NOrrTH

I gotta start playing around with jet sizes. There's popping on decel and the power curve seems kinda wiggly with a slight flat spot in the middle. The plug tests I've done are inconclusive in that they aren't showing if she's running lean or rich - I see both

mikstr

If memory serves me right you adjusted your TPS too? Perhaps you should try moving it back to stock as a few others have reported this type of behaviour post-TPS adjustment. I know mine runs better since going back to the stock setting (or very close to it).

I guess start with the easy stuff and work your way over to the mosre difficult. Good luck and let us know how you make out.

cheers

P.S. If, after trying various jetting combos, you can't get it right, you should consider going back to the stock air filter just to see how it works. I don't mean to sound like a broken record (which I am sure I do) but the tuner who installed my kit and did my dyno tuning specifically recommended against the K&N on the VTR stating that they are hard to jet as a result (the very result you are dealing with). Hang in there

NOrrTH

Ya I hear ya. Its always in the back of my mind. I really like the extra bottom and top end it gives me. If I can just work out this issue which is minor really. The popping is annoying though.

I never did do the TPS mod. My throttle response is more than satisfactory.

penst8grad

I don't understand why you think longer runners cost you at high RPM? I helped build racing(car) motors and using a longer runner was for higher RPM performance but hurt lower RPM. That's why auto intakes like the "performer"series have a smaller plenum area.

I'm not being a know-it-all. Are MC engines different?

mikstr

My reasons for thinking that the longer runners help me in lows and mids in exchange for top end are many:
1) some have tried running two short runners on the VTR and reported a 2 hp increase on top end (so it stands to reason, then, that the shorter runner helps top-end. The flip side then, is that the long one must hurt top-end. My seat of the pants also shows that lows and mids are definitely stronger with two long runners)
2) I questioned Roger from Revolution Racing in the UK (very knowledgeable VTR tuner) about it and he supported the idea of long runners helping mids (with loss on top)
3) based on my snowmobiling experience (granted, with two-strokes) I know that going to shorter carb boots on some models gives a top-end increase (with subsequent loss at lower rpm)
4) not sure if this is relevant, but (again in a tow-stroke, and on the exhaust side to boot) lenghtening the exhaust pipe on a two-stroke reduces the peak hp (or torque) rpm whereas shortening it increases the peak rpm. See below for my undestanding of this one.

Finally, in theory, it seems that longer runners would help with cylinder filling at lower intake velocities as they would help generate more momentum for the incoming air. However, at higher intake velocities (approaching flow limit for any given venturi size), they would become an obstruction (as the alternative to having a given section of runner is having none, which means that there is now no resistance in that area). In other words, wehn approaching the limit of airflow for a given opening, the shorter the runner is, the less resistance it will offer to the flow and hence the engine will flow more air and thus generate more hp.

I am certainly not claiming to be all-knowing and will gladly welcome input on this one (no background in aerodynamics,...). Any help in understanding this would be appreciated.

cheers

penst8grad

Roger is a great guy! Helped me with setting up my forks. He gives away so much knowledge for free. If he says it, then it's good enough for me.

Nevermind everything I said...It's been 10 years since I raced and I remembered it ***-backwards

Good explanation

Rollingalong

Your lean on the slow circuit . Try turning the idle mixture screws out and make sure your slip-on connections are not leaking .


Do you have the pair valves disabled ?

NOrrTH

Ya, the PAIR's been disabled.

I thought I was rich low and lean on top lol