Finally dynoed

[robo]

Well, finally got the bike dynoed with the home made cans.

With the standard cans, 94.89 HP @9000rpm. Then one with the new ones 95.07 Hp. Not much of an increase but there was an increase in the mid range between 5000rpm and 7000rpm of 5 horses and the power came in late @ 3000 rpm in the beginning. The bike was running real lean in both cases.

Then the jet kit was put in 180s front and rear and got 102.27 HP @ 9000rpm. A 7.7% increase, but the power comes in at 2000rpm and I have a little flat spot at 4000rpm to 4500rpm.
Hoping an air filter will get rid of this. I couldn't afford $360NZ for a K&N (a ridiculous price), the dyno and getting the jet kit put in was only $330.

Anyway the mechanic is pricing a DNA air filter. Anyone tried one of these?

Seat of the pants test. Definitely running heaps stronger, and real responsive, it was a bit vague on the throttle response before, I think being way to lean.

Definitely like to get rid of that flat spot and increase that 3 to 5 grand mark. Do you guys think a decent air filter will do it? Or is it the exhaust cans? Whats your ideas? Thanks for any input.

[billzilla]

I don't know about the specific quirks of the VTR engine, but it's very common for a twin-cam multi-valve engine to have a bit of a dip in the torque curve at around those revs.
But yes, a good air filter will improve things a little more.

[shayne]

My experience with these bikes has shown me that this can be tricky! So no easy answer I am afraid.

In your case your exhaust may be the problem. With a one-off design who knows? I suspect it is not, but you never know.

I doubt the airfilter will cause it either, in fact you may find it is worse with an aftermarket filter. Many people have found that a K&N or similar can cause dips, that is why many owners swear by the OEM filter. I have a k&N myself. As far as I know the DNA is a good product, but not as common as K&N or BMC. Do not use a Unifilter, as I ended up with a flat spot with mine when using it. It lets in lots more air than the others.

I would experiment with you needle clip position a bit, and also the slide holes. These may be the solution for you.

The VTR has a dip in the power curve from factory, and this can be removed by changing your velocity stacks. Hpower make a set but they are pricey. Your other option is to get a second long OEM stack and fit it with the other one. The bike comes with one long and one short one, so you can use two long ones. Thius may be enough for you, but the custom velocity stacks are the best option I think.

The aftermarket stacks will mean the bike needs to be re-jetted, as they have quite an effect on the airflow. They will need smaller mains for sure. I am running 170's.

[hargs]

What type of cans do you have?

[robo]

Aug 15, 2009 19:33:34 GMT 10 hargs said:

What type of cans do you have?

I made them myself here, ozfirestorm.proboards.com/index.cgi?board=mods&action=display&thread=9736

[robo]

Aug 14, 2009 8:16:09 GMT 10 shayne said:

I would experiment with you needle clip position a bit, and also the slide holes. These may be the solution for you.

The VTR has a dip in the power curve from factory, and this can be removed by changing your velocity stacks. Hpower make a set but they are pricey. Your other option is to get a second long OEM stack and fit it with the other one. The bike comes with one long and one short one, so you can use two long ones. Thius may be enough for you, but the custom velocity stacks are the best option I think.

The aftermarket stacks will mean the bike needs to be re-jetted, as they have quite an effect on the airflow. They will need smaller mains for sure. I am running 170's.

Yeah the mechanic did say maybe to play with the needle position. Just seems funny that it improved every where except between 4.5 and 5 grand where the power just goes back to the original line before re jetting.

It has no slide holes in it at the moment and mechanic probably didn't do it because of the standard filter.

Got any idea why the vtr comes out with different size velocity stacks? A mate and I were having a look at it yesterday and thought it might have to do with air pressure maybe be greater at the rare of the air box and the front VS facing backwards.
Am i right in saying that the longer the V stack the less air the carb gets?

I might do as you say and try and find a second hand air box with the stacks. First I will try the air filter, just to eliminate that area, if the DNA comes in at the right price that is. Then do the stacks and then adjust my Cans. A may find a solution yet.

Cheers

[shayne]

The stacks can be bought from Honda for not too much money, so don't discount buying a new one.

Honda use varying length stacks in a number of their bikes. The VFR800 and SP1 also have different length stacks on each cylinder. There are a number of factors that come into their design, such as intake and exhaust length, airbox shape etc.

In general terms longer stacks will promote airspeed at lower revs but can be restrictive at high RPM. Better torque but less horsepower. Shorter stacks will do the opposite.

[manek]

dunno how it will go in a vtr but i had a dna air filter in a 05 gsxr750 and there was a noticeable change in the bike. i'm currently looking to get one for my 03 vtr now, just have no pennies for it.

[billzilla]

Aug 16, 2009 14:47:37 GMT 10 shayne said:

In general terms longer stacks will promote airspeed at lower revs but can be restrictive at high RPM. Better torque but less horsepower. Shorter stacks will do the opposite.

FWIW it's actually for Helmholtz resonance, or pulse tuning. The inlet trumpets (to give them their proper name) greatly affect how the engine breathes, with a good general rule being the longer the inlet system (long trumpets) the lower the revs the engine will make best torque, and the shorter the inlet/trumpets the higher the engine will make best torque/power.
It's why some engines have variable length inlet systems, to try to maximise the spread of useful torque.
The old big block Chevy used in the Can-Am cars of the late 60's/early 70's often also had unequal length trumpets to try to get rid of a nasty dip in the torque curve.
I suspect Mr Honda might use unequal length trumpets for the same reason, to try to make the bike nicer to ride.
But you can play with the exhaust and cam timing to do the same thing and still use equal length trumpets.

[nzspokes]

Aug 14, 2009 8:16:09 GMT 10 shayne said:

My experience with these bikes has shown me that this can be tricky! So no easy answer I am afraid.

In your case your exhaust may be the problem. With a one-off design who knows? I suspect it is not, but you never know.

I doubt the airfilter will cause it either, in fact you may find it is worse with an aftermarket filter. Many people have found that a K&N or similar can cause dips, that is why many owners swear by the OEM filter. I have a k&N myself. As far as I know the DNA is a good product, but not as common as K&N or BMC. Do not use a Unifilter, as I ended up with a flat spot with mine when using it. It lets in lots more air than the others.

I would experiment with you needle clip position a bit, and also the slide holes. These may be the solution for you.

The VTR has a dip in the power curve from factory, and this can be removed by changing your velocity stacks. Hpower make a set but they are pricey. Your other option is to get a second long OEM stack and fit it with the other one. The bike comes with one long and one short one, so you can use two long ones. Thius may be enough for you, but the custom velocity stacks are the best option I think.

The aftermarket stacks will mean the bike needs to be re-jetted, as they have quite an effect on the airflow. They will need smaller mains for sure. I am running 170's.

If Shayne was still about I would ask how he came to using 170s. 

[vtrstormer]

Shayne is still about but only pops in every now and then... Will message him for you