Made some new V-Stacks

[Stocky]

I made some stacks for my GSXR a while back.

They are 45mm ID so they sleve down the larger top part of the throttle bodies and increase velocity.
Just this mod gave some good mid range torque with no loss of peak power.
When I was messing with the lengths on the dyno I found a really good length for good power all round and the power didn't fall away after peak so much.

This is what I have run for quite a while now.

I measured the lenghts and found I'm using the 3rd and 4th harmonics but too short to be using the 2nd.
http://www.streetfighters.com.au/forum/upload/835157706105970.JPG



Even the stock stacks are too short to use the 2nd harmonic.

Suzuki's can't really use long stacks as they have STV's and airbox fitting problems but I don't have those restrictions anymore.

Fitting the 45mm ID sleve stacks made me wonder if going right down to 42mm might be even better.

I didn't want long stacks and 42mm all the way as I imagine it would hurt the top end too much.

So I got some tappered stacks and adapted them.

They tapper right down smooth to the min throttle body ID but are long enough to use the 2nd harmonic.

I've been for a short ride and the ass dyno says they definately fill the grunt in at 4000rpm (where the old ones were lacking)

I've got to give the AFR unit time to retune the fueling before I decide if it's better all round or not.

I'll also back to back them on the dyno.

Just thought I'd share the new mods .....
http://www.streetfighters.com.au/forum/upload/83515770680082.JPG

http://www.streetfighters.com.au/forum/upload/83515770685958.JPG

[rod185651]

Ok so I am going to ask a stupid question,,, so by increasing the length you are actually making the air straighter or smoother? So the air is not swirling around so much? There fore getting denser air and improving the air to fuel ratio? I'm not a mechanic but by fuck its interesting.
cheers Rod

[Stocky]

It's actually about the resonance of the inlet system.

To over simplify things. Imagine the air going into the engine.

It gets up some speed filling an open cylinder (inlet valve open) and then the valve shuts.

A whole bunch of air on it's way to the cylinder all piles up behind the valve and gets ready to bounce back and head out the way it came in.

If you time things right you can have the inlet valve open again (for the next cycle) right as all the air is piled up.

The longer the tube (Velocity Stack) the more the air piles up at low RPM and vice versa.

This stop/go in the inlet happens at different frequency for different rpm etc.

If you can get it to "resonate" then you get better inlet efficiency.

The "Note" of the inlet has harmonics.

The 1st harmonic being the stongest (but you'd need a 2ft long Vstack) and so on.

The problem with using 2nd harmonics is there is more variation from 2nd to 3rd to 4th so there can be big holes in the power between the 2nd (4500rpm or so) and the 3rd (9000rpm or so) and the 4th (11500rpm or so)

When you just use 3rd and 4th it's easier to get smooth power.

But the 2nd harmonic is right where you use the engine in town and at speeds within the law ;) so it's worth chasing.

Other things like cam timing , air box volume and especially exhuast tunning play a big part in it too.

It also changes the fueling a little so you have to custom tune a different setup like this.

I'm fortunate enough to have a self tunning (Closed Loop) Fuel Injection system so I only need to go ride for a while to get the fueling right.

Please note, this entire post is very much over simplified and the numbers (rpm etc) are quoted out of my head not from the actual calculations.

It's not designed to be a lesson in velocity stack tunning or anything just a peak at some fun I'm having learning about it and trying stuff.

[Stocky]

Hey I just noticed the 3rd pic is a cool shot of the CF fuel tank.

You can't normally see that much of the carbon pattern through the paint.

[BANDITROD]

thats fucking awsome dude good work

[Large]

quote:Originally posted by Stocky


Hey I just noticed the 3rd pic is a cool shot of the CF fuel tank.

You can't normally see that much of the carbon pattern through the paint.





I just noticed rotary triples...possibly cooler than carbon [8D]

[DaveK5]

Awesome stuff Stocky...regarding the calcs are you using software,rule of thumb or other to work out your stack sizes...I've thought about making some up for my 1400 and fitting them into the rubbers as they enter the air box but not knowing the intake runner length to the back of the valve,exact cam specs etc I thought I might be just wasting my time with trial and error...any help?

[Stocky]

You can get very close with rule of thumb and a tape measure from the back of the valve.

If you are prepared to have a few goes at it then it's a good way to go.

I've got "Pipemax" software and "rule of thumb" and some experienced tuners that all generally agree on the lenght for each harmonic.

I really need to have some time on the dyno and figure out a way to move them 5mm at a time to get them perfect.

[fimpBIKES]

very nice stocky,

and large, i also vote for "cooler than carbon" on those triples!



where are the stacks coming from, or do you make them?
i've heard interesting things about making them from cake-tins, jelly-moulds etc over the years

[Stocky]

The triple's are Yoshimura adjustable ones

http://www.streetfighters.com.au/forum/upload/83515951862307.jpg

[Anakist]

Is the stack a nice venturi shape? A friend of mine who races rally cars is limited to a 32mm inlet restrictor and found he got a lot of power playing with venturi designs. Could be worth a play.

James

[Bear]

Cheers for the explanation, Stocky. I've always wondered what the effects would be and which way to go for more torque etc.
It all makes sense to me. :)

[rod185651]

Hey Stocky,
thanks for the explaination mate, very interesting feel like I was sort of on the right track but it makes total sense now.
cheers Rod

[rod185651]

and yeah I can't spell for shit

[Stocky]

quote:Originally posted by rod185651

and yeah I can't spell for shit


That makes 2 of us mate ;)



And yes the stacks are a specific bell shape at the top and taper down to 42mm

[Large]

quote:Originally posted by Stocky



The triple's are Yoshimura adjustable ones




oops

I thought they were the flash ones from outlaw[:I]

[ozzy1100]

fuck me stocky you make what i know look like shit lol top job mate