Velocity Stacks

[Hooligans]

I read the sticky and I'm going to try it out, I couldn't find copper than wasnt exorbitantly expensive so I went with some 2" stainless exhaust pipe from autozone for 16 bucks, I also found that the 2" fernco fittings were 2 and a 1/4 so I went with 1" 1/2 ferncos that fit with a little persuasion.

I am doing this because I feel I can get a bit better power/response in the midrange and I'm sick of fooling with the carbs so what the hell. Switching the mains and the pilots and changing the needle clip position/turning the a/f screw have each helped in their respective areas but having ridden other Vmaxes with similar set ups I know I can get it a little better.

My bike - 95 motor (no internal mods) stage 7 jet kit and UFO 4 into 2.

My question is; has anyone actually verified that this mod improves the low/midrange, as in on a dyno? I guess I'll feel the difference, if any on the butt dyno but figured I'd ask.

The thing pulls hard mostly everywhere so maybe I'm being ridiculous but something tells me I can get a little more.

Thanks.

 

[Hooligans]

By pilots I meant PAJ2

 

[Traumahawk]

By adding velocity stacks, it should give you some midrange torque back. Let us know how it works out.

 

[Hooligans]

Test fit on some extra carbs.

Can't get the picture upright - posting from my phone.

 

[Itgoes]

By adding velocity stacks, it should give you some midrange torque back. Let us know how it works out.

+1.... long stacks for low/mid TQ, short ones for high rpm HP.

 

[Fire-medic]

Here you are
http://www.vmaxforum.net/attachment.php?attachmentid=51426&d=1448858555

 

[MaxMidnight]

By adding velocity stacks, it should give you some midrange torque back. Let us know how it works out.

As they act as a resonant pipe their length will determine where the maximum gain would occur.
According to H at Exactrep the optimum length is 3.6".
This also happens to be the length of the inlets within the OE airbox.

 

[MaxMidnight]

By adding velocity stacks, it should give you some midrange torque back. Let us know how it works out.

As they act as a resonant pipe their length will determine where the maximum gain would occur.
According to H at Exactrep the optimum length is 3.6".
This also happens to be the length of the inlets within the OE airbox.
By shortening or lengthening the length of the stack you will move peak torque higher or lower down the rev range.

 

[Hooligans]

I've got them at 3" exactly, I have about .5" of play (up or down) due to the size of the grommets. It's raining and wet down here in the Old Dominion, as soon as it dries up enough to get on it I will post the results.

I wonder if jamming foam into the stacks would be sufficient enough of an air cleaner as they are too tall to fit under the faux cover with the KN&Ns perched atop, that way I could bell them out some as well like the stock air box inserts.

 

[sdt354]

I've tried them and used a rubber reducer grommets from Home Depot. They fit tight. I left the metal band on. I never did dyno with them on. I think mine were 2 1/2" long to allow room for the K&N filters.

 

[Vinmax]

I've got them at 3" exactly, I have about .5" of play (up or down) due to the size of the grommets. It's raining and wet down here in the Old Dominion, as soon as it dries up enough to get on it I will post the results.

I wonder if jamming foam into the stacks would be sufficient enough of an air cleaner as they are too tall to fit under the faux cover with the KN&Ns perched atop, that way I could bell them out some as well like the stock air box inserts.

I think by putting foam into the stacks, you're going to reverse any gains you would have otherwise seen.

The purpose of the stack is to speed up the velocity of the air going into the throat of the carb. Putting foam into it, will definitely slow down the velocity and also the volume of the downward traveling air.

You want free flowing, clean/filtered air, around the area of the velocity stack, with no restriction to the flow into the stack.

Vinnie

 

[Itgoes]

I think by putting foam into the stacks, you're going to reverse any gains you would have otherwise seen.

The purpose of the stack is to speed up the velocity of the air going into the throat of the carb. Putting foam into it, will definitely slow down the velocity and also the volume of the downward traveling air.

You want free flowing, clean/filtered air, around the area of the velocity stack, with no restriction to the flow into the stack.

Vinnie

+1 That'll be no good at all.

 

[Hooligans]

Roger that - makes sense. I finally got around to fitting them on the bike - can't get the KN&Ns on, they are slightly too high. I had some EMGLOs sitting around, does anyone use these? I guess if I use them I will have to drill holes in the front 2 for the stage 7 puke can.

 

[gentsvmax]

As velocity stacks go there needs to be some radius or flute to introduce the flow your looking for.
Look at any injected hotrod V8 or just open a stock vmax air box and look at the velocity stacks built in.
Blunt edges screw up air flow.
I had used PVC and fluted the stacks with a Dremel grinder.
I looked for my pics of the set-up but cant find them.

 

[Hooligans]

OK results are in, I had to switch out the PAJ to make it run right. It smoothed out the throttle considerably, added a bit more of a punch to 3-7 but flattened out 7-9500. I supposed I could mess around with trying to flute the ends or maybe shorten them some, but honestly for round town riding I really like it...if I am cruising at 2500-3k in 3rd or 4th and punch the throttle it really gets up and goes. If I am trying to wheelie from first into second gear, it's not gonna happen with this set up - at 7k it pretty much falls onto it's ***.

Conclusion - it gave me the middle range that I was looking for but took away the top end. Suggestions to make it smooth all the way through are welcome.

 

[Traumahawk]

What is your current settings? Including PAJ#1 and 2, air correctors or not. Stage 7 springs or not. Drilled slides or not, and of course main jetting. What needles are you running, and on what clip from the blunt end are you? Do you have tubing on the carb vents?

EDIT....working V-boost, or always open?

This should give everyone on here enough information to help diagnose the issue.

 

[Hooligans]

Main jets DJ 165, all other jetting stock (PAJ1 90, PAJ2 170) Stage 7 air correctors, drilled slides, Stage 7 slide springs, A/F screws 2 1/2 turns out, tubes on the carb vents, Stage 7 needles with clips 4 down from blunt end.

It runs great everywhere but falls flat at 7k.

 

[Hooligans]

No Vboost (stage 7 intake connectors)

 

[Traumahawk]

Well unfortunately the Dynojet directions have everything set up pig rich. So drop back to the DJ 160's....that is equal to the MK 150s. Move the clip to 2 to 3rd clip from the blunt end. By drill out the slides, the needles actually start coming in about 3300 rpm instead of 4000, and the A/F requirements are also a little bit higher at that point, so try 3 to 3.5 turns out on the a/f screws and see how that is.

The Vmax actually likes to run leaner than most bikes and will make best HP with an A/F of 13.5 to 14.0. That is not too lean for a Vmax....remember its water cooled.

Strictly my advice I would hook the Vboost back up, because the carbs are harder to sync at idle with the vboost open. That way you can close the vboost to sync, and then open it back up to give it that choppy sound.

With Vboost being open all the time, the A/F will be leaner at part throttle, but richer at full throttle. These settings should get you in the neighborhood.

 

[davesax36]

It smells a lot, but with that tire, it sure does go fast...