HarleyTechTalk

does anyone supply velocity stacks for hpi throttle bodies, specifically the 62mm.

Paul Morris posted this link a while back:

http://www.baggersmag.com/tech/0705_hrbp_carburetor_velocity_stacks/viewall.html

If they would make one for the HPInc tb I would might be interested in one also.

http://www.novi-tec.com/index.php/motorcycleproducts-harleydavidson

and then maybe one of the Exotx torque screens for street use:

http://www.exotx.com/filters.htm

Ya I was looking at those for the D carbs but they are a few mm too small.

I might get a machinist to make me on depending on price

I sent novi an email asking if they could make something or have one thats close.

Are you looking along the lines of what I did?

Just a rookie question but are velocity stacks as effective with throttle bodies as they are with carbs?

Sure they are.

Look at the novi stack.

Maybe high end factory cars have Velocity stacks in the intake manifold.  They increase air speed.

I want to adapt the novi twin stack to the 62mm HPI...

Mercedes seems to think velocity stacks help with cylinder fill.

Carb or FI, air needs to be smoothed out of turbulence and put up to speed. In most applications as far as HD mods are concerned, it's not needed.
I did mine this way because it was the easiest way to plumb the air cleaner to the throttle body on a HPI 62.

Why are all the big racers running stacks or twin stacks than?

I guess it is just because of what you said,"racers". Otherwise, I think they would be in the way of the riders right knee. I can see your point about a bike that is used for drag competition though.

Ya I'm just going to use it at the track.  Something to switch out before heading there.

Hpi makes a small velocity stack that's built into a backing plate. They also make plenum spacers, both are things I've been thinking about trying. Maybe contact them and see what info they have on velocity stacks?
What about adapting the larger version of the heavy breather elbow and the velocity stack end? You could tune the length, there would be no leg room issues, it would eliminate the 90* issue at speed and actually work like ram air, and you could just clamp a filter on for the street. I have the smaller version laying around I've been thinking of doig some dyno comparisons to see if it has any potential on my 58/62. It might not be the correct size and taper to work like a veloctiy stack but you never know what will work til you see the mph on the slip.

Like this
http://www.wegnerautomotive.com/BikeExhaust/IMG_9077.jpg

Is that the big sucker in pic?


I have the velocity stack (behind the air filter) and 1 inch spacer from HPI.


I still want to try a longer stack mounted without the air filter, something like the drag bikes run.  I'll probably nd up machine something machined.

It's a screamin eagle velocity stack kit that they sell right in the book, it's built off the heavy breather. They make it for the 62mm se throttle body but not sure how the bolt pattern compares to the hpi.

Wondering how the 90 degree bend will work.. u dont see that stuff on drag bikes, I think it can cause lean issues on top end.