My have found an option (though still very open to working something out with AZspeng)

58m ID shorty bellmouth stacks here (need to remove that screen) http://www.dimecitycycles.com/vintag...-pos-shrt.html

Rubber flanges that I believe (need to double check...) will fit here Genuine Mikuni Carburetor Mounting Flange VM36 VM38 | eBay

Worth a try?

First link is broken. Delete the "\" from the end of the URL and it works. (Fixed in the quote above)


Which air boxes are you using? I took a look at my spare set and they don't look anything like what's in the pic in your first post.

^^^ Thanks :tup:

OEM airboxes split in half -- the front pries away from the rear without any structural damage with a bit of firm but gentle coaxing with a flathead.

The other ones I posted a pic of, which already have stacks installed, are ones from a 35DE motor I think.

Ah. I took a closer look at your pic and what I thought was a plastic "grille" was just reinforcements molded into the case. Doh!

I still don't see you getting much out of a velocity stack. I can see where it might help a little bit on the 350 box but the walls/throat of the 370 outlet look pretty aerodynamic to me. But I hope you prove me wrong. ;)

Honestly, I'm only expecting 5 or so and maybe a little snappier response. But, that, plus K&N + smooth tubes would mean like 15+ whp with the OEM airbox, which is pretty nice.

I'm hoping that if this works, I can figure out a way to at least offer a good DIY or, hell, maybe people can send me their airbox to mod for a small service charge.

Anyway, phase 1 is find stacks that fit, phase 2 is test ;)

Okay, I said **** it and ordered the velocity stacks -- now I just need a way to mount them... looking for some of those rubber flanges -- AZspeng still interested in collaborating on this if possible as these stacks may not work out...

Ah, the allure of tinkering on car projects...

ebay might be your best bet

I can't find any rubber flanges specifically for stacks with an ID of 58 mm... I may have to get creative -- I'll figure something out.

Maybe a silicone reducer and some hose clamps will work?

I think there may be holes for some small flathead bolts to fasten in directly to the inside of the airbox -- I can make a gasket out of rubber easily enough.

Failing that, yeah, I'll have to experiment with something along the lines you are describing.

First thing I need to do is see what's involved in removing the screen -- hopefully easy to pop out -- no need for that there.

Somebody on here mounted bellmouth velocity stacks on the end of his G3's and claimed he picked up an extra 8 whp. Seems reasonable -- and I am expecting at least 5, but we'll see... no harm in trying :D

Velocity stacks came today -- and oooh they are quite pretty. Screens will pop right out. Will confirm fitment and see what can be done to mount later this evening.

Looking forward to progress :tup:

1st problem...

The bellmouth inlet effectively is only 2.125", NOT 2.25"... the lower portion has an ID of that, but I would need to find someone to grind and polish inlet section to base for smooth transition and to maintain same ID.

Or... I could great creative and get an insert that will transition to the OEM ID, sort of like an inverted funnel.

So, my thinking is: Bellmouth + slight narrowing of inlet should smooth air and also speed up flow, improving responsiveness and low speed power, while maintaining OEM ID before the MAF should keep measurements accurate without needing any re-scaling in uprev.

On the other hand, any narrowing at the inlet could simply kill power everywhere, especially up top... or, I might break even up top due to the overall flow benefits, and just gain down low.

Or nothing will happen or it will run like ****. Oh how I wish I knew enough of the right math to figure this one out... :icon17:

Anyone have any thoughts on this one...?

Actually, might just return these -- found another place that makes custom stacks to order on the cheap...

Racer X Fabrication | Formed Velocity Stacks

will try these next...

The increase in velocity due to a narrowing of the duct doesn't do you any good. The velocity decreases as soon as the duct gets bigger again. It will actually reduce the flow.

Since the sensor is measuring mass flow, there shouldn't be any need for re-scaling.

The math for figuring the loss due to narrowing of the duct is pretty straightforward - it's just an orifice. Flowrate Calculation for an Orifice Flowmeter looks like a good place to start. You will probably need a manometer or other differential pressure measuring device.

Figuring loss due to turbulence is much too complicated for me.