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.

Or you could just get the JWT Pop Chargers.

http://www.z1motorsports.com/g37_370...WARE_SMALL.jpg

Thanks for the link!

Yeah, I figured the restriction would only kill power... our meters aren't hotwires? If they are, flow rmass is based on flow rate over the wire, which is very much affected by diameter, although the section before the MAF wouldn't have changed, so voltage readings should still reflect OEM scaling.

Of course, abrupt transitions can throw things off... a problem I sort of hoped would not come up, but who knows until I try.

Anywho... I ordered a different set which should definitely have a smooth transition from bellmouth to the OEM diameter, so we'll see how that goes.

That was the original plan -- I had a set! But, after deciding that fabricating decent airboxes for them would be too much of a PITA (I have zero experience working with fiberglass...), I sold them off and have started this new project using intact (but separated into F & R halves) OEM airboxes.

On that note, I have some fiberglass repair kits I should just probably sell off...

When you have a restriction, the velocity goes up but the flow goes down. It's moving faster but has a smaller hole to go through.

As long as you don't change the duct size at the sensor (plus a diameter or two up- and down-stream) the sensor output should remain the same.

At long last, the new velocity stacks have arrived!

http://www.the370z.com/members/jordo...40625-0001.jpg

These have the right dimensions, so next step is to see what I need to do to fit them, in keeping with my plan to use the OEM airbox.

More details coming soon!

Test fit -- so far so good.

http://www.the370z.com/members/jordo...40625-0003.jpg

http://www.the370z.com/members/jordo...40625-0004.jpg



I might be able to just "snap" them in with some careful dremeling of the inside of the intake neck. If not, I'll have to make a bracket of some sort.


http://www.the370z.com/members/jordo...40625-0007.jpg

However, I'll have to have the filter sit forward a bit -- fits fine, so shouldn't be an issue; might make something to ensure it stays flush -- and figure out something for the top.

More soon...

After some additional thinking on this, I think my plan will be to bore out the inside of the OEM intake neck enough to have the v-stacks slide/snap in. Then I need to maybe drill in two flat head screws to secure it, or perhaps a thin layer of jbweld to keep it in place.

For the filter's slight relocation, all I should need are two thin strips of metal, similar to battery ties to ensure it doesn't pop out of position. Based on how snugly it fits, it should require much to secure it.

The top can simply be the OEM one, with the "frame" modified or removed so it just covers the opening. I might even simply bolt it to the front section to ensure that the OEM lid clamps will still keep it all together.

Essentially, the rear section would go in separately, then the modified front section plus filter would be locked down and sealed to the rear section. That should actually work, and make changing filters only moderately more challenging that it would have been on a totally OEM airbox.

So... question: What sort of hole saw like tool/accessory do I need to shave the inside of the neck precisely?

Also, is there something I could use that would create a slight tapering as I get to the desired depth to snap in the v-stack, and help ensure a smooth transition from V-stack to OEM intake neck?

Would I be better off taking this to a machine shop or something???

Looks like I need a tapered shell reamer -- something like this http://canadatool.ca/php/images/stor...rs%20taper.jpg ?

Anybody have any advice/relevant experience on this one?

While I applaud your efforts and don't want to discourage you, I don't think that setup is going to do any good and may decrease performance. You are increasing the length of the "restricted" section between the box and MAF and the air to the right of the stack in the last pic will have to make a turn. You may also be affecting the tuning of the intake/manifold.

I was a bit worried that it sticks out too far, but other OEM's have designs like that which work (see page 1), so it may or may not matter.

I'm hoping if I can ream out the intake neck enough, I can recess the v-stack further into it, which will minimize the degree its even an issue.

The stacks shown in the second pic of the OP look like they might do some good. What you show in your last sets of pics looks like it would interfere with the flow. But I'm not an Aerodynamics Engineer (or Engineer of any sort). I'm looking forward to seeing your results and hope that my guesses are wrong.

A big dowel pin reamer may give you the taper you are looking for but not sure how it would work on plastic.

I think it all comes down to how much of a restriction is the filter. The lip of the bellmouth in it's current position just barely touches it. Otherwise, it has a direct path to the entry way on the airbox duct, maintaining the same "line of sight" as the OEM neck, just extended.

I'm hoping to recess the thing in by a few inches so it will be less of an issue. That might even give me enough room to just keep the OEM filter location, instead of having it sit a bit farther forward.

On that note, I'm not sure if filter position will make a difference either...

I'm committed to this experiment now, so win lose or draw, it will give me some useful info on what to do next (e.g., have even shorter v-stacks made) or whether to abandon the project entirely...

BTW, thanks for all of your input -- I very much appreciate it :tiphat:

The portion of the airflow that is to the right of the stack in your pics doesn't look like it will have a straight shot to the stack unless the stack is a lot shorter. Can you cut the stack to make it shorter? That would avoid a lot of "machine" work on the plastic parts.

I don't think the position of the filter will have much effect on flow but it certainly would be a lot easier to R&R if it were in the original position.


Hang in there! This is one of the few time I'm hoping someone proves me wrong. :)

Minor update: After having NO luck finding a drill attachment that could smoothly bore the inside of the airbox intake tube to 2.625" (i.e., 2 5/8"), I attempted to bore it out manually with my dremmel...

Ehhhh... the short version is that it's too sloppy and needs more honing and, even worse, I cracked the outside of the tube trying to wedge my v-stacks in. D'OH!

So I am now considering a different route. If I just cut out the outer intake tube and cram the v-stack inside the hole, I can then simply use coupler to connect the intake tube to the v-stack, with the end of the v-stack poking through the hole in the airbox.

So long as I cut it right, it should be airtight (or easily fixed to make it so), connect perfectly to the OEM intake tube, take advantage of the OEM heat shielding as planned, and work almost identically to how I had originally envisioned the final version.

Moreover, it will allow me to recess the bellmouth further back, which may allow me to use OEM panel filter frame or at least minimize the likelihood of inadvertently losing part of the effective volume of the box because the v-stack protrudes too far.

More on this soon -- I may need a fresh set of airboxes... anyone willing to sell them to me on the cheap in the name of experimentation and adventure? :D

I'm leaving town tomorrow and will be gone for a week -- BUT, the above method worked beautifully! I should even be able to keep the filters in the OEM frame without any issues!

I will post pics when I get back, and in due course, dyno test -- but this will all have to wait until at least the end of July.

More details coming soon :tup:

Update: I am within days of bolting everything together and within a week of doing testing.

Tons of pics and dynos coming very soon -- finally! (or a sad report of failure devoid of worthless pics... hoping on the former, obviously.)

It will have the V-stacks recessed in box, coupled to OEM MAF holder and neck, make use of a modified OEM filter bracket and lid, and should all snap in and bolt down just like OEM, but with a nice V-stack, exactly as planned.

We'll see... report on success or failure soon... to be continued....

Good luck. I've got my fingers crossed.

you could have mine if you pay for shipping

Thanks!

Just assembled them tonight! Test fit and dyno coming soon. Succeed or fail, I'll report back :tup:

Thanks -- I'll keep you posted :tup:

Rats.

Finally made it to the dyno and the result is no gains. Nada.

Even datalogging MAF voltage showed no evidence of better flow. No change whatsoever from stock.

Sadly, this project is a bust :(

If anyone is interested in experimenting where I left off, shoot me a PM and I'll sell you my v-stacks and other odds and ends.

Not true. We now know that velocity stacks in the air box won't do much good. ;)

Thanks for sharing the experience. It was an interesting journey. :tiphat:

Sorry to hear that jordo, but just like southark mentioned, thanks for taking the initiative and experimenting with this :tiphat:

Thanks, guys -- that's much appreciated :tiphat:

Yeah, there was only one way to know, and I'm glad I didn't just throw them on without testing.

Also glad I didn't clog up a thread with all the build pics just to announce the uselessness of it... :icon14:

Great idea in priciple.However,think the gains you may think you may get
could be elusive.Velocity stacks work great on carbs like Webers.I've got some on
a Lotus I own.Fabricating and installing on a stock air box is pretty futile.
a air box opening ducted directly through a grille does work.If you are serious about poer gains in the intake system,I'd look at improving yourthrottle body.I had a Mines
throttle body in the 350 I previously owned.There was(after tuning)a substantial
power increase.

You ever consider getting the stacks outside the box, say up in the grill where the G3 filters sit? Have some tubing run from the stacks to the front of the box. This was an idea that I wanted to try, but never have had the time to do it.

I'm in the middle of that Idea now :)

Just ordered some silicon pipes and aluminum pipes. Hope there here this Friday

I just don't see velocity stacks doing much good. The longer/bigger the intake/manifold system is, the less good velocity stacks do. If they were mounted mani->TB->MAF->VS, without all the duct work, it might do some good; on a modified factory setup, not so much. While the bell of a VS can give some very small gains, the VS's main function is to tune the intake/manifold. By the time you get from the heads to the air intake, there's not a lot you can do to affect the tuning significantly (without major mods).

Velocity stacks are great for small carbs/TBs with short ducts/plenums/manis but aren't going to do much for a more-or-less stock 370Z setup.

But I'm no Engineer, so YMMV.

hmm kind of touching on it but kind of not, a velocity stack prevents boundary layer separation which basically reduces restriction at an air (or fluid) inlet, they do not aid in the tunning of an intake manifold but are merely a feature that stabilizes the incoming airflow, the manifold is tuned by adjusting the length, taper, and diameter of the runners(longer velocity stacks are just runner extensions with the same entry profile as a shorter one. The reason that Velocity stacks loose effectiveness in a longer intake system is that they are no longer the primary restriction, the tube wall friction, bends, and pressure loss is.

The other thing to take note is that not all velocity stacks are created equal, I can't remember the name of the text but there was a good book on air velocity that described the differences between the airs density and velocity and the path a of the boundary layer for a tube inlet (a velocity stack is basically designed to follow the path of the air closest to the tube that wants to bend and enter it.

^^^ I know elliptical bellmouths are supposed to be better than perfect circles. Mine was not elliptical...

I saw a few examples where they made power on the airbox inlet going into the bumper -- that's a good idea! Keep us posted. If you succeed I guess I could try that next.

Yes. In the proper application, vortexes, boundary layers, laminar flow, &c are an important part of what a VS does. But just sticking one on the end of an intake will more than likely not have any appreciable effect, positive or negative - as Jordo! has shown (at least for his setup).

I could be wrong (my personal experience with VSs is, for all intents and purposes, nil but I have a lot of experience with gas/fluid flow measurement), but everything I've read on VSs says they are an important part of tuning the intake system. If I'm wrong, please show me the light - I'm not too old to learn something new.

Ok on an itb or carb setup you can get longer or shorter stacks and ones with different tapers, like the throat part is different below the bellmouth, by changing the length of the throat you add or subtract from the runner length, this effects hiemholtz reasonance freaquency of the runner/stack assembly which shifts the point at which accoustic pressure helps ram air into the engine which tunes the power band. The reason jordo saw no gains was because the inlet on the factory airbox is not the choke point in our cars intake system. If his intake system were optimally designed everywhere else then he would have seen minor gains from this. And heres another hint, you can only suck so much air into a cylinder that csnt get all its exhaust out.

Sent from my HTCONE using Tapatalk

Well, I have LTH and can tune VVEL... any thoughts on what I could feasibly adjust, or are you saying this would this require a completely different IM?