Bigger is not better ?!?!?!?!?!

[jondee86]

Does anyone know what these little guys do ??

http://www.jubiride.com/shopping.cgi?cmd=v&no=PO16-20071228210056
They are used to sleeve down the entry side of AE101 ITB's, but I
haven't been able to find any theory as to WHY you would use them ??

Cheers... jondee86

[fangsport]

port velocity?

[xsspeed]

create a turbulent flow for better mixing? I',m assuming the velocity stacks sit around the outside?

[NA Drifter]

They are "choke"?? ... to increase intake flow speed by downsizing the intake port size... just like 4age big port vs small port... smaller port, greater air velocity...
I believe alot of carbs/weber/etc tuner know about this..

[jondee86]

As far as I can figure, they are straight bore on the inside and
tapered on the outside, to slip inside the entry of the throttle body.
They are available in various bore sizes (36, 38 and 40 from Jubiride)
and similar items are available from other manufacturers. Toda have
the same thing actually actually incorporated into their velocity stacks.
But otherwise, the velocity stack just attaches in the normal way.

Obviously, the smaller bore will increase the velocity into the throttle
body, and having a step in the bore (36=>42) will cause a bit of
turbulance and pressure loss. It also means that you would use a
smaller bore velocity stack to match the bore of the "sleeve".

Buy WHY would you do this ?? Are the AE101 ITB's too large
for a 1600 16V ?? Is this a way of choking them down ?? Improving
bottom end ??

Cheers... jondee86

[jondee86]

Hey NA Drifter... didn't see your post

Choking down a carb increases the throat velocity and improves
low speed atomisation. But injection doesn't care about velocity thru
the throttle body, as the squirters are on top of the valves (in a 16V).

And if your intake runners are too big, putting chokes on the inlet
side of the throttle body won't change the velocity at the intake valve.

I was thinking maybe it changes the intake resonant frequency or
something along those lines ??

Cheers... jondee86

[TRD Man]

NADrifter is right. They are to increase velocity. The TOM'S trumpets are a one piece trumpet that incorporates this section.
The purpose is as you've described here

Is this a way of choking them down ?? Improving
bottom end ??

They're now discontinued but when used with the accompanying airbox they were very very effective with driveability and lower end acceleration noticeably improved.

[jondee86]

OK, I'll go with that

TRD Man... were the TOMs velocity stacks tapered or parallel bore ??
And do you remember what the bore size or small end inside diameter
was ??

I think I'll have a go at fabricating some one-piece items, as I am
keen to have as much bottom end as I can get with the ITB's.

Cheers... jondee86

[TRD Man]

The TOM'S trumpets were tapered but at a much shallower taper inside the body than out.
I've got a set in the shed. We have looked at making these commercially ourselves but they appear to have been cast and then individually machined which makes for an expensive item. It's still a work in progress.

[jondee86]

Sweet !!! Hey, I'd love to see some pics, or if you are still around
the Hutt Valley, maybe take a look at them. I have discovered some
info on "drop-in" tapered chokes, but they are designed for parallel
bore ITB's, not taper bore like the AE101.

Cheers... jondee86

[TRD Man]

You're welcome to have a look at them.

Meanwhile, I've just had a closer look at one.

The overall length is 110mm.
From the outer lip to the inside edge of the flange is 80mm. The flange is 5mm thick.

I haven't got my vernier here but using a steel rule I'd say that the ID at the outer lip (before it starts to roll outwards) is approx. 57mm.

The ID at the butterfly end is approx. 39.5mm.

Looking again, but without the vernier, I would say that the part that goes inside the throttle body is not tapered (as I suggested earlier) but maintains this 39.5mm ID for 35mm (being 30mm inside the ITB and the 5mm of the flange).

I hope that's all understandable.

Fitting these trumpets on a Silvertop in FWD mode did require the larger TOM'S airbox.

[jondee86]

Thanks TRD Man... that's cool

I found some good pics on a forum, so I know what they look like
in general, but I didn't have any info on the small end diameter. I'm
going to make something along those lines, but based on a standard
aftermarket spun trumpet.... maybe a bit longer if I have enough
room to fit them in.

There is a whole lot of "rule of thumb" and "this made a crap load of
power for the guy my brother bought his engine off..." type info on
the interweb, but bugger all hard facts or empirical data. So choosing
trumpet size and length is pretty much pot luck

I'll not be running them in an airbox, and will probably use an ITG
style filter and back plate in the final build. What I am desperately
hoping to avoid is the classic ITB's on 16V conversion that loses 10 kW
and a bunch of torque, but... sounds wicked bro !!

Cheers... jondee86