well im in the middle of a a project, fabbing a intake manifold.

my problem is that i have a piece of aluminum plenum, in a half circle shape.
here is what im talking about:


and my throttle body flange is a larger circle:


i was thinking of using a exhaust pipe expander with heat to get the circle shape from the half circle shaped plenum.

what do you think, will it work?

have a better idea to get these two pieces of aluminum to match up for welding???

 

Well you can buy a flange with the same bolt pattern made to fit that plenum.

Q45 throttlebody adapter plate

Or you can adapt it to what you need. In witch case the easiest would be something like this.

www.ka-t.org • View topic - intake manifold differences


On the other hand you could use some small pieces and "work" the end of the plenum to fit the flange better.

 

I wouldn't try to reshape the aluminum extrusion, even if it 5052 (if it's 6061, then definitely not).

Aluminum cracks so easily. Even if there are no visible cracks, chances are you'll cause some stress points, which once bolted to a vibrating engine, will result in cracks. You're probably better off cutting/milling the corners down and welding in plates, so that on one side, you'll have a Hexagon profile instead of an arc.


-Zach

 

how large is that TB?


is the hole of the TB flange, the same as the opening of the plenum?

 

I would ditch the flange, and have one milled to match your throttle body bolt pattern, but have the inside match the rounded/square opening of the manifold. Contact Tim and give him a bunch of money, I'm sure he'd whip it out in a day.

 

yes i believe it is 6061, since the flange is 6061. so ill take ur advise and i will not try appling heat to it and expanding the plenum.

 

i bought a longer length than i needed, just in case i couldnt stretch it, and i had to cut it up and weld it together.

now if i cant stretch it, is it ok to bend it? and how far till i start to comprise the integrity of the piece of aluminum.

 

Depends on the alloy. Alloys such as 5052 will bend without much drama. 6061? - not so much.

I advised against reshaping due to the 90deg corners, as that extrusion will likely not tolerate that much reshaping.

As Curly stated, the nicest/most baller way of going about this is to machine a custom end cap. Such as this:



The cheaper approach would be to either created create a hexagonal profile using some well placed corner cuts, or, just weld an end plate cut from sheet stock.

I'm under the impression that much of the gains with custom intakes are had by tweaking runner length, i.e., a flat plate is probably "fine".

-Zach

 

why do you even need to do that?

Why can't you cut a plate the same shape as the plenum, cut a hole in it that matches the TB hole. Weld the plate to the TB flange, and then weld the plate to the plenum?

 

because the throttle body hole is bigger than the plenum.


OP.

cut the intake plenum to the proper length for the floor ports and if your using them the velocity stacks.

Then your going to need to form some aluminum (3000 series is formable if not heat treated) into a semi truncated cone to fit both the throttle body and the plenum shape.

The way I would do it is to put the throttle body flange at an angle (point it down in a Miata to help with the cold side charge pipe) to help smooth out the transition over a longer period.

Its a lot of work.






Last option would be to run a smaller throttle body that isn't an LS1 throttle body so that its much more reasonable and it will fit better. I think the LS1 TB is way too big for our cars anyways.

 

in my thinking, I have remembered a reference to what I kind of just described.

An inlet elbow for an RX7.


It look tough to do and I guess it could be... but it is what I believe is probably the best Miata solution.


(PS, Im going to be building an intake manifold for an FE3 Miata similar to what Im describing now in the coming weeks.)

 

is it?

Then I'd get a hemisphere or cone, and cut it so the diameter of the small end matched the plate that was sized accordingly for the plenum, and the diameter of the large end matched the TB flange.

or add the flaccid ***** to the front of your car.

 

Either thats a small plenum, or that throttle is way too big. The last thing you want is an oversized throttle. It is a nightmare. The car will drive like **** even if you can manage to get the tune dialed in right, which you wont.

A 70mm throttle will support miata horsepower records.

 

i was thinking the same thing about the size of the TB.

 

You're not having fun unless you're chirping tires at 2% throttle.

 

If that is the Ross machine extrusion its 3.5" ID, which is roughly 88mm. That plate you have must be for like a 100mm throttle or some crazy ****.