Aluminum intake manifold

[Dez]

How thick would be good for a sheet metal plenum? i will be modifying a 1 piece intake manifold for this project.

I have searched online and it seems that 18g is the most popular for sheet metal intakes, but i could be wrong.

Any thoughts?

[shadow88]

Mine's 1/8" and has been tested above 25 psi.

[BadAssPerformance]

1/8" is common too. :thumb:

[mock_glh]

A plenum should be built with as much resistance to pulsing as possible. Round tube plenums are good for this. Flat sided plenums are much more likely to crack along welds and long edges due to fatigue caused by flexing of the sides over time. The larger the surfaces are, the more likely this will happen. 1/8 inch thick for round tube and 3/16 to 1/4 for flat sided are my recommendations And make sure the welds are plenty thick.:nod:

[Dez]

I am most likely going to go with 6061-.100. Which is around 11-12g, plenty thick, also i won't be bending so i won't worry much about it cracking.

I will probably get working on it on Saturday, so hopefully an update will be up shortly.

[8valves]

I make mine out of 1/4", alot of people have good luck with 3/16 as a compromise between weight, flex, and strength.

[BadFastGTC]

Mock, I agree completely with the weld issue! I experienced a couple of cracks myself. I am curious as to why you say to stay away from a box intake and runner pulsing?

Steve M.


A plenum should be built with as much resistance to pulsing as possible. Round tube plenums are good for this. Flat sided plenums are much more likely to crack along welds and long edges due to fatigue caused by flexing of the sides over time. The larger the surfaces are, the more likely this will happen. 1/8 inch thick for round tube and 3/16 to 1/4 for flat sided are my recommendations And make sure the welds are plenty thick.:nod:

[johnl]

A rounded section, resists flexing, or pulsing, better than a flat panel.

Think of a door way - the Roman arch vs the Greek lintel - an arch of multiple wedges supports far far more weight better than a single header of stone. In the same way a curved section resists metal fatigue because it doesn't move with intake pulses.

[BadAssPerformance]

Circles are strong... Boxes can work too...

[2.216VTurbo]

Used 1/8th on mine, and it's a box shape. Sure enough, within 2k miles or so it cracked along the seam-on the bottom where it baffled me for quite some time as to why the motor had such strange symptoms.:confused: It would seal shut under vacuum conditions so no high idle or other teltale signs. During boost though the crack would open and end the fun. Thing is I was only breaking in the motor at 11psi or so and since I didn't ask the turbo for more than that, it seemed to be achieving the desired boost level... Eventully when it fully let go boost fell off to 6psi and that was enough of a clue for my thick skull to pull the manifold and check it.:(

There are pics of it here posted last year if you search for 'found my missing boost";)

[mock_glh]

Mock, I agree completely with the weld issue! I experienced a couple of cracks myself. I am curious as to why you say to stay away from a box intake and runner pulsing?

Steve M.

What I meant was that the plenum must be rigid enough to resist the flexing caused by the pulsing. Box plenums work fine, and they're usually better looking, they just crack easier if they're too thin.:nod: