Intake Manifold Plenum

[mazzo]

I start seeing a lot of intake manifold plenum with throttle body listing in e-bay for E30 M20. I wonder if they have any actual performance value or just for show...anyone?

[digger]

Without specifically showing what you mean it's hard to answer

[mazzo]

Something like this...

[nomansland92]

Junk, runners are different lengths and probably doesn't have stacks in the plenum.

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[digger]

Short runner intake might make it more topend based power curve on a boosted motor if done well. On a NA engine forget about it just way too short

[Mazdayasna]

Junk, runners are different lengths and probably doesn't have stacks in the plenum.

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This is correct. Also consider that many of these boxy eBay intakes just flow poorly period, the factory one is more than sufficient for the majority of cases apart from itbs.


Here's a conclusion page from a good study on the matter that I've had bookmarked for a few years






And a pic of the stock manifold for reference because I'm sitting right next to mine




Very smooth! But also very oily unfortunately

[mazzo]

Cool - so basically unless I am turbo-ing my car there is no need to check this thing out.
Thanks for all the info from all of you. :)