Help! aftermarket intake logistics

[travis_e30]

does anyone understand how the afm and other electronics are supposed to work with an aftermarket intake manifold like the one pictured, if so can you please let me know what is needed? please and thanks.

[Northern]

I'm a little confused because that's an RB20 manifold and as far as I know, ISR doesn't make any BMW stuff?

Even if there's one for whichever engine, it would usually use a larger aftermarket/generic throttle body, so you'd need adapters to run the stock stuff.

Lots of ebay/aliexpress crap intakes out there that look like this but are complete garbage as well.
Even if the quality is top notch, you're going to lose low/midrange power with runners that short, and probably not going to rev high enough to see any benefit.

[Shadye30]

Interestingly enough I was just thinking about this the other day (about whether any aftermarket companies manufacture a manifold like this and whether is would actually make power)?

[digger]

Normally you’d use a standalone ecu with this style of intake. It may make a higher peak than stock manifold but give up on midrange as runners are too short.

on a NA engine a waste of money but on appropriate snailed spec engine it may peak higher

[e30davie]

I always look at inlet manifolds like that and question how the air can be equal from front to back. I guess if you can get the manifold under pressure (boost) then it matters less. but you look at all the performance orientated (or just high quality) engines and they always do their best attempt to have equal length headers, or at least long headers so the difference in length is reduced. The OEM Nissan rb25/rb20 that that looks like its been designed for has a centre entry intake manifold that goes over the rocker cover, but then many guys remove that and bolt on these style where to me it looks like the air can just short circuit to number numbner 1cylinder and then number 6 misses out. I mean sure not having the inter cooler piping crossing over the rocker cover looks better, but at what cost.

Alot of engineering has gone into the bmw m20 manifold. Id be very cautious of removing it of something that doesn't have BMWs design budget. But its also been designed for a street car, not necessarilly peak power. i feel like you'd want to make changes to the oem one to improve, or mimic the oem one but make it bigger. Not just throw a chinese spec one on and hope.

Has anyone ever made a tubular version of the intake manifold (simliar to oem) but with bigger tubes? would be a hell of alot of effort.

[digger]

I always look at inlet manifolds like that and question how the air can be equal from front to back. I guess if you can get the manifold under pressure (boost) then it matters less. but you look at all the performance orientated (or just high quality) engines and they always do their best attempt to have equal length headers, or at least long headers so the difference in length is reduced. The OEM Nissan rb25/rb20 that that looks like its been designed for has a centre entry intake manifold that goes over the rocker cover, but then many guys remove that and bolt on these style where to me it looks like the air can just short circuit to number numbner 1cylinder and then number 6 misses out. I mean sure not having the inter cooler piping crossing over the rocker cover looks better, but at what cost.

Alot of engineering has gone into the bmw m20 manifold. Id be very cautious of removing it of something that doesn't have BMWs design budget. But its also been designed for a street car, not necessarilly peak power. i feel like you'd want to make changes to the oem one to improve, or mimic the oem one but make it bigger. Not just throw a chinese spec one on and hope.

Has anyone ever made a tubular version of the intake manifold (simliar to oem) but with bigger tubes? would be a hell of alot of effort.

boosted or not distribution is much the same sans for some density effects. the reason things that intuitively look bad but still work ok with intakes in general is that at any given time there is only 2 and bit cylinders drawing on a 6 cylinder manifold. In any case an end entry manifold is easier to balance distribution than a central entry like most OE manifolds at the expense of packaging.

Runner length is probably the most important design detail though, in reality distribution probably helps things live better more than give power gains. obviously diameter and alignment are important but get the length wrong and its an absolute dog

if I was building a FI manifold I’d start with RHD adapter, add the spacers (no itb required so need an adapter piece) and add or mod the plenum so it is more designed for consistent sealing of boost. On a NA engine the RHD matches the OE manifold at low to mid and exceeds it easily at top end. Theoretically the OE longer runners should be better than the RHD in midrange due to length but it makes up for a few inches in length by being much more efficient i.e. flows better, aligns and matches port better.

[mikey.antonakakis]

100% agree that for NA application those runners are wayyyy too short. They’re too short for a 600cc sportbike.

[e30davie]

boosted or not distribution is much the same sans for some density effects. the reason things that intuitively look bad but still work ok with intakes in general is that at any given time there is only 2 and bit cylinders drawing on a 6 cylinder manifold.

I had not considered this, and of course its obvious now that you have pointed it out. perhaps i will give these end mounted throttle body style manifolds a bit more credit.

[jbontke]

Engineer explaining some manifold design, good insight: https://www.youtube.com/watch?v=d87svo4ELuU

[TobyB]

Valvetronic.

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