Intake: How to make a difference you can actually feel.

[10/10ths]

Swap your cone filter back to the stock airbox.

I had already done this 4 years ago on my track car but I finally got around to switching back to stock on my wife's 325i. It's crazy but you can really feel the difference between them, but only when switching back IMO.

For me anyway, I think it's harder to detect a small power loss from the cone filter, maybe the induction sound makes you think you feel a positive difference. But I swear the low end "off the line" power is much better with the stock box, which makes sense to me as far as temps go, but it is surprisingly noticible, at higher revs they both feel the same.

These are stock (and mostly stock) M20's and to be fair, either one had a heat shield which I'm sure would have helped, but I still can't imagine getting MORE power than stock with a heat shield. I don't have dyno proof to back it up, but if you are running a cone and have a stock airbox laying around this is an easy one to check for yourself.

Justin

[jlevie]

I'm not at all surprised...

Before the rules outlawed intake changes, members of the Spec E30 community have spent time on a dyno looking for that last horse power or two. To the best of my knowledge no one has ever found anything that out performs the stock airbox and clean OE filter.

This isn't limited to E30's. I've spent an afternoon on a dyno playing with intakes on E36 M3's. There again the stock airbox was just as good, if not better, than any of the cold air intakes we had available to play with.

[Sagaris]

I made a thread about 2 months ago with the same findings. I would like to make+try a phenolic intake manifold spacer though.

[10/10ths]

I would like to make+try a phenolic intake manifold spacer though.

I did a quick google on this and read into it here

http://www.s2000.org/mods/insulator/

Sounds interesting, has anyone done this on an E30?

[nando]

stock isn't always better. I picked up quite a bit of power with a good filter.. measured on a dyno (10whp in the upper RPM area). I was also measuring a 5-10kpa pressure drop across the stock airbox/filter, so I wasn't that surprised.

Putting the stock airbox on results in a noticeable loss in power. basically anything more than a 20-25% increase in power over stock, the stock airbox will be a restriction.

the next restriction is my stock manifold and TB. Still pulling vacuum at WOT.

[10/10ths]

Putting the stock airbox on results in a noticeable loss in power. basically anything more than a 20-25% increase in power over stock, the stock airbox will be a restriction.

Sounds right, I would love to have that "problem" where the stock airbox is a restriction but there is no reason to pull the motor anytime soon. I have thought about doing a cam but even then with miller/headers I'm sure stock is still fine.

(and as always, when I am ready to buy the cam, at the last minute I will change my mind and spend the money on tires)

I forget what your setup is, or maybe it has changed, do you have a boxed in cone? How much mure surface area on your filter over stock?

[nando]

it's not currently boxed in, but it really needs to be. I have an extra set of headlights with the high beam deleted and a funnel in it's place, directed at the filter. This keeps intake temps down quite well on the track and at autox - easily ambient. On the street they can get quite high, but I don't care that much when I'm driving to work. But the filter would stay cleaner shielded. I will do it eventually..

the HP increases I saw on the dyno were unshielded too. I don't know how much a shield would have helped, but I don't think my intake temps were too bad. maybe 1-2hp? but if I sit long enough it can get heasoaked quite badly, 50-60c isn't uncommon. That's a 5-10hp loss right there. That puts me about even with the stock airbox. I run the stock airbox during the winter though, since the oil definitely gets dirtier with the higher flowing filter.. no way around that!

as far as surface area - quite a bit more. I chose the largest filter that would fit in place of the stock airbox/afm. I don't have a square area measurement, but it's about a 1-2kpa pressure drop compared to no airbox/filter at all. I think that's about as good as any filter element is going to be.

[10/10ths]

I have an extra set of headlights with the high beam deleted and a funnel in it's place, directed at the filter. This keeps intake temps down quite well on the track and at autox - easily ambient.

I tested that years ago on my first E30, both temperature and airflow, I don't know what the actual HP difference can be with or without but the temp difference can be huge. I originally did it on that car out of curiosity, then did it again on the track car for autox. Even when shutting off on grid, hood open between runs, you still spend a good deal of time idle on the way up to start. It looks kinda stupid...but it WORKS!

I have since deleted the other side HB on this car to make it look even and also throw some cool air on the header side. Looks better, stays cooler, don't really need the highs anyway on this car.

[nando]

Yeah, I was surprised. even at 25mph, it made a huge difference. I have datalog screenshots somewhere that show the difference at 3 speeds, I'll have to find those.

[10/10ths]

I have datalog screenshots somewhere that show the difference at 3 speeds, I'll have to find those.

I would love to see those...my testing back in 2000 was with a home-made U-tube manometer (imagine the crudeness) but it did confirm it was working. My boss at the time, who had worked in aviation, was convincing me that tucking the diving boards would further increase the flow to the filter.