K&N filter and on boost AFR

[Chris_chch]

Hi all, I have an 84 930, with a fresh engine, K27 and SC Cams. Runs fantastic.

I recently swapped out the factory air box with a K&N that fits directly onto the metering plate housing. Did it purely for access to the engine bay, and a by product is it sounds fantastic as well.

Question I have is others doing this mod... did it throw you on boost AFR off much?

Previously I was at a nice and consistent 11.5-12 on boost. (at approx 12psi)

Swapping nothing except the filter, and on-boost is now dipping into the 9's and making the engine bog down. Only reason I can see for this, is the air coming into the engine can now hit the metering plate at a more direct angle, therefore pushing the plate down a bit further, for the same amount of air?

I've started to tap in the boost threshold plug on the bottom of the wur, and am getting back to where I was. Currently into the mid 10's, but taking it a small tap at a time...

Like to hear if my experience is common?

Chris

[flightlead404]

So your hypothesis is that switching the filter made the engine richer?

Seems pretty unlikely to me, especially on the order of magnitude you note.

Possibly, although pretty unlikely, there is a hair more mass of air hitting the plate, but either way its highly turbulent.

Are you sure nothing else changed between measurements? Ambient temp, engine temp, altitude...

[Mixed76]

Very possible for a different intake arrangement to cause the airflow sensor to read differently, and hence cause the car to run differently. If you're adjusting based on exhaust wideband o2 you're doing the right thing.

Had the same thing happen on an is300, but it ran more lean. The only change was a 4" shorter intake pipe.

Sent from my Nokia 7.1 using Tapatalk

[Chris_chch]

Originally Posted by flightlead404

So your hypothesis is that switching the filter made the engine richer?

Seems pretty unlikely to me, especially on the order of magnitude you note.

Possibly, although pretty unlikely, there is a hair more mass of air hitting the plate, but either way its highly turbulent.

Are you sure nothing else changed between measurements? Ambient temp, engine temp, altitude...

I actually swapped back and forth between the new and old set up twice on the same day as I thought I may have messed something up.

I'm guessing its that the factory intake directs air at the metering plate from right to left... were-as the K&N has air entering from all angles.. if that makes sense

just to be clear... new set up removes the entire filter housing... Now I have a filter directly on the metering body.

[full quack]

You might want to make sure the K&N installation is not hitting the spring plunger right next to the metering plate.
The k&N filter flange and/or clamp may be interfering with the needed free movement.

Just a thought.

Mark

[Chris_chch]

Originally Posted by full quack

You might want to make sure the K&N installation is not hitting the spring plunger right next to the metering plate.
The k&N filter flange and/or clamp may be interfering with the needed free movement.

Just a thought.

Mark

Thanks Mark. I notched the filter housing to clear the Spring plunger. Had to adjust a tiny bit as well for idle, so know its clear.....

I'm not really concerned, was just curious to hear if this is a common result of the swap. Having to pull fuel out is a nice place to be if I'm honest.. car goes fantastic

[flightlead404]

Originally Posted by Chris_chch

I actually swapped back and forth between the new and old set up twice on the same day as I thought I may have messed something up.

I'm guessing its that the factory intake directs air at the metering plate from right to left... were-as the K&N has air entering from all angles.. if that makes sense

just to be clear... new set up removes the entire filter housing... Now I have a filter directly on the metering body.

Fair enough. I didn't notice an AFR change when I did that swap

[ficke]

The small K&N that fits directly over the metering box reduces the air flow, you will run richer as a result. less air filter surface area, more restriction.

[Alan L]

S..t Walt - you mean it will run better if I take it off?
Chris - PM me if you want - I am in H Bay and get to ChCh from time to time - daughter is there.
Regards
Alan

[Rawknees'Turbo]

^^^

I couldn't find the info/thread just now, but that filter has been run on a dyno and there was no loss or gain versus the stock mailbox filter housing (no different than running with the hole wide open, either). I think it was either TK Chris or RarlyL Brian that did some comparative testing.

[Alan L]

Thanks Rawknees - feel better now.
Alan

[Dominik 930]

https://www.youtube.com/watch?v=JwQMR7q9eMg

https://www.youtube.com/watch?v=Grx8OFkgRrw

https://www.youtube.com/watch?v=_YrCGkeheAg

Mod: K27 7200 + Kokeln LLK + Engine completely rebuilt with all bearings and valve guides, 22 k

[ficke]

Any restriction of the intake is a power loss, that is why if possible race cars have open trumpets intake systems, why clean air filters are important.
Filters that do not clean as well like a K&N provide less restriction and more power why replacing a stock paper filter with a K&N in the same housing works for power gain. Nothing is free every thing is a trade off.
Providing Less surface area like the K&N over the meter box will require more air speed to get the same volume that the stock filter housing has , more disturbance and more restriction.
The fact you have done no other change to your car other than the airfilter shows this.

[flightlead404]

Originally Posted by ficke

Any restriction of the intake is a power loss, that is why if possible race cars have open trumpets intake systems, why clean air filters are important.
Filters that do not clean as well like a K&N provide less restriction and more power why replacing a stock paper filter with a K&N in the same housing works for power gain. Nothing is free every thing is a trade off.
Providing Less surface area like the K&N over the meter box will require more air speed to get the same volume that the stock filter housing has , more disturbance and more restriction.
The fact you have done no other change to your car other than the airfilter shows this.

which is a great hypothesis. however as pointed out above, experiments were performed which generated data to refute this hypothesis.

[ficke]

Originally Posted by flightlead404

which is a great hypothesis. however as pointed out above, experiments were performed which generated data to refute this hypothesis.

Not a hypothesis, I have seen dyno results that showed the HP. loss from the different filters. I have had a lot of personal experience readjusting many different types of engine fuel mixtures because of the different filters used.

[Chris_chch]

Thanks for all the feedback... 1 thing I hadn't properly considered or even mentioned, is that my factory airbox/snorkel wasn't exactly stock.

Pic attached.. the previous owner had cut the end off (the filter housing end) and welded a flat plate across the opening, and put a 3" pipe into the end... all so he could fit a pod filter.



I actually think this was a restriction over stock... All air had to get sucked through a 3" hole. So now I'm back to running with a much larger intake area, I'm getting more air in.

I've got the AFR's pretty close to being in spec again (10.8-11.4 at WOT), and its definitely pushing more power than before. Car has really woken up.

Again... thanks for the feedback!

[Alan L]

Chris - FWIW, I run mine at 12-12.5, up to 1 bar boost. For extended periods. No issues. You still have some headroom to go if you want.
Regards
Alan

[Chris_chch]

Originally Posted by Alan L

Chris - FWIW, I run mine at 12-12.5, up to 1 bar boost. For extended periods. No issues. You still have some headroom to go if you want.
Regards
Alan

Yeah... Creeping it up a few points each day.. With the vagueness of CIS, I want to make sure it doesn't creep leaner after a long drive etc

I'll be aiming for 11.5-12


Appreciate the feedback

[Alan L]

Yeah - pulling the WUR apart for each adjustment can be a PITA.
If you see my pic I have a WUR pressure gauge permanently installed. And have modified the WUR so I can adjust it in place - for WP and Boost dump. The simplest mod you could do is to drill a hole in the base plug so you can get the allen key in there for WP adjust without having to split the WUR. You still have to break the fuel lines etc to remove it - but at least you aren't splitting it every time. From where you are now a 1/4 turn should get you close.
Regards
Alan

[Chris_chch]

Originally Posted by Alan L

Yeah - pulling the WUR apart for each adjustment can be a PITA.
If you see my pic I have a WUR pressure gauge permanently installed. And have modified the WUR so I can adjust it in place - for WP and Boost dump. The simplest mod you could do is to drill a hole in the base plug so you can get the allen key in there for WP adjust without having to split the WUR. You still have to break the fuel lines etc to remove it - but at least you aren't splitting it every time. From where you are now a 1/4 turn should get you close.
Regards
Alan

Have to agree! The hole in the bottom to get at the 4mm allen head is a god send! I can get at it with the WUR still installed, and the car running which has been amazingly helpful. I have the warm pressure dialled in already. I'm just slowly creeping the bottom plug in to increase the on-boost AFR. going about 0.5mm at a time... Trying not to over shoot it!