Intake manifold - removing flaps worth it? 2.5 auto

[AlexF75]

As the title.

I don't (yet) have a problem with the intake manifold, but when I do, I'd like to know whether completely removing the flaps would make a positive or negative influence on the engine performance and economy.

I wouldn't mind just a bit more oomph from my 2.5 KV6, to be honest, not slow at all but I had an E46 30i and E36 28i convertible which are both just a tad more powerful - that "tad more powerful" can definitely be felt though, I'm used to 200-ish horsepower.

So the questions are - and sorry if there is another thread about this where my question is answered, I couldn't find it, so if there is please provide a link:

1) Will engine performance improve by removing the flaps? My guess is it should, since even when the flaps are open, they are blocking a few percent of the airflow which would be "added" if I removed them.
2) How will engine characteristics change? My guess is low down torque would be somewhat compromised, and since I have an auto box (which tends to keep revs low unless it's absolutely necessary to accelerate quickly - so unless I pretty much floor it), would that effect be noticably negative?
I'm also thinking top end is where I would get slightly more power.
3) How will fuel economy change?
4) Does the software need any tweaking (and if so, how) to adjust to the removal of the flaps? AFAIK it does not.


Thanks for the replies in advance, and if that reply is a link to a thread where all these questions had already been answered, I'm sorry.

+1: If you have any cheap ways to slightly improve performance of this engine, please don't hesitate. I'm only thinking bolt-ons though, no taking the engine apart for modding internals or anything of that scale.

[xsport]

a lot of time and effort involved in removal of the flaps. at the end of the day there will not be much difference. the kv6 is known not to be torquey at low revs anyway so you wont achieve much. stick with the flaps if they are functioning ok and keep your vis motors working well. i dont know if anyone on here has ever tried removing the flaps and then a remap but again more trouble than what its worth in my opinion. if you have an auto you can use sport and hold manually through the gears but have some respect for the old girl ... its not a BMW engine at the end of the day. ...

[vitesse]

Sure you can remove the flaps but it will be gutless lower down in the rev range. I have a ZS180 which has been de-flapped by a previous owner, one of the plans I have is putting in a standard manifold.

Regards

[SD1too]

Hello Alex,

Originally Posted by AlexF75

I don't (yet) have a problem with the intake manifold, but when I do ...

Err ... I think you mean if I do. The only fault which requires replacement of the manifold chamber (the black plastic assembly as opposed to the inlet manifolds which are aluminium) is damage to the power valve linkage. If you keep your VIS actuators in working order this shouldn't happen.

Originally Posted by AlexF75

I'd like to know whether completely removing the flaps would make a positive or negative influence on the engine performance and economy.

Negative. The VIS system tunes the inlet tracts to smooth the peaks and troughs in the torque graph. It's well known that when the balance flap sticks partially open, the engine torque noticeably suffers. Imagine what will happen if it's removed completely.

Originally Posted by AlexF75

If you have any cheap ways to slightly improve performance of this engine, please don't hesitate. I'm only thinking bolt-ons though, no taking the engine apart for modding internals or anything of that scale.

There is a cheap way to restore engine performance but not via "boy racer" bolt-ons I'm afraid! If you're curious, here are the details.

• Check that the balance flap can move freely and isn't sticking partially open (a common fault).
• Check that the power valve linkage is also free to move with minimal play.
• Check that both actuators are operational.
• Remove the cam covers* and clear the blocked pinhole in the breather circuit to be found underneath the gauze filter.

* This is definitely a job for whoever services and repairs your car.

Best wishes,

Simon

[ZedTeeT]

The long and the short of it is, don't bother if it's all working, you'll gain hardly anything, if anything at all, right up the very top and loose plenty low down. Why would anyone want that, the overall drivability would be much reduced. The KV6 has its limitations.

[trikey]

Debs old 180 had the flaps removed by a previous owner, no low down power at all, the top end was ok if you were thrashing it!

I swapped the manifold for a standard one and the low down torque was restored.

[AlexF75]

Thanks loads for your tips, it's clear in my head now! I'll just keep it working then. Fortunately I received three replacement VIS motors that work with the car, so that's a plus.

Not too bothered by the "lower performance" than my previous cars, I usually just cruise around with my 75 as that's what it does best - but I do occasionally go to the deristricted German autobahn with it, and that's where I sometimes wish it had some more power.

Not a BMW engine though, that's true! I love the character of the KV6 and much prefer the sound it makes to the straight 6 of BMWs that I had and have, but those engines were absolutely bulletproof, my 46 had 400k kilometres without any major engine repair ever, 36 running close to 300k so far not even any oil consumption. Not sure this can last that long, but I'll do my best to make it do! 170k kms as of yet though so I have to keep it long to make it there, so far I love it and much prefer it to the 46 it replaced in my "fleet" so we'll see

[trikey]

Still plenty of miles (Or Kilometres) Left yet in your KV6, some have done well over 200k miles.

[xsport]

yes R40 built for comfort not speed. the ZT models were better suited for a drivers car and hold the road well. lovely cars the 75 for the motorways where they seem to be at their best. ...