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      01-29-2020, 07:51 PM   #1
patsgarageonline
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BMW blocked the air intake on the i8 with a flap!

I read in the technical training guide that there was a flap installed on the intake side of the air cleaner of the BMW i8 internal combustion engine. This flap closes on the performance side of the intake between 3000 and 4500 RPM in order to quiet an annoying noise. There is another path that air can enter the intake, but this is a smaller hole. I removed the flap and didn't notice any annoying noises. I can hear the turbo a little bit better, rather than the silence that would normally occur at 3000 RPM, but nothing annoying. I also looked at some online dyno graphs posted by tuners, and it looks like the flap negatively affected HP and Torque numbers. I think this flap is actually robbing the i8 of power. What are your thoughts?

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      01-29-2020, 08:31 PM   #2
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Let's see a before/after dyno...
Might reduce weight by a pound if you can remove actuator and cable.
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      01-30-2020, 01:29 AM   #3
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Assume the car isn't road legal at least in Germany with that mod. BMW will have had a reason to install it. If it's a technical reason you will find out sooner or later.
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      01-30-2020, 05:02 AM   #4
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I find it har to believe that bmw would spend the extra cost and weight on this device for no other reason than to suppress an annoying sound.
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      01-30-2020, 10:19 AM   #5
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From page 19, published by BMW http://rotory.com/bmw/I8.pdf

"The air inlet of the performance path is located behind the left wheel arch cover at the rear axle. It the end of the unfiltered-air pipe is an unfiltered-air flap, which is also the intake for the intake silencer. Via an integrated unfiltered-air flap controller the DME can control the unfiltered-air flap with help of a pulse-width modulated signal and thus close the performance path. This happens between an engine speed of 3000 and 4500 rpm. If the performance path is closed in this engine speed range, the intake is carried out via the acoustic path. This measure prevents an annoying, higher frequency noise."

I'd love to see dyno results but I don't want to pay for it. I can't really tell a difference. The MAF likely sees more of a charge and modifies the valvetronic to compensate. Oxygen sensors would give the data for proper combustion of the air/fuel mixture. So, I'm not sure if this will change many things at all. But only the charts could prove it. Maybe it gives an extra 1-2HP. But those dyno graphs from tuners show a dip and that's bothersome to me. I'm not sure why a country would forbid removing this flap since the flap is open during the other RPM ranges and there is another open-pipe for air.
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Last edited by patsgarageonline; 01-30-2020 at 10:24 AM..
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      01-30-2020, 11:31 AM   #6
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Great video Pat. Would be good if you can also have a look at alternatives to fixing the fuel door issue. Such as modding the flap to ignore the lock. Replacing the sensor is only really viable with a warranty.
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      02-03-2020, 11:24 AM   #7
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I remember when i had my Subaru Impreza, if you have the cone filter induction kit, its useless letting in more air unless you set up the fuelling correctly on a rolling road and generally have to have the car 'mapped'.

As BMW intended this 'flap' to control airflow, i think it will be the same situation?
I guess the software mapping guys would be able to advise more on that?
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      02-03-2020, 11:40 AM   #8
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Great stuff Pat. I enjoy watching your videos and appreciate your work. Thanks for this info.
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      02-03-2020, 12:08 PM   #9
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My assumption is that the MAF sensor should detect a larger air mass passing through the intake after the air cleaner, telling the ECU that there's 60% more air available. But, if the valvetronic is coded to ensure good mileage over performance, the extra air won't result in more fuel being added. Therefore, no more performance. But, I'm not sure.

Thank you, all for the comments. I appreciate it.

I've been looking into fuel door mods and the only thing I can come up with is removing the loop attached to the inside of the fuel door so that the pin doesn't prevent us from opening the fuel door.
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      02-04-2020, 07:06 AM   #10
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Has anyone actually had this car 'mapped'? Usually the turbo is good for another 20% of boost. Sure i've seen a couple on youtube going down that route to more power.

My subaru also had a MAF sensor like all modern cars. To make the most of the mods done, it had to be mapped. The difference was very noticable with the increase from 310 to 350 bhp.

Last edited by Swiss tone; 02-05-2020 at 04:16 AM..
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      02-04-2020, 07:33 AM   #11
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Pat, just noticed on your video that your shocker bellow cover is badly split top and bottom (approx 8:19 into the vid) like described on one of my other posts.

Seems common as made from very thin material but worrying that they arn't effective at keeping the dirt out. I guess the rods will corrode very quickly without protection and won't be cheap as a complete unit?

I am looking into a repair for this but waiting until the weather improved in the UK so i can give it a go. Not sure if yours look too far gone to repair though!

Have you any thoughts on a repair instead of a major strip down to change them? Some people have had them changed under manufacturers warranty if lucky to spot in time!
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Last edited by Swiss tone; 02-04-2020 at 09:06 AM.. Reason: Added pic
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      02-05-2020, 06:44 AM   #12
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Quote:
Originally Posted by Swiss tone View Post
I remember when i had my Subaru Impreza, if you have the cone filter induction kit, its useless letting in more air unless you set up the fuelling correctly on a rolling road and generally have to have the car 'mapped'. As BMW intended this 'flap' to control airflow, i think it will be the same situation? I guess the software mapping guys would be able to advise more on that?
I agree that adding a cone filter will actually cause some problems with the system. I've seen where an open air aircleaner has added an extra 1-2 HP on some cars while decreasing it 1-2 HP on other cars. I don't know what effect this is truly having since I'm not replacing the system, completely, from a closed air intake to an open one. I'm merely removing a programmed restriction in the factory plumbing. The question is whether or not the Valvetronic is also functioning as if the flap is restricting the airflow. Valvetronic is BMW's elimination of the throttle in the equation. The throttle is always open and a cam adjuster changes the cam lift on the intake side of the engine, turning each intake valve into it's own throttle plate. That's called Valvetronic and it ensures that charge air is available at the valves at all time to reduce delay under immediate acceleration, as well as control air flow during low engine load, to reduce gas consumption. From what I've read, there is no map that can alter this. The dyno charts I've included in the video show pre- and post-map tunes. The dip in the curve is still there before and after mapping the vehicle. So, either the flap can't be re-programmed to stay open or tuners just aren't aware of it. By removing the flap, a smart Valvetronic would compensate by seeing additional airflow at the MAF and meet throttle demand at the pedal with increased lift at the intake cam. Only a good dyno run would tell for sure.

Quote:
Originally Posted by Swiss tone View Post
Has anyone actually had this car 'mapped'? Usually the turbo is good for another 20% of boost. Sure i've seen a couple on youtube going down that route to more power. My subaru also had a MAF sensor like all modern cars. To make the most of the mods done, it had to be mapped. The difference was very noticable with the increase from 310 to 350 bhp.
The post-map dyno charts in my video show that the dip in HP and Torque is still there post-tune in the 3k to 4.5k range, so my feeling is that this flap is doing something to contribute negatively to HP and Torque. Or the Valvetronic is performing the same way, regardless if the flap is installed or not.

Quote:
Originally Posted by Swiss tone View Post
Pat, just noticed on your video that your shocker bellow cover is badly split top and bottom (approx 8:19 into the vid) like described on one of my other posts. Seems common as made from very thin material but worrying that they arn't effective at keeping the dirt out. I guess the rods will corrode very quickly without protection and won't be cheap as a complete unit?

I am looking into a repair for this but waiting until the weather improved in the UK so i can give it a go. Not sure if yours look too far gone to repair though! Have you any thoughts on a repair instead of a major strip down to change them? Some people have had them changed under manufacturers warranty if lucky to spot in time!
I wouldn't expect that the metal in the piston rod would corrode. It appears to be stainless steel. The seal between the piston rod and the shock housing, however, can get contaminated by debris, causing wear and ultimately a leak of hydraulic fluid. Under factory warranty, the repair for this is to remove the shocks, replace the strut boot, reinstall the shocks and realign. The front shocks require a special tool with a laser, prism and mirror in order to ensure proper alignment of the individual shock components during reassembly. However, several folks have done a DIY replacement of the springs, eyed the front shock components up, and reinstalled without issue.

I'm in the process of acquiring inexpensive replacement boots and want to develop a procedure to cut them lengthwise, install them over the i8 piston rod, and melt the cut back together using a soldering iron that has a flat blade on the end. These are available for folks that are doing "plastic welding" on components such as cracked bumpers on vehicles. I don't know how well it will work but that's my thought process at this time. This is the only one of my shock boots that is worn so badly.
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      02-05-2020, 09:15 AM   #13
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Good work on the flap mod Pat, very interesting.

With regards to the shock gaiters/bellows, most cars have these so they must be important and as you say, if not for stopping the rod corrosion, its to prevent muck getting into the shocker seal.

I was thinking on the same lines as you. Splitting one lengthways and offsetting against the split and secure with a tyrap?
The genuine part i have priced up and around £33 in the UK so about $43.

Using other gaiters or the type that are already split to fit on steering racks might be difficult to get a good tight fit?

Depends how badly split they are i guess to determine the best repair but i also thought:

1) 'Stitch' the split areas back together using a cord or lace then apply flexible adhesive or silicone sealant over the top.
2) If a small split, perhaps wrap round a ruberised tape like 'Arlon' Mox tape used in the aircraft industry that bonds to its self but this tape needs to be bound tight and the bellows might distort.

All 4 of mine have some sort of damage but i am worried about my local mechanics stripping down this area in case of causing more problems as past experience has made me causious about disturbing things unless absolutely necessary! Especially when they don't work on these cars very often and the time and effort involved.
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      06-01-2020, 02:28 AM   #14
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Yes thank you Pat!!!
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