How far can you go with a stock or maybe modified Z4 35is N54 airbox?

pbondar

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May 30, 2020
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I‘ve ordered a pair of TTE 500 turbos for my Z4 35is N54..


Looks like they may be good for 500WHP/550BHP with suitable support on 98-100 Ron petrol.

I’m not keen on DCI primarily due to their poor filtration and since this car is destined to be a high mileage street sportster I’d prefer to keep the paper filter.

As I understand it the 35is plumbing is ‘better’ than that found on the 1/3 series powered cars.

I see some people have attached an extra air intake direct to the box with some plumbing to get fresh air in.

it’s asserted via the DCI guys that sucking warmer air in the engine bay has a negligible effect on performance compared to the compressor/ intercooler issues.

So my questions are..

How much of a theoretical say 550 BHP would I lose with a stock airbox?

What would be wrong with drilling a number of holes on the inlet side of the airbox to increase flow to the filter?

Any other solutions I’m missing?
 

carabuser

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I think the restrictions are primarily at the inlets and outlets of the turbo.
 

Torgus

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Those turbos should make around 500whp on 98RON or 93 here in the states. I would call that 600 BHP. If not add some meth and you will easily get there. The main advantage is these will be pulling to redline ;)

Why do you say DCI have bad filtration? They have more filter element that the stock filter by far. Even when they 'look' dirty as fuck if you pull them off and look inside the inside filter element is not dirty, meaning they are filtering well. This is from my experience ymmv. They are cheap to replace and you can always clean your second set and have it ready to swap out every 6 months if you are anal and want a 'clean looking' filter element as one of my friends does.

As said by @carabuser get inlets and outlets 1st. Get your tune set. Then you can start logging and experimenting with taking the cover off etc. Personally I would just run DCI w/ inlets and outlets. It is the most tried and true way on the stock twins to give them the least restriction. The last thing you would want is the paper filter to be a restriction causing the silicone pipe to collapse under vacuum.
 
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pbondar

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May 30, 2020
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Those turbos should make around 500whp on 98RON or 93 here in the states. I would call that 600 BHP. If not add some meth and you will easily get there. The main advantage is these will be pulling to redline ;)

Why do you say DCI have bad filtration? They have more filter element that the stock filter by far. Even when they 'look' dirty as fuck if you pull them off and look inside the inside filter element is not dirty, meaning they are filtering well. This is from my experience ymmv. They are cheap to replace and you can always clean your second set and have it ready to swap out every 6 months if you are anal and want a 'clean looking' filter element as one of my friends does.

As said by @carabuser get inlets and outlets 1st. Get your tune set. Then you can start logging and experimenting with taking the cover off etc. Personally I would just run DCI w/ inlets and outlets. It is the most tried and true way on the stock twins to give them the least restriction. The last thing you would want is the paper filter to be a restriction causing the silicone pipe to collapse under vacuum.
Thanks for your comments and observations…

Reference the filters , the primary issue that has been much reported is the amount of dirt passed by those cone / K+N type filters..

The consensus seems that on a tuned car, the DCIs may give a very small advantage…the question in mind is whether that few ponies is worth the possible long term engine damage?

some pictures from the much discussed test..
 

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JohnDaviz

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Jan 6, 2019
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With my car, HP650s, 2" inlets, Hydra outlets at 21psi the DCI reduced WGDC about 3%. IMHO this is a significant number.
Also in high rpms i now have stable boost vs declining on stock airbox without touching the map.
 

RuskiRacer

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Where is the engine damage coming from using a air filter? Many single turbo guys including myself dont use a filter. Some don't even use a screen. Alex merkeshkev doesn't even use filters on his dynamic autowerks and they've been doing really well for him for many miles and his is a street car
 

pbondar

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Where is the engine damage coming from using a air filter? Many single turbo guys including myself dont use a filter. Some don't even use a screen. Alex merkeshkev doesn't even use filters on his dynamic autowerks and they've been doing really well for him for many miles and his is a street car
I can’t speak for automotive engines as I’ve always used stock type air filters …I did use lots of K+N filters in my various bikes I had, some 24 of them..

On aircraft engines we used to sample the oil at each change and have it analysed.

What we saw was that engines that injested dust had elevated levels of wear on bores shown as excess iron residues plus there was bleed over residues coming from plain bushes, copper and aluminium as the dirt particles work their way past the rings etc.

I guess I’d put it the other way…why does an OE manufacturer spend a lot of money building air boxes and filters if they didn’t do something?

Strange my Jeep friends swear by stock boxes with OE filters..
 

RuskiRacer

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Oe isn't going for power. As the box was designed to flow about 280hp worth of air. Will it work up to 500 whp sure but will it be a restriction maybe. Unless you live on a gravel road or rally drive your n54 I don't see the need to shy away from dcis I've never seen a n54 fail from having dcis no matter how dirty they looked from the outside. Id be more concerned about carbon buildup on the intake valves and breaking off and entering the motor than I would be dust.
 

fmorelli

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Not all DCI are the same. Not a fan of K&N. AFEPower are much better on filtration from my recollection of testing.

Manufacturers build an airbox, in part, because air intake noise is significant, and an airbox reduces that sound.

Nothing wrong with paper filters, as a rule of thumb. That said, I'm unaware of anyone that has tested and categorically answered your original question.

On the Z4 there have been some alternate solutions put together using the later 740i N54 airbox and custom inlets to the turbos. There are posts here on Spoolstreet. Then again, no testing.
 

carabuser

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I don't think there's any gain to be had from DCI, the Z4 airbox is better flowing already. WGDC is too variable to be a useful measure, I get quite large swings in WGDC just depending on the time of day due to air temps, humidity and atm pressure.

The stock airbox is so neat compared the those blingy cone filters. I think if you're going to spoil the engine bay with something like that you'd be better just doing relocated inlets to get rid of the pipework behind the engine.
 
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JohnDaviz

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Not all DCI are the same.
I don't think there's any gain to be had from DCI

If you take quality DCI´s you get an improvement. Not speaking of those cheap ones. Don´t even know which ones are cheap. I searched for a long time and found a quality supplier who makes ones like Injen. These are top notch 8-Layer oiled Cotton Gauze

The 335 airbox became restrictive on my car and i have it proven in my logs for myself. Too lazy to cut the logs together to present, but this is my experience.

Wonder what is different from the 335 airbox to the z4 airbox.

So 335 stock intake vs. Quality DCI there is big gains. I had to re-write my WGDC Base map new as it was mapped close to after PID.


This is a log after i switched to to Injen Styl filters. Before After PID was always below Base.
 
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pbondar

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May 30, 2020
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Thanks for the comments ref air box..

I think I’ll do a fit n tune with the stock box n filter and get a dyno run..fortunately I have relatively easy access to a dyno which I’ve used many times.

Whilst I’m there I’ll pop the cover and filter off the airbox and see what gives…

I realise without a re-tune it may not show much..but I’ll take it from there 👍
 

Tzaks

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May 30, 2019
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I have a Z4 with hybrids and testing on the same bit of road, same day, same conditions, I am 0.2-0.3 faster 60-130 (dragy) with DCIs over stock airbox with K&N filter. The K&N filter definitely allows more air through so I'd imagine the results could be even worse with the OE paper.
 
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pbondar

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May 30, 2020
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I have a Z4 with hybrids and testing on the same bit of road, same day, same conditions, I am 0.2-0.3 faster 60-130 (dragy) with DCIs over stock airbox with K&N filter. The K&N filter definitely allows more air through so I'd imagine the results could be even worse with the OE paper.
Interesting thnx…

I’ll stick to my original plan with stock airbox n filter at this stage…

I will get the upgraded plumbing to/from the turbos and the VSRF charge pipe, plus TMAP sensor and some fresh (Forge) DVs..

I’m not keen on the induction roar of DCIs…so with paranoia about dirt / dust and the noise I’ll go down fighting looking at the other options..👀🙈😂

I may look at extra vents in the airbox plus hi-flow drop in filters..

Work by others suggest holes in air box plus higher flow drop in filter gave good results too..

Also it’s suggested that getting the plumbing sorted out all the way through scores a higher result than the DCIs..

Good news is that the dyno is not that far away and we can ‘play’ a few options over time 👍
 

RSL

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Aug 11, 2017
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Increasing the pressure going into the stock box (scoops) will have the same pressure ratio effect for turbos as DCI or Mr.5, probably more.

Do inlets for sure and add scoops with the stock intake, if they make them for Z. Once you're running the turbos with some decent boost, it would cost $50 and take 5 minutes to toss used DCI in for quick back-to-back tests against the closed system. Even if you don't plan to run them, you won't have to guess or rely on presumptions.

I've tried everything there is, except hot side inlets, and have run stock box with paper filter for the last 2 years (with scoops and inlets).

Scoops won't show on a dyno, the car needs to be moving. Shop fans/blower can barely recreate front end air flow at low speed, let alone 100mph+. Use virtual dyno and log in the same place for all. 3 with box, swap DCI in a parking lot, 3 logs same place and compare averages.
 
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pbondar

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May 30, 2020
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Increasing the pressure going into the stock box (scoops) will have the same pressure ratio effect for turbos as DCI or Mr.5, probably more.

Do inlets for sure and add scoops with the stock intake, if they make them for Z. Once you're running the turbos with some decent boost, it would cost $50 and take 5 minutes to toss used DCI in for quick back-to-back tests against the closed system. Even if you don't plan to run them, you won't have to guess or rely on presumptions.

I've tried everything there is, except hot side inlets, and have run stock box with paper filter for the last 2 years (with scoops and inlets).

Scoops won't show on a dyno, the car needs to be moving. Shop fans/blower can barely recreate front end air flow at low speed, let alone 100mph+. Use virtual dyno and log in the same place for all. 3 with box, swap DCI in a parking lot, 3 logs same place and compare averages.
Thanks for your comments and advice…

i have a brand new set of VSRF DCIs so as you say pretty easy to check out..👀

I’ve got a gps logging box as well MHD/xHP/Protool so should be able to get some logging done…😳

We don’t have any flat open roads but plenty of long fast climbs so I’ll use them for the a/b/c comparative testing 👍