Air box restriction testing.

martin33100

Veteran Member
Joined
Oct 13, 2015
Location
UK
TDI
VW T5 2.5
Hi, I am having my VW T5 2.5 PD mapped on Friday as I have just fitted a hybrid turbo and tubular manifold.

As I have an accurate negative pressure meter for setting up boilers I have fitted a measuring test point in the top of the airbox to see how restrictive it is at the top end.

Just wondered at what amount of negative pressure would you start to restrict power?
 

Markus L

Veteran Member
Joined
Feb 12, 2015
Location
Finland
TDI
Caddy (14D) 1.9TDI 2-stage 400+bhp, Passat 3BG 4motion AVF
Some engine manufacturers allow 35 mbar. With ~70 mbar the intake piping is usually going to collapse.
 

hey_allen

Veteran Member
Joined
Nov 25, 2006
Location
Altus, OK
TDI
2000 Jetta TDI
There were a set of performance articles written for an online auto magazine in Australia a few years back which included a write-up on the intake restriction of a Skoda 1.9 TDI.
Their testing showed initial restriction of ~14 in/water peak, and averaged ~12" cruising.

That said, after the whole set of articles, and dyno testing before and after various tests, they found that they barely gained any power, and initially lost power after opening up the intake restriction.

This is not to say that you can't gain any performance, but you may find that the manufacturer actually did their homework and tuned the car accordingly.

Here are the 5 articles that were posted on the subject:
http://www.autospeed.com/cms/A_113074/article.html
http://www.autospeed.com/cms/A_113075/article.html
http://www.autospeed.com/cms/A_113076/article.html
http://www.autospeed.com/cms/A_113077/article.html
http://www.autospeed.com/cms/A_113078/article.html
 

Digital Corpus

Top Post Dawg
Joined
Mar 14, 2008
Location
Ontario, California
TDI
'97 B4 w/ 236K mi body, 46K mi soul
Since you're turbocharged, the intake restriction does matter a bit more. If you're at 70 mbar of restriction, this limits the output of the turbo and its highest absolute pressure from its pressure ratio. I'm running 30 psi in boost and if I had 70 mbar restriction at STP, that goes from a PR of 3.04 to 3.27. Change that up to 140 mbar, and you have 3.53.
 

martin33100

Veteran Member
Joined
Oct 13, 2015
Location
UK
TDI
VW T5 2.5
Just done my first test

Just tested the standard OE air box, I have just under -18mbar in the top of my airbox at max revs at WOT.
Is it worth trying to improve or just leave alone?
The OE airbox was designed for 130 or 174hp, I am currently at 245hp.

Video link below

 

Markus L

Veteran Member
Joined
Feb 12, 2015
Location
Finland
TDI
Caddy (14D) 1.9TDI 2-stage 400+bhp, Passat 3BG 4motion AVF
You should measure closer to turbo's intake to see also the restriction of MAF and intake pipe. -18 mbar is not bad for the airbox only.
 

Digital Corpus

Top Post Dawg
Joined
Mar 14, 2008
Location
Ontario, California
TDI
'97 B4 w/ 236K mi body, 46K mi soul
That's a manometer and it uses a differential pressure gauge. It doesn't matter if he takes the reading before the MAF or at the turbo inlet, as both will be the same.

Martin, is that a clean filter? I have less than a 5 mbar drop @ 20 lbs/min airflow. What is your maximum pressure and what altitude do you live at? Rounding to 20 mbar, if you had a PR of 3 on the turbo at 1000 feet, your PR is effectively 3.06 with that restriction. Once you hit 30-40 mbar, consider changing the air filter. Other methods of reducing the restriction is adding a few holes to your intake box, fwiw.
 

Yucca

Veteran Member
Joined
Apr 13, 2007
Location
Finland
TDI
ALH 388bhp, Polo 6R 2.0TDI CR GTC1752VZ
I have dyno tested restrictions of Polo 6KV ALH airbox, it is worse than Golf mk4 airbox. Polos airbox did not restrict power at 300bhp power level. When polo made 330bhp restriction was -10bhp. So only 320bhp with polos original airbox.

I think that Golf airbox can flow approx 350bhp, but it will limit big turbo spool before that...
 

martin33100

Veteran Member
Joined
Oct 13, 2015
Location
UK
TDI
VW T5 2.5
Just an update if anyone is interested, my OE airbox with a 90mm cold air feed and just over 300hp now give a 24.5mbar restriction.

Just for a test I fitted a Honda S2000 cone filter straight onto the MAF and this restriction went down to 3mbar!.
 

turbovan+tdi

Top Post Dawg
Joined
Mar 23, 2014
Location
Abbotsford, BC.
TDI
2003 TDI 2.0L ALH, auto, silver wagon, lowered, Colt stage 2 cam, ported head,205 injectors, 1756 turbo, Malone 2.0, 3" exhaust, 18" BBS RC GLI rims. 2004 blue GSW TDI, 5 speed, lowered, GLI BBS wheels painted black, Malone stage 2, Aerotur
Just an update if anyone is interested, my OE airbox with a 90mm cold air feed and just over 300hp now give a 24.5mbar restriction.
Just for a test I fitted a Honda S2000 cone filter straight onto the MAF and this restriction went down to 3mbar!.
Wow, great info, thanks for posting.
 

martin33100

Veteran Member
Joined
Oct 13, 2015
Location
UK
TDI
VW T5 2.5
And what is the particulate size and surface area between the two?
I haven't bothered to work out the area yet but it has more surface area than the OE panel filter, on a Honda S2000 it does still go inside a airbox.
It's a paper element so should filter as well as any other OE paper filter, a few people use them as an upgrade as the neck is 80mm ID, common VAG MAF size.
 

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
My current filter is from an 09-11ish ford escape
it's an 6" OD cylinder with one closed end and a 3" ID outlet
mashes over the various 3" ID maf sensors and has a good amount of area to it, currently it's tied to my intake using safety wire twisted through the metal mesh outer liner of the filter.

I'd have used the stock airbox, but didn't have room for it any more... :\
 

martin33100

Veteran Member
Joined
Oct 13, 2015
Location
UK
TDI
VW T5 2.5
Just an update if anyone is interested, I found the standard MANN paper filter to work the best with the bottom of the airbox removed, I also used some insulated foam sheeting to block of the back so no warm air can be sucked in from the back of the engine/turbo etc.
Peak power with this setup was 335hp, with a K&N big cone filter fitted direct to the MAF it lost aprox 5hp.
 
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