[vadonchez]

Hi

I recently purchase VRSF catless downpipe for my Z4 35IS in order to run MHD V7.1 stage 2+ .

I read on another forum that 1M has highflow catted DP OEM compared to 135i or 335i.
For the Z4 35is it's not so clear, somebody says that z4 35i/IS have too highflow catted OEM DP like 1M, somebody says that it's not true....

Because i was not certain i purchased catless DP and installed them last week.

On the road to be honenst i can't feel few to any difference with my OEM DP...My logs looks exactly the same than before VRSF installation. The only thing that really change is exhaust sound. It's now louder on lower rpm with more burble.

For me it's a little bit too much, i was in loved with oem sound with exhaust flap always open by tee golf mod.

Today i took a look at my OEM DP here are some pictures:




From what i can see this is BOYDEN company that supplied DP for BMW.
I can read a reference 7 591 480 9. This reference isn't the one on realoem, i think that's a reference for the catted part only.

When i search for this PN on google I can found an OEM 1M DP and can see that the reference are identical:

https://www.kleinanzeigen.de/s-anzei...27261-223-1920

335i BOYDEN catted DP have another reference wich is 7 553 622 1 if i trust this link:

https://www.ebay.com/itm/37477160061...Bk9SR9bvgpKvYg

So my quick conclusion is that z4 35i and IS have same DP as 1M and they are less restrictive than 335i/135i ones.

You guys by seing my pictures, do you agree with me?

Does somebody have a picture from the cells into an OEM 335i or 135i DP to compare the cells density?

Regards

[studio54]

Hey,

I have a regular N54 135i and still have my old stock OEM DP so I went into my basement, both have the number : 7 553 622 1 on both of them.

And here is a pic of the inside if it helps !

[studio54]

Anyway I think you have the same DP as the 1M :

[vadonchez]

Originally Posted by studio54

Hey,

Yes, the 1M have a better airflow cat than regular 135/335.

I have a regular N54 135i and still have my old stock OEM DP so I went into my basement, both have the number : 7 553 622 1 on both of them.

And here is a pic of the inside if it helps !

Thanks a lot!!

On your picture we can clearly see that you have more cells than mine!
There is no doubt, Z4 35is have less restrictive DP than 135i/335i as 1M.

the only question that remains in my mind is Z4 35i DP, on realoem they are the same as 35is but the Z4 35i engine is the N54 not the N54B30T0 so why??

Maybe for budget reason because of small z4 35i/is sale quantity

I think I will put back my oem DP and sale the VRSF on ebay....

I think that my oem DP are ok for a modest V7.1 stage 2+ wich target only 17psi tapering to 12 psi at redline

[studio54]

Yep, I didn't count but it does look like I have more cells than your pic

Ask Carabuser he has a z4 too, and I am pretty sure he knows about it.

[CarAbuser]

Yes, the 35i cats are the same as that.

I don't know if they are less restrictive or not. I still have both my 335i and 35i cats in storage and they weigh about the same and got offered the same price for both from a cat buyer.

I also noticed a huge improvement in both spool and power when removing them from both cars so I certainly wouldn't entertain keeping the stock ones in. You can pass UK emissions testing without them as the secondary cats do enough work when hot.

For US readiness checks it's easy enough to tweak the tune to pass without cats, no need for DP fix or any messing around with hardware.

[vadonchez]

Thanks for your reply.
When you say 35i you lean 35is right ?

[CarAbuser]

No, just the 35i. 35i and 35is cats are the same

[vadonchez]

Ok

I agree that reference are the same on realoem but i would like to have both DP 35i and 35is in my hands to confirm that because 35is has n54b30TO and 1M technical training documentation says that 1M has same dp than 35is but this document dont speak about 35i....

I was thinking that your z4 was a 35is.

[CarAbuser]

Originally Posted by vadonchez

Ok

I agree that reference are the same on realoem but i would like to have both DP 35i and 35is in my hands to confirm that because 35is has n54b30TO and 1M technical training documentation says that 1M has same dp than 35is but this document dont speak about 35i....

I was thinking that your z4 was a 35is.

Well if yours is a 35is and those are the cats that came installed then they do have the same ones as mine have the same ID and BMW part number.

Sealed by Boysen, coated by Delphi and sold by NGK.

[studio54]

I edited my post cause I don't want to spread misinformation and I am not sure anymore that the 1M has better flowing cat ?
Some reading :
https://www.1addicts.com/forums/show....php?t=1438926

And vadonchez I know I am a bit crazy, so I counted cells on your picture, then on my picture, and it does look like we have the same amount of cells.
(Comparing quickly two pictures was misleading)

[vadonchez]

Okay thanks.

And when you look at inside cells did you see any differences between 35i and 335i?

I dont really feel huge diference in spool or power between my oem DP and vrsf one....

[vadonchez]

Originally Posted by studio54

I edited my post cause I don't want to spread misinformation and I am not sure anymore that the 1M has better flowing cat ?
Some reading :
https://www.1addicts.com/forums/show....php?t=1438926

And vadonchez I know I am a bit crazy, so I counted cells on your picture, then on my picture, and it does look like we have the same amount of cells.
(Comparing quickly two pictures was misleading)

Sorry i had'nt Saw your post reply....thanks
So why BMW Said into 1m technical documentation that downpipe are the same as z435is ans different from 135i/335i ones....
And why cat reference are the same on 1m and 35i/is
And different from 135i/335i....

[studio54]

Originally Posted by vadonchez

Sorry i had'nt Saw your post reply....thanks
So why BMW Said into 1m technical documentation that downpipe are the same as z435is ans different from 135i/335i ones....
And why cat reference are the same on 1m and 35i/is
And different from 135i/335i....

Honnestly, I don't know :

- Maybe 1M/35i-is and 135i/335i have different catalytic converters
or
- Maybe just a different design to have a more sporty "sound" but same catalytic converters

What we can do, take your right downpipe :

If you want to be sure of the number of cells, cut a 2.5centimeters per 2.5centimeters (1inch square) of paper square and put it anywhere on the cat surface (aligned to cells), take a picture, and count the number of cells for 2.5centimers, then multiply this number per itself and we will know the CPSI.

Measure the circumference of the catalytic converter case/can with a string,

Measure the lenght of the case, weld to weld.

I will do the same and we can have a definite answer about the catalytic part at least.

(That said, on Google images, the downpipe of 1M vs 135i look identical?)

[vadonchez]

ok you're right, you're crazy

Good news IS that me too.

I will try your idee today and let you know my discovery !

[vadonchez]

ok time for science!!

I made some measurements and that's the result:

Both CATted parts from my OEM Z435IS DP are 11cm length (4,33inch):



For the diameter measurement, i cut a strip of paper and adjust the length until to reached the right dimension. Result is a diameter of 9cm (3,54inch):




For the measure of the cells density i cut a square paper of 2X2cm and I found that into this area I have 19x19 "cells":




Ok let's go for the math:

Total area is PIxR^2= pix45x45= 6362mm2

I have 19x19=361 "cells" into 2x2cm wich is 400mm2

So i have (6362/400)x361= 5740 cells in my oem catted DP.....


When we are talking about catalytic converter cells density it's for 1 square inch wich is 645mm2.

SO if I have 361 cells into 400mm2, then I should have (645/400)x361=580cells per square inch

It seem's that my OEM DP is a 600cells catalytic DP.

[studio54]

Hello,

I did the measures :

Lenght of my case is 10.5mm strictly between weld to weld, according to the picture, you measured a bit differently so we should be equal I think.

I used 2.54cm square (I tried to cut as much precise as possible but you know there is some margin error), not a 2cm, and I have 25 or 26 cells (cause I cut it maybe a little large). If I used a 2cm square, I think I will approximatively have around 20 cells. I imagine cats are either 100/200/400/600/800, so 135/335 primaries are most likely 600 cells cats (same density as for the secondaries, I made the measure in the past).

(The unity used to measure cells density is CPSI (cells per square inch), so you have to base your measure with an inch (2.54cm), not 2cm. The diameter of the pipe doesn't matter, just put a 2.5cm x 2.5 cm square on the cat surface and count a row of cells.)

The true circumference is around 32.3cm (I couldn't tight the string while taking the picture).

Try to make a paper square as much as possible close to 2.54mm and take another pictures so we can count it

[vadonchez]

Ok

I made the same method than you with a 2,54X2,54cm square paper and I have 25x25cells so 625cells:



My first calcul gave me 580 cells, this one 625cells so I think we can conclude that we both have a 600cells catted DP.

So we can confirm that BMW lied in her technical 1M documentation by saying that 1M and 35is have different catted DP than 135i/335i....

Maybe 1M hav a less restrictive catted DP than 35is but because of the same reference from BOYSEN supplier, i have to say that i have my doubts about that....


A last note:

From what I can see from your picture and mine, it seem's that my cell is more "square shape" than yours....do you agree with that?
My mind is that maybe we both have 600 cells but each of my cell are more empty....

[studio54]

Yes, I measured number of cells vertically and I have 25 cells as well, on the horizontal count maybe the angle of the picture makes me doubt if it's 25 or 26 but maybe my paper isn't really well cut. When I measured the secondaries, the density was the exact same : 25x25 = 625 cells, so I think 25x25 is correct for both primaries and secondaries.
( for reference : https://www.1addicts.com/forums/show....php?t=1856881 )

I don't think the 1M has a different catalytic converter than your Z4 35is, I just now believe the 1M having more airflow cats is just a myth.

[vadonchez]

could you take a more high resolution picture to confirm my mind about cell shape?

[studio54]

my phone is a bit shitty, if I look at normal distance with eyes, it seems to be square, but I look very closely, you are right it looks like circles.

I tried to take pics with the sun but it's the best I could got.

I think now you have spotted the difference, square will let pass more air than circle, and that's make the difference in airflow then?

If CarAbuser have both 335 and Z4 cats in hands, maybe he could see if the pattern is different.

[vadonchez]

yes it's certain now that they are not exactly the same.

I think that design is not the same even if total cells number is the same.

This is why bmw talk about difference between 1M/35is and 135i/335i