Z4 e89 N54 Downpipes with race-cats and silicone intakes.

Armando1969

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Dec 10, 2020
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I want to take the next step in the tuning of the engine , but I have some limitations to do this.
I live in the Netherlands, that means I can't eliminate the cats in the downpipes, because then the car will fail it's yearly inspection. But downpipes with race-cats are almost impossible to find (at least in the Netherlands), so I decided to try to get something constructed.
For that goal I bought VRSF downpipes with race-cats for a 335I and downpipes without race-cats for the Z4 with N54 engine. Let's see if we can get a decent marriage of the two.

I just got the parts in and my first conclusion are:
- One of the downpipes for the Z4 is longer.
- The flange to bolt the downpipes to the rest off the Exhaust are 90 degrees offset for the z4 in comparison to the 335i.
- I don't know jet how well they will fit on the car, but the quality looks very good, nice welding and general appearance.

PS: I also got silicone turbo intakes and I am still waiting for the metal turbo outlets.
 

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Armando1969

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Dec 10, 2020
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Here you can see the off-set off the flanges.
 

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Armando1969

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Dec 10, 2020
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It is hard to see, but the downpipes for the Z4 N54 are longer.
 

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Krampus

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Aug 8, 2020
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Finland
I solved it myself according to the picture. Matching flange with four bolt holes. At first it was just bolted, but later I welded the flange to the DP and cut off the extra bolt holes. The connection was difficult with just bolts, so welding the flange directly to the 335i dp made sense. It was easy to weld with two bolts holding the flange in place. Flanges are easy to find.
 

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Armando1969

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Dec 10, 2020
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I solved it myself according to the picture. Matching flange with four bolt holes. At first it was just bolted, but later I welded the flange to the DP and cut off the extra bolt holes. The connection was difficult with just bolts, so welding the flange directly to the 335i dp made sense. It was easy to weld with two bolts holding the flange in place. Flanges are easy to find.
Thanks for the tip.๐Ÿ‘๐Ÿ‘
 

Armando1969

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Dec 10, 2020
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Do those have a wire in them? I decided to go with the RB ones just to be sure.
I think so, Just checken them and the ends were they connect to the turbo's are very soft so they make a good seal. But when I try to squeeze the rest of the tube it feel very rigide.
Hope this helps
 

Dumaurier7

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May 19, 2020
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They've been known to collapse under high boost so the ones with the spiral wound wire in the wall are preferred.
 
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Armando1969

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Dec 10, 2020
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They've been known to collapse under high boost so the ones with the spiral wound wire in the wall are preferred.
Just checked and their data-sheet says they have Reinforced Wires.
Below is the link to their website.

 

Hejnfelt

New Member
Jul 30, 2023
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Very cool solution, @Krampus you also bought the catted 335 downpipes and fitted them successfully to your Z4? I am in Estonia and thinking to follow this same solution you showed. Did you just use at 4 way flange with 90degree spacing off the shelf?
 
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Krampus

Specialist
Aug 8, 2020
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Finland
335i DPs have been installed for 3.5 years. At first, the flange and pipe were attached with four bolts, but it was not good and I mentioned this earlier. It was difficult to get the gaskets to hold and at the time you needed two of them in one pipe. I put the flange on the DP by welding and cut off the extra bolt holes. The welding was easy to do because the bolts held the flange in just the right position. The Z4 DPs are a bit longer than the 335i DPs. Welded flanges help with that.
Flange
The dimensions of the flange are the same as in the link, but I chose stainless steel. I don't know if the link flange is stainless steel. Yes, you can find flanges if you are willing to look for them.
I believe for sure that you can order the flanges in Estonia like I did in Finland. I don't remember where I ordered the flanges from. You can probably find it at a good local hardware store or auto parts store.
 

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Hejnfelt

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Jul 30, 2023
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Thanks thatโ€™s exactly what I was hoping you would say. From where did you buy the VRSF 335i catted downpipes in Europe?
 
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Armando1969

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Dec 10, 2020
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Thanks thatโ€™s exactly what I was hoping you would say. From where did you buy the VRSF 335i catted downpipes in Europe?
 

Armando1969

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Dec 10, 2020
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Finally got round to putting everything on the car, some insights from that:
1 You just need the 335i downpipes with race-cats (so now I am left with the new downpipes for the Z3.5i๐Ÿ™„, anybody need those? ). You just have to saw off the flanges, rotate them around 90 degrees and weld them back on.
2 Despite the race-cats in the downpipes, the O2 sensors gave a fault warning. When I went to stage 2+ on MHD and selected aftermarket downpipes, the warning light went away. But it's still logged in the system as a fault.
3 Sound: very subtle change, a little bit louder than before. Till you step on it, then you get a very deep growl. ๐Ÿ™‚
4 The difference between stage 1+ and 2+, I can feel there is more power. Just had a short drive and the roads where wet. But when is stept on it in 3th (manual car) gear the traction control immediately came in, it didn't do that before.

End conclusion, I am happy with the result. Not to loud, but a nice subtle muscular sound. Plus nice power gains.
 
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Armando1969

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Dec 10, 2020
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Also put the VRSF Turbo outlets on, they don't add much at the power-level I am now. But when your doing the downpipes and intakes why not go all the way and add the outlets.๐Ÿค”
 

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pbondar

Sergeant
May 30, 2020
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Unless you dyno, then change h/w, adjust tune for that mod and dyno youโ€™ll never know what each change in isolation does..

Mine with with stock pipes and stock inlets etc did 389bhp..then with decat it did 399โ€ฆit was v9 vs v10 but later we saw both v9 and v10 gave same peak power on the same day..

DCIs added 6-7 BHP..

So my guess until you are heading past 450 BHP crank is that most of the stock systems do quite a good job๐Ÿ‘Œ
 
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Armando1969

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Dec 10, 2020
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Unless you dyno, then change h/w, adjust tune for that mod and dyno youโ€™ll never know what each change in isolation does..

Mine with with stock pipes and stock inlets etc did 389bhp..then with decat it did 399โ€ฆit was v9 vs v10 but later we saw both v9 and v10 gave same peak power on the same day..

DCIs added 6-7 BHP..

So my guess until you are heading past 450 BHP crank is that most of the stock systems do quite a good job๐Ÿ‘Œ
I think you are right, but I was in there and then it's not so much extra work. Also price wise it's not to extreme, that's really why I did it. ๐Ÿค”๐Ÿ‘๐Ÿ‘
 

pbondar

Sergeant
May 30, 2020
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I think you are right, but I was in there and then it's not so much extra work. Also price wise it's not to extreme, that's really why I did it. ๐Ÿค”๐Ÿ‘๐Ÿ‘
Would be churlish not to do soโ€ฆon the same logic surprised you didnโ€™t slip a pair of nice hybrids at the same time ?๐Ÿ™ˆ๐Ÿ˜ณ๐ŸŽ๐ŸŽ๐ŸŽ๐Ÿ‘Œ๐Ÿ˜‚๐Ÿค”
 
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