Background:
In a Mk8 owner’s Facebook group, I saw one of those posts where somebody asks, “Is a downpipe needed?“
Some of the answers the person got were the following:
Even a couple of representatives from businesses had comments about the Mk8 downpipe:
Note: I’m not sure what Tyler At IE meant when he said the Mk8 turbo doesn’t have the restrictions older platforms (turbos) did.
Question
While the comments sounded good and well-informed about the properties of the Mk8 downpipe, I was curious about what had changed to produce a different outcome from the Mk7.
A quick search led to a picture of the MK8 downpipe and its catalytic converter.
The catalyst section off the turbo looks similar to that of the Mk7, but as a couple of commenters had stated, a more modern DP is improved, is more efficient, has thinner cells, and has higher flow rates.
However, the Mk7 has a component missing from the Mk8 DP in that picture: a second catalytic converter.
Oddly, nobody in the discussion, enthusiasts or Tuner reps, mentioned that the Mk8 has a single catalytic converter off the turbo. In contrast, the Mk7 has a similar catalytic converter but an additional one just past the flex joint.
Might adding a second catalytic converter reduce airflow compared to a downpipe with a single catalytic converter?
That’s a rhetorical question; of course it does. The cat is the exhaust’s most restrictive component, and the Mk8 has “half” the amount of catalyst restriction that the Mk7 does.
It’s no surprise that, according to these and other reports, the Mk8 performs better with the stock DP than the Mk7 does.
Conclusion:
Reports of improved performance from the Mk8 downpipe compared to the Mk7 have cited technological advances in the design when the most likely cause of the change is the elimination of the Mk7’s second catalytic converter.
One thing about “stage 2” files for a DP I have always had is…is it really just a stage 1 tune adding the DP is where the little extra hp comes from or is it actually meaningfully different from a tuning (boost/fuel/timing) perspective? I agree…1 cat vs. 2 is the likely source of the extra flow here. The one IE comment regarding “stage 2” being for an intake/intercooler goes back to my first question – is it actually any different than running their “stage 1” tune and just having the extra bolt-ons?
I can only speak from my experience from swapping from the Baun/GESi downpipe to a catless DP. In that case the reduced back pressure made it possible to increase the boost pressure, and that increased the power output. I presume many tuners would use the back-pressure reduction to make some more power.
That’s one obvious explanation. But does the Mk8 downpipe not having the indent the Mk7 does right after the turbo also improve flow rate?
https://i.imgur.com/R9J7nLM.jpeg
Just guessing, probably not in a meaningful way.
Have you thrown it on the flow bench yet? I’m interested to see the exact number difference between the two. If it’s a cost effective solution for the MK7, I’d consider picking one up.
No, unless someone offers one up who can deliver it to me I don’t have any plans to try and acquire one for testing.