ptuomov

It will be a challenge for future generations to fit a bigger exhaust under 928 that is structurally sound and that doesn't drum!

infinity pipe:

ptuomov

Here is the cat to infinity pipe transition, or rather the planned one:

ptuomov

This will fly way under that kind of radar screen. More to the point, with stock intake manifold and dual 3.5" exhaust it'll be just like Sir Mix-A-Lot said:


"L.A. fits with Oakland booty"

BauerR

Why bother with catalytic converters?

ptuomov

For the same reason that explains the whole project: Because I can. ;-)

More seriously, those cats together will flow enough for the pump gas tune, so there's not loss. They will also knock out 4-5 dB of noise over a broad frequency band. They will clean up the exhaust gasses.

Here's an estimate of how much a (generic) cat will quiet the exhaust:





Finally, it's just an option: they are v-band clamp attached and I can put in straight test pipes whenever downpipe pressure would otherwise get a bit higher than desired. Optimally exercised, options are valuable, right?

ptuomov

On the infinity pipe area: For reference, ignoring the wall thickness, dual 3.5" pipe gas area of 19.2 sqin. The infinity pipe with 6" overall width and 1/2" segment taken out from both pipes will have an area of 17.6 sqin. It's only a 8-9% area reduction after the gas has already cooled somewhat and after the pulses have already combined. My judgment is that it's never going to be a bottleneck in a system that is dual 3.5" upstream of the infinity pipe. And most importantly, it fits.

ptuomov

These photos in a sense document the revenge of the nerds. High school geometry does work in real life! Savor the Wise Owl stamp that you got if you stayed awake and paid attention in the math class! ;-)

In any case, this is a one gentle and well flowing y-merge from the dual 3.5" cat outlets to the 6x3.5" infinity pipe:








The iPhone editor that rennlist uses sucks hairy *******, by the way.

Chris Lockhart

Damn that's impressive!!!! Some serious engineering going into that car.

V2Rocket

because non-catted exhaust REEKS.


tuomo, the fab work on the exhaust is killer.
infinity pipe is a good name...

ptuomov

That’s all John Kuhn. And maybe a little bit his high school geometry teacher from way back when...

Imo000

Is that a giant bag of weed?

ptuomov

Well, first of all, whatever's in it, that's not a giant bag. That's at most a medium sized bag, given that we're living year 2017. What's inside the bag is a proprietary mix called "Spec 18".

Chris Lockhart

Damn I almost fell outa my chair on that one. LOL.

Chalkboss

My son agreed- not that big. Maybe a half pound lol.

ptuomov

The muffler packing material is actually quite dense. The best performance comes around 180-200 g/l, after which packing it tighter no longer helps.