M97 exhaust manifold design, power loss, torque gain?

[f0xy]

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Edited by f0xy on Friday 28th June 09:40

[f0xy]

E-bmw said:

I stress that I am no expert, however my thoughts would be that you have fundamentally changed the way the engine breathes, and in doing so you seem to have made losses & gains.

These aren't necessarily going to be where you want them unless the exhaust is specifically tuned for what you want.

Although someone more knowledgeable than I may well be able to tell you how to get what you want where you want it at the other end of the engine breathing cycle.

On a different note, if the car is used on the road and your MOT tester is on the ball it won't pass an MOT again.

It's more so to determine what these flat six engines "like" or "dont like" really - it is a new subject for me. Ive come from a high compression, ITB, straight six world where good, developed factory manifolds exceed the task and just work. MOT isn't an issue, its not a road car, its a circuit car:

stevieturbo said:

It's maybe an optical illusion, but the header tubes look massive compared to the exiting system ?

And the collectors themselves, perhaps not the prettiest thing either ?

Is that supposed to be a proven setup ?

How does it compare build wise compared to standard ? Do the two sides remain completely separate on the factory car ?

They look bigger in the picture than they are, as they're ovalled at the head then work back into round for the collector. They arent the worst I've seen, they merge cleanly internally with nothing out of the ordinary or strange shapes.

I'd say proven lightly... I've yet to see any real data for any exhaust setup back to back on Boxster/Cayman, however I'm only starting along this path. People buy these "eBay/Toyosport" headers as they are cheap and decently enough put together, not cheap thin stainless - and the original ones rust/rot away.

All models run seperately to the back from factory, just the route they take differ between 986 and 987. The (older) 986 runs the route I chose to take as pictured, however the 987 used a non-equal length manifold with an incorporated cat, which then through the wheel arch instead, directly behind the shock absorber. I didn't really want to run this route - as putting a red hot (larger diameter) exhaust next to expensive suspension isn't going to do much good when it is only used flat out on circuit. Here are the original items:



The factory back boxes have a balance pipe between them and various internal cross baffling, which still remains. I did keep the back box with the mindset of it has made factory power, and is obviously designed for that (or more, being the same internally on a 3.2/3.4L), so really the only variable left is the headers or 986 style route.

The headers are so cheap and the fabrication done myself so I'm not overly concerned about that side of it - just doesnt really add up at the moment.

[f0xy]

stevieturbo said:

And do you have any dyno graphs from when it was completely standard exhaust ?

Perhaps something in there cleaned up the area in question, or perhaps it is just inherent in the engine ? intake ? other ?

This isn't my graph, but its a completely standard car, of the same model with the same 2.7L engine.



My intake, throttle body, etc are stock. It's not driving a PAS pump any more either