Timing for exhaust manifold/extractors/headers

[VX L67 Getrag]

What ever you like to call them, the piece that draws the hydrocarbons out of the cylinder head...

I've touched on this with my gen3 LS1, I had it tuned with stock headers & then put nice clubsport extractors on it & made no difference on the dyno, then tried chucking more timing at it but couldn't take it!

It could have made a difference after 10 back to back runs with heat soak from stock headers, but really who's gunna get the chance to keep your foot in it for that long out on the road & you should have enough clean air going through it out on the road!

But haven't tested but thinking on a forced induction motor it may make more of a difference & wondering if anyone has tested it & then tested even more with long or short primaries?

Reason I bring it up the l67 I tuned yesterday couldn't take anywhere near the amount of timing I did on an identical setup 2 weeks ago, only real difference was stock headers & long primary extractors!
The 1 yesterday I put down to bad fuel, but thought headers could have influenced it to?

What's other peoples thoughts & tests?

Cheers VX L67 Getrag

[blownvp]

yea if the exhaust is restrictive and can't get rid of the gases properly its more likely to detonate probably more critical on fi where the induction temps are higher