Astor XS XU7J4RS (For Sale £1000)

[Dan86]

I think it is something to do with the pulse tuning of the different manifolds. Both have resonators meaning that some thought went into the design of them. The 1.8 tb is so small I expect the pulse tuning was optimised at a lower rpm than the gti6 one. I guess that the fixed fuelling program in the ecu increases the fuel amount to match the better volumetric efficiency at the lower rpm power band of the xu7. With the gti6 manifold fitted the pulse tuning of the manifold is able to cram more air in at a higher rpm which the ecu can't compensate for making it lean hence the timing being out and spitting back.

If the ecu was able to be re mapped to fuel more to match the tuning of the gti6 mani, I feel it would enable the engine to breath better. The gti6 tb would be better to use if being remapped anyway.

My theories.
Dan.