Ill firstly provide the reason for my question. Ive recently discovered my head gasket is leaking in my XG, which is running an EL XR engine, so the head is going to have to come off in the coming weeks. I have an AU head that has been recoed and surfaced already in my possession. My question is can I expect a performance decrease from swapping to the AU head, or is it worth me sticking with the EL head and getting it cleaned up?

I thought I read somewhere that valve sizes are the same, can some confirm this?

Regards
Dan

Have searched hi and low for the info im after, does anyone have the link for thread containing valve sizes for each model?

I think you will find the cam and rocker gear is different between the AU and EL XR motors.
Just something to keep in mind.

YEah au has the larger valves already. Does your EL have the normal early head or the hybrid motor au type already ?
The au heads have smaller ports and flow less than the early heads, I don't know if the XR's had any hybrid motor au heads or if they got the better ports from the earlier design (or if they are ported).

This will be a interesting read

also you can use E series rocker gear in AU heads and retain the E series cam shaft so thats looked after

Really? I didnt realize E series cam and rocker gear can be used in AU head.

Cam doesnt play any part in my decision all the same, going to get one ground after I decide what head will be used. If I wont see any significant loss in performance ill go the AU head thats ready to go.

I am going to have to get a sniffer set of valve springs for the AU head if I use that as ill be using 1521A cam