If you change your exhaust headers make sure the restrictor point of the new set is similar in overall opening size to the original set.
The original outlet is: 35mm – 43.5mm diameter externally at its most restricted point.
I’m not sure what the wall thickness is but I reckon it must be somewhere between 1.0mm and 2.00mm, my original pipes are still in good condition and I was loathe to saw them up to find out.
In any event the Motad replacement header system outlet pipe is has a clear open area of 1364sqm. Whereas the original outlet is restricted to somewhere between 962sqm and 1075sqm.
When I fitted the Motad headers the power band almost evaporated and a gas analyser showed it be running far too weak, this being supported by the plug colour.
A further test was done by a lazer temp gauge on the exhaust clamp bracket of both original and new pipes and this showed the exhaust gas temp had risen.
To solve the issue the Motad pipe was sleeved down first to 1075sqm which improved things no end, and finally down to 975sqm, which seems to be better.
Plugs were checked and exhaust gas analysed and the results were as good as I could get them.
However if you don’t get the right back pressure the engine will run too weak and it is possible that you may end up damaging the exhaust valve edges and seats.
The photo below is the restrictor point in the original header set.
