Originally Posted by mrgsr
After the modified the head yeh i polished up the groove with fine wet sandpaper then used aluminium polish and then finally cleaned it off with fuel.
the engine was a missile in the 3 qualifiers going down the straight but the punch out of the corners was not there so were trying to tune a better low end. then we found the clutch to be not set correctly.
i gues when the first plug blew we didnt open the engine then to remove the plug wire, i guess this is what caused the second plug to blow and kill the engine
i was still using the standard shim setup under the head. when creating this scoop is it best to add or remove a shim ?
Milling one combustion chamber if isn't done properly, you could be doing more harm than good... needs to be perfectly squared (if not squared, something horrible could happen). The small grooves on the aluminium could lead to hot spots and detonation.
Is much better to leave the satin finish from the carbide or the HSS cutter rather than trying to mess with sandpaper. Which kind of bit you used for making the scoop?. Using diamond bits here is a no-no... much cleaner and better to use a suitable bit for aluminium.
Your lack of punch could be too due to the lesser compression (in fact, with the scoop you raised the volume on the Cc). If you plan to continue using that engine is mandatory to do a height clearance checking (use plastigauge or similar), if you have too an original (unmodified) combustion chamber a check of the volume could be great (do it with straight methanol or suitable alcohol because has much lesser surface tension and is easier to measure it rather than using water).