I tried the grooves on my 1600 cc vw engine. I put new pistons, rings, and rebuilt heads. I set the compression ratio at 7 as per my knowledge at the time (Geen Berg book). I edged the heads (as per Dana 44's edging from the alpar forumn.) My heads had 2 grooves pointing toward the exhaust point side of the spark plug. The rebuilt heads with the grooves pulled very well smooth power up to the limit that my small carberator appeared to set. I ran the car around the block to seat the new rings and raced it up and down. With the engine tuned in it would idle at 500 rpm with the vac advance /retard distrbuitor set at 5 deg after top dead center to ~`28 at 3000 rpm. The alternator did not like 500 rpm as the gen trouble light would flicker untill I reved it. The generator light stayed out with the idle set at 700 rpm. Upon return from my trip to seat the rings I noticed that the rear wheels were smoking!! My car having sat for so long (~12 years) seized the brakes which I did not reconize as the motor pulled right through them. Upon inspection I found that only one side of the front was working the rest were siezed from sitting so long. While I was waiting for a new right hand drive master cylinder and wheel cylinders from England, I would run the motor once a week for ~10-15 minuits. One day the tune changed. It had a nice low rumble at idle. I shut it off after I heard a "put put " sound from #3 spark plug area. The rebuilt head had a thread insert in it on the #3 plug. Something I did not like but as I traided for the rebuilt heads it was what I got. The insert failed and I found the spark plug was dangling outside of the head.
I have since started a complete rebuild with new parts. The reason I did the top end rebuild was the previous heads overheated and cracked from the exhaust valves to the spark plug when the fan ate part of the tarboard insulation that I put in to deaden the engine noise. (My fault It had a tear and I drove alot on the high way. )
I think the grooves worked well. I ran 7:1 compression which I should have bumped up to 8.5 or 9. My new heads will have dana44's edging and one somender singh groove aimed at the left of the spark plug. The grooves speed up the burn a little and appear to like less timing. However I do not have much time playing with them due to the failure of the spark plug insert.
