mpgmike wrote: There are 2 camps, those who have tried it and those who are against it.
it does seem that way.
http://i65.photobucket.com/albums/h205/ ... 220112.jpg
[/img] <-- tag editor is giving me lip.
i didnt want to do them in the head because the deck surface had been milled into a flat quench configuration from a formerly open chamber. plus, the piston grooves i feel gave me more control in directing the gas. i was trying to make the two squirts collide half way between the dome and spark plug, hence the ramps ground into the dome. compression was low 12:1 range, 81.5mm bore, about .038" piston to head. mild cams and stock intake/exh at the time.
i have no scientific evidence. here is what stood out to me.
-the motor had to come back apart immediately to correct an issue after startup and obvious flame marks were centered on the piston. probably means nothing, as it was only idle time and i have nothing to compare it with.
-first engine ive built that started and idled on what seemed like the very first spark on initial startup. it was 35 degrees outside and it ran like the car was daily driven and shut off just a moment before. normally takes me a few starter cycles to get them running during warm weather, harder in the cold.
-during a very basic a/f ratio street tune, the throttle position log would show about 8% tps angle while cruising. it would go to 11% and the car would accelerate as if it was given a quarter throttle. the driver/owner was saying he thought something was wrong with the cruise control, the car was taking off on him and he hadnt stepped on it yet.
i am convinced that grooves are the cat's ass with respect to cold starts, part throttle, low load, economy, emmisions and so forth. im anxious to build a test mule for myself and see how it does on 87 octane with a good dose of compression, before and after grooves. [/img]