Post by 90GTVert on Jan 27, 2011 12:24:37 GMT -5
Adding spacers and base gaskets to raise ports or enlarging ports aren't the only ways to add more duration. This trick is especially handy for transfer and boost ports, because you often need expensive specialty tools to reach them and the angle of their entry should only be modified by experienced tuners. This method involves only files and a bit of sandpaper.
My original durations for this cylinder were 184 exhaust / 112 transfer. I wanted to keep the exhaust the same, but increase transfer duration to 128 degrees. I filed the piston crown by the transfers enough to get 128 degrees of transfer duration.
I use a degree wheel. File a little and check duration. If not enough, file a little more and check duration. Take very small steps because a tiny amount of material can change the port duration significantly, and if you go too far you'll be needing a new piston. Once the duration is where you want it, smooth out the work you've done with sandpaper. Also, make sure you clean the piston thoroughly before inserting it into the bore each time. You really don't want to be scraping aluminum shavings around in there.
I'm not sure exactly what the minimum amount of material is to leave above the upper ring land, but I advise playing it safe. Have a good look at the piston's underside to be sure there is a lot of supporting material in there before filing at all.
\
You can clearly see the difference in the filed and untouched portions of the piston crown in the bore.
My original durations for this cylinder were 184 exhaust / 112 transfer. I wanted to keep the exhaust the same, but increase transfer duration to 128 degrees. I filed the piston crown by the transfers enough to get 128 degrees of transfer duration.
I use a degree wheel. File a little and check duration. If not enough, file a little more and check duration. Take very small steps because a tiny amount of material can change the port duration significantly, and if you go too far you'll be needing a new piston. Once the duration is where you want it, smooth out the work you've done with sandpaper. Also, make sure you clean the piston thoroughly before inserting it into the bore each time. You really don't want to be scraping aluminum shavings around in there.
I'm not sure exactly what the minimum amount of material is to leave above the upper ring land, but I advise playing it safe. Have a good look at the piston's underside to be sure there is a lot of supporting material in there before filing at all.
\You can clearly see the difference in the filed and untouched portions of the piston crown in the bore.