Joined Nov 2001
17K Posts | 774+
Ely, England
hello chaps
well i've mentioned porting the exhaust port and replacing my 27s with 29mm valves. for those that don't bother to read "taff's racing season" (in race reports) i shall just recap by saying that i had a flat spot' lugging off the bottom in second gear from a 'dead corner' but otherwise had a very noticeable improvement from 1/3 throttl on or third gear + as some might say...
so let's discuss the inlet tract. the rubber inlet spigot i have measured and it feeds off the bottom lip UP into the head and DOWN -and even steeper-from the top edge.
by carefully placing the rubber where i want it i realised that i need to take .5mm (0.020") all the way around the entrance to the port. the top edge has a hollow and yet on the bottom edge the head doesn't align to the rubber inlet shape. then the area before it becomes 2-branch is massive, then tiny as it goes past the guides and then too big again from the guide to the seats.
i bought some devcon and it ain't cheap but it is the muts nuts!
i filled in the cavity at the top, i then created a mound on the base inside the head and brought the central 'split' forward and towards the inlet with a razor sharp edge. this has reduced the CSA right infront of the branch split. i welded a rod onto my best rotary file and then proceeded to file around the guide area so that the profile each side is effectively like a horse shoe. i've left the middle hump so as to protect the guide. i had shortened the two guides by 6mm BTW. i used water on a bic biro cap to roll out the devcom and get a smooth finish. using an old inlet rubber i used my rotary files to get the angle into the head right. i then started using rotary abrasive pads to smooth out the ports rough spots but found that the area behind the seat, despite being the right shape was now too big. so out came the devcom again and i have built up/reduced the diameter behind the seat.
having measured everything again at the end with internal calipers i'm fairly happy about the finish and it's now off to the engineers to have a 3-way cut on the inlet seats. the valves themselves were re-shaped a few weeks ago.
i shall put the proper inlet rubber back on and build it up. hopefully the dead spot will be gone off the bottom and i may notice if i'm lucky more power and lower for sure!
will keep you posted!
regards
Taffy
well i've mentioned porting the exhaust port and replacing my 27s with 29mm valves. for those that don't bother to read "taff's racing season" (in race reports) i shall just recap by saying that i had a flat spot' lugging off the bottom in second gear from a 'dead corner' but otherwise had a very noticeable improvement from 1/3 throttl on or third gear + as some might say...
so let's discuss the inlet tract. the rubber inlet spigot i have measured and it feeds off the bottom lip UP into the head and DOWN -and even steeper-from the top edge.
by carefully placing the rubber where i want it i realised that i need to take .5mm (0.020") all the way around the entrance to the port. the top edge has a hollow and yet on the bottom edge the head doesn't align to the rubber inlet shape. then the area before it becomes 2-branch is massive, then tiny as it goes past the guides and then too big again from the guide to the seats.
i bought some devcon and it ain't cheap but it is the muts nuts!
i filled in the cavity at the top, i then created a mound on the base inside the head and brought the central 'split' forward and towards the inlet with a razor sharp edge. this has reduced the CSA right infront of the branch split. i welded a rod onto my best rotary file and then proceeded to file around the guide area so that the profile each side is effectively like a horse shoe. i've left the middle hump so as to protect the guide. i had shortened the two guides by 6mm BTW. i used water on a bic biro cap to roll out the devcom and get a smooth finish. using an old inlet rubber i used my rotary files to get the angle into the head right. i then started using rotary abrasive pads to smooth out the ports rough spots but found that the area behind the seat, despite being the right shape was now too big. so out came the devcom again and i have built up/reduced the diameter behind the seat.
having measured everything again at the end with internal calipers i'm fairly happy about the finish and it's now off to the engineers to have a 3-way cut on the inlet seats. the valves themselves were re-shaped a few weeks ago.
i shall put the proper inlet rubber back on and build it up. hopefully the dead spot will be gone off the bottom and i may notice if i'm lucky more power and lower for sure!
will keep you posted!
regards
Taffy
