Forum for competition engine enthusiasts. RIP Guy Croft 09/11/2020 - This forum will continue both as a source of information and as a memorial to Guy.
Guy Croft wrote:You first need to read GC V/W article about 'matching' in head prep.
GC
Thanks I read it, but there is nothing about the theory that the downstream step in the exhaust port is left to stop gases traveling back to the cilinder as they hit the turbo f.e.
What view do you have on this?
It seems to be true that having the header bigger than the port works both in software simulation and in practice. I'm afraid I do not know the exact reason.
Yesterday I was about to finish my porting job. Made a fork for that with 80 grid paper but discovered that the fork is useless on the bends. It is possible to grind only flat parts with it. How do I finish parts on the bends? by hand? Spent 1.5 hour rubbing it by hand but got nowhere near the finish I was hoping
no, a split fork tool will only finish, it won't give you a high enough metal removal rate to use for smoothing straight after removla burrs.
However, the ATA Ataband at 50 or 80 grit will do this, and if you overhang the band over the end of the tool it copes beautifully with curvature, and there are no bends in the CVH that it will not reach.
You need to get some, that's what I use. You won't get the results I do without the same tools. I tend to go burr-Ataband-split fork. Buy maybe 2 off 15 x 25mm Ataband holders with bags of 50 and 80 grade bands and life will start to look a bit easier.
Anywhere 10,000 - 20,000 rpm with a Metabo variable speed die grinder and 6mm collet flexi shaft. The machine has torque feedback so you get high power even at lower speed.