Velocity porting mod

griff851

Well, by golly gosh it went like the clappers. The whole amazing 400km worth. Steve, 42mm inlet wasted stainless valves. 36 exh valves. Standard S2 cam’s dialed in by juggling. As I used JB weld for testing, I’m pulling it out of the port. The results are pretty awesome, 165-150 is standard main jetting. Got down to 94, before the plug cleared. B8hsc. El cheap arse veglia tacho crapped out towards the end, but gave me enough information to tune. Pulling up a hill with a rather nice sweeper. Easy 180kmph in it, not far in push behind the 888, which is similar to a 996. An OMG moment. “Well that seems to work”
But of coarse everything has its price. There is so much flow going on, 2 thing became apparent. Valve guide seals. Viton standard ones we’re letting a little bit of oil through. The low profile ones were better. The inlets really need oring and low profile, to make that issue disappear.

Bore. Gets a bit nasty here. Omega race with full ceramic coating. As recommended 0.07 bore clearance, rings at 0.018”. Honed to equivalent 600 grit. I can’t up load pictures at the moment but it’s rather shiny. More like 4000km run in, not 400km. Light scratching and piston has same plus piston rocking marks lower skirt thrust face. The issue is by effectively supercharging, the gas pressure is pushing the rings way too hard against the bore. Eyeballing nikasil bores. New pistal HC pistons arrive Monday and a rebore shortly following. I’ll de-tune the ports (I’ve made casting for references) and run it in normally, then belzona 1111 ports this time, but possibly not quite as wild. Cases are 80000km old, I’d like to use them for a bit. 😁
Sports Motorcycle fork valves with 5wt work. With 4-5 compression and max rebound available or that setting is not a bad place to be on open road. AG1 rear mazzochi need 3 -3 1/2 bar to actually work.( bladder issue there at max being 2 1/2 bar. (7wt I think, bit bad in the memory.)
Stainless disks with sintered pad are a good step up in braking.
Oil pressure, wow not kidding with hiflow low pressure. Idle when hot is scary but all well above that. Bevel gear drain from oil filter blocked and bung removed. Oil lines to cam caps with restricters.
Tried D shape exh port inserts with tongues 13mm high. Crap. Just restricted flow, reduced performance noticeably. If there is a resonance gain it was out weighed by flow loss by lots.

MarkT

Carry on-------

griff851

Thanks Mark, spoken like a true pump bloke. 😁

MarkT

Griff- I will take that as a high compliment.

griff851

Finally worked how the stupid iPhone works

Piston photos. The light rub mark at the bottom looks a lot like rocking to me.
The crown coating has darkened slightly and it’s got a dark bit. Thing could have only gotten much worse from here.
And a nice shiny bore.
Anyone got any ideas other than stupidly high cylinder pressure?

griff851

Ceramic coated crown.

Mr.R

What's the piston skirt to bore clearance?

...and a bit late here but where did you measure the 13mm on the exhaust D that you tried?

Steve R

griff851

0.07mm, I went tight because of coating.
13mm is off the od of the ring, which is the same diameter as the gasket.

griff851

I clocked my ports for those that might be interested in actual physics other than cutting off valve guides flush. Here is a CAD drawing I got my mate to do for me after I sent the data. It's the port up to the valve guide. The initial taper is 7° borrowed from the drag car loons. The glue on the short side then is used to direct and speed up the charge flow into the cylinder.