ducati 900ss engine head mods

continuing on the efi conversion topic, I finished that engine, I'll try to remind myself to refresh that thread with all the info... but I've been spending the last couple months modifying the heads, I took my first ducati build to loudon to get my racing license and loved it but it really made me want an even lighter and more powerful bike, the one I took dyno'd at 75hp and weighed 330lb, so I feel like I could get a lot more power from that engine.

I talked to bruce meyers who has been building these engines since they came out, and he gave me a lot of good info, most of the power gains come from the intake port, cam and bigger valves, he even reangles his valves slightly so the larger valves don't hit on overlap. I couldn't wrap my head around reangling the valves without changing the angle of the rocker pairs, and how that would actually work without changing the running clearance of the opener and closer during rotation, so I chose to run standard valves. I couldn't get my hands on a racing cam, apparently no one makes these anymore unless you order a batch, then you're still calling a place in australia and trying to convince them you're the real deal, so I gave up on that and bought an st-2 parts motor for a couple hundred bucks and swapped in the st-2 cam. from what I read, it's a good mild race cam when used in the 900ss.

to modify the ports, I milled out parts of the head and welded in inserts, then welded and blended the ports to the original head, I aimed for a wider intake port at the mouth, with a good taper to the valve seat, this should increase port velocity and take advantage of the greater overlap in the st-2 cam, these motors really fall on their ass above 7000 rpm.

after all the welding and stuff, I had to re-heat treat the heads because they lost all their temper in some sections, namely around the seats, which wouldn't be good, so I found a kiln on craigslist for cheap, fixed it up, and ran a t-6 solution, then aged, seemed to work fine. the heads were also pretty warped after that process, so I remachined the head sealing surface and re-reamed the rocker pin holes, it assembled fine, the cam bearing caps were quite tight but they still went in, so I say send it, let's see what it does.



Is that intake port still work in progress or have you deliberately decided against a port-side bias, if so... why?
(That is unless this is a professional secret, which I totally accept...)

both ports are finished, the angle of the intake port is based on changing the vertical angle first, then basically figuring out where the new port runs into the old port casting to minimize the amount of fill welding needed, from what I know from people who build these engines to race, any side bias in the ducati ports has more to do with packaging than generating swirl, they'd work just as well with the ports directly in line with the center plane of the cylinder
I'm going back in time a bit, but put together some process pics of the heads in this engine, part of the fun was doing the valve seats in house, I bought a foot of 630 bronze and machined the blanks, it was a ton cheaper than buying them from someone else, and also made sure they were what I wanted.

The choice I made for the seats in the racing ducati head I'm building is to use 630 bronze, both for its great wear resistance properties, as well as its great heat conductivity. In a racing engine, one of the goals is to get heat from combustion the hell out of the engine post haste, sintered metal seats may have the wear resistance of bronze, but they most definitely don't conduct heat, and that'll be a problem here. I designed these seats to use a blended radius instead of a 3, 5 or 7 angle valve job, I didn't have any particular reason other than I'd like to try it, I can make it happen, and I've heard good stories about it.

The first challenge was to figure out how big the radius on the valve seat needed to be, for the valve to seat at a proper depth, and to have the 45 degree contact area line up with the middle of the valve face, if I designed the radius wrong, the valve would either seat too deep in the head, or the contact area wouldn't line up. I used solidworks to model the valve and the seat, and made sure that I had a shape that would work. At that point, I needed to translate that into a cutter, you can't simply cut the seats, drive them into the head, and expect things to line up all nicey nice, so you've gotta drive them in uncut, then do all the machinework in place, which ensures both a pain in the ass job, and that things are all concentric with the valve guide bore. I used my surface grinder and some angle chucks, along with a wheel I cut the blended radius into, to make some 7 degree clearance hss cutters for my valve cutting tools (which I made earlier on the mill).

Once the head gets lined up in the mill, the cutters go in on top of a spring and the Z handle is used to do the fine cutting, they really work like a charm and the nice thing is I can grind some new cutters for different size valve seats or different blends or whatever, it's a great simply diy system.

After the blend cut goes in, the 45 degree cutter is used to put the seat contact area in, this 45 degree face mates with the 45 degree face on the valve and ensures good sealing but almost more importantly, good heat transfer from the valve to the head, exhaust valves in racing engines are subjected to extreme exhaust gas temperatures and WILL fail without a good surface to transfer heat from the valve head to the cylinder head.



1,400.00 for carbs...that's reasonable
The port shape looks good. Did you open the intake seats to .9 of the valve OD? I am glad you mentioned the heads losing their temper after welding. Try milling a head after it has gone soft.....you will pull your hair out. ;D

DTT Bike Of The Month Gallery

DTT Light or Dark

Top Bottom