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74 Posts
Discussion Starter #1
Though I have ported heads for some bikes over the years with fairly good gains, for a "maximum effort" project, and my level of expertise (or lack thereof) I had to employ downdraught inlet ports for my 2V 1100 heads.
Dating back in the '60s, when members of the "Cycle" staff modified a 250 Single (Diana I think it was), up to the present with DSM's "Snella RS", it is evident that, for some, it's clearly worth the trouble.

I'm very reluctant to having any welding done on the heads, although I know it is a legit procedure, when done by an skilled welder.
I also didn't want any epoxy putty built up, waiting for the right moment to detach and wreak havoc to my engine.
The valve guide bosses should also be mostly left alone, as I didn't want to chance the guides becomeing loose.
Gaps between the machined ports and the spigots, in places exposed to air/fuel mixture, should be no more than 0.1 mm.

So the plan was to (shallow) taper mill the heads to accept likely tapered spigots and secure them additionaly with high temp Locktite and alloy pegs.
The internal, where the air/fuel mixture flows, geometry was arrived at, after many iterrations useing "Lesoft" engine simulation s/w.

After some sessions with the flowbench and the die grinder, the now downdraughted heads were flowing just shy of 30% more, than what they started from.
That is wth minimal increase in port diameters.
I'm pretty sure, an expert could achieve this by welding/modifing the standard ports, but I'm not one.
Anyway, it was a fun and chalenging job for me.

Port in plaster and test spigots.

Jig to hold the heads

Before assembly

Almost ready


Later, I added 5mm thick sleeves to the tensioner rollers.

Ready for the airbox and 999 throttle bodies.


515 Posts
Ooooh this looks interesting! Followed!

74 Posts
Discussion Starter #4
Not much more to it, Neil.
Some noteworthy points as I remember them :
  • I used big (47/41mm) valves to work with the hairiest camshafts that Kaemna sells.
  • A nearly perfect valve seat job at a Serdi equipped shop.
  • Stayed a bit on the wide for the seat widths.
  • Steel valves, heavier than titanium but more reliable, with MBP colets.
  • At some point I plan to shot-peen the rockers, if I can find a shop to do it in the EU.
  • No return springs - no problem idling at 1200 rpm when hot either.
* I'm a big proponent of squish band action, where applicable, to combat detonation, but when I went about to set the piston (Pistal HC racing) to head clearance, I realized that, apart from the small (about 5mm) band width, witch in my opinion is insignificant, the flat piston with the combustion chamber forms an (about 12mm) wide thin wedge where mixture could be trapped unburned, heated and pressurized until detonation.
Same goes for all flat, at the periphery, piston crowns.
A friend with a 1000SS and HC pistons had one fail on him catastrophically because of detonation.
Bad gas plus he hadn't retarded the ignition a few degrees did it for him.

Where mixture might be trapped (in red).

* So I went ahead and milled the heads, 'till I had about 12mm wide squish band of 24% of the piston surface area.
I also had to mill the top of the dome of the piston crown a bit, to bring back the compression ratio.
Thankfully, the Pistals have plenty of meat there.
A convenient side effect was, that the combustion chamber was somewhat more compact now.
I never did like high domed pistons.

* I wish I could tell you, I 3D scanned the heads and molds, CAD designed the new ports and spigots then let an 5-axis mill to machine the lot.
Instead, I used my lathe and a modified drill press along with the jig do do the machining.
The time consuming part was, to match the spigots to the heads at the valve guide boss area, using Prussian blue and a pen sized die grinder.

Where the spigot meets the rest of the port.

* Working the on chamber to unshroud the inlet valves, I found out that one side of the valve head was flowing somewhat more than the other, hence the slightly asymmetrical appearance of the combustion chamber.

* The gadgets at the floor of the spigots are vortex generators which gave me an easy 3% increase in flow rate.
Didn't bother to optimize their configuration further, as I didn't know how much more I could get out of them, plus I had achieved my target gain.

If anyone is interested, I could go on about the inlet manifolds, the air box and throttle bodies.

I am expecting good gains, back in the day similarly modified heads were worth the effort on both 750 and 900 motors. We were disappointed that Ducati never saw fir to build them this way when the 1000 heads were made as they also knew the benefits.
Nothing's new under the sun :)

How the guys at DSM did it.

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