multi angle valves/seats

[double diamond]

Acknowledging the limitations of the Ducati head described above, what then can one do to realize some improvement? First of all, what constitutes “improvement?” as we’ve not yet established what the objective of your efforts is. Moving up a few positions on the racetrack? “Happiness is a low e.t.”, probably the essential statement of drag racers (sprinters), impromptu or otherwise? Or a satisfying Sunday flog ‘round the bends. All of these aspire to maximizing performance but at the sharp end, priorities diverge. At any rate, if you choose to persist (and I salute you for that!), you’ve accepted the limitations. What I’m reading, though, is “what are the possibilities?”. Here are a few I’ve considered worth pursuing if you have the time, skills and facilities: 1) machining a “dome” centered on the intake and exhaust valve axes. The Ducati head is a classic hemispherical combustion chamber (with squish band), the consequence of which is the unfortunate disposition of the intake and exhaust valve seats. This configuration shrouds the valves in the combustion chamber. I’ve seen a few efforts to address this shrouding. One is the head on my 350 W/C racebike, apparently effected with a die grinder. I’ve seen a similar effort on a Reno Leoni bevel twin head. Again, apparently done by hand with a die grinder. The best example of what I’m proposing is the production head of a Ducati Pantah (attached pic) of a certain model (695?) that shows unambiguously what this combustion chamber would look like. BTW, I’ve been told this model is among the highest output/liter among the 2 valve, air cooled Pantah motors. The other idea is a “D shaped” intake port. Again, due to the limitations of the Ducati head, this port profile may offer advantages. I’ve been advised by an acquaintance more knowledgeable than I in such matters that port area would have to be recovered by widening the port. Which is about as far as I’ve gone with the idea. For what it’s worth.

[double diamond]

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[LaceyDucati]

Hi
Further to my previous post about original seats, I took some pictures of some original seats I had kicking about to show what I was commenting on regarding under cutting.

As you can see some of the original widecase (large valve) seats have little support on one side and is one good reason to use a "small valve" head when looking to increase performance/go racing. Undermined seats like this is pretty poor practice in automotive design, both from flow and mechanical integrity. Probably fine in road use, but a poor basis for an increase in performance.

You will also note the large valve seats are "recessed" as original, I have lost count of the amount of times a customer has requested new seats because they are like new

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Regards Nigel

[Jordan]

Regarding the recessed as standard seats, is it possible to fit conventional types instead?
Or, is the Ducati seat face design a necessary evil?

[Duccout]

Jordan, regarding the Monster cylinder head, the shape has been used for years on the two-valve heads, introduced by Massimo Bordi, who referred to it as a bathtub combustion chamber. Brook Henry at Vee Two modifies heads to this spec and Eldert does too, so maybe he can explain the details and thinking behind it. I've always thought that the shape was a way of raising the compression ratio without masking the valves. To create the same shape on a bevel Single you would need to fill in the area at the sides of the combustion chamber with weld, but I think that it would only work with a flat-top piston and shallow valve angles.

[LaceyDucati]

Jordan

The recess in the original seat is necessary to get the valve on the seat and only just clears the squish when the seat is matched to the squish. Alternatively you can bowl the head out around the seat to improve flow, but you then lower the compression ratio and you then need a larger dome to restore the ratio. Of course there is a happy compromise regarding valve size, installed height, masking and piston shape, but that's the art of tuning. The original set up was a compromise with production in mind. Of course there are those that would tell you that it was all part of Taglioni's design for performance, but on a flow bench and dyno, I've never seen any evidence.

Duccout

Regarding bowling out, I've always steered towards a more pear or egg shape as the flow out of the inlet is somewhat different to the flow into the exhaust. plus I generally use a larger % size difference between the valves than original. I think the example bathtub shown is more relevant and works better with the later belt drive 30 degree heads with flatter chambers. One off modification of single heads does lend itself to an element of machining and careful hand finishing of the combustion chamber. Fancy CNC profiles don't really lend themselves to one off modifications, unless you are fortunate enough to have the equipment, programming skills and time to carry it out. Of course as has been mentioned, for most road engines these type modifications have little relevance. I will perhaps dig out some pics of some of my modified heads sometime, the last being a 450 machined from a Misano casting. Hopefully that will eventually spurn a production version.

Regards Nigel

[Jordan]

It's interesting to get these insights - Thanks Matt, Duccout, Nigel etc.
I don't race and shrink from major alterations on my own Ducati engines.
I could just as likely make it worse.

It does strike me as curious how standard Ducati singles, for all their faults, go very well anyway.
Compare to Honda 250 of the '70s, which on paper should have been a cracking performer, but was unimpressive - maybe too heavy.

[Duccout]

Eldert posted a picture on another site of his recently finished 450 head, with re-angled valves and bathtub combustion chamber, which was impressive, but has been mentioned, that sort of work requires a lot of skill and is beyond the scope of most home tuners, and I guess what is more important on a road bike is to get the engine running as well as can be expected. I love to read about tuning though - I found an article on this site where Nigel related what he had done to a 450 racer (48 BHP?) which was very good when compared to a Manx Norton's 50 BHP, and that was from a full 500 that was designed to race.

[blethermaskite]

If you check the specs.I think the Ducati 250 is about 20% lighter than the 250 Honda of the period, so a pretty big jump in power to weight ratio, I would also suggest that the frontal area of the Honda is significantly larger than the Ducati making it aerodynamically challenged in comparison. Plus of course on another tangent the Honda wasn't able to go round corners properly
Cheers,
George

[LaceyDucati]

I will confess that my first motorbike was a 1971 Honda 250K2, it was impressively fast and was a match for some mid 70's Japanese 400's. I think those Honda horses were larger than the Ducati ponies! Having worked on a 350K4 for a friend, I have no illusions that those Honda's are a step on engine period wise and the porting is in a different league. Mind you when it comes to weight, handling and stability of the Honda, the Ducati is wildly superior! There is much to learn from other marques, if only to improve ones Ducati

For a laugh

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Nigel