Race Engine Forum UK

Thanks for the tip and Excel sheets.

Once I get to grips with Excel i shall plot the graph to 15mm as the modified head reached 200cfm at 15 where as the stock head maxed out at 12.5mm at 180 cfm.

Seeing as this head is using a road cam would you say the gains up to 11.5mm lift are poor ? Please compare stock 998 (JHP ported - lime green line) to 42mm valve mod (in pink) and 42mm valve mod with vanes added (in yellow) please.

I have decided to make a few models of the head from clay and try some less steep valve angles as i think the mid range lifts need to be pumped up a bit for it to work well with the 11.5mm camshaft.

All comments welcome.

Nothing wrong with those gains Chris

if you can measure them on the flowbench and as a measuring device the unit is giving repeatable & reliable readings, those are gains, even if only 1 cfm!

But your gains are way more than that, the losses in the lower lift region are fairly modest by comparison. Whether it will be possible to get rid of the losses compared with the 40mm valve I don't know, and I think a dyno test is needed at this stage to find out if you need to at all. If the 40mm unit has better pickup and lower-end/mid range torque this may be one area to look at.
My concern is really - how big the ports are (they are BIG) and what effect that will have on the throttle response etc. That said I know nothing about Ducati engines.

GC

Hi guys iam on the next big valve conversion 998 ducati.
I was a little dissapointed by my last job as the lower lifts were poor.
I decided to try fully radiused seats on this weeks job and ok the lower lifts were slightly better but high lifts were poor. Just as guy mentioned earlier the less intrusion of the valve seat into the airstream the better the high lift on a downdraught head.

Any how i sent 75 degree throater on the peg fm1 down the port and did the blending. I found results exactly as the last job no gains in the lower lift. I began to take a closer look at the combustion chamber and realised it could do with more combustion de shrouding. the result was a modest gain at the lower lifts.

I then went for some enlargement through the splitter that took me too 33.8 wide 33 high. There was no change so i have come to the conclusion that a 33mm port is an ample airfeed for a 42mm valve that lifts to 11.5mm.

As a side note my last job made 151hp before fuel correction up from 138hp.Thats with 2mm oversize valves, advanced inletcams and a little skiming to bump the compression up into the thirteens. When i get some time i will post the new flow and dyno charts.

I must say without the wisdom of GC and others that post here my port development would have been so much slower.. Thankyou all. chris

Excellent!

Can't argue with an increase like that. Well done Chris - and thanks for the detail and feedback in your posts, keep up the goood work,

GC