Race Engine Forum UK

Hi all

posting picture of 2 identical heads both have seats cut for 2mm oversize inlet valves and both heads done by the same company.

You can see that one has a big seat area and the other has almost 90 degree throats. Both heads use penny on a stick type valves. Has anyone any ideas on the 2 different designs regarding flow? Both heads are using the same cams with 11.5 max lift.

I have recently myself finished one of the same heads as above. I cut 3 angled seats 75 degree throats to fit the 2mm oversize valves did the blending and left the port size alone. I gained 15cfm through the range but cfm stayed the same until reaching 5mm of lift.

I'd expect that the 998 head would flow better, it looks like we have quite a steep downdraft angle and in my experience the less intrusion of the valve seat into the flow the better, and - the greater the downdraft angle the smaller the short side radius needs to be to achieve high-lift flow. I would not expect the 999 heavily radiused throats to be any good at perhaps anything except low lift. 75 degree throat is what I would likely use here too.

Does this agree with your own test findings?

GC

The pictures in the above post are same head types, but each head has been prepared in different ways to get a different result. Both use 2mm larger valves. One has heavily radiused seats with smaller ports and the other larger ports with 80 degree throats or maybe more. I'm wondering what the benefits of each would be ?

I have tackled this job myself a couple of times now but i have only ever gone for with 2mm oversize valves 75 degree throats and standard port size with 30/45/75 angles. I found the cfm stayed identical with the 2mm oversize valves until 5mm lift where it rapidly gains cfm from there . I have yet to experiment with the heavily radiused seats shown in the picture.

On a side note yes these heads have a non existent short side radius i just make a smooth radiused transition from the floor to the seat

Below is a shot of my work

Chris, hi

Always wanted a Ducati. Tell me (if you'd be so kind) the valve sizes in millimetres, typical lift, cylinder volume on those units.

Are these the units with desmodronic valve gear - no springs?

I'd be interested in the power and torque & associated rpm too. Also, can you take a side view of a head showing the downdraft angle?

Thanks,

GC

Its a piece of art

That's amazing. I thought I was looking at one of my Peugeot Mi16 heads when looking at the 998. Also looking forward to hearing of the specifications.

Here is another ducati head prepped by another expert. Note the port shape and what i believe to be vortex generators welded in. The man who prepped these gets serious results.The inlet valve angles i believe to be 30/45/60 unlike the factory race teams 30/45.85 ish.

Has anyone seen or used this methord before ?

These weld-in is actually no real vortex generator.
A vortex generator has one or more sharp edges, which are placed in an angle (typically 5‚°-15‚°) relative to the passing flow, which makes part of the flow rolling over the edge and thus forming a vortex. Most vortex generators have a sharp cut at the trailing edge for clear separation of the vortex.

In the Ducati head I can see a smooth transition of shape towards the and from the weld-in.
To me it looks like the weld-in's purpose is to counteract the protrusion of the valvestem and guide. Without the weld-in the valvestem would push the flow more towards the lower end of the channel, resulting in higher flow velocity at the short side radius (and maybe flow separation). With the weld-in, the flow mass and velocities may be distributed more equal, when approaching the valve.

You could try to visualize the flow with a fine thread, like GC shows on some Pictures.


Thomas

That does make sense. Hope fully more people will contribute to this thread as i think it could get quite interesting.

Here is another using this same methord.

I have seen pictures of similar vane additions in raptor heads by Reher Morrison. I used to have photgraphs but i can't find them anymore

Darrin Morgan (http://www.darinmorgan.com/)states, and i quote:

"It does absolutely nothing other than smooth out the flow transition at the convergent point and upper lift areas and help to atomize a little fuel that has fallen out of suspension. You will find it extremely difficult to get an SSR to work under dynamic conditions at 400FPS no matter what you do with the shape, wing or no wing. air speed limitations still apply. No, it does not change swirl at all"

but this is a 2v 12 degree "raptor'' chevy head for huge displacements. the vane could well do something differnt in this application.

Has anyoe else got any theorys about the modification to the humps in these heads ?