Ducati downdraught port modification and test

[Guy Croft]

Chris, hi

that std unit peaking at 11,000 - what's the typical working powerband?

GC

[superbike]

They pull strong from 5-10.000 rpm

torque allways peaks at 7000 then they fly till 10.500

[superbike]

I cannot believe what happened today.

I was messin around with the head in queston and for fun i decided to lay clay on the port floor. It lost some flow but when i made it stream line i gained another 5cfm from 6mm upwards.I removed and put it back several times to check the results.

The port barrells were 35mm wide by 33 high they are now 35mm wide by 26mm high its now D SHAPED .

I then checked bpf thinking that this too had gone down but its stayed the same.

Gaining flow with a smaller port means better velocity and more power right and it should not hurt top end as the smaller port flows better than the large ?

[superbike]

Guy

I will tomorrow make something so that i can test at over 12,13,14mm then report back and let you know what happens.
Would you also let me know your findings on the mach index.

Thankyou

[superbike]

Ok

from 11-16mm lift it went up 10 cfm to 189. Wiith no valve in its 204cfm so still 15 cfm away from bare port at 16mm.

It was similar when using plastercine in the ports to make a short side radius but from 6mm upwawrds a gain of around 5 cfm was had with the plastercine no change in bare port though.

[superbike]

Hi all

Just as i thought i was banging my head against the wall and inspecting the flowbench for damage due to making no more gains on thease heads i made a discovery.

I began to look at the combustion chamber more closely and decided to de shroud a little more. Gain followed. Im now at the same point as i was with my home made short side radius from clay.

I then decided to put the clay radius back in as well and ended up with a big gain.

The first numbers are of stock with a clean up by a well known firm the second set of figures are with 2mm oversize valves,de shrouded chamber and a short side radius made from clay.

02mm was 47 now 52 +5
03mm was 66 now 73 +7
04mm was 87 now 94 +7
05mm was 108 now 115 +7
06mm was 127 now 133 + 6
07mm was 139 now 150 + 11
08mm was 150 now 165 +15
09mm was 158 now 175 +17
10mm was164 now 184 + 20
11mm was 169 now 188 + 19
11.5mm was 172 now 191 + 19

so now im only 16 or so away from bpf at only 11.5 mm lift im feeling happier now and the ports are no bigger than stock with the clay added.

All comments welcome ..

[Guy Croft]

Well done, and your careful documentation of the dev work has made this an interesting thread.

Like I said:

3. Poor valve performance can be the result of shrouding or poor exit flow, if there is no shrouding, the top grind on the valve seat may need to be changed. I have seen a marked difference on some heads between 15 - 20 - 30 - 35 deg top grinds of varying width and depending whether the grind is smoothed out or left sharp. That aspect is hugely difficult to optimise.

I think the shape of the back of the valve (behind the contact face) and the top cut angle are closely related.

GC

[superbike]

The downdraft on these Ducati 4v heads is so steep they do not have much of a short side radius so I decided to make one from clay.
I built up the port barrels with clay and the result is a smaller port which flows some 6cfm more at all lifts - on top of what I gained installing the larger inlet valve.

The port barrels are 33mm stock - the revised design is 34mm wide by 28mm high - almost D shaped. My question is ok, so the smaller port flows more - but will it make more bhp - or will it run out of top end? The power normally peaks at 10.000rpm on this engine. Or - will the smaller port make more power ?

The straight short ports of these heads (the manufacturer states) send swirl deep into the cylinder for a good burn. I'm wondering if the swirl will be as good on my new design.

Shall I go for it and lay chemical metal or re shape with weld ?

[Guy Croft]

Yes, now and again you hit on things like that and it really makes you stop and think..

The first thing Chris is to recheck your results at all the lift points just to be sure you have not made a mistake. Next you need to check the head with inlet manifold or empty carb body and rampipe on and see how it works then, before clay and after, again at all lift points. The results with the outboard section (s) fitted could be markedly different. You must also note that the shape of the clay infilled region may well be very critical and you may struggle to repeat it - ever.

If the gains are real, I mean + 5% at everything over 3mm lift - two points:
1) if it flows that measurably more on the flowbench with the D shaped port and built-up SSR it would tend to give more peak power, perhaps also better bottom-end mid range torque due to higher filling velocity in a port of smaller cross section. However the pressure ratios on-engine are far, far higher than any flowbench can generate, so there is no way of really knowing if it's better on the engine - the airstream might just behave totally differently.
2) the mods could just upset the designed-in turbulence and thus burn rate (I have no idea on that one) wiping out your perceived gains..

so whilst interesting it's really a bit 'chancey'..

As for modifying an actual head, OK for dyno dev but not to supply to a client.
I'd use the quite expensive Loctite chemical metal or Devcon, and yes I have done this on the dyno in-heads and use it from time to time on inlet manifolds. However the chances of it coming off in a port are too high to retail or race it like that.
As for welding, forget it. It's the worst possible region to work in and there will be X amount of porosity and cavities - however well done, so you'll be fettling and re-welding over and over and there won't be a straight line on it after all that heat has gone into it. That is even assuming it is a weldable alloy.

If you really do get substantially better dyno results then that is the time to consider making your own heads, but it's a huge step financially and maybe not as much fun as being able to say ' I bettered a Ducati design', even if you never go into production with it.

GC

[petert]

Guy, have you heard of a two part epoxy called Belzona? It's the only epoxy product my local head gurus will guarantee. One of it's primary uses is repairing erosion in centrifugal pumps. You can feather it out to nothing and it's guaranteed to adhere to the parent metal. My friend OwenW has recently bought a kilo so he can repair heads with bad core shifts. I was lucky to be at his place when the rep. arrived. I was amazed at applications where it can be used, particularly in automotive areas.

[Guy Croft]

Peter, hi

no - it's new to me.

GC

[superbike]

Guy, have you heard of a two part epoxy called Belzona? It's the only epoxy product my local head gurus will guarantee. One of it's primary uses is repairing erosion in centrifugal pumps. You can feather it out to nothing and it's guaranteed to adhere to the parent metal. My friend OwenW has recently bought a kilo so he can repair heads with bad core shifts. I was lucky to be at his place when the rep. arrived. I was amazed at applications where it can be used, particularly in automotive areas.

Yes belzona is an amazing product but expensive.
A good freind of mine manufactures centrifugal pumps here in the uk and coats the inside giving amazing corrosion resistance and helps the waterpumps flow Ha Ha Ha....

[superbike]

Guy i decided against making a short side for the ducati head.
Firstly yes it may change the swirl pattern, secondly you were right its very hard to replicate and even playing with the clay i cannot get close to replication that super shape i made that got me these results .


02mm was 47 now 52 +5
03mm was 66 now 73 +7
04mm was 87 now 94 +7
05mm was 108 now 115 +7
06mm was 127 now 133 + 6
07mm was 139 now 150 + 11
08mm was 150 now 165 +15
09mm was 158 now 175 +17
10mm was164 now 184 + 20
11mm was 169 now 188 + 19
11.5mm was 172 now 191 + 19


So now im back to the figures listed at the bottom of the page and i think it will have to stay this way for now.

The only other mod i tried was opening out the throat a little more as even at 15mm lift the flow would not go over 190 and bare port is 210.
After opening the throat i get 200 at 15mm lift but everyware else stays the same. On these heads with 33mm ports the smallest part of the seat being 35mm standard is the restriction. To get the flow this had to be opened to 37.5mm.

I think if this had a race cam with 15mm lift this would make a very good head but this will never go be-ond 11.5mm and i have had almost identical results up to 11.5mm lift on the last job but with 33by33 barrells . I now have 34.5 wide by 34 high barrells so i guess i went to far (luckily junk head)

Next time i think i use different angles or a radiused cut as i feel the 35/45/75 straight into the port doesnot do much justice untill 8mm of lift or so and then its over by 11.5.

Please comment on the gains below (was it worth it for a 2mm oversize inlt valve ???

stock 33mm barrels on 40mm valve and 35mm x 34 barrels on 42 valve

Lift (mm) vs flow (cfm)with 40/42mm valve
2 - was 47 now 50 (+3)
3 - was 66 now 69 (+3)
4 - was 87 now 90 (+3)
5 - was 108 now 110 (+2)
6 - was 127 now 128 (+1)
7 - was 139 now 145 (+6)
8 - was 150 now 157 (+7)
9 - was 158 now 167 (+9)
10 - was 164 now 176 (+12)
11 - was 169 now 181 (+12)

11.5 was 172 now 183 + 11 end of road cam lift

12 was 175 now 187 + 12
13 was 178 now 192 +14
14 was 180 now 196 + 16
15 was 180 now 200 + 20

bpf
40mm valve 179
42mm valve 210

I know this is going on a little now (hope fully its use full to someone )
but i found putting two little clay humps on the port floor adjacent to the valve guides gained me another 2 cfm from 6mm lift upwards ontop of the results obove. I also found by spraying brake cleaner down the ports the 2 clay humps lifted the the brake clean up off the floor and split it into 2 streams.

I basically copied this picture

[superbike]

Here are so fars results.



On the yellow line i added vanes onto the port floor like in the picture above.

[Guy Croft]

Chris, hi

Print this off. To upload an Excel graph:

1. In Excel first set the zoom to 100%, stretch the graph display to fit the full screen, making sure the top left corner of the graph with white border is set at top left corner of the worksheet. Make sure the cursors are full retracted. You can usually make the graph taller than the screen but if you make it wider the reader has to scroll right-left to see it so I normally stick to screen width.
2. Right click on the white border of the graph and select 'format chart area', set the font say to 9. Make sure the titles etc all roll over if not set them individually by right click method.
3. Right click on the legend and 'format legend' and place it where you want. I usually put it on the right.
4. You can stretch the graph and reshape the legend to maximise the display of your data and get rid of wasted background.
5. Save your file and then pick the whole display by left-clicking on the white border then right click 'copy'.
6. Now open Windows 'Paint' and click on 'edit - paste' and your graph will appear. Don't edit it with Paint as it will mess the layout completely. That's best done in Excel.
7. Use Paint to save the file to your chosen folder as a 'GIF', this seems to give better repro than JPEG and bitmap won't upload. When it says 'there may be some loss of formatting do you want to proceed?' just click 'yes'.
8. Upload your graph to the site and have a look at it. If you're not happy delete the attachement and have another go at prepping it before you paste into Paint. I am not at all concerned if you upload and delete in your threads till you're happy with it.

That's what I do, seems OK. Hope that helps.

GC