Setting new standards in technology

griff851

In the interest of playing around in the shed I have been mucking around with my bevel heads porting. Knowing full well that they are a crap design and that any gain is a bonus I decided to play with old concepts. I'd originally did some cleaning and increasing of the port as well as a bit of port matching. Being young and stupid as opposed to old and stupid, I hooked in, but conservitally. I suppose I got marginal gains. Anyway reaching into the supply of high tech gear at my disposal. I made a smoke chamber out of plastic container you get from the supermarket deli (olives I believe this particular one had in it), and a PC chip cooling fan plastasine, and a bit if rolled up paper from the printer. Whalla, the world of flow opened up. Having seen the unseeable. I went straight for the JB Weld as so many have done before and created the ledgendary "D" port. Still not knowing jack shit about the ports actual performance, and after reading some stuff that another fellow suffering the same curiousity about his Imola cam powered head, I decided to build a flow bench. The cost for the bits from the hardware store was $13. 90mm down pipe stuff is stupidly cheap. It took about an hour to build and is powered by the household vacuum cleaner. Now before this I had done some pretty heavy calculations( about 3 pages worth), involving Mach index numbers and all sorts of stuff involving Pi valve size piston speed and shrouding coefficients created by cylinder wall etc etc. I had eventually come up with an optimum port diameter and some other figures relative to around the valve seat and valve guide. I found that I had way back gone 0.6mm over my optimum. So pissing around with choke area was my only option.
Well today I fired up the el cheapo home flow bench and compared one head done with glue and the other I hadn't touched since 1984. Now due to my casual approach to building the flow bench I have no scales as yet and the water levels were just a test to see if it worked at all. The water was 48cm high and I full control of the inlet valve so I could see the sort of movement I could get. From fully closed to max lift I got about 8cm of movement. So I compared heads. Low and behold there was a differance. The glued head had close to 1cm more pressure drop than the unglued head, so according to all the blurbs I've read, I now have supposedly greater port velocity, which combined with the larger than standard port volume, means I have increases dynamic cylinder pressure. And because while I was there I made some minor swirl assisting changes, I believe more torque should be generated. Only the road will tell.
It does go to show that with a little bit of planning and a bit if a think maybe a step in the right direction can be made in the shed.... By anyone. Just like in the old days.

Mr.R

That sounds interesting Griff,

But yesterday and today the sun's out here, temp' in the 80's (not in the shade), so instead of playing around in my workshop, I went out on my 851/916cc.
Went over to the North Cornish cost yesterday, bought a fresh 1kg+ crab for tonight's tea and visited an old female flame for coffee.
Today I arranged to meet up with some old (now mostly retired) bikers on the South Devon coast, at a cafe where we admired each others bikes, ate a hearty breakfast, smoked fags, drank tea/coffee talked bollox, remembered old times and caught up with old mates.
5 of us had all ridden (on Ducati's) over to France for the 24 hour Le Mans Moto race 12 years ago now.
There were 4 Ducati's there this morning inc' mine, a mates '92 851, another mates 1198R and a Monster of some sort amongst the Vincent's, Velocette's, BSA Rocket Gold Star, 60's Triumph's, Classic Jap' bikes and modern bikes.
The topic came around to... Do any of us miss full time work?
We all looked out over Plymouth Sound into the heat haze at the yachts, power boats etc messing around between the RN warships and had a good chuckle about that one.
The old ex Cafe Racers these days are more like Cafe Pootlers, but they're still enjoying themselves out on their bikes...
Happy Days mate.😎

Steve R

griff851

Makes life worth living hey.

wgsvintage

...and to think there must be zillion guys out there that think that playing golf is as good as it gets....

griff851

Well I set it all up properly this time, emptied the vacuum cleaner and everything. Got the water lines all neat and nice, put dye in the water and stuck on a ruler. Set the valves to 0.25 valve diameter lift, and remembered to put the spark plug in the unglued head. Results 53mm of water lift on the unglued and 70.5mm on the "D" shape with the angle of the flat set to induce swirl. Thats 17.5mm increase in pressure drop hence velocity increase. which equates to 33% increase. Now flow benches are like dyno's, only good for seeing changes, this has to be remembered. I have to calculate CFM later to see if I haven't created stalling at the valve lip due to mach index going above 0.5- 0.6 after which volumetric efficiency drops off.
But I can say for myself that dealing with the stupid short side edge of the valve seat definitely is an improvement. As well as ports surface done with 80 grit surface finish. Others have done this and found similar results, just nice to confirm it.

griff851

After finding calculators and doing math until my brain hurt I have come up with some data. It's not the most accurate but gives me a rough idea of where things stand.

Here are my results, but there are a couple of things to consider. First I've only used the choke size for calculations. This does not include the valve stem and guide. So CFM will be lower and so will port velocity which is good as my Mach index is too high. So it should I guess drop to under .6 the engine will still start to run out of puff some where above 7-7.5k which is reasonable for playing on the road. But as have tapered the port, the drag boys say this should help above 7k
Now the flow bench I made is very basic, but combined with the calculator ( you have to adjust CFM until you get choke size) gives me a rough idea of how it's going to perform. Like anything you can get really carried away with finer detail. But that just requires some more calculations ie valve and guide flow coeffients
Next I'm going to use 10" water to give me a better scale so I can see if rounding or angling the valve seat before the contact section makes much difference.
All this does apply to a 4 valve engine but some slight changes have to be made in calculations for valve sizes and the way they flow as a pair rather than single.
I will have to play with cam timing probably as the Mach index is a curly one.

Flow data 22C
70.5 (2.77") glue head 10.1mm lift
Port 35.5 choke 29.7 valve 42 70% choke to valve.
28.34" of water
Vacuum cleaner Can lift 650mm
Inlet pressure 14.6
Outlet pressure 25.52 inH2O
265 cubic ft per min

53mm(2.08) non glue @10.1mm lift
Port 33.47 choke 31.55mm valve 42mm
Inlet pressure 14.6psia
Outlet pressure 26.26 inH2O
298 CFM

Limiting port velocity at 8000 rpm 1031.23ft/s (314m/s) for glue head.
Peak torque @6381 for glue head
Mach index 0.61
To get Mach index down to.5 peak torque at 5500

Griff

hauge

Sounds great!
pictures? (

griff851

Well here it is. It aint pretty but it works. The manometer tubes are attached to the rack with good old electrical tape. The gold stuff on the combustion chamber is the new ceramic coating stuff (old stuff was grey). The pink stuff is plastacene from when I made the smoke chamber.