One of you chaps posted a photo of a modified cylinder head done in the Harley KR style a month or 2 ago. It was in a thread that did not relate to performance mods and I can't find it using the search function or scanning the forum entries.

Any help is appreciated.

Jeff

email (option): jjbandoo@aol.com

i think this is what you were looking for: THREAD- sidevalve performance

also here's a link to a blog on a chap and his factory Harley WR racer. there are some good pictures of the heads here: http://www.wrdaytona.blogspot.com.au/2011/03/top-end-wonders.html

Just what I needed, Nick! Thanks!

Jeff

email (option): jjbandoo@aol.com

Jeff: The current issue of one of the US m/c magazines (I think Cycle World) has a commentary-style piece on cylinder head modifications for KR which concludes, in effect, that gas flow mods are just as important or more than compression mods. You may want to look at that, as well. It's not technical but more editorial in style.

email (option): jonny.rudge@verizon.net

Interesting stuff on the WR...Does anyone know the carb size for a WR or KR Harley?...Ian

email (option): ian@wright52.plus.com

1 1/2 inches.

The Cycle World article by Kevin Cameron got me going on this. Not sure it's legal to post it in its entirety. He emphasizes the importance of "pop-up", or piston protrusion above the cylinder, to allow a larger flow area as the piston drops after TDC on the intake stroke.

How much pop-up do the KR's use? I'm guessing 2mm.

Jeff

email (option): jjbandoo@aol.com

Thanks Douglas..Such a large carb would indicate they are revving those motors well..Not surprising really when you take a look at the cam timing figures for the KR...Piston 'pop up' on the KRs was in the .080"-.120" range...
This increases the 'throat' size for the gas to flow into the cylinder on the induction stroke without compromising the compression ratio and 'squish' clearance. I got a piston made for the M20 sprinter with the extra hieght above the rings to include this feature. I used a figure of 1/8" for the 'pop up'.
What is interesting about the WR heads is that they don't include a 'dam' between the inlet and exhaust valves..though it is partially present as a result of the relieving of the cylinder head around the inlet valve.
That raises the question of what stops incoming gas, which begins to be drawn in towards the end of the exhaust stroke by the outgoing exhaust gasses, going straight out of the exhaust valve and not towards the cylinder?. I am making the cylinder head from scratch for the sprinter and whilst I have a basic idea of the shapes I am after for most of the combustion chamber this is one feature I am unsure about....Ian

email (option): ian@wright52.plus.com

Ian, you may well get more than one opinion on the matter, but here’s mine.

What stops the incoming mixture disappearing straight down the exhaust during the overlap period? At low to medium engine speeds, basically nothing, and the longer the overlap period the worse it gets. Never stand behind a highly tuned engine when it’s ‘idling’ else you’ll end up covered in fuel.

At high engine speeds however the exhaust gas stream has much greater inertia (if only because the rising piston provides more impetus), which helps to evacuate the cylinder to near-atmospheric pressure by the time the inlet valve is effectively open. Now add a positive pressure wave in the exhaust system just before that valve closes, and the small slug of fresh mixture which has escaped past the exhaust valve will be forced back into the cylinder. The trick of course is to get all the timings right.

Personally I wouldn’t worry much about trying to separate incoming and outgoing gas flow with some form of physical barrier. I’d design the cylinder and head reliefs to maximise the inlet flow potential because, as has been discussed before, this is the major deficiency of any SV engine.

ChrisJ

Ignore most of my previous posting - it's past my bedtime and my thinking was a bit muddled. I'll stick with the last paragraph though.

ChrisJ

Hi Chris...Yes, it's hard to get your head around exactly what is going on in the cylinder (and exhaust pipe) As the engine I am putting together has one off cams, non standard valves, non standard stroke to bore ratio, a one off piston, heavily modified ports etc. etc. the only thing I can do initially is set up on some 'best guess' inlet tract and exhaust pipe lengths and sizes and get ready to expend some cash on 'Dyno time' to get everything running at its best.
It is highly likely the ignition timing will need 'tweaking' as well as the burn characteristics will be quite different.
I've pretty much got my baseline figures for the inlet and exhaust worked out and I have plenty of time to think about it all as the engine is some way off being completed. I haven't started work on making the cylinder head yet, though I have done some modelling of the basic shape. I hope to get to that soon...'It's an M20 Jim..but not as we know it' ...Ian

email (option): ian@wright52.plus.com

I think the basic idea of ChrisJ's "recalled" comments is correct. A physical barrier may do more harm than good. It restricts both intake and exhaust paths, and probably reduces the vacuum effect of the exhausting gas as well as the speed of both gases. Getting the timing of exhaust/intake/overlap right would probably be of much more benefit than a barrier and the momentum of the exhaust can help maximize intake. With the timing right you would not waste much gas down the exhaust pipe since, ideally, the exhaust valve would close as soon as the fresh mix gets to it. A barrier would also complicate the path of flame propagation.

After all, a barrier would have been a simple thing for manufacturers to include, especially since it probably increases fuel mileage (albeit, if I am right, at the expense of performance). No modern or ancient flathead that I know of, whether m/c or car, uses a barrier, although I am certainly willing to be schooled on this point.

Before you spend money on dyno time you may consider just hooking up the engine to an electric motor and measuring gas flow with various setups to reduce the numbers of permutations that you would need to test on the dyno.

email (option): jonny.rudge@verizon.net

can i add my pennies worth when a general dogs body at a stockcar engine tuner he would experiment with porting on some single and twin cylinder motorcycle engines(trying to diversify) would get good bhp readings on one cylinderhead then just just reshape the inletport exhaustport or polish the ports a little more trying to make a smoother run for the air or exhaust and the bhp would be half of the original standard bhp another head in the scrap bin i think there is a very fine line between max and low bhp

email (option): roger.beck@node6.com

Hi John..Another point about a 'dam' between the valves is that it would be narrow and projecting into the cylinder head so may well end up working like a second spark plug!...I have already concluded I'll pass on that idea.
The electric motor hook up sounds like an interesting possibility...Ian

email (option): ian@wright52.plus.com

Nah, I don't see it. The nearest point of the "dam" will certainly be more than a few thousands away from the center electrode. Electricity tending to travel the shortest route (the route of least resistance) the spark will never get to the dam since the side electrode will always be much nearer. (But since you've given up on the idea, I may be beating a dead horse.)

email (option): jonny.rudge@verizon.net

Hi John...I was thinking more of the narrow section of metal heating up and causing pre ignition...Ian

email (option): ian@wright52.plus.com

Oh, yes. The old "trembler" engines did that but their top speed was about 300 rpm.

email (option): jonny.rudge@verizon.net

Roger makes a good point. From everything I’ve read, this damned stuff we call air is most contrary and you need a PHD or a lifetime’s practical experience to be able to predict what it will do. Opening out the inlet port to match a bigger valve and carb may be a no-brainer (as long as you remember to include a slight taper) but anything much beyond that needs to be tested on a flow bench.

There’s a wonderful photograph in one book which shows someone holding 2 flow wands (just a metal rod with a short length of thin string/twine attached at one end) at the mouth of an inlet port under test. One piece of string is being sucked into the port and the other is being blown out of it. Not exactly intuitive!

ChrisJ

Let me throw an extra ten cents in here. Something I did when I built my M20's engine was to send the piston, head and cylinder off to a company that provides heat reflective coatings. I had the piston top and skirts done, along with the combustion chamber of the head. On the cylinder, again the combustion chamber area, plus the item that provided the most benefit - coating the exhaust port. The cylinder hasn't turned red since. I cleaned up the intake and exhaust prior to sending them off. The bike, with slightly taller gearing, will cruise at 55mph easily without the massive heat buildup that I'd experienced before. My primary reason for doing this was an attempt to stretch the life of the various components. Less heat - less wear and tear. Seems to be working so far!! Cheers.

Hi Frank...I'd like to ceramic coat the inside of my sprint engine...Unfortunately I can't get it done cost effectively in the UK. For coating the two header pipes on my Harley Sportster I was quoted £480!!...Ian

email (option): ian@wright52.plus.com

Ian, Been busy - would have gotten back a little sooner. I believe here in the US you can get all of the coatings that I'd mentioned for about 200 US. You might look in to the costs involved with shipping them over and return. Customs normally shouldn't give you any hassles with that. ------ That being said - Customs has always given me hassles no matter what my dealings with them were. I've been searched, jacked up, fined and harrassed by the best of 'em!! The wife SAYS I don't look like a terrorist????????