Head flow testing.
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hobot said:
Smaller valves would decrease the velocity in the measured "straight" area of the port.
Bigger valves would increase the velocity up to the point where turbulence took over.
Since bigger valves also means increasing the valve angle, then making the turn to the valve without turbulence becomes harder.
lcrken
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A little more info on the head Jim just did. This is the head I was running this year on my 920 at Bonneville. It's an engine combination I ran in the ex-Jim Schmidt monoshock road racer for a while, and was a very sweet engine, with both top end and midrange power. The head was originally used on a short stroke 750 in one of the factory flat track bikes run out of the NVT shop in Duarte, California. I obtained it when I bought the bike from John Hateley after NVT folded. The engine was built by one of the factory tuners, might have been Jim Massey (sp?), who did the port and valve work. I always suspected it would have really good flow characteristics, and it's nice to see the details.
Kudos again to Jim for starting this test program and sharing all the results. For a Commando gearhead, this has to be one of the most interesting threads on the forum, and a great education in the intricacies of getting a Commando head to flow better.
Ken
Kudos again to Jim for starting this test program and sharing all the results. For a Commando gearhead, this has to be one of the most interesting threads on the forum, and a great education in the intricacies of getting a Commando head to flow better.
Ken
lcrken
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SteveA
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lcrken said:
This head is very interesting for me too Ken, having once owned a similar head, which I always understood was ported by John Baker, but it was from Thruxton whatever.
The thing for me has always been that the ports measured 34mm, which according to conventional wisdom doesn't work.....but I know that one did, when working with the combination of parts....cam. valves, hemisphered head and Omega 10.25s and 36mm carbs.....with mid range and top end...
Its good to see something similar that also 'works'.
Steve
Jim/Ken,
Could you please compare the RH7 head casting to the std heads for 850s - RH10 and RH4. Per your earlier description the RH7 head tested here is fit with 44 mm IN valves. We know that the IN valve size of std Norton 850 heads (RH10 & RH4) can be increased from the stock size of 38 mm to the common OS of ~ 41 mm, but can stock heads be further modified to receive a 44 mm IN, or is this unique to the RH7 head casting? Anything else worth relaying about the head casting - does the sphere size, sphere location, and or quench area differ from stock, are the guide angles different, are the guide diameters different, etc? Thank you.
Could you please compare the RH7 head casting to the std heads for 850s - RH10 and RH4. Per your earlier description the RH7 head tested here is fit with 44 mm IN valves. We know that the IN valve size of std Norton 850 heads (RH10 & RH4) can be increased from the stock size of 38 mm to the common OS of ~ 41 mm, but can stock heads be further modified to receive a 44 mm IN, or is this unique to the RH7 head casting? Anything else worth relaying about the head casting - does the sphere size, sphere location, and or quench area differ from stock, are the guide angles different, are the guide diameters different, etc? Thank you.
SteveA said:
comnoz said:
Are we taking a too blinkered view here ?
That hot-rodded 850 factory NV bike that John Baker developed Dave Rawlins rode to a 143 mph 2 way average had big ports, and the 4S cam, as detailed in the 2 factory tuning sheets that NV put out, on how to build your own Combat 850 version. Also had the big bore exhaust, big carbs, etc.
For a stock looking 850 to do those speeds, that ain't hanging around.
And reportedly it was quite tractible on the street, if a little tall-geared - it was ridden to those speed meets..
I am not all that familiar with the factory literature, especially the factory tuning sheets referred to above. I've seen some literature titled Stage I and Stage II sheets that are prints of suggested mods for heads, pistons, exhausts, etc. Are these the sheets referred to above or are we talking totally different literature? If different, where can a person see such literature and is it viewable/available on-line? Thank you.Rohan said:
lcrken
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WZ507 said:
The RH7 head starts with the same casting as the standard 850, but has the intake guide at a steeper angle (26.5 instead of 28 degrees off vertical) and has a fully sphered combustion chamber with no squish band. The standard RH7 has stock Commando exhaust valves and 1 5/8" intakes. It's basically the same design they used for the RH2 750 head that was homologated for AMA racing, but applied to the 850 bolt pattern head.
Ken
SteveA
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Rohan said:
I used the head on an 850, which would have been a similar spec to the 850s that they did actually build at Thruxton for use where rules allowed 850s.
I bought the engine as a kit of parts from Dave Sadler, who had the engine from the Baker Rawlins drag bike in his own Metisse, which was a circuit race bike. Dave expected the engine he sold me to be faster than the one he alreasy had, and was planning to build it for himself until he was made redundant by Norton in '75 and went off to mechanic for Alex George. I just happened along when he needed cash...thanks to Dave Rawlins who gave me his number and Griff Roberts who told me to talk to Dave...
I take Jim's point, and reflect on John Hudson's own tuning notes which was my build bible at the time. He said he personally prefered standard size valves but made sure to get the best flow around them. I think that relates to what Jim is saying...with a 73mm bore you won't get enough 'demand' and 'flow' to make it all work, but with a bigger bore and a port matched to valve size it can work. My view is that I know that from my experience and ended up with a bike that both fast and rideable on 34mm prts and 36mm carbs...... but that does not mean I advocate a big port or want one now. I am starting out with standard FullAuto...we will see where we need to go when next we know how rideable that is....
But I think I agree with you too, dogma is not the way forward...'only this works' or 'only that works'....various things 'can' work, it depends on the sum of the parts....what else is in there....port size related to port shape and valve size, piston shape/compression/squish, carb and manifolds, cam and bore/stroke....etc...
Looks to me like Jim and Ken have had various things work over the years
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SteveA said:I take Jim's point, and reflect on John Hudson's own tuning notes which was my build bible at the time. He said he personally prefered standard size valves but made sure to get the best flow around them. I think that relates to what Jim is saying...with a 73mm bore you won't get enough 'demand' and 'flow' to make it all work, but with a bigger bore and a port matched to valve size it can work. My view is that I know that from my experience and ended up with a bike that both fast and rideable on 34mm prts and 36mm carbs...... but that does not mean I advocate a big port or want one now. I am starting out with standard FullAuto...we will see where we need to go when next we know how rideable that is....
But I think I agree with you too, dogma is not the way forward...'only this works' or 'only that works'....various things 'can' work, it depends on the sum of the parts....what else is in there....port size related to port shape and valve size, piston shape/compression/squish, carb and manifolds, cam and bore/stroke....etc...
Looks to me like Jim and Ken have had various things work over the years
+1
What I have found for sure is:
If you have two heads that fit the same engine, have the same sized valves and flow the same CFM - one has 34mm ports and the other has 32mm ports -the head with 32mm ports will be the fastest around a road course and will usually make more peak power.
I did have a head one time on which I spent big bucks with a well known west coast tuner to port it and install big valves. [30 years ago]
He made the ports 35mm. I put it on my 750 longstroke racebike. No amount of cam changes or tuning would make the bike run as fast as a cleaned up stock head had before.
It was not until I filled the bottom 1/3rd of the port with epoxy that the motor made good power. Jim
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It looks like Dan Gurney has had luck with port design similar to my findings.
http://www.gizmag.com/dan-gurney-moment ... ult-widget
http://www.gizmag.com/dan-gurney-moment ... ult-widget
Kvinnhering
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It is very impressive effect. 262 HP with 1800 cm3 and 9.5:1 compression ratio.
Can not wait to finally assemble big valve Fullauto head that you have made for me. Dyno test will be performed during the winter / early spring.
Can not wait to finally assemble big valve Fullauto head that you have made for me. Dyno test will be performed during the winter / early spring.
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comnoz said:
Interesting stuff. More details here for those willing to trudge through patent language.
https://www.google.com.ar/patents/US9103277
This is apparently an over square motor. It looks like they use variable cam timing.
Using the above Google Link to access the patent I could view the text and placeholders for the images, but could not figure out how to actually view the images. If anyone encounters this same issue they may want to try this link from the USPTO where the images are visible.Dances with Shrapnel said:
http://tinyurl.com/jhcqdr3
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