Good one!
The port size is adequate but the shape causes backups from velocity eddies and slow sluggish speeds. On the intakes raise the roof gradually and open the bowls but don’t do anything to the floor after the turn. I use a bowl hog the size of the valves then keep the floor narrow and widen the top all the way to the manifold (intake) and if you can try to keep that shape in the manifold and if you are running a magneto or deleting the electric start, block it off get a battery that will allow you to attach 2-3 more inches of manifold the same shape, btw I used Virago intake valves, then attach the boots and carbs with pods. The exhaust just wants out and they are plenty big. The intake with that spread \_/ shape with the roof Wider than the floor and a double length manifold the same shape is worth torque and without swirl and backups hp. I wish I could draw it out, but David Vizard can help you get the most out of the head.,at 45 ci, 70 hp and 65 ft lbs is not out of reason with the long intake ports and good exhaust. And a 300 degree rephased cam similar to the XS2 specs. I port my wedge heads the same way.
Lengthening any way you can on the intake ports and manifolds will improve your performance in daily use. Long intake ports will pick up torque and my post on hogging the intake bowl and keeping the floor after the turn narrow and widening the roof of the intake port and manifold will surprise you with how much useful power you gain 3000-6000 and still rev out. Longer ports will amplify the flow in the low to mid range and all the way out. You only have atmospheric pressure on the intake side, so the more mixture you can have ready when the valve pops barely open will be almost like what a supercharger does just by the amount of mix there. Exhaust just wants out and during overlap you are in that period pulling the air at higher than atmospheric pressure for that short time.
Exactly! Those from my magnifier appear to be Delortos, I can’t read any text on them, are they pumpers with the atomizer accelerator pump? I do like that manifold, that’s like a tunnel ram! I bet it would about pull a house with that induction. Did yo make it or scavenge pieces from another bike? How much did it knock off of the top end?
On V8s I have built Ford FE s mainly that is exactly how I have my pistons, a good dome, light balanced skirts and with floating pins as light of pins as will live as a fulcrum for the reciprocal mass kept in place by springs or Spirolox. I have a 500 hp 390 that I built in 1999 weighing everything, and matching it all up, and none of it was exotic expensive material. Just carefully machined and matched, I drag raced it for a few years, daily driver a few years, and my son can take the car out to get everything “wet” and 7000 rpm’s seems to do it and that strategy is pretty well descriptive of how to build a long life engine without going broke. I really hope that future generations can absorb this as it way more important than the parts that are thrown into the battle. I have also used 352/360 rods and tool steel pins with Spirolox because they improve the rod ratio and allow the pin to be higher in the piston and with this reduced force to the crank pins you maintain a better wedge of oil and a more stable environment that reduces friction and temperature variations.
My XS heads took some work but shape is still a big game changer when it comes to flow, especially with a hemispherical shaped chamber. You can’t use wedge principles with a SOHC Hemi. I learned that from working with Ford aftermarket design to possibly reassurect the 427 SOHC to complete in AA/S with the Chrysler Hemi. Ford Engineers had painted themselves into the same corner the XS 650 head was. The SOHC with 1:1-1.2:1 buckets and followers put a choke chain on ratio. The cams had to grow and we know that the Single valves on each side required lobes that ran air speed either too fast or too slow. I managed by porting a head from a Heritage Special 447. I reshaped the ports on both sides to flow a balanced 242intake and 200 cfm exhaust. But the trick was to create a trapezoidal port on the intake side so that this peak plow occurred at .300, the exhaust at .250 by reducing the size so that during overlap the exhaust would blast out and using the right cam, the XS2 specs with generous overlap would pull much more airspeed to get the air flowing. The engine made good torque and hp a real overachiever, and the 427 SOHC when scaled up was a really strong. Surprisingly though a pushrod Hemi with 1.8 ratios had its number. The project was dropped in favor of the 7.3 Godzilla as the future, just GM saw the same writing with LS and Mopar…. So a 750 SOHC will always be a 70 hp 70 lbs ft engine and that is more than than most people need on the road. 4 valve, you get more but not proportionally. 2 more cylinders with the 4 valve head, but it loses that 2 cylinder 270/90 277/83 or 360 degree charm. A 750 air cooled SOHC at 70/70 on a nice lithe frame is pretty darn sweet, and if I could see to ride and build it, be on it like a chicken on a junebug. How’s about you guys? It’s 1.53 per cubic inch on pump gas built as an air cooled engine and 1.53 ft lbs per cube. That will sound as wicked as any Harley, make more power on a cafe racer than even a Vincent Black Lightning and you won’t have to lay flat in your skivvies on the salt to break the records that Vincent set. On an XS2 style cafe profiled racer, what in the world would anyone need, maybe the long intake DelOrto setup could get you to 77/85 hp and tq? Man I want that intake ? Lol. That would be 1.68/1.81, are you talking orders for these intakes? Man a 45.7 ci 1.7 hp per ci and 1.81 ft lb per cube, har har har! CB750 with a little Kaw MK 4 thrown in?Hey Jack,
Good seeing you still around.
We're pushing 133cfm/sq-in through the MCSA of the head. Peak flow is 235cfm @ 28" @ .600" lift (230cfm @ .500) through the spigot.
With the carburetor and velocity stack bolted on, it goes down to 216.3cfm @ .600 and 208cfm @ .500
A TM-38 will flow 277cfm @ 28" H20 at full open, or 156cfm/sq-in.
This is by all means, not a 'maximum effort' deal. Looking to peak around 7000rpm on a 540cc deal on the street engine. A 40-42mm dia "MCSA" will allow the head to reach a bit over 240cfm.
The two biggest limitations with the stock Yamaha castings are:
1) material in the port sidewalls. This limits how far you can widen the short side radius. We're about at the limit of what we can do.
You can see here:
MCSA is at the port entrance to the head - it needs to be back that far as the port needs to gain area from there to slow down the air enough to get it around the short side radius without separation.
2) Valve lift. Being an OHC set-up, you're ultimately limited on how much valve lift you can run. On a pushrod set up, you can juts keep putting longer valve stems in and work with a rocker manufacturer and come up with a higher rocker ratio than stock. The Royal Enfield guys have done exactly this and are seeing over .600" valve lift without Myhaving to use more lobe lift. A win-win.
We're great on velocity - averaging about 300fps through the port. Believe it or not a bigger valve for us did not gain much in cfm, but did make the port more stable and quiet with work. A great thing since running depression can be over 3x what you can measure on the bench.
I d think it would have to have the alt rotor for balance. And the trans may need the sprocket?
I can’t stop looking at that beautiful pair…. Is the video an 880 rephrase 270/90 with a 533 crank? It has a really good snort!
The test was done at 28 hg like an automobile head. The port shape is very easy to get great numbers at low lift numbers with a v shaped port narrow at the bottom and wide at the top. The overlap is also very strong in the blowdown and the opening of the intake right off the seat they move fast, and I used Virago valves. I did some filling and the Coefficient of velocity is very strong and this points to a very aggressive flow and action right off the seat. The way that Shell Thuet did his ports is a good blueprint on what these ports like.
