Porting Pics for your Perusal

[NONclow]

that still doesn't address why a pronounced D shape is better than what would in effect be a blended C with a flat bottom.

Six of one, half a dozen of the other. Now you're really splitting hairs. Expensive. Multiple head iterations, AND dyno runs??? Smooth it out and ride!

...gotta do some more reading, but this head is pretty much done for my purposes.........the more you look at your work minor imperfections become obvious...

Bingo! How much reinventing of the wheel do these ol' shakers need?

 

[hoffman900]

Head porting is not a black art. It's basic physics.

It's all about matching piston CFM demand at a targeted RPM while making sure the port isn't too slow or too fast.

Often when people think of porting causing the an increase in RPM, it's because material was removed, making the port slower - THUS the engine has to spin higher to equal the same port velocity.

You can port to increase efficiency. This will increase CFM and increase velocity (and decrease it in other areas) without removing so much material to cause the engine to want to peak higher.

In other words the engine will continue to rev higher and higher until it reaches a point where flow goes sonic (air reaches the speed of sound) somewhere in the port, and the amount of mass the engine sees is level despite an increase in pressure drop in the cylinder (piston CFM) demand. This is the point where engines nose over.

If the port is bigger, the it will require more piston cfm demand (rpm) to reach this point.

If the port is too smaller, it will occur at a lower point.

The 4 cycle otto engine is happiest with velocities in the 280-320fps range @ 28" H20 depression.

The straighter the port, the higher the average velocity can be.

The flatter the port, the more you have to slow down the air around the short side radius to get it to turn.

Valve shape and valve seat angles are critical.

There is a lot of good reading on the above elsewhere (there is also a lot of bad reading about it too). I'll post some links when I get a chance, but you should look into buying this book:

http://www.amazon.com/Practical-Engine-Airflow-Performance-Applications/dp/1613251572

Here is my head (SR500):

The head was sized to peak at 7200rpm with an average velocity of 300fps (1.77in^2 MCSA)

I graphed the flow numbers:

You can use a program like PipeMax to help with the math:
http://www.maxracesoftwares.com/forum/viewtopic.php?f=13&t=242

We tried several valve shapes, valve seat angles, etc. The biggest problem we had was port stability, but Nick (my head porter) spent a lot of time working on the short side radius. The port never backs up now and it is quiet on the bench. The depression numbers on the bench are stable as well. You look for this because a running engine will see higher depressions than most flow benches can flow at. If it's not stable at 28", it won't be at higher depressions. Our limiting factor was actually the casting. He ran out of room on the sides of the ports over the short side - so what you see there is about as wide and flat as the short side can be without adding material to the outside of the head.

As for the exhaust, you do NOT want to put a restriction right off the port. Match the port area to the tubing and carry that for about 8" before stepping up. The trick with the exhaust is to make it as small as you can without restricting - this requires using large 6" bend radii.. anti reversion should not happen at the head. which is partly what the D-shape port is trying to accomplish. The other is the ports on the vintage Yamahas are much too big for any power the castings could withstand.

I'll post a lot more later when I'm not pressed for time, but in the mean time, I have a lot posted here: http://www.xs650.com/forum/showthread.php?t=25773&page=3

 

[barncat]

hoffman900- skimmed through all of your posts. lotta info there, thanks. it's instructive to see how someone with a family racing background and access to exotic equipment approaches a high-budget motor build. as mentioned, i'm more of the "buy a used crotch rocket if you want to go really fast" camp, but more power to you, no pun intended. the art of optimizing these old motors is of course very satisfying...

agreed that porting is not rocket science, just envisioning how streamlining works. my port shaping appears to be on the right track, generally bearing in mind not to increase the OD of either IN or EX or remove any port floor- just reduce restrictions. also appreciate your pics, and on next build i will experiment with building up the IN floors and working on the short turn area. the tip re a smooth transition large radius EX outflow for approx 8" is i think a good one. competition valve work certainly runs up costs but duly noted.

also noted your flow observations with various carbs. before i knew much about tuning carbs i put a pair of TM's on a CB450 i built. thing ran horribly rich and fouled plugs routinely ( i switched to VM's), which has scared me off from flat slides on 4 strokes, but clearly by other threads on site they can work very well with proper brass.

intrinsically related to porting: care to offer an opinion as the the efficacy pro/cons of a single flat slide feeding a 1 into 2 carb intake of equal length runners for the XS head? and whether equal length runners matter? seems to me it would.

 

[barncat]

motor finished and ready to drop in to next build... sorry pics are sideways, very frustrating. they are correct orientation on phone. not familiar with new PC file management.

 

[Jack]

been playing with the Dremel. this head is going back on the '73 motor that's getting top end work for the next build. figured i'd document it for possible resale down the road. valves were cleaned up and lapped in thoroughly. i think later i'll build a symmetrical 2 into 1 carb intake for a 36mm VM...

that last time around Jack suggested i cut down the exhaust valve guides. opted not to then but this time i did. it's easy to drill them down with a sharp 5/8 half inch shank drill (low speed with a bit of lube), but you're left with a concave guide end. it's not easy to grind and dress that out manually and would be better to mill the guide off flat...

virtually all the material removed is roof and guide bosses on all ports, without enlarging the IN or EX OD's.

i was considering JBwelding up the intake port floors a couple mm but decided to save that for another more highly modded motor. just to double check- i know i've seen a post or two that says JBweld will safely stick to intakes. if anyone has horror stories about that technique failing please chime in here...

one other concept that crossed my mind while making aluminum dust is that the cavity behind the intake valve guide could be dramatically streamlined if a built up shaped feature was "glued" in. velocity would likely increase but perhaps the turbulence in the intake pocket is more desirable?

pics are of right side IN and EX valves from inside and outside, all inverted.

Photo one exhaust port, you don't want to feather or leave a sharp edge on the guide boss, it's a resistance point that'll deflect flow in making the turn,You want a smooth round profile.

Photo two, the exhaust guide in the bowl should have more of a radius on the shoulders,again to reduce resistance.

Photo 3 & 4 would be to address the length and 10 degree taper of the guide and more profiling of the guide boss area. There's more flow in those area's. There are no gains by back filling guide of the intake. You'll gain more by raising the floor and reworking the short turn radius to maximize port flow to cam lift. You know how I like my intakes reshaped(LOL)

In reference to the step in the exhaust port,in there's enough meat in the floor,or weld it in,make a aluminum insert with a tight interference fit thick enough to reshape that area and cant the floor up and out.

Valve margins, valve head shapes and valve job are key players also as mentioned by Mr. Hoofman.

 

[barncat]

hey Jack- thanks for the critiques. i did address your first two points some by making another pass at exhaust ports some time ago after pics were taken. perhaps a bit more feathering on boss than you'd recommend, but made sense at the time... this head will breathe pretty well i think, it's just a stock early cam. i'll fashion a press fit aluminum insert for the exhaust step when i get to pipe building.

did not attempt D intakes on this head. maybe next time. 3 motors left to rebuild. i'm more curious about running a single carb on this build. i believe you share my opinion that manifold intake tracts should be equal length? you referenced a UK made symmetrical casting for a motor in a sportbike frame in another thread somewhere...

 

[Jack]

The exhaust ports are looking good and yes the engine will breath 10 times better than stock. As for header building,a three step header starting with 1 1/2, 1 5/8 to 1 3/4 is what I'd shoot for good bottom end to top end performance,make the 1 1/2 as straight as possible before the radius turn with the radius being 1 5/8 ,this will allow less resistance in the radius turn to maintain maximum velocity to pull real hard on the port. I will look for a photo and post it to illustrate what I'm trying to get across.

There was UK member who was casting a beautiful 2 into 1 manifolds,don't know what ever became of it. Yes we share the same opinion on equal length runners on a two cylinder.

The red xs840
http://www.650motorcycles.com/AbbeWinterson.html

 

[650Skull]

I posted up the Pics i had of Jacks Porting in this thread
http://www.xs650.com/forum/showthread.php?t=12301&page=2

 

[barncat]

thanks 650Skull for the link. i'd heard of but had never seen those pics.

from your pics Jack and those from hoffman900 i can see i could be a bit more aggressive with reshaping the valve guides. since they are steel they are of course harder to deal with, literally, than the aluminum casting. more grinding than cutting for those, plus i need a few new and longer reach tools in my arsenal.

i'm pretty sure Speedway Motors carries 1 5/8 mandrel bends. i've just been using their
1 1/2 stock for headers, but i'll try the step up design. i used a pair of 1 3/4 ID x 17" Thrush glasspacks on my fist build which worked out well, though they are not the lightest parts out there... maybe fork over the cash for Cone Eng megaphones... the cheaper ones on ebay are not true unobstucted perf core designs as far as i know. anyone know of other good glasspack "phones"? these motors seem to run best for the street with about 17 or so inches of baffle. the smaller aluminum cans i welded up for my cafe bike are a bit raspy.

i think that UK guy with the 1 into 2 manifold is called Green Sand Foundry or similar. i'll probably weld up my own intakes when i get around to it. tricky to make a good tube junction though, and they have to be tacked up bolted to a head.

on an unrelated note Jack- i'm driving back north from FL soon with cafe bike on trailer. may detour to Asheville region. looks like roads 197, 80, 276, 215, 209, 63, etc... could all be huge fun. any recommendations, how bad/prevalent are the cops, and how's the pavement generally?

 

[Jack]

thanks 650Skull for the link. i'd heard of but had never seen those pics.

from your pics Jack and those from hoffman900 i can see i could be a bit more aggressive with reshaping the valve guides. since they are steel they are of course harder to deal with, literally, than the aluminum casting. more grinding than cutting for those, plus i need a few new and longer reach tools in my arsenal.

i'm pretty sure Speedway Motors carries 1 5/8 mandrel bends. i've just been using their
1 1/2 stock for headers, but i'll try the step up design. i used a pair of 1 3/4 ID x 17" Thrush glasspacks on my fist build which worked out well, though they are not the lightest parts out there... maybe fork over the cash for Cone Eng megaphones... the cheaper ones on ebay are not true unobstucted perf core designs as far as i know. anyone know of other good glasspack "phones"? these motors seem to run best for the street with about 17 or so inches of baffle. the smaller aluminum cans i welded up for my cafe bike are a bit raspy.

i think that UK guy with the 1 into 2 manifold is call Green Sand Foundry or similar. i'll probably weld up my own intakes when i get around to it. tricky to make a good tube junction though, and they have to be tacked up bolted to a head.

on an unrelated note Jack- i'm driving back north from FL soon with cafe bike on trailer. may detour to Asheville region. looks like roads 197, 80, 276, 215, 209, 63, etc... could all be huge fun. any recommendations, how bad/prevalent are the cops, and how's the pavement generally?

http://www.blueridgemotorcycling.com/ride-maps/cold-mountain-loop/

276 is a blast to ride in a fast mode but use some caution on 215 as the twists are close the edge of the mountains and one mistake in misjudgement will send you over. 63 is a boring ride IMO. Be careful on the Blue Ridge in regards to speed,they are cracking down and the fines are steep if caught. You will always have some type of gravel on the roads down here as what little shoulders there are have gravel on them.

One of the best sounding exhaust system I've heard on the XS is a 2 into 1 with a Yoshimura can,another option would be D&D canisters off ebay cheap.

 

[barncat]

thanks for the local road info. it would be similar to some of the riding i do in northern PA, but bigger mtns... spent a couple days in Asheville area about 12 or 13 years ago when i was considering relocating, back before i got into motorcycles. many years ago i bicycled a long stretch of the Parkway- started in Orlando and made it Roanoke before getting snowed off the road in April, but that's a story for another time. i do know to keep the speed down near 45 on the BRP... big federal ticket.

i suppose a 1 into 2 intake would be a good match design-wise for a 2 into 1 exhaust.