High Performance Cylinder Heads??

[Highside]

Well, after getting my hands on an XS650 cylinder head and taking a close look at it, I can see right away some of the performance restrictions built into it.

The valve angles are too steep, resulting in a chamber that is too large. You can't get good CR's without risking detonation or combustion dead spots (maybe that's why they went with the cast iron chamber inserts?).

The exhaust port is poorly designed. It starts its horizontal bend right before the valve guide, causing bad flow bias around the valve stem. To compensate for this, they made the exhaust valve too big and gave the port too much cross sectional area for the airflow requirements. With some heavy meatball surgery, I bet I can get this port to flow the same, or better, while reducing its volume.

650 Central.com sells a head for $1400 which it claims is the best thing on the market. For that price, you could almost make a custom billet head that would solve the design flaws of the stock head and make 70+ HP with little effort.

Are there any other high performance heads on the market for the XS650??

 

[Rexxis]

I've heard that getting these engines to push 70+ hp is tough on the cases, the engine wasn't designed to handle that kind of horspower and will tear itself up over time unless you start to reinforce the cases. I think I remember reading that the cases start cracking often near the oil delivery pipe.

Something to think abt.

 

[retiredgentleman]

There are lots of bikes in the 70 to 100 HP available in the used market. Why not just buy one of those. These bikes are 45 to 50 HP, and work well in that power range.

 

[Ironsled77]

That would be no fun RG! But what do I know I run a stock motor

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[Highside]

I've heard that getting these engines to push 70+ hp is tough on the cases, the engine wasn't designed to handle that kind of horspower and will tear itself up over time unless you start to reinforce the cases. I think I remember reading that the cases start cracking often near the oil delivery pipe.

Something to think abt.

Pushing the case to the point where it cracks isn't what I'm after here.

What I AM getting at is that the XS650 has a poor cylinder head design, and performance modifications that work well, are designed to compensate for its design flaws.

If you start from the begining with a well designed cylinder head, you can get a powerband that is broader and more useful than one than one that is trying to limp its most important part.

Cylinder heads are the weakest link in the performance chain, which is why good heads are so important. Fix the cylinder head and making the powerband that YOU want becomes easy.

 

[Highside]

There are lots of bikes in the 70 to 100 HP available in the used market. Why not just buy one of those. These bikes are 45 to 50 HP, and work well in that power range.

A proper cylinder head would give the 650 engine a broad power band in the 65-70 HP range.

Look at my OP, I'm talking about droping the exhaust valve size down to as small as 1.187 with the exhaust port opening at 1.2.

Also, a small chamber that can achieve high CR's with flat-top pistons will make more power from idle to redline. (not to mention, lighter pistons)

 

[xstra]

The OÜ/OW head series were developed by US yamaha racing to counter this problem. They're pretty rare.

 

[Highside]

The OÜ/OW head series were developed by US yamaha racing to counter this problem. They're pretty rare.

Is this what they're selling at 650 Central for $1400??

I'd like to look at one to see what they did, but I can already guess.

If I had the time and money, I could draw up a billet head in Mastercam and try to talk Alan Johnson Cylinder Heads into making a prototype for me. I think I'd have to convince them that there would be a market for these. They didn't have much luck selling Harley heads.

 

[jchrisk1]

"They didn't have much luck selling Harley heads."

Maybe they should have chromed them.

 

[xstra]

Is this what they're selling at 650 Central for $1400??

No, completely different.

 

[650Skull]

This is why doing a good port clean up, (and no 2 heads are the same), and free'r exhausts, (still need a restrictor), is a better value option for power than bolting on a 750. the thing to be real carefull about is not to enlargen the ports but to remove the casting marks and redefine the shape around the valve guide. Some of them can not be worked on without building up some material first.

 

[Highside]

"They didn't have much luck selling Harley heads."

Maybe they should have chromed them.

 

[Highside]

This is why doing a good port clean up, (and no 2 heads are the same),

Yes, that's called "core shift".

and free'r exhausts, (still need a restrictor), is a better value option for power than bolting on a 750.

That's because the work is cheap and easy to do. The stock pipe ID is smaller than the port. A bad exhaust design if there ever was one.

the thing to be real carefull about is not to enlargen the ports but to remove the casting marks and redefine the shape around the valve guide. Some of them can not be worked on without building up some material first.

Yes, that confirms what my eyeball flowbench (thechnical term there. ) saw right away. The exhaust ports and valves are too big. That's why you don't want to take material out.

If I was to go hog wild porting the exhaust, the first thing I'd do is cut the entire port roof off and weld up the port floor. I'd also weld material to the top of the exhaust flange to re-machine it, and move the headpipe flange up .125 or so.

 

[Highside]

No, completely different.

Do you know who has one of these or where i could find one??

 

[PHeller]

So what can be done on a budget to cure the problematic stock heads? Anything?

It sounds as though the head needs to be redesigned from the ground up, this costs money.

As much as I, and probably anyone would like to bolt on 20hp for $800 or less, it aint gonna happen.

By the time you solve all the problems, mill the thing, and get it to my door, you'll want what the competitors are charging.

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[Rexxis]

I've heard somewhat noticeable gains can be achieved just from cleaning up the casting defects within the ports, just smoothing everything out, not polishing but just taking out all the inconsistencies. I'll be doing this in the next couple of days before my 750 kit gets bolted in.

 

[Highside]

I've heard somewhat noticeable gains can be achieved just from cleaning up the casting defects within the ports, just smoothing everything out, not polishing but just taking out all the inconsistencies. I'll be doing this in the next couple of days before my 750 kit gets bolted in.

Not exactly.

There's very little flow loss due to casting defects (unless severe). What there is, is a mis-match between the casing and the machine work. This is most noticable in the valve pocket/bowl area. Blend the two together (commonly called pocket porting) and you should notice gains there. Also, the short turn radius needs to be worked to smooth it out. Form what I've seen of the 650 port, it might respond to some material being removed from the outboard wall in the area of the valve guide.

You might also want to put a 30 deg back cut on the intake valve, if it doesn't already have one. Thst usually gets you a few CFM on the bench,

 

[Highside]

So what can be done on a budget to cure the problematic stock heads? Anything?

It sounds as though the head needs to be redesigned from the ground up, this costs money.

As much as I, and probably anyone would like to bolt on 20hp for $800 or less, it aint gonna happen.

By the time you solve all the problems, mill the thing, and get it to my door, you'll want what the competitors are charging.

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I'm not sure that there's any competitors, but if I was to do a billet head for the 650, you'd be looking at ~$2,000 because I'd change the valve angles, shorten the rocker arms, and re-design the head cover.

 

[mrriggs]

I have been toying with the idea of casting a head for the XS. Instead of going radical, it'll just be a refinement of the stock design; less valve angle and smaller ports and chambers.

I want to use a stock style camshaft so it would need shorter rockers to accommodate the narrower valve angle. That has been my latest hangup. Can anyone suggest a bike (or car) with suitable rocker arms?

 

[xstra]

OU/OW heads have steeper valve angles, shorter rockers, completely aluminium hemi combustion chambers not with a steel insert like the production ones, different port shape-where the production angles outwards these are straight ... these are some of the differences, i have a head but no rockers ... i have also personally seen billet heads for these made in short runs