modern motorcycle 4 valve head porting 1

[jk12r]

I have a bmw k1200r and am looking to get the head optimized. I have a spare head and looking at it the casting is pretty good already.

Valve angles are tight at 11 and 10 degrees, exhaust and intake.

The "short side" radius is nearly straight and flat into the combustion chamber.

You can see the obvious "production" nature of the head with a distinct transition between the machined valve and the cast runner, but other than that, I don't see much can be done.

The combustion chamber has sharp edges that probably should be softened and maybe a little unshrouding.

Am I wasting my time and money? Are modern motorcycle heads pretty much "maxed out" without spending thousands.

I see head porters advertising outrageous claims for head porting that I just can't believe.

 

[jk12r]

Just to be clear, because rounding the quench edge and reducing compression keeps being brought up, I highlighted the area that I meant to fill in. That'll smooth the edge without having to lose compression or quench.

http://i220.photobucket.com/albums/dd94/jcwk12r/P1030751-1.jpg

 

[patprimmer]

Are you going to continue to ask the same question in hope of eventually getting the answer you want?

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[jk12r]

No. Sorry. But it seems that you keep bringing up that you wouldn't round the squish, and I wanted to make it clear that wasn;t what I meant. That's all. I understand everyone's point not to touch the quench pads itself. It's the chmaber ceiling that I'm rounding off though...

Appreciate the suggestions. Now to find a good head builder.

Any thoughts about tumble vs flow ports and porting? A few SAE papers on this that I might have to find. Unfortuantely, online they want $15-$20 per copy of the articles. I don't know if they let alumni back in University libraries?

 

[jk12r]

I guess my motivation to post this question here is to see if anyone felt (or had first hand experience) that modern motorcycle heads had very little area to improve in terms of porting and chamber work for more power. (Mainly to confirm my suspicions that many head builders for motorcycles are padding their dyno numbers.)

Also, I see a few SAE papers refering to improving fuel economy in modern 4 valve heads allowing them to burn much leaner while still producing good torque. A lot of these topics include improving tumble in the cylinder and quench areas. Unfortunately, more tumble usually means less flow and possiblity less high rpm hp.

It's an interesting topic, to me, and I wanted to see if anyone had thoughts about this...

Hope this wasn't a thread killer.

 

[marcusaurailius]

JK 12 R, looking at the pics of the head, the sharp edges around the exhaust valves[the lip in the head] should be rounded off,

doing this will allow the gasses to follow the contours more easily, and go out of the valve, rather than cause a bit of .. stand off/breakaway.. in that area,.

..imagine lets say water, running down a wall, it will go to the floor where the two meet, ..in the edge, yes!
Now put a sharp lip on the wall, the water will then be thrown out, past the edge of the wall/floor,.

this is what you have got, ...but rounding the lip off, [a half round ] will allow it to follow the contour, ..without.. breaking away, and still end up in the edge



this is more pronounced at valve openning,than full lift,.
as at 1/4open to full lift ,the stand off/breakaway, will be flowing in to the port, as it is now at the same ,or greater height.

where as when valve is just starting to open,it will not be, because ,it is below the lip.

this is a little like what i said earlier ,about gasses ..going ..over the valve, and not out off it,.

but is slightly different,because it is the lip that is doing it, not the over lap,.

hope you can follow this, ,its easy to visualise when you know what one means!!

regards Marcus

 

[evelrod]

There is only one real way to sort this out, sadly. I have been through this all too often in playing at porting...I port my own heads cause I'm cheap. I just enjoyed the building as much or more than driving race cars. A character flaw, I guess. Anyway, you will need to modify a head and try it out. If it's an improvement, go with it, if not...

One caution, well maybe a couple...Careful about piston pop ups as in any centrally located sparkplug head, they can really disrupt the flame travel if not 'just right'. From the photos, I'm guessing that your idea of adding metal will not help overall power. I'm guessing bottom end and maybe even mid range will improve, but top end will die.

Just my ideas...I'd open up the head in those areas for max flow, a moderate pop up on the piston taking care not to mask the flame front and do some serious testing with camshaft design, paying close attention to lobe separation and timing events. Wow, that should only set you back a few months and a bag of gold or two!!!

I wish there was an ironclad way of doing all this on paper or computer, but...It all comes down to the "cut and try" approach, even for the best of engineers.

Best of luck. Keep us posted, especially interesting for me as I have never done a four valve engine.

Rod

 

[jk12r]

I've read that the best head porters stand head and shoulders above the rest. Literally, because they stand on all the trashed cylinders heads they've experimented on and didn't work.

 

[jk12r]

marcusaurailius, if you have a similar forum name on the Kawasaki boards, I've read your posts on shrinking the zx-9's heads. Thanks for your input.

Thanks to everyone. I think I'm just going to have to trust someone and just do it, then dyno it.

Evelrod, I agree completely about experimenting with cams and timing. The stock cam looks a little short on duration. I just wish they weren't $600 a pop. Yeow! Slotting the stock cam sprockets should be doable, though. Delaying intake valve closing may help. Any thoughts about long rod engines and cam timing?

 

[evelrod]

If you are using aggressive cams and simply switch to longer rods, pay close attention to valve interference. I personally did not find the long rod conversion I did on a Lotus twincam to be as big an improvement as expected...it was, however, an improvement, so I changed the cams to a less aggressive grind. Lap times at RIR were similar with either engine, long rod or short rod, but the rev range was lower on the long rod engine, by about a thousand rpm. Long rod engine was for endurance races and worked out quite well. I still have all the pieces minus the crank on the shelf. One day maybe I'll put it together again.

Rod

 

[jk12r]

Fortunately (or not depending on how you look at it), the BMW engine has a rather long rod to stroke ratio. A little over 2:1. I was wondering if there were any significant differences in cam timing tuning.

Because of a longer "dwell" period near TDC (piston moves slower at TDC), I've read that less ignition timing is needed and less duration is possible. On the flip side, the piston moves faster at BDC and intake valve closing should be slightly earlier. I have no firsthand experience to back this up though.

 

[mburgess]

Before you touch enything I would do a dummy assembly & determing. Squish clearance & piston to valve clearances. While at it I would also burette the chambers as often actual compression is not exactly as per specs. If you a have no room to skim the head or deck I would leave the chamber well alone unless you want to machine the pistons. With regards to welding the chamber to back fill to the ridge you are very close to the valve seats & the heat from the weld may dislodge the valve seats.

If you have room to skim I would limit myself to deburring the pads at best, blend the valve seats to the chamber on the long side radius, blend the valve seats to the throats & also blend the inlet to the rubber manifolds. Look at the port suface not to promote fuel adhesion. A good valve seat cut makes a difference. On high octane pump fuel I wouldnt go over 13.5:1. But would try to optimise squish clearance down to 0.6 - 0.7 mm.

As others ghave said there are no set rules, often optimising inlet & exhaust lengths to cam & ignition timing can yeild greater gains than a port job alone.

It can often be very time consuming for small performance gains. HP may be one thing but look at the weight of the bike as well is it all worth it?
Regards,
MB

 

[jk12r]

Thanks for the suggestions.

The squish clearance shouldn't change if you skim the head should it? The quench area is flat with the head surface in this application. But piston to valve clearances certainly would. As you suggested, I would definitely check piston to valve clearances with ANY head or cam changes. Cc'ing the chambers would be part of the head work, I'm assuming.

Good point regarding the seats. If not dislodge, the welding will "soften" the metal to the point that the valve seats "walk" and cannot create a good seal. Even if a valve job is done after the welding. I'll leave that up to the expert head welders. If they think they can do it without harming the parent metal casting too much, I'll be willing to give it a try.

I've been told by someone that has modified this head that it is VERY detonation resistant and claims to run 14:1 compression ratios. He unfortunately is very vague about what he's done and has no pictures although he said he did machine the pistons for proper valve to piston clearance.

What kind of finish do you recommend finishing the walls with. Currently it is a rather rough casting. More rough than I would think would be beneficial. Otherwise, a good standard variable radius port and valve job seems to be what is called for.

Another good point regarding optimizing the intake and exhuast systems. Have to think of the engine as an enitre system rather than just the head or cams or pistons. Thanks. Unfortunately, it's easy to send the head out to get worked on. Harder to find someone to build you exhuast systems and complete intake systems.

Weight, ahhh yes. I agree completely. The bike is rather a cow compared to the modern liter superbikes. But I've done my best here so far. Magtan forged magnesium wheels, some carbon fiber pieces, lighter exhuast, titanium bolts. All rather standard stuff.

 

[patprimmer]

From an engine builders point of view, the best way to reduce weight is for the driver to go on a diet. I know, not nice.

To reduce quench gap, shave the top of the block or run a thinner gasket then correct compression elsewhere, like increasing the depth of the dish.

If you shave the head or the deck or use a thinner gasket or change cam timing in any way you will need to recheck the piston to valve clearance. If you need to increase the depth of the valve relief in the piston you will lose some of the compression you gained, so measure first and do your sums to avoid several trips to the machinist.

Do not weld the head. The risk of damage and reduced performance is not worth the slight potential gain, especially when there are non risk methods to get the gain.

Unless you have flow bench data to the contrary, do not increase the size of the port upstream of the area where it divides as this area already looks to big.

If you have good tight quench, that will do more for chamber turbulence than any tumble or swirl introduced by the port design.

Remember the action of quench is to introduce turbulence away from the edges toward the plug or flame kernel just after the plug has fired.

The action of swirl or tumble from the ports is as it enters the chamber and by the time the chamber fills, then the piston moves up the compression stroke, most of it is lost.


Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[jk12r]

I really appreciate your suggestions. Thank you.

 

[marcusaurailius]

JK12R, be very cautious about increasing the compression figure, as you can have too much!!



regards Marcus

 

[evelrod]

Port finish:

Leave it rough. At least, do not polish it to a fine shine.
That mirror finish may look great in a photo, it may even impress your girlfriend...it will not help flow at all. In fact it probably will flow less.

There was an old demonstration I saw by a very famous engine builder...long time ago...It may or may not be the final solution to the question, but I was convinced. Put a drop of alcohol or fuel on a piece of glass and one on a piece of sandpaper...Now take your air nozzle and blow it off.

I have never since 'mirrored' a port. Saved my sanity, for sure and, has never lost me one hp.

Rod

 

[patprimmer]

I like satin finish on long side of port and don't care to much about short side which can be as cast or as cut with a carbide bur.

I like to polish the chamber for other reasons, although I think the gains over satin finish are marginal. The reasons are retaining heat, not flow.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[evelrod]

Your kinda our 'chemical' guru, Pat. Did you ever try some type of coating? I did a combustion chamber with white heat resistant paint once, as well as the piston tops. It seemed to work ok and did NOT burn off in a couple races. Never tried it on the dyno for comparison. Only did it on the one engine... the long rod Lotus twincam @ ll:1 CR and Cosworth L1 cams. I don't have the head any longer, but I still have the pistons and the paint is still mostly there. I think that engine made a zillion races...it just kept on keepin on through several owners. Hmmmm. Maybe I'll look into that aspect of cylinder head work again. There must be some stuff about...Google?

Rod

 

[patprimmer]

Rod

Ceramic coatings designed specifically for the purpose do stick and are very good insulators, but to stay stuck, they need to be thin, which reduces the time it takes to transfer heat through them, so on bench tests that take seconds,the heat transfers through with little delay in relative terms.

It is argued that in the time of a power stroke, little heat is transferred before t is cooled again by the incoming charge. Hole n that argument is that as the incoming charge is heated, the advantage is lost.

Many top teams use thermal insulating coatings on piston tops, cylinder heads and valves to improve thermal efficiency and to reduce especially piston crown peak temperature to reduce the occurrence of holes burning through.

I give it some credibility on logic, but I have never seen back to back statistically significant proof.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[Rob45]

Jk12r:
This seems to be a long and informative thread, but there's one topic I haven't seen mentioned, and that is the generally large difference between 2-valve and 4-valve heads, since, for similar specific outputs a 4-valve head will have less valve lift and much less valve overlap.
So, your porting work should be focused then on things that improve flow at small valve openings, you are less concerned about intake charge blowing out the exhaust, and the engine is less sensitive to exhaust backpressure.

In short, what works on 2-valve engines may not work so good on 4-valve engines.