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modern motorcycle 4 valve head porting

modern motorcycle 4 valve head porting

modern motorcycle 4 valve head porting

(OP)
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.

RE: modern motorcycle 4 valve head porting

I find the steps with sharp-ish edges in the chamber interesting.  They appear to be intentional; I just wonder what they do.  I'd want to know before I hacked them off, but that's just me.

In what way is the current head unsatisfactory?





 

Mike Halloran
Pembroke Pines, FL, USA

RE: modern motorcycle 4 valve head porting

(OP)
It's not, I was just looking to squeeze 190hp out of the engine without having to split the cases.

The combustion chambers of performance heads I've seen are smooth. I thought that the sharp edges at prone to start detonation.

Engine stats- 13.0:1 compression ratio, 2:1 rod stroke ratio, 1157cc, 79mm bore 59mm stroke. intake 32mm. exhuast 27.5mm. Cam duration advertised 268deg. lift 9.1mm. Intake valve closing @ 0.04" 38 deg (?)

RE: modern motorcycle 4 valve head porting

(OP)
My other question is are most modern motorcycle engines primarily a tumble type of port?

With the very straight intake port, they look like the mixture tends to shoot a little past the valve. It hurts ultimate flow, but the quality of the mixture in the combustion chmaner is good.

Too much porting would kill velocity and hurt power, no?

Problem is, with the very small valve angle, maybe the head flows better and tumbles less.

I need to go back to school, or buy a $30000 engine sim program. :)

RE: modern motorcycle 4 valve head porting

www.mototuneusa.com presents some interesting ideas on this.

You will probably find that the port areas are already too big.

RE: modern motorcycle 4 valve head porting

JK12R although not a B,M,W** head/engine he principle is still the same, as what was done to an engine i had,.

if you are looking for better low down grunt,
then ..set .. the exhaust valves 20-40 thou deeper in to the head, than standard

this will go a little way in altering the flow of the incoming charge,.

because the exhaust valve is now  ..below..the inlet valve, the charge tends to ..go over.. the exhaust valve ,and not ..thru it..  So more mixture goes into the cylinder to produce more power

i.e,  overlap conditions,[both valves open together] the trade off ,is a little less poke at the top end,but a little more at the bottom /mid range

i have this mod on my car, and it pulls from below idle now, where as before it would not pull well till about 1100rpm

** this was done on a 2 valve flat roof combustion chamber,so might not work as well on a hemi head

 

RE: modern motorcycle 4 valve head porting

The ridges in the combustion chamber are there to provide quench, which is used to create turbulence. As the piston nears these pads it squeezes the air into the center of the chamber. Besides that, if you grind these down you will obviously lower the compression ratio.

ISZ

RE: modern motorcycle 4 valve head porting

(OP)
I realize what quench is. I am not talking about getting rid of that. But you can fill the valleys formed by the unusual square edges at the "top" of the combustion chamber.

It's not my idea, if you look at perfomance heads, you can see that they gradually build up to the squish area.

Here's one from DPR...
http://www.se-r.net/about/200sx/scc/feb98/feb6.jpg

And from endyne...
http://www.gbrtuning.com/S2000_endyn_record_holder_head.jpg

This would require welding some material and smoothing it out. And would increase CR.

RE: modern motorcycle 4 valve head porting

(OP)
I should have said corners instead of ridges. :)

RE: modern motorcycle 4 valve head porting

From a personal experience...My Lotus twincam head has significant squish areas...two valve semi-hemi configuration.  By simply blending the edges of these areas I LOST FIVE HORSEPOWER...It took several times on the dyno to find out what had happened and only by accident, at that.
Since that episode, back in the '80's, I am VERY careful about what I smooth, blend, or grind...bigger, smoother may NOT be the solution.  In fact, I'll bet there is a lot of hp lost to overly aggressive head grinders!

Rod

RE: modern motorcycle 4 valve head porting

Polishing, smoothing sharp edges and de burring the chamber will help reduce heat transfer out of the chamber, reduce the build up of carbon and reduce the tendency to detonation.

A very slight lay back of the pads around the exhaust valves may improve FLOW and will reduce squish or quench. Where the trade off lays Will be very dependant on detailS that are beyond the scope we can cover here, but basically more Flow for less quench can POSSIBLY (BUT NOT PROBABLY) help top end BUT NOT BOTTOM END OR MID RANGE.

The photos don't show enough to predict if a flow gain will result, but if the shrouding is equal distance or more from the valve than the valve lift at any point, then no gains are likely, ie if the curtain area around the valve to seat is not larger than the curtain area between the valve and the chamber at any point.

It would also be necessary to see a clay imprint of the space between the pads and the piston to be used when it is at TDC to have any chance of predictiNg harm to quench.

Unless you shave the head or the deck or run a thinner gasket or have a set of pistons with semi finished crowns that you can optimise, you will lose a small amount of compression by carefully polishing so as to remove minimal amounts of metal. This might also do as much harm as good depending on whether or not the  engine is prone to detonation as is AND HOW THE QUECH AREAS OF THE HAD AND PISTON MATCH.

I would certainly very lightly de bur and blend out edges in the port in the area of The valve seat. Some work in The valve guide area might also help top end BUT IT WILL NOT HELP MID RANGE OR BOTTOM END.

To reduce scavenging at overlap, INCREASE THE SEPARATION OF the lobe centres on the cam rather than sinking the valves. This can normally be done with offset dowels to re index the timing gear on the cam.

Regards
Pat
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RE: modern motorcycle 4 valve head porting

Good grief

Even a typo in the correction of the previous post.

AND HOW THE QUECH AREAS OF THE HAD AND PISTON MATCH should read AND HOW THE QUEnCH AREAS OF THE pAD AND PISTON MATCH.

I promise to give up drinking.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: modern motorcycle 4 valve head porting

To support Rod's comment. In every engine where I optimised quench it performed better than expected.

By comparison, in the engines where I maximised flow, especially on the exhaust, they sometimes disappointed me. A lot depends on what you have vs what you really need for you particular requirements.

Preserving quench areas on the head only matters if there is a matching quench area on the piston. Optimising your piston to the potential quench in the head can only help.

Regards
Pat
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RE: modern motorcycle 4 valve head porting

(OP)
Thanks! for taking the time to respond.

Here's the piston top. The squish area appears to correlate well with the combustion chamber.

http://i220.photobucket.com/albums/dd94/jcwk12r/P1030732.jpg

I've read of engine builders that will machine the squish tighter on the intake than the exhuast to preferentially force the mixture toward the exhaust ports.


I don't want to round off the actual edge of the squish, but fill in the corners on the sparkplug side of the chamber. This would increase CR and should help flow and combustion. But would it be worth the cost of welding the chambers and reworking them?

I've added arrows to a larger picture of the combustion chamber to point out the areas I'm referring to.

http://i220.photobucket.com/albums/dd94/jcwk12r/highlighted.jpg

Here is a view of the intake runners from the other side.

http://i220.photobucket.com/albums/dd94/jcwk12r/P1030713.jpg

RE: modern motorcycle 4 valve head porting

(OP)
BTW, in regards to exhuast flow, I understand that it should be a certain percentage of intake flow. Too much and torque suffers.

Pro stock heads are around 60%.

RE: modern motorcycle 4 valve head porting

Foran NA engine exhaust at 60% of intak sounds about for a modern racing engine.

Adding metal where some of the arrows are will shroud the valves and reduce airflow.

You basically have a flat top piston. Small domes would be the way to increase compression, although you already have a lot of compression and unless you have some fncy fuel, yu probably don't want more.

You may be able to deck the block to reduce piston to head clearance and gain some compression there.

I like to run the piston to head clearance in the quench area so tight that it almost touches at full prolonged power high speed. That number varies quite a lot from engine to engine depending on rod stretch and expansion, crank flex and expansion, block expansion, piston rock and expansion and stretch and bore size and running piston to bore clearance. All these are impacted by design, manufacture, materials and running temperature profiles.
 

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: modern motorcycle 4 valve head porting

(OP)
Piston is flat top, yes. And has a little dish where the combustion takes place.

With such small valve angles, 10 and 11 deg, the combustion chamber itself is rather flat as well. There's not much area to dome into. But I understand what you mean.

Here's a close up of those nasty corners and the flat top.

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

RE: modern motorcycle 4 valve head porting

In the photo looking down from the port from the manifold, the port does indeed look to big as previously mentioned by Brian, that presume no distortion due to the lens on the camera.

The area where the single port divides into valve pockets certainly could use some blending of the pocket into the main runner.

I would be very cautious about modifying the chamber beyond a very careful polish and some very frugal radiusing of the area adjacent to the valve seats to sooth the transition between the valve and the quench area of the chamber at very low lift. I would not remove the peninsular between the exhaust vales. I would polish the chamber and in doing so would just barely break the sharp edge on the quench areas so as to not effectively reduce their area to any measurable degree. I would also do some minor gentle blending of the pocket to under the valve seat. Sae applies to the piston top and valve notch edges.

The other heads shown are of little value as a reference as they have much higher valve angles resulting in somewhat different geometry. Also one looks like it was modified to maximise flow with no thought of quench.

Also, photos are a poor substitute for actual parts and flow benches and trial assembly with clay, so any advice given based on photos should be considered as based on poor data.

 

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: modern motorcycle 4 valve head porting

(OP)
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

RE: modern motorcycle 4 valve head porting

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

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: modern motorcycle 4 valve head porting

(OP)
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? :)

RE: modern motorcycle 4 valve head porting

(OP)
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. :)

RE: modern motorcycle 4 valve head porting

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














 

RE: modern motorcycle 4 valve head porting

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

RE: modern motorcycle 4 valve head porting

(OP)
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.

:)

RE: modern motorcycle 4 valve head porting

(OP)
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?

RE: modern motorcycle 4 valve head porting

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

RE: modern motorcycle 4 valve head porting

(OP)
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.

RE: modern motorcycle 4 valve head porting

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

RE: modern motorcycle 4 valve head porting

(OP)
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.

RE: modern motorcycle 4 valve head porting

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
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RE: modern motorcycle 4 valve head porting

(OP)
I really appreciate your suggestions.  Thank you.

RE: modern motorcycle 4 valve head porting

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



regards Marcus



 

RE: modern motorcycle 4 valve head porting

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

RE: modern motorcycle 4 valve head porting

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
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RE: modern motorcycle 4 valve head porting

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

RE: modern motorcycle 4 valve head porting

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
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RE: modern motorcycle 4 valve head porting

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.

RE: modern motorcycle 4 valve head porting

Very well put, Rob.  I've had some pretty heated arguments over intake flow rates and intake port sizes lately.  What works well on a four valve is crap on my two valve Lotus head. Even the carb sizes are in question.  I'm using 45mm with 36 chokes and thinking of dropping to suitably modded 40's with 36 chokes to increase intake speed with very little loss of volume.  Working out new data on these very old heads is difficult since most of the "experts" are schooled on four valve heads.  Particularly the exhaust side of the equation.

Rod

RE: modern motorcycle 4 valve head porting

Rod:
That's interesting:  it seems not so long ago that nobody knew anything about porting 4-valve heads.

A friend of mine had both a small engine dyno and a home-made flow bench, and using them we learned that almost everything that people *knew* about porting was wrong.

Especially for showroom stock engines, with modest valve lifts,  the most important thing we could do was to match the valve face contour to that of the cylinder head seating surface,  so that, viewed in cross-section,  when the valve was near the seat the flow passage looked like a venturi.  That and matching the inlet runners and outlet pipes to the ports were the two most important things we could do.

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