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]

Combustion chamber

 

[MikeHalloran]

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

 

[jk12r]

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 (?)

 

[jk12r]

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.

 

[BrianPetersen]

http://www.mototuneusa.com

presents some interesting ideas on this.

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

 

[marcusaurailius]

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

 

[IceStationZebra]

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

 

[jk12r]

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.

 

[jk12r]

I should have said corners instead of ridges.

 

[evelrod]

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

 

[patprimmer]

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

 

[patprimmer]

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 for tips on use of eng-tips by professional engineers for professional engineers

 

[patprimmer]

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

 

[jk12r]

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

 

[jk12r]

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%.

 

[patprimmer]

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 for tips on use of eng-tips by professional engineers for professional engineers

 

[jk12r]

It may not shroud the valve if done right. Take a look at this beauty...

http://www.theoldone.com/components/cylinderheads/Honda/S2000/1ChExh21.jpg

Even my old zx-11 head looked better in the area between and lateral the intake and exhausts. Also, the valves look more deshrouded.

http://i220.photobucket.com/albums/dd94/jcwk12r/P1030736.jpg

 

[jk12r]

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

 

[patprimmer]

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 for tips on use of eng-tips by professional engineers for professional engineers