Port Approach to Seat Angle

[SchmidtMotorWorks]

I have seen that some cylinder heads have intake ports where the walls of the port near the seat are parallel to the valve axis for a long distance and other heads where the port leans toward the intake port opening right from the beginning of valve seat, looks like it is taking a shortcut with no tall SSR.

Just looking at it, it appears the idea is that a larger proportion of the air is intended to flow over the valve head and exit from the far side of the port.

I was trying too think of any example of an American wedge or canted valve head that has a similar port but couldn't think of any. Does anyone know of an example or know of any tests on a wedge type head to see what the consequence is of these type of ports?

All the Japanese 4 valve stuff that I have seen lately has this design and the angle seems to be getting more extreme.
I think some BMWs have ports like this too.

[Ape]

Hi schmidt

Are you talking about the portthroatarea having some sort of bulge on one side, on the sidewalls?? did i get that right??
Quoting d. vizard thats supposed to give the port a bias angle for high rpm flow. On the heads i work on the most (500cc xt500 2 valve) there is also something like that and its tilted to the outer side of the bore in order to let the flow exit aiming more to the middle while high flowing. Havind somewhat both traits, swirl for low rpm, centered flow while high rpm.

hope thats what you ment??

christian

[SchmidtMotorWorks]

Sorry for the poor explaination, I didn't have access to CAD so I drew it in Paint, I hope it makes sense.

The blue shape is supposed to look like the side view of the bowl area of a SBC head.

The green shape is the side view of the style port I am wondering about.

They both have the same valve angle but one has the port coming down along the valve axis. The green one has the air flowing at an angle to the valve axis as it gets to the seat.

The consequence I imagine is that on a 2 valve head the swirl would be high and on a two valve head the tumble would be large.

I wonder if the flow is increased or decreased by this shape, I guess it is reduced but I have never seen a shape anything like this on an American angine that I remember. I vaugly remember that maybe a 392 had this characteristic to some extent.

[68corvette]

i have done couple 2L OHC ford heads that has very flat floot.

On rally engines they have been allways filled at the floor, it gives lots of more low lift flow and makes lots of more torque on living engine that way.
Max lift flow and max engine power doesn't change radically with larger radius and stock intake location.
I shape shortside before filling so if KOP looses the engine is still working.

Some heads like 1.6L OHV Ford kent witch have many different floors make very same alike power curves if max lift flownumbers are same (higher shortside has a little more torque).

Flat shortside does not show any sings of flow separation on higher lifts and i think it could have some advantages in some desings if valve is liftet very high and you are stuck vith these two desings (higher shortside hits water before good shape).
It does make some tumble at some lift points, but usually calms down at higher lifts.

[DavidHarsay]

You know this one... Ford Modular PI intake ports... Wedge is goint the other way, but air exiting on one side of the valve for sure.

How do I link pictures here by the way?

[dbusch]

Let me take a shot:

the port style of the green example is the latest and greatest design for higher rpm stuff. It gives the most direct line of site entering the cylinder. If you cut the backside of the bowl out for flow, you also make the angle coming up to the seat more severe, and this can kill wet flow. So, the newer design gives better line of sight (with no dead areas) and better wet flow, even though it may flow a little less air.

hope i got that right...

[MysteryMAN]

Hi port will net better low lift numbers ....

[SWB]

They do that to increase mixture motion in the cylinder (turbulence for better burn).

On a two valve engine that will mostly relate to oriented turbulence like swirl or unoriented random turbulence and on a four valve engine you are talking about tumble (which I consider only slightly less random).

If you're looking to achieve the most performance from a two valve engine, you'll need to maximize the flow through the valve to achieve the best _oriented_ mixture motion that will enable the maximum amount of burnable fuel-air mix to enter and be trapped in the cylinder. That sounds elementary, but it's easy to get caught up in some 'all or nothing' game with any one of the specific factors needed to achieve this.

For maximum flow through a valve, the entire periphery of the valve must flow the same amount. This concept is similar to Smokey's "flow cone". Unfortunately that isn't going to happen when you place the valve in any typical two valve engine chamber and add the proximity of the cylinder wall into the mix. Even if the port were perfectly shaped to allow this when dumping into an open environment (all port walls equal in length), the added chamber/cylinderwall constraints would preclude it.

Therefor the maximum flow will be achieved when the best compromise is had.

Keeping in mind that the flow will take the shortest path it can (not necessarily will the fuel however), we can guess that designing the port with a really short turn to the seat is going to bias the flow to a more narrow region around the periphery of the valve. On the other hand, a higher short side turn, a longer turn, and a higher port inlet will all tend to allow the more even efflux from the valve's circumference.

Like everything in engine building, it's a compromise and everybody is trying to come up with the best one.

SWB

[SchmidtMotorWorks]

SWB, nice explaination, have you ever seen this port shape tried on a SBC head?

[SWB]

Schmidt,

No I haven't.

I have worked with some two valve engines having a -simialar- layout and a sharper short turn, but not specifically the SBC.

If you start modeling this port idea and flowing it you'll probably find that a higher port like an SB2.2 is a heck of a lot better in the flow department.

SWB

[SchmidtMotorWorks]

SWB,

Thanks for the explaination. This design is the default for new four valve engines at an OEM I visited Japan in both racing and passenger car engines. I couldn't get an answer that made sense about why they do that, but that was the case about almost every other question too.

Some other reasons that I guess might have lead them to this design are:

Shorter distance from the valve face to the valve guide could allow a shorter and maybe smaller diameter shaft.
Maybe the cooling is better with the shorter stem?

The shorter valve makes a shorter head, maybe in some cases the pressure to reduce size could influence port shape? I guess it is possible, look at some of the sport bikes, their cylinderheads look 2x taller than the cylinders.

Maybe this is part of a trade-off for raised and angled port entry?

[Ape]

Hmm??

But with such a port approach wouldnt that mean that on a 4 valve engine you would have serious blowthrough into the exhaustports, during overlap.
I had a look recently on to a recent bmw series 3 head and they still do have somewhat vertical hi ports.
I dig and understand the idea of increased turbulence and wetflow and everything, but wouldnt that only work sufficiently on a non opposite exhaust valve engine??

[John Haskell]

I'm giving my age away here but, all of Ford heavy duty truck engines used this approach in the 60's/70's. I took note of that & looked at it for a reason why.

They did use valve lift of under .400", they used smaller ports obviously for torque, more overlap, more duration. -------- If you knew trucks at the time, the Ford was stout & no real reason to be.

In the 70's, I tried this on the oversized Ford Cleavland because of that truckhead, when everyone was trying to do something w/Glidden. We found it didn't hurt a thing in those elmentary days. Obviously we were far enough off in those days & frustrated due to being behind but we tried this.

In all, if the port volume would have been found, I have a suspiction it may have been better.

[SchmidtMotorWorks]

In all, if the port volume would have been found

That's a good point, the bowl volume is much smaller. Could it be that having the smaller bowl volume gets the air in the port and manifold moving sooner?

[John Haskell]

Well to me that was pretty obvious for the use in the day. Fact is, it's seen everywhere today & I believe these Ford truck heads were a preview of what has shown up again. I see nothing but response time/recovery based on rpm.

For years before computors & just using your brains, I always used my ear. Always listening for the sound the engine provided at the gear change. Off the corner, same thing. That was everything & here we are today back to the same thing but using computors instead. Recovery. I have an idea that may be the deal.

Air can achieve so much speed & there is no more improvment, NA. Seems that mark has been reached & here we are with very little to improve on.