Intake porting vs not porting

[mark houghton]

Originally Posted by gsxrken

I think your guy has it reversed. A normally aspirated car likes the small ports to speed up the air column rushing into the cylinder. The better engines can best 100% efficiency in their sweet spot because the momentum of the air column causes it to keep moving into the cylinder even as the piston is rising. Bigger ports kill this effect- see the Ford Cleveland 4V cylinder heads as example.

Whereas the turbo is creating another atmosphere of pressure, so the pressurized air is going to want to go anyway, as the delta between the vacuum in the cylinder and the pressure in the manifold is greater than in a N/A situation. Bigger ports mean more volume, and less heat as the fan can move more into the cylinders without it packing up in the intake system waiting to get in. The more air, the more fuel... this is more important than the pressure or speed of less air and fuel.

But's that's all bench racing. Can't help you with the dyno proofs and I doubt you'll find a guy that had enough willpower to ONLY widen his ports and do nothing else while he was in there. Maybe Chuck Norris could.

Good description!

[Cajundaddy]

In the world of small bore motorcycle racing, cleaning up the intake ports of all flashing and casting irregularities was always a win. Making the ports bigger was a very mixed bag. Volume, velocity, displacement matching, and acoustic resonance tuning all played a role and we ignored one at our peril. Get it exactly right and we could add 2hp to a 30 hp motor. Get it wrong and we ended up with extreme narrowing of the powerband that was very difficult to manage on a race track. YMMV

[Edelweiss]

We tried it and so I can give first hand information:

We did an engine for a customer and three months later he came up with the idea to try extrude honing. So - ok off with the heads and the customer gave it to a specialised company. Two weeks later we assembled the engine and put it on our dyno.

Result: zero plus hp.

So what I think is, if people refresh their engines and do this extrude honing the same time the butt dyno is reacting on the refreshment not on the honing.

A good head work is rare to find - you have to understand the ports structure and change the shape and sometimes size into the right direction. It must work with the seat and valve design.

Here in Germany there are maybe fife to ten people who I would say they are good in porting a cylinder head.

The others are thinking bigger is always better and they polish and polish and polish.....

To optimise volumetric efficiency you have to give direction to your flow.

So working on a flow bench and just looking for the flow rates can be very misleading.

The next essential is to get the right cam on the port.

I always work with anti reverse steps - on the inlet and exhaust side.


Best reg.

Dirk

https://www.facebook.com/edelweissmotorsport

[JFairman]

When enlarging 2 valve head intake ports it's often best to remove most of the material from the top side of the port around the valve guides and none from the bottom or short side radius. This is so the air flow is lifted up as much as possible inside the port before it makes the turn going over the short side radius so it straightens out as much as possible before hitting the back of the open intake valve.

Some people add a little aluminum to the bottom of the port before the short side radius to lift up the air flow and make a smoother turn over the short side radius so the airflow straightens out more before the intake valve.

When I did mine I didn't reshape the bowl I just smoothed out the casting marks. The first inch and a half or so of 930 intake ports are 32mm and then they get much bigger in the bowl area.
My aluminum injector blocks are 40mm ID so I opened up the 32mm part to 40mm to match up with the injector blocks.
I installed brand new Mahle pistons and cylinders at the same time and the 1976 930 heads I ported and installed had been previously rebuilt with new guides, teflon valve seals, and a fresh valve job and they had been milled down .018" so the compression was raised a little too. I can't say what difference my porting made but it all works really good. I imagine it helps above 4000 rpm.

I smoothed out the exhaust ports a little with the sanding cones but didn't make them bigger.
I've done this kind of stuff many times before on BMW motorcycles and a bunch of BMW 2002 and 635 heads. I have all the tools and Harbor Freight sells boxes of the sanding cones for porting for around $25. The Harbor Freight arbors the sanding cones thread onto break easily from the side loading so I bought some good ones from a mail order tool place and they are much stronger and last.

[TurboKraft]

Originally Posted by DSPTurtle

Are you sure the butt dyno increase wasn't from the reduction of dollars in their wallet insulating their butt from the seat?
Sorry, I couldn't help myself Brian!!!

E-H can do great work.

But man, can they destroy a 930 magnesium manifold.
Or three.
Well documented in another thread.

[smurfbus]

Glad you brought that up, did not want to go there myself. What is the limit when enlarging the stock manifold block flange?

[Edelweiss]

Hi Fairman,

solid knowledge !

When it comes to the port bowl it is the spot to generate most of the effect.

Sometimes it's reasonable to make one side a little worse to over proportional make the other side better.

The short side is hard to get around the corner - the long sides are flowing anyhow, so I use the long side to give direction to the load.

This makes less good numbers on the flow bench but much better numbers on the dyno.

Since quite a time we use radius valve seat cutting - on BMW motorcycle and Porsche engines.

This was generating a big step after we found out how to exactly machine the correction cut in the combustion chamber area.

Best reg.

Dirk

https://www.facebook.com/edelweissmotorsport

[Edelweiss]

Originally Posted by TurboKraft

E-H can do great work.

But man, can they destroy a 930 magnesium manifold.
Or three.
Well documented in another thread.

Hi again Chris,

how is life going ?

I'm currently on vacation in Bavaria - Schnitzeloverkill...

What is E-H doing different ?

Are they changing the shape ? Diameter ? Or just the surface like others ?

Thanks,

Dirk

https://www.facebook.com/edelweissmotorsport

[Tippy]

I do find it funny in the Porsche world how taboo porting is talked about.

Every shadetree mechanic doing a crappy port job has seen benefits from my experience.

Stick with the original port shape and everything should be ok.

Change the port shape and you're on your on if it will make an improvement or not.

[TurboKraft]

Hi Dirk -- have a nice holiday! Ich habe dir über Nockenwellen gestern angerufen , schicken Sie jetzt eine PM.

E-H is smoothing out the manifold's casting inside, wherever there is flow resistance to the abrasive putty. This same thought process applies to their opening of the ports -- material is removed where there is flow resistance, theoretically increasing flow in an optimal manner. The flow should be matched when the quantity of abrasive material coming out of the port is consistent on all runners (i.e. X kilos of material in Y seconds. The ports are *supposed* to be opened evenly and on-center -- they swear they have tooling/fixtures, and use them...

...but last time we used them they turned a 930 manifold into a magnesium paperweight, making the ports off-center and randomly shaped, plus taking many weeks (months?) longer than normal.
Thoroughly p*ssed off the owner in the process (I think I still have singe marks from the flame job).

Now we do them all on a CNC with hand-finishing. Reliable results.


BUT back to Harold's question about whether it is worth it:
I think so, on an engine running bolt-on upgrades and camshafts.
I wouldn't do it to a 930 with a K27, muffler, and 1.0bar spring -- the money and effort would be better spent on other exterior bolt-on upgrades first.

If the engine has these other things, and the heads are off, and it is a performance build looking for all-around performance -- good torque, power, and response -- then yes, worth it.

[kenikh]

I'd also suggest that the "quality" of port work is more critical in NA engines. Forced induction solves what optimal port geometry attempts to solve: Getting a fully charged intake tract, as close to zero vacuum as possible. Fancy CNCed ports are designed to pressure load the intake tract and accelerate and compress the intake charge, which is no issue for a turbo, except off idle.

[Edelweiss]

Originally Posted by kenikh

I'd also suggest that the "quality" of port work is more critical in NA engines. Forced induction solves what optimal port geometry attempts to solve: Getting a fully charged intake tract, as close to zero vacuum as possible. Fancy CNCed ports are designed to pressure load the intake tract and accelerate and compress the intake charge, which is no issue for a turbo, except off idle.

Hi Kenik,

this is one way to see it.

My experience:

If you treat a turbo charged engine like a n.a. Engine in first place you will build the better Turboengine at the end.

For example - a big valve always performs out a small valve, if it is done right.

So you can reduce boost pressure and see the same power or keep the boost where it's is and you will see significant higher numbers.

Same with ports and cams !

Chris - what is your opinion ?

Best reg.

Dirk

https://www.facebook.com/edelweissmotorsport

[kenikh]

^ I completely agree with you as arguing against the laws of physics generally means you lose. �� I'm painting with an intentionally broad brush for simplicity. I do think gains in NA motors are more dramatic.

[Tippy]

IMO, cleaning up casting irregularities, rounding the bowls smoother, and shaping the valve guide boss should always net some benefit.

Making aggressive changes to the overall port shape should only be done with a flow bench.

But then again, what happens when your pioneering design fails?

You gotta paperweight....

[kenikh]

That's why I've always entrusted the pioneering to guys who make a living at it. (that's a little shout out to Steve Weiner and Dick Evelrude).

[JFairman]

Bill at Xtreme Cylinder Heads in S. Florida is the best.
He does CNC machined ports that look and flow amazing.
Video of it: https://www.youtube.com/watch?feature=player_detailpage&v=DyvXsgIPlPU
You can see them on his website.. Xtreme Cylinder Heads And Castings

[kenikh]

Bill's heads are unbelievable... Those raw castings are nuts.

[JFairman]

Yeah I've been to his shop and seen his heads. If he ever designs and builds a new cam tower for them he could change the valve angles too.