CFD simulations for head porting

[bohutch]

Hello,
I’m curious who does CFD (computational fluid dynamics) on 911 cylinder heads for the purpose of improved CNC porting? I’ve scanned many posts here and came up empty. I have owned my own machine shop and taught CNC manufacturing for many years and I also have owned the same 911 for 30 years (1970 911t). With a decent CMM or perhaps laser surface scanning (tough inside ports but doable) you could do a precision surface map to start with, using Comsol or other CFD software and setup dynamic and thermal simulations as a baseline. Any thoughts, I know I’m not the only mechanical engineer in here.

[lvporschepilot]

I have no doubt there are some out there with this information, but it is likely held close to the vest. The most I think we can humbly ask for here might be flowbench numbers, which we have seen a bit in the past.

[Trackrash]

Originally Posted by bohutch

Hello,
I’m curious who does CFD (computational fluid dynamics) on 911 cylinder heads for the purpose of improved CNC porting? I’ve scanned many posts here and came up empty. I have owned my own machine shop and taught CNC manufacturing for many years and I also have owned the same 911 for 30 years (1970 911t). With a decent CMM or perhaps laser surface scanning (tough inside ports but doable) you could do a precision surface map to start with, using Comsol or other CFD software and setup dynamic and thermal simulations as a baseline. Any thoughts, I know I’m not the only mechanical engineer in here.

So, you are saying that the shape of the 911 port can be improved, beside just enlarging it?

That would be an interesting undertaking.

[Steve@Rennsport]

Originally Posted by lvporschepilot

I have no doubt there are some out there with this information, but it is likely held close to the vest. The most I think we can humbly ask for here might be flowbench numbers, which we have seen a bit in the past.

This is quite true.

[Steve@Rennsport]

Originally Posted by Trackrash

So, you are saying that the shape of the 911 port can be improved, beside just enlarging it?

That would be an interesting undertaking.

OMG, yes!

Bigger isn't always better.

Its all about enhancing velocity as well as flow at ALL valve lift numbers.

[Tippy]

Subscribed. Where are you located?

[BURN-BROS]

[racing97]

I would be interested in any situation where someone has offset the inlet port, lets see 15 to 20 degrees or so. As of yet I have seen probably the best use of straight up cross flow, and that is Extreme Cylinder Heads and the best flowing Porsche creation in the 993 but never one with a offset port to induce swirl.

regards

[bohutch]

Hi,
My idea was to perhaps scan and model six to ten cylinder heads and run a CFD simulation for comparative flow rates (of course backed by empirical data from a flow bench) making them all identical would be the goal. That would be a starting point, you could model with twisted internal grooves and experiment with depth, pitch and shape to induce better combustion. I’m in Washington state. Is there a way to post cad drawings and data on this website? I think sharing this information (if it’s effective) would be great for other Porsche enthusiast like myself. I think I could program a Cnc machine to run a porting program and post a video showing how it could be done.

[Tippy]

Don’t think you can attach CAD files here, but we can send through email. What CAD software do you use?

[bohutch]

Hi I mainly use Mastercam or solidworks but I can export files as IGS, STEP....... tons of options.

[Speedy Squirrel]

This is an area I know a little bit about, so I will download some info, some of which you might already know.

We seldom use CFD in the industry for port design. We definitely make models of finished designs though, and couple them with combustion simulations. CFD is overkill if you just want the bulk flow and pressure drop through the port. The mesh has to be very fine at low valve lifts, since the cell size has to be smaller than the turbulence scale. You also have to keep opening the valve. That means multiple meshes and multiple runs. $$$ and time.

Why not print a 3D port model and use a real valve and a flow bench? We basically rock sort with flow boxes like that, and then capture the finer granularity with a model.

There is a relationship between port volume, length, and diameter that provides the best trade off between pressure drop and momentum. We treat it like it is a big secret, but I have seen it on ‘net. Just Google around.

Flow under the lift curve is what performance is all about. There is a good reason why multi angle vale seats were invented. The game starts when the valve opens, and doesn’t finish until it is closed.

You don’t want swirl, ever, unless you are a diesel. Whatever energy went into making the flow swirl could have been used to get more air into the cylinder.

[tom1394racing]

I used to be associated with a business that did 3D CAT scanning of intake manifolds and heads for the NASCAR guys. The NASCAR wizards would do the hand porting followed by flow and track testing. They would select the best "designs" from these tests and then send them to us where we would scan them and produce 3D models. Our business also had state of the art CFD capability but the reverse engineering produced the most reliable results.

[Tippy]

Originally Posted by Speedy Squirrel

This is an area I know a little bit about, so I will download some info, some of which you might already know.

We seldom use CFD in the industry for port design. We definitely make models of finished designs though, and couple them with combustion simulations. CFD is overkill if you just want the bulk flow and pressure drop through the port. The mesh has to be very fine at low valve lifts, since the cell size has to be smaller than the turbulence scale. You also have to keep opening the valve. That means multiple meshes and multiple runs. $$$ and time.

Why not print a 3D port model and use a real valve and a flow bench? We basically rock sort with flow boxes like that, and then capture the finer granularity with a model.

There is a relationship between port volume, length, and diameter that provides the best trade off between pressure drop and momentum. We treat it like it is a big secret, but I have seen it on ‘net. Just Google around.

Flow under the lift curve is what performance is all about. There is a good reason why multi angle vale seats were invented. The game starts when the valve opens, and doesn’t finish until it is closed.

You don’t want swirl, ever, unless you are a diesel. Whatever energy went into making the flow swirl could have been used to get more air into the cylinder.

That's the difference between the Porsche world and the American V8 world. You can find all the data out there with very little secret. Sure, the top engine builders will keep some things secret, but their world moves so fast, it doesn't take long for the beans to be spilled.

If we all shared these things, we could start making more and more big hp to L engines IMO.

[Tippy]

Originally Posted by tom1394racing

I used to be associated with a business that did 3D CAT scanning of intake manifolds and heads for the NASCAR guys. The NASCAR wizards would do the hand porting followed by flow and track testing. They would select the best "designs" from these tests and then send them to us where we would scan them and produce 3D models. Our business also had state of the art CFD capability but the reverse engineering produced the most reliable results.

That is pretty cool, Tom! Wished I was involved with some stuff like that. Sign me up.

[tom1394racing]

Originally Posted by Tippy

That is pretty cool, Tom! Wished I was involved with some stuff like that. Sign me up.

That business was right there in your home town!

[reclino]

I have a 3d printer, and would be happy to print multiple versions of cylinder head ports if someone has a flow bench we are set.

[Speedy Squirrel]

I would chip in to rent a flow bench. I am pretty sure that Ricardo here in the D has data on Porsche heads already. I also have 2.7, 3.2, and 3.3 heads.

I can already guess where this will go though. You will want some kind of D shaped port that is higher on the head.

[Tippy]

Originally Posted by tom1394racing

That business was right there in your home town!

No way?!

[Tippy]

Originally Posted by reclino

I have a 3d printer, and would be happy to print multiple versions of cylinder head ports if someone has a flow bench we are set.

Me too