Pelican Parts Forums - Intake Port Size Affects

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- - Intake Port Size Affects - CIS (http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/846843-intake-port-size-affects-cis.html)

Good question, I also don't know the limits of the air meter plate. It seems to handle 400WHP just fine but 500WHP is now 2x the power it was originally designed for.

copbait was referring to the throttle body diameter.
IMHO, throttle body has little effect as long as the intake tract isn't compromised by it. In the case of the 930, I doubt it is. I think people may go to another throttle body, but only because the abundance of intake of intake signals in newer designs.

On this subject of port design, I worry about atomization of fuel due to a change of port diameter at or near the injector. A loss of air velocity at or preceding the injector will cause a loss of velocity and atomization (reverse-venturi effect).

Dirk, have you seen cases where the CIS manifold is ported to a larger size only to find there's loss in performance?

Brian,
Personally, I think the 3.2 head is a very good starting point. They are probably the best flowing factory heads leading up to the 3.6.

Quote:

Originally Posted by WERK I (Post 8454923)

Yes we have seen this - a good example is the first generation Golf GTI 16 V and the two generations of plenum. There even was a part from VW Notorsport which was significant bigger in diameter.

Today we know the smallest one was the best one, making the most power with the best torque and the nicest curves.

In the further development of this engine later used as stw and kit car engine the 2,0 l race heads are manufactured with smaller ports then the first 1,8 l street heads called kr.

These engines are making 300 plus HP with smaller ports then the 129 HP street engines !

And if you remember a 1,6 l first generation GTI engine making 200 plus HP with 40,5 mm inlet valve and 35 mm exhaust valve you have to see the very small ports to realise when a port really gets too small.

Please hold in mind that we can take as a fact:

The way from air filter to the inlet valve is always working as its smallest spot.

Also I prefer to start with small ports since shape rules diameter !

There is nothing better then a set of turbo heads with a good porting.

These heads have a good amount of meat for someone who knows how to make them work.

The most important place to work on is around the valve seat, port bowl and port flor.

All na porsche cams are a compromise, if it is SC or 964 - you can do much better with a dedicated turbo cam - say this because the port / valve must me triggered by a good lobe to make it work.

A relatively bigger port can be useful but it is more sensitive in shape - a smaller port needs less know how to make it work, same with valve size.

The bigger you go the more you have to know what to do - this is the reason why we very often see ports destroyed making less power then beeing standard.

So under the line: no need for new heads - use the turbo set you have and find someone who knows how to do a good valve seat with a corresponding port.

Best reg.

Dirk

Interresting reading :D

Wow very nice.
So you're saying the limitations are the port? Not size either but smoothness?

Quote:

Originally Posted by quattrorunner (Post 8456375)

Wow very nice.
So you're saying the limitations are the port? Not size either but smoothness?

It is all about the shape.

To achieve what we all are looking for you have to modifie it with a strategy behind what you do.

First analyze the port and understand the concept of the layout.

In the next step you promote the strength and fight the weakness.

The Porsche ports are quite simple and they just follow the reality that its a flat six boxer with the inlet on top and an upright carb in the beginning.

There is no great finesse in it and the development was even going backwards from 964 to 993.

So starting with a small beefy port there is a lot to improve.

I always start with the smallest base port I can possibly get.

Best reg

Dirk

This excites me for the next rebuild.

You want to reshape the port to lift the airflow towards the high side of the port so less of the air fuel mixture is flowing over the short side radius. That way the air flow has more room to straighten out before it hits the backside of the open intake valve.
That improves and maximizes flow.

Don't take material away from the short side radius or else the airflow will drop lower in the port and will be hitting the backside of the intake valve at an angle and that's not good. It will create bad turbulance that makes the port flow worse than stock.

Just smooth the short side radius a little if it needs it and that can be carefully done by hand.
If anything you add some aluminum to the short side radius by tig welding it in and then carefully and evenly smooth it out by hand or with CNC port milling machinery.
Surface turbulence grooves machined into the port walls like the ones in the pictures above make the air fuel mixture laminar flow tumble along the surface and that keeps the port walls from wetting out with fuel and helps to keep the air fuel mixture atomized.

The best place to have hand done or CNC head porting work done in the USA is: Xtreme Cylinder Heads And Castings in Palm City Florida.

Watch a cool video of it being done here:
https://www.youtube.com/watch?feature=player_detailpage&v=DyvXsgIPlPU

They're a 45 minute drive north for me so I've been there and the owner Bill is a really good guy.

... but you better be sitting down when they tell you the price. I'm doing my own.

Yes indeed. I had Steve Weiner do a set of 69S heads for me, too. Porting and heads were $5K, soup to nuts, IIRC. We designed the entire intake tract as a tapered bore venturi, from air horns at the top of the MFI stacks, through the stacks, through the TBs, from the edge of the port, through the valve seat. 2.25L, naturally aspirated 911 motor made 240HP at 7300 RPM. Made power to 7800. The torque curve was silly far down low, too. I never quote port diameter on that motor. The size of the port was immaterial, as it was just a cross section at an arbitrary point in a larger system.

A diligently designed intake system is time consuming, costly and pays amazing dividends.

I've seen pictures of ports Steve Weiner has posted and they were the exact same pics that are on xtreme cylinder heads website.
I've talked to Bill and mentioned that and he said Steve is a customer that sends them to him.
So.. you can skip the middle man and send them directly to xtreme heads and the final cost will be much less.

Quote:

Originally Posted by JFairman (Post 8460435)

That's news to me - Dick Evelrude used to do his port work. Dick and Steve had a nice business relationship, in that Steve would manage the projects and Dick would get a steady stream of work - and not have to deal with clients. I also know from previous conversations that Dick and Steve spent a LOT of time on the flow bench and in the dyno room coming up with those port profiles.

Admittedly, Dick has been on the verge of retirement since I was knee high to grasshopper, so maybe he finally decided to hang it up. Or maybe Extreme's capability and port geometry is just that much better...hard to know without asking.

I'll call Steve to catch up and see what the latest scoop is. Just for fun, my old heads...don't look like Extreme heads:

http://i25.photobucket.com/albums/c7...n/IMG_0487.jpg
http://i25.photobucket.com/albums/c7...n/IMG_0493.jpg
http://i25.photobucket.com/albums/c7...n/IMG_0502.jpg
http://i25.photobucket.com/albums/c7...n/IMG_0497.jpg
http://i25.photobucket.com/albums/c7...n/IMG_0498.jpg
http://i25.photobucket.com/albums/c7...n/IMG_0499.jpg
http://i25.photobucket.com/albums/c7...n/IMG_0500.jpg

Interresting. That golfball effect in the port looks nice.
Wonder how much extra effect that gives.
My 930 tops was ported by extremecylinderheads. Wish hey had this tool then :-)

I have to think that you can't get away with so little of the valve guides left on a turbo engine.
I once saw a solid model of ports on a NASCAR engine. The ports were increased in diameter gradual transition around the valve guides to gain back the lost volume. Looked like a snake that swallowed a tennis ball.

Those look just like the CNC Rottler P69 machined ports that xtreme cylinder heads does.
Maybe someone else in the states has one of those machines too. All you need is a laptop with a well written 930 head porting program on it to run the machine and make it happen and hope the power doesn't go out while the cutting is going on.

The small oval grey areas in the intake ports looks like JB weld or Devcon marine epoxy that was put on the outside of the port area of the heads so the intake ports could be cut higher up in the heads without cutting completely through the port.
I've done that on old single cam BMW 4 and 6 cylinder water cooled heads so I could grind more material away on the top side of the port leading up to and around the intake valve guide.

When doing that I would port match the bottom and sides of the intake manifold runners to the finished intake ports but not the top side. That way a nice almost 1/4" deep anti reversion cut was created on the top side of the port where the intake manifold bolted on to the cylinder head.
Anti reversion cuts improve high rpm performance when using long duration high lift cams in normally aspirated high compression engines.

Here's my heads done by Xtreme. Opened up to 42mm. 52mm intake valves/42mm exhaust. Philip http://forums.pelicanparts.com/uploa...1422494441.jpg

Quote:

I have to think that you can't get away with so little of the valve guides left on a turbo engine.<br>
I once saw a solid model of ports on a NASCAR engine. The ports were increased in diameter gradual transition around the valve guides to gain back the lost volume. Looked like a snake that swallowed a tennis ball.

Like a cobrahead intake duct?