Declassified porting pics?

[BReyes]

Any one care to show their porting work (pics) on a 3.2? My understanding is have to clean them up a bit especially around the guides, not a great deal much more.

Stock valves, racing valve springs retainers, hot cam, twin plug, race fuel only.

[Henry Schmidt]

IMO:
3.2 ports are already too large and cleaning the ports offers little or no performance enhancements. Even in a race engine.

49 mm valve x 85% = 41.5 mm This would generally be consider the max size. Some engine builders believe a rough intake surface offers better mixing and higher flow. Leave the port alone and put your energy into something that will offer something possitive.

[Steve@Rennsport]

Bernard:

Since we've done a great deal of airflow R&D on various Porsche street & race heads over the past 30 years, I can tell you that the 3.2 Carrera heads are really very well done.

Henry is correct in that generally speaking, they should not be touched since its FAR easier to reduce, rather than enhance their performance. All they need is a high-quality valve job and they will support up to 345 HP in stock form.

[Dennis Kalma]

Just a clarification for my simple mind......I have a set of '79 SC heads (European), would you bother porting or polishing those heads for a street 3.4 litre (Mahle 10.5 p/c's, S cams)?

Thanks

Dennis

[Henry Schmidt]

There would be very little if anything to gain by porting an already large port.

Street engine running a redline of 7200 rpm would not gain from porting.

Porting does give you something to brag about but not much else.

A 49 mm intake valve with a port size of 39 mm would have an 80% ratio. More than enough for a street engine.

[beepbeep]

What they said. Unless you are running turbocharged engine with oversized valves and high amounts of boost, you might even drop HP in low/middle range by enlargening ports further. You want reasonably gas high velocity to help fill the cylinders.

[snowman]

In general POLISHING intake ports is a bad idea, an 80 grit sandpaper finish is better. If there is any casting flash on the short side radius (highly unlikly) remove it, otherwise leave them alone. Even the older Porsche heads will support more HP at higher RPM than the engine can deliver.

[BReyes]

I understand it as, just a couple rough spots, and near the the guide using 80 grit. And non-polished chamber.

[sewell94]

Your lucky being on the treasure coast, u have one of the best 911 head guys in your backyard. Xtreme Cylinder heads in palm city is amazing with 911 heads (there speciality) he has a new cnc machine that he uses to cut the seats with, theres alot of flow that can be picked up with just from a good valve job with the correct angles on the seat.

[BReyes]

Thanks. I already have a builder/machine shop I use in Taveres, but I will look to see what these guys do too.

[snowman]

Do not worry about the stuff near the valve guide, its secondary. Its the SHORT side of the intake radius that is important. Take your finger, with the valve out, and feel the shortest way from the intake to the cylinder, thats the short side radius. If you feel any roughness, or bumps, remove them. The long side, ie roof isn't impotant, the long side is where the valve guide is. Porsches are already port matched, so don't bother. The bump, even a little bump on the short side radius can hurt your flow by as much as 25%, thats 25% LOST POWER!

Get some books on porting, especially english ones as they have got more power out of a mini than thought possible. But the bottom line is SHORT SIDE RADIUS. Thats where all the loss is. You might pick up another 3 to 5 percent in other places, but why bother, compared to 25 percent they are nothing.

If you do not have a flow bench, do not do anything other than smoothing out the bump or roughness on the short side. You will get 90 percent of whats available and will not hurt your flow. It only takes 5 min per cylinder, so don't pay big bucks for more.

[eapcpa]

Snowman, help me understand this. I am used to building american V-8s and they are just the opposite of what you are saying. The high velocity flow in the port on a V-8 is the upper part of the port and no gain is to be made by massaging the bottom of the port as the flow is slowest and cannot be optimized there. When enlarging 911 ports the material should be removed from the bottom radius where the port turns the corner to the valve in order to improve the efficiency of the port?

[snowman]

Thats not correct. I have ported many chevy heads. Chevy heads need port matching first. But then its the SHORT side radius that makes all the difference. For example I started with stock chevy 307 heads (junk) with 1.5" ex and 1.75" in. Initial flow was 160 cfm at 28" water. By simply removing gunk from the short side I was able to get the flow up to 195cfm, not bad for a junk head. With a lot of work and 1.95 or 2.10" intakes the flow can go up to 225cfm, but 90% was from the short side. I KNOW because I flow tested using a Super Flow 600 Flow bench. To Flow is to KNOW. But if you do not have a flow bench, ITS THE SHORT SIDE RADIUS that counts. The high side of the port will do NOTHING to improve flow. Relative speaking of course.

It's sort of like this. If the port velocity is already high, there is nothing to do here, but if the port velocity is low, you must imporve it, make it high as well, thats why the short side radius is the answer.

[EarlySport]

Guys,

I have a 1980 3.0 litre motor with the small port heads. My soon-to-be-completed mods are 3.2SS 10.5:1 comp, and S cams. I'm already running 40mm Webers ( 36mm Venturi's ) and an early exhaust.

Would I gain much by finding a set of used 3.2 heads ?

Thanks.

[eapcpa]

Snowman, I am not disputing your findings, however in all of the books I have it is saying the opposite. There is obviously no replacement for hands on testing yourself. The science of porting heads has always been best left up to those who do the research and even then the information is contradictory. I guess each engine port configuration is different and the only way to do it properly is trial and error testing. By the way, I am partial to Fords over chevy. LOL

[Henry Schmidt]

Originally posted by EarlySport
Guys,

I have a 1980 3.0 litre motor with the small port heads. My soon-to-be-completed mods are 3.2SS 10.5:1 comp, and S cams. I'm already running 40mm Webers ( 36mm Venturi's ) and an early exhaust.

Would I gain much by finding a set of used 3.2 heads ?

Thanks.

Just open your small port SC heads to 38-39mm and you'll be as good as 40mm Webers will need.

[}{arlequin]

Originally posted by Henry Schmidt
Just open your small port SC heads to 38-39mm and you'll be as good as 40mm Webers will need.

what about the same scenario but for 46mm carbs? also, do the carrera heads just bolt right up to an SC case?

[Facey]

i'm not sure if my heads were ported or not, they don't really look like it, but i have not head or any stock porsche heads this large, has an interior dia of 46mm.... exhaust port is 44mm....

[snowman]

Dosen't look ported to me. I see factory flash marks that are usually smoothed out when porting.

The last picture is very imformative. See where the valve guide steps out, all the so called porting books will say smooth this out, taper and boat tail it. I won't disagree, BUT there is a huge, much more important problem that shows in this picture. Look at the back side of the valve seat, where the head was borred for the valve seat. It extends quite a ways back from the valve and leaves what looks like a small ridge. If the valve is removed and you stick your finger into the valve side and feel around the short side radius, thats the 10:00 oclock position on the picture, you will feel this "bump". Its the SINGLE most important thing wrong with this head. If you break this edge, flatten and round it so all you feel with your finger is a smooth continuous curve, you will pick up as much as 25% in air flow. All the other things, combined might give you antoher 3% flow on this head. Generally you would be safe in smoothing out this small bump without the benefit of a flow bench, but again "to flow is to know"

There is only one good book on porting, by an english guy on small english engines, I haven't found any others that seem to be based on actual flow bench experience. There are some papers available that give some details, I think you can find them by going to the Superflow home cite and look for links, referances. They also offer a course in porting and flow bench testing (at least they used to).

Porsche and most other engine manufacturers placed the valve guide where it is for a reason. In the long side it dosen't do much of anything to mess up airflow. Mother nature, the ***** she is, tends to be consistant, so the short side is usually the same for any engine. Chevys are an exception because they leave so much trash in the port its hard to know where to start.

[len911]

I don't know who did my heads since I bought my engine in boxes, but here they are for reference... Comments from those who know? Lou