Home porting? Like Home perm?

[Scott Clarke]

I've spent months trying to feel ok about using my E heads, with their 32mm ports, in the short-stroke 2.5 I'm building. Careful study of various motors built by Porsche, in addition to much discussion in this forum, indicate to me that 36mm/35mm ports would be the best choice for this motor. I will be using my E cams, JE pistons/re-plated cylinders, 7R case, and MFI.

Budget precludes having the heads ported. $650 for the heads, plus the associated work to the throttle bodies and stacks.

Given a compressor, a die grinder, an original S head (for use as a model), and some time and patience, what would prevent a guy like me from modifying E heads to S spec? Porting is usually thought about as a mysterious black art, only to be executed by those belonging to some secret fraternal organization. While I can understand how executing 906 spec ports, or something of that scale, could go really, really wrong in the hands of the inexperienced, how much experience would it take to accurately replicate ports, given a reliable model, 4mm larger in diameter than the original? Any feedback would be appreciated.

Thanks,
-Scott

[350HP930]

If you got good grinding skills it wouldn't be that hard. If you can get access to a mill to make fast work of the straight part of the runners it would be even better to insure consistancy.

If you even want to have some creative fun you can even build your own amateur flow bench using a shop vac, some cardboard, duct tape and a clear tubing/water manometer. That way you can verify with great accuracy that your port work is dead on.

[911pcars]

How much does it cost to Extrude-Hone these; that is, given the fact that this works?

Increasing air flow might take a little more know how than merely enlarging the ports to a certain size. However, if you've got an S head to mimic, and can do it, go for it. With that in mind, I would get some S cams so you can take advantage of the increased VE at high rpms. You might find the S ports aren't the best match for Ecams and smallish displacement. It also depends on how you plan to use the engine/vehicle.

Sherwood

[Scott Clarke]

Thanks for your input and words of encouragement. Sherwood: It is my understanding that even the 2.4 E motor suffered from undersized ports. There has been much discussion on this board concerning gas speeds in the ports of these motors. As my 2.5 will actually be close to 200ccs's larger than a "2.4", It seems that even my E cams would benefit from larger ports. Also, I have an idea that down the road I'll scrounge up some S cams and get a S space can for my MFI pump. This could be a relatively simple upgrade in that I wouldn't have to tear down the motor again. I'd like to put it together, and not need to take it apart again in the forseeable future.

I'll look into extrude honing. I don't know anything about it.

-Scott

[jluetjen]

Scott;
If you are going to do it -- and have the patience -- I'd do it the way that you described it orginally and try to "copy exactly" the S ports. Note that none of the heads that I've looked at (about 4 different flavors, a TK, early E and S) have "straight lengths" at all. If Porsche never did that, there must be a reason why they didn't just plunge a straight pipe. In all of the heads that I've seen, they gradually increase in cross section (about 1 mm for every 1/2 inch in from the manifold face to the bend. This would have the affect of gradually slowing down the airflow before it needs to make the slight turn in the bowl.

Extrude honing is a pretty blunt instrument and will not necessarily make or maintain the proper shape for the port.

[TimT]

An easy way to do this is a comprimise, have the machinist plunge a milll to open the ports up... then you do the finish work.

I bet alot of the cost you were quoted was for the hand work to finish the job

[David]

You could have a machinist chuck up the heads in a lathe and taper bore the port to get you started.

[Wayne 962]

Hmm, for $100/head, I would probably have an expert do it - someone like Walt who has done these before and can do them in their sleep. It's not like bolting in a replacement part - you're actually modifying the part, and if you messup, it'll cost you a lot more than $100/head to replace them...

-Wayne

[350HP930]

Porting is an art. I would never tell someone who wants to be an artist to go out and have another artist paint something for him, but at the same time you don't want to **** up a very expensive canvas.

I worked at a performance shop where we ported many an automotive and motorcycle head where I learned from one of the best people in the business (Mike Riley if anyone here knows him).

Its not rocket science if you have an understanding of what needs to be done and the skill to do it.

Rebuilding a porsche engine is no easy task either but if someone asks if they can do it themselves I also say yes if they have the appropriate skills.

[aigel]

I think you need two things to be able to decently port heads. Any heads that is: You need a flow bench and you need a bunch of expierience!

So, unless you are starting to work over half a dozen or more sets of heads and see this first set as a guinea pig, I'd leave my hands off it. If you fubar the heads, you lost some decent $. I am all for DIY, but besides gasket matching and some polishing on the exhaust side, I have never laid hands on cylinder heads...

I think you may end up with something half way decent if you are lucky, but these engines are just too pricey to do anything half a$$. I'd do it on a chevy 350 any day, but not on a flat six.

It is a bit like buying a collector car and use it as your first body and paint project. Not a good idea. I guess you get my point, just my two cents worth.

Cheers, George

[David]

This reminds me of a discusion I had with a very prominent motorcycle head porter in Texas. After I got to know him, he opening up a little when I went by to visit him. One day he showed me a head off an FZR1000 that had been ported by a VERY well known aftermarket motorcycle parts manufacturer for use on one of their pro bikes. Then he showed me the head he just finished for them to replace their's. The ports on his heads were much smaller, but according to the flow bench data he showed me, they had much higher flow due to the better velocity.

The moral of the story is that I'm all for DIY'rs, but I also limit my 4-stroke porting to gasket matching and exhaust polishing.

[Scott Clarke]

Remember that I'm not proposing to invent anything, just copy what is known to work. I would never think that I could improve upon what either Porsche or an experienced person could do. Again, I'm just talking about making my E ports into S ports.

[aigel]

Scott:

Thanks for clarifying. Still, can you recreate the 3 dimensional shape of an intake or exhaust port using a die grinder? I sure would not think I could by eye. I have no good idea on how to use a mold or model you can get off the S port either.

Good Luck, George

[TimT]

Guys.. its easy to improve your T heads...have a machine shop plunge the mill.... then YOU smooth all the transitions... heck you can say you ported your own heads....

Do you want the ports polished or not? what about the boundary layer?

If you want to make your T heads, S heads it really easy...

Improving the Porsche heads flow would be tough..

[Scott Clarke]

Tim-
It is my understanding that leaving the ports a little rough is the best move for a street motor. The roughness, by creating a boundry layer, should help compensate for any shape imperfections. By "plunge mill" do you mean that the machinist would cut the ports near the manifold surface to the S shape? Would this process result in a purely cylindrical void, or would it be tapered? How deep would the machining be? Also, how close to the valve would reshaping be required? Is the area surrounding the valve guide affected?

George-
It seems to me that an S head could be measured and marked at intervals parallel to the manifold sufrace (every quarter inch?). After establishing the new diameter at the manifold surface, the diameters at the quarter inch intervals marked on the S head could be replicated in the E head. The closer to the valve, the less work required. Some attention would need to be addressed to any lack of concentricity between the E and S ports.

I appreciate any clarifications of my incorrect assumptions.

[BK911]

I have a set of stock S heads and a set of polished S heads. The polished heads look pretty nicely done. However, the stock heads flow about 10% more air and are more consistant.

Moral of the story? Good luck!!

BK

[350HP930]

Since the 930 has straight ports and practically no pulse tuning to be concerned about my heads are going to be a cake walk.

I'm just looking to bore about a millimeter out the straights and get rid of the bottleneck right before the valve seats.

[911s]

BK,

Did you polish your heads yourself?

I think that polished heads that flow 10% less than S heads is still better than stock E heads.

[snowman]

WOW What a bunch of total HYPE!!!!

I have flow tested stock T heads. they will support more HP than you can do with any likely cam and compression, unless you go for a full racing engine, ie one that will turn over 7500 RPM.

Just match the gaskets, take out any flashing that feels rough and VIOLA, you have ported heads that will flow more air than you possibly need.

Bottom line... Porsche did such a good job on the desgn of these heads that you do not have to do much of anything! The S heads are almost a figmaent of a marketing merchants imagination. Nothing more!!! To put it even more clearly, unless you expect well over 300 HP from your engine, the stock T heads are all you need.

By the way DO NOT POLISH your head ports. This will do nothing but hurt your HP and torque. A slightly rough finish is optimum for max HP unless you turbo or supercharge your engine.

This is not only my opinion its supported by every authoritive publication on hp engines ever published the ones that use real engineering data to support HP claims and back it up with dyno data.

[Wayne 962]

I tend to slightly agree with Jack on this one - the stock heads are typically pretty darn good in most cases. Unless you're doing some really high-RPM racing, then you don't really need to open up the ports that big. The same reasoning goes with using Weber 40s on a 3.2. They work very well in the low-RPM range where you need and want low-end torque. On the upper RPM range, they show some slight limitations (on the 3.2), but how many times are you going to be revving up that high on a street motor? Using an oversized carb, or opening up the ports too much can have a detrimental effect on the power band at the lower end of your RPM range. For a street car, this is where you typically want the power - not at the high end...

-Wayne