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Need some help for porting the intake port in 964
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kondzi  



Joined: 02 Jul 2018
Posts: 485
Location: Poland/EU

PostPosted: Wed Dec 07, 2022 7:13 am    Post subject: Need some help for porting the intake port in 964 Reply with quote

Guys, I know it's not 924, but I need some help on a cylinder head of my friend's 964 I'm helping with.

The short story is valve guides are worn out, seats and valves got out of tolerances and stock valves got so expensive it's cheaper to get bigger aftermarket valves (intake 52mm vs 49 stock Exhaust 42mm vs 41.5 stock) with double springs and titanium retainers... Exhaust port is covered with ceramics, so not much to improve there anyway.

I tried to find a knowledgeable machine shop here in Poland, but it seems that market for Air-cooled 911s and their tuning is just at the very beginning and the shops are both afraid of the works on the 911 components (expensive) and not experienced.

So I got my first head from the machine shop with guides removed and new valve seat rings fitted - now I'm on my own. They flow benched the stock head before doing any works and will do same after I give them back the head when I finish porting it on my own.

I took some photos from different angles for ease of discussion.

Obviously changing the valve from 49 to 52mm and replacing the valve seat with 993RS one introduced a step in the port, just below the seat.



So obviously I need to enlarge the port to the diameter of the ID of the seat - any suggestions how make it most effective - going straight down as factory did with milling tool I expect will not to be the best option?





The area around the valve guide needs some tuning, and while on the "attack" side [top of the valve guide hole in the photo] my idea is to create kind go knife edge that gradually widens into water drop shape, not sure what shape should have the back side of that area [area closer to the exit of the port - below valve guide hole in the photo].



In general I don't want to make it worse than it is, that's the biggest success criteria But if I can make it better...

There are "stitches" and porosity that I want to smoothen with sanding tools and sanding paper.




How the "lip" should look like on the shorter wall and longer wall (the one that has valve guide in it)?



Some more photos...






There is a "bump" on the almost 9 o'clock that I will flatten as well (blurred area / out of focus) in this photo.



I posted this also on pelicanparts forum, but not many want to share their experience openly... Which seems not be the case on this forum

Many many thanks for any hints (before I do the job according to my educated guess).
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Konrad
'89 951 US
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'84 911 Carrera 3.2 RoW (factory specs)
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MikeJinCO  



Joined: 08 Jun 2010
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Location: Maysville, Colorado

PostPosted: Wed Dec 07, 2022 11:26 pm    Post subject: Reply with quote

I'd cut the valves down to fit. Running a boring head down thru the intake ports is going to create all kinds of issues in a port that looks quite well done, by the standards of the day. Those heads are too expensive to take any kind of a chance with.

David Vizard who is one of the most recognized cylinder head development people wrote an entire book on the BMC A engine development and should be required reading prior to doing any port work. He cut a head into three pieces and then tested each, the straight part of the port flowed 130 CFM, the curve with the valve guide 90 and the valve seat area 50. Obviously the valve seat area is where to concentrate. Most of this work was done in the 1980's so there have been many advancements since then. He tested and showed the results of every incremental change he did.

The valve seat needs a minimum of 3 angles, the 45 degree seat and then a 15 degree lower(net 30) both going from the port to the valve seat and from the valve seat into the combustion chamber. My local machinist has a 5 angle cutter he used on the local circle track racers heads. On that particular mtor he specified that the valve size be .060-.062" wide, being off either way had a negative effect. He does not speculate at all o if that is common to other motors. I also have his book on porting and flow testing written years later and he never mentions the valve seat size. The intake valve should also be cut with a 30 degree back slope above the valve seat. The intake valve should be sharp edged while the exhaust gently radiused. That allows the exhaust gases out easier and the sharp edge on the intake impedes exhaust back flow during the cam overlap period.

In the curved section blend in any discontinuities from port machining and around the valve guide. Make sure the valve guide has a tapered tip, but not to a sharp edge and don't shorten it. The heat transfer from the valve to valve guide is critical, that appears to be one reason Porsche and VW used large valve stems on their air cooled motors.

The straight section of the port should merely be smoothed with a 60-80 grit sanding roll, any polishing finer than that is just cosmetic. No enlargement is really necessary.

That is my take on his book and probably applies to almost any cylinder head. His graphs showing the affect of every incremental change is convincing.
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safe  



Joined: 18 Mar 2017
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Location: Sweden

PostPosted: Wed Dec 07, 2022 11:43 pm    Post subject: Reply with quote

On the 964/993 heat isn't a big issue.

On earlier heads Porsche used sodium filled exhaust valves to transfer heat better. Wjth the 964 they put in ceramic liner in the exhaust port (like the 951), doing that they removes the sodium filled exhaust valves for regular and put in sodium filled intake valves to get a little more heat into the intake valve.
Apparently that was of little use because they skipped sodium valves for a smaller, 8mm, normal valve in the 993.

Weapon of choice for porting is an electric die grinder with 6mm shaft and a 6mm rotary file, both short and 6" long.
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kondzi  



Joined: 02 Jul 2018
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PostPosted: Wed Dec 07, 2022 11:50 pm    Post subject: Reply with quote

I got the grinder and some attachments. I also got dremel for smaller radiuses. And it’s aluminum, so will not be that hard as with cast iron heads I was dealing with my other old cars
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Konrad
'89 951 US
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Fifty50Plus  



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PostPosted: Thu Dec 08, 2022 12:54 am    Post subject: Reply with quote

Konrad,
I also saw your post on Pelican. Looks like you are getting some great advice here also. It's been many years since I did porting work on 911 heads but Mikes advice about the seat is spot on.
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kondzi  



Joined: 02 Jul 2018
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PostPosted: Thu Dec 08, 2022 3:16 am    Post subject: Reply with quote

Well I'm learning all life, we all are. Not sure why, but I missed Mike's post.
I know David's book about Ford 2.0 SOHC engine (I had that engine in my Capri with 2x Weber IDF Carbs), good stuff. Need to read more it seems
It's really amazing, that when there is some will, we now can exchange ideas and experience worldwide, which would not be the case years ago.

I did not post here the photos of the Valves:



Intake are super thin, more than a back cut. 4 grams lighter than stock even though 3mm bigger.

Exhaust are similar shape to stock, but 14 grams lighter!

I use 993RS valve seats. These are already 3 angle cut by factory. The machining company I work with have for sure 3 angle knife for the seat job. Not sure if they have 5 angle one - I will ask.
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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safe  



Joined: 18 Mar 2017
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PostPosted: Thu Dec 08, 2022 6:46 am    Post subject: Reply with quote

Looks good! Bigger valves are better as long as they don't shroud themselves.
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Mike9311  



Joined: 14 Dec 2004
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PostPosted: Fri Dec 09, 2022 6:01 am    Post subject: Reply with quote

I just saw this and quickly tried to read through

The straight section of the port right below the valve seat (like Mike said pay attention to Vizard.... and others like Speier) Do not make that diameter section any larger than 91% of the valve size (typical 88-91). This is called the "throat"

Bunch of very good vids out there from both guys mentioned above

Also its the seat that pulls a majority of the heat from the valve. Around 80% Its why I chose the seat material I did for my head for the small 6mm stem valves
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kondzi  



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PostPosted: Fri Dec 09, 2022 6:54 am    Post subject: Reply with quote

Thank you guys, it all adds up to an idea. I've studied like 200 shots of heads done by xtream, ed pink, turbokraft I think they get them from xtreme anyway). There is one area that I'm not sure what to do. Looking from the inlet side, behind the valve guide. Before the guide I will "sharpen" that area slightly (let's call it shark's fin), but behind? I see either similarly sharpen as in the front (shark's fin, but slightly less - with material removed to the sides and deeper to the big radius) or more like water drop shape that blends into the big radius alternatively.

The other thing is I also noticed that in some heads it looks like there is some material removed on the big radius behind the valve guide (to a shape more like ice cream scoop would make) - does it make sens or it's just my imagination?

Started reading mr Vizard's book about porting already.

My plan is to make a mold of the port from silicone to measure all the diameters of the port easily in different places.

I need to decide if I leave the port with the smallest diameter as is, or I will enlarge it slightly (like 1-2mm diameter more) to get closer to the 964/993 RS heads.

The engine will get VarioRam induction from late 993, SSI 41mm OD headers and rather hot cams.

Not sure about the muffler yet, but probably something like Flowmaster ones with chambers only.
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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Mike9311  



Joined: 14 Dec 2004
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PostPosted: Fri Dec 09, 2022 8:25 am    Post subject: Reply with quote

At least you have material in that spot to manipulate. Unlike 924. I am right in the middle of porting too so everything is fresh in my mind

You see how that spot in pic below is turned slightly toward the center of the chamber to direct or bend the air in that direction? In this v8 case the chamber favors this move (obviously doesn't apply to your chamber) but its the idea of directing away from the cylinder wall.

You subtly bend the air once it passes the stem/guide toward the open center of your cylinder

EDIT I stated this sentence wrong, its the other way around (see later post): Vizard wants cylinder wall side of the intake port wall straight to the seat/throat so the air will come in straight and not turn into the incoming directed air on the other side of the stem you just turned using your shark fin.

Think of it as directing two flows around the guide/stem

The area of the port around your guide stem should be slightly larger to expand and slow the air before hitting the smaller throat (accelerating the air) and finally the seat / valve opening. You see why you need the smaller throat size (88-91 %)? You re-accelerate the newly directed and slowed air



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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car


Last edited by Mike9311 on Sat Dec 10, 2022 12:27 am; edited 1 time in total
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kondzi  



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PostPosted: Fri Dec 09, 2022 9:03 am    Post subject: Reply with quote

I noticed this slight turn of the shark fin in the xtreme cylinder heads work. My expectations were it’s to introduce more swirl though…
I’m familiar with the throat size theory / Venturi effect or so in the end.
Also I’m aware that not only flow, but velocity matters (hey, we don’t have 4inch ports and valves right?). So it’s not only about flow, but also velocity and direction it seems (and swirl!)

The 911 head is quite nice straight from a factory - there are no water passages in the head to interfere and so on.

It flows nice, the guys at the machine shop were surprised how good they flow (stock) compared to other cars’ heads they have flown.

So Mike, removing the material behind the valve guide on the long radius is to slow down the velocity before reaching the throat? Am I getting this right?
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
'79 Ford Capri 2.9 (heavily modded)
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Mike9311  



Joined: 14 Dec 2004
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PostPosted: Fri Dec 09, 2022 10:30 am    Post subject: Reply with quote

kondzi wrote:
I noticed this slight turn of the shark fin in the xtreme cylinder heads work. My expectations were it’s to introduce more swirl though…
I’m familiar with the throat size theory / Venturi effect or so in the end.
Also I’m aware that not only flow, but velocity matters (hey, we don’t have 4inch ports and valves right?). So it’s not only about flow, but also velocity and direction it seems (and swirl!)

The 911 head is quite nice straight from a factory - there are no water passages in the head to interfere and so on.

It flows nice, the guys at the machine shop were surprised how good they flow (stock) compared to other cars’ heads they have flown.

So Mike, removing the material behind the valve guide on the long radius is to slow down the velocity before reaching the throat? Am I getting this right?


This is why I wouldn't do too much to the head if they flow well already. But

Its removing material on both sides of the port in the guide area guide not the long side radius. Air has to split right and left around the guide in that area. Do your silicon molds and see how this looks. I highly recommend the Vizard videos too. You will see before and after molds and it all should make sense.

Edit: Actually, you may not be able to do much there but a clean up since its right at the throat. Unique situation for you
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1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
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1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
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safe  



Joined: 18 Mar 2017
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PostPosted: Fri Dec 09, 2022 5:40 pm    Post subject: Reply with quote

The 964 heads are pretty good for a 2 valve head, a clean up does take care of the low hanging fruits. Bigger intake valve is nice too. This and bolt-on parts will take you a bit over 300 crank.
If you want more, 350-380, you need to think about RSR stuff, pistons with bigger valve pockets, more cam, ITBs to handle the cams, rods to handle the increased rpm. Not recommended to go above 6800 with stock rods.
A friend have a 964 based engine built like an RSR and it made around 370.
Taking the head porting further I think will net limited results without going RSRish.

Easier to slap on a turbo and make 400+ with just a little boost....

You are changing the valve retainers, that's good, the stock ones has a tendency to split and drop valves when they become older and you rev to 6800.
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Mike9311  



Joined: 14 Dec 2004
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PostPosted: Sat Dec 10, 2022 12:25 am    Post subject: Reply with quote

I realized last night a lot of my advice doesn't apply since you have opposing valves. Your intake is centered (so much better BTW)

Also I got this part wrong (backwards).

"Vizard wants cylinder wall side of the intake port wall straight to the seat/throat so the air will come in straight and not turn into the incoming directed air on the other side of the stem you just turned using your shark fin. Think of it as directing two flows around the guide/stem"

Its the cylinder wall side of the port that gets shaped to direct away from the cylinder wall. Not what I said above

Again, your situation is different. Just think of it as directing air. Don't do too much and remember the throat rule

EDIT: This looks like a nice example

https://forums.pelicanparts.com/911-engine-rebuilding-forum/652723-cylinder-head-porting.html

https://rennlist.com/forums/964-forum/791282-9m-964c4-project-car-9m64rs-lightweight-the-likely-outcome-11.html
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1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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kondzi  



Joined: 02 Jul 2018
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PostPosted: Sun Dec 11, 2022 7:21 am    Post subject: Reply with quote



24 hours to cure fully. Clock is ticking Just hope I will be able to take it out in one piece or so. Covered the walls with PTFE grease prior to filling in the port with this silicone for molding thing
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Konrad
'89 951 US
'88 Mustang 5.0 LX Convertible (factory specs)
'84 911 Carrera 3.2 RoW (factory specs)
'81 931 RoW (TBD)
'81 Ford Capri 2.8i (factory specs)
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