924Board.org

[Mike9311]

[Mclaren924]

Glad to hear it, spend way too long reading through all of this last night and while I can't hold a candle to your knowledge, I have a much better understanding of how I want my head to be setup if I did want to sink some money into it. It seems like those wanting to really push the hp number while looking for a better curve, would gain from the valve shift. Also seems like a much more inline intake manifold could save some heartache in a non stock manifold situation? I understand that the whole point of this project is the stock manifold constraint. Just my ignorant synopsis of your findings. Can't wait to see more mate! Don't worry we all need time off sometimes.
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1980 931 "Salt" Bucket wannabe racer (not started)
1979 924 "Pepper" Restoration (almost done)
1980 924 "Donnie" (Parts car)-DEAD
1977 924 Slicktop "Pennie" Bucket turned Silver Spoon

[Topls82]

Guys
Any update on final version
Thanks for all efforts

[Mike9311]

I wasn't going to post yet but your timing is perfect.*

*Side note in all of this. Someone convince me to get a CAM too. I have been looking at CATCAMS since their dual pattern looks interesting. It would be great to favor the intake especially with what I mention below about exhaust valve. Its so much work to set up the proper valve lengths and get the lash right with the lash caps that the thought crossed my mind to get a cam.

Anyway back to question:

This was never finished but its in full swing right now. There have been several things holding me back one of which is a cnc issue since I wanted to cnc port the other intake ports (Down one axis on the machine). Working on that situation and its one of my biggest frustrations. When I have something in my head it eats at me to complete things the way I originally wanted. I should know better that it not how it works

There has been way too much time to think about everything done so far but its time. Can't wait for Morghen to show up again to comment on longest project ever If anything, Morghen is truly the inspirational push I need

One of my last tests was to back cut an intake valve to see if it improved off-the-seat flow. In this case it didn't. As of a few days ago new valves are on the way. One to replace the back cut valve I wasted on the test and four more just in case I want to do a second "simple" head.

All along my plan was to only do the very least to the exhaust side. The issue was the super alloy I chose only came in 38mm which I always thought I would machine down to 37 or 36. To save time and keep it simple for this one I will leave it at 38mm which leaves the size ratio similar and I don't think it will affect anything in a major way. The previous owner of the head had done some port clean up and I am not going to do anything but clean up the new seat install. Keep it Simple

One of the things I did was weld up the chamber to re-imagine the shape for better pressure recovery. In hindsight, this just added work and I should have kept it simple but now I will finish (seriously this time)

Working on cnc parameters for the chambers over our holiday break here in the US. Scanned the head and worked through the process to develop a CAD surface which was then 'simulation machined'. I could then lay that simulated chamber back over my scan mesh to see if anything needed fixing. This needs to get done so I can install the rest of the seats

The last pic is supposed to be a switching gif to show the over laid images but it doesn't work













_________________
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

[Cedric]

I simulated a couple of thousands cam profiles when i had acess to that, the best ones always had more intake duration than exhaust duration, at least on my setup with the std log exhaust manifold. Though i never tested if it was correct or not, but a cam is definitely a good idea.

Nice to see the machinig process, my head only has some hand finishing of the combustion chamber, nothing as fancy

How will you find a good way to set references for CNCing the ports?, these castings dont really have laser precision in my experience
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1980 924 Turbo
www.instagram.com/garagecedric/

[morghen]

I'm happy to see that you're still going at it with the combustion chamber development.
This is real development, this is the truly difficult work and this is the kind of work that requires in depth understanding of the subject related phenomenon and mastering of the complex tools required to do even the basic work.
My hat is off sir!

I imagine referencing for the machining to be done using the valve stem holes/cylinders and the machined flat face for depth.

I'm done for the year with the big efforts, sending the last 10 kits of the year by Wednesday and then i'll just work on improvements, documentation and planning for next year now for my own stuff.
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https://www.the924.com

[Mike9311]

Thanks guys, always appreciate the input and encouragement

As far as the cam, I am leaning toward the smaller of the two catcams turbo cams. Drove me crazy, Dutchpug never tried it in his crazy build. I am not really a fan of the wide LSA but its due to the dual pattern design so it intrigues me over all

That is correct, I do use the valve guide which was referenced by the tappet bore as well as the flat machined surfaces on the outside of the head. To extend the surface for a dial indicator, there is a plate (vice parallel they are called here). I can sweep back and forth on the machines X axis with the dial indicator on that plate (0.0001 inch resolution (0.00254mm)). This works very well along with the centering on a valve guide but there was a story to this as well

The plate can be seen in this part of the head scan


The old guides (installed by a previous owner) did not reference the tappet bores well. After the first round of guides were installed I dropped in exhaust valves from the tappet side. It was easy to see they were not centered and at an angle. New guides without holes were then installed in 7 of the 8 holes and then drilled / reamed while installed in the head

In the end , the centering is done from tappet bore but in a series of steps. For this head and probably from now on because I am paranoid

Bad One. Some didn't even go down into the bore.



Good one with pic at odd angle. Always hard with a phone. Side note: I just figured out how to post non-zoomed photos


_________________
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

[Mike9311]

You can really see what I am talking about with this view of a valve in the OEM guide and tappet hole on the NA head I tested. Better angled pic. If it looks good here after you do the guide then its right


_________________
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

[Mike9311]

This really intrigues me. It must have done the same for Dutchpug and his insane NA Turbo build back in the day (sadness...miss those days )

Intake lift is around 0.8mm (0.0315") more intake lift all around (according to graph anyway). This head project as it stands right now, follows stock flow to about 4mm Lift and then starts flowing all the way to 175-178 with intake (without intake even more). Since the head keeps flowing upward with additional lift, it would grab a tad more cfm over the nose of the cam vs stock (tip of my hat to Gegge thinking No wonder he says lift is key). Just think of the area under the curve this adds in combo with the additional head flow. I think this would match nicely. Also have this vintage adjustable cam gear to install which I plan on copying in the near future. I like the vintage look. Cam is ground already a bit advanced, so straight up would also be the plan.

Sorry for my crude overlay graphics




_________________
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