924Board.org

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

Just to add some info about the injectors. I like where they are at spraying right to the valve. This way they are directing atomized fuel right to the point of entry without relying on anything to keep the fuel in suspension (atomized). Simple and straightforward.

What happens though when the nozzle enters the port from the opening is that I hear the port turbulence it causes. It goes from quiet to noisy. Super obvious

I have played with clay here since I was thinking it could function like the start of the guide area "air guide" to direct area around the guide as well. Imagine a ceiling vane/baguette. Nothing worked to my satisfaction. That is when I figured why not raise up the injector so the spray starts right at the port ceiling which is not too much of a change.

Don't get me wrong, I have come up with other odd ideas like when switching to v8 or v6 CIS head I could have shower injectors opposite the openings in the intake plenum that partner with the stock location injectors. Obviously this isn't needed for the HP level. I think I mentioned this before and its overkill.

Back to the porting. I need to run the exhaust side so I can see how the ratio looks between the ports with the new larger 38mm exhaust valve. I am only going to blend it in. No other porting other than what the previous owner did to the port which wasn't much. I have been running the numbers through Vizards software and things look good there including the mean velocity of the Intake port. Nice to be able to compare to a few other heads.
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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

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

Another update coming soon. Worked on seats yesterday and this is continuing. The plan is to run new stock vs ported with double the lift points (@ 0.05")

See how weird this heads was? Previous owners port work vs new port as its sits yesterday. Will say its hard to take a pic that really shows shape.

_________________
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 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

Yesterday I was able to get the Intake seat out to its final diameter and position. Interestingly it lost low lift and then gained at the high end? Totally the opposite of what I was expecting and trying to achieve. Everything I study says the valve seat work dictates low lift flow which is exactly our situation with our cams (.25D). The only thing I can think of is that the velocity increased at the seat throughout the lower lift range and once it passes .25D (.25 * 42mm = 0.413 or 10.5mm) the flow goes up more than before when non-turbulent. The flow ball trick has it easily over 200 now and its also easier to tell the active sections of the port. To clarify the port is more actively even but the one side I like to concentrate on is clearly different than the other which is good. Also software results so far has the port velocity pretty high and the seat adjustment may have pushed it a bit higher

(Small Edit: See how the seat affected high lift flow with above comment. Really wasn't expecting that.)

I am letting my mind work the problem in the background. So far the only conclusion is that I will have to continue to apply what has been working porting wise as the port becomes even more efficient with any change like with this seat work adjustment.

Exhaust: I am thinking now I may reduce the 38mm super alloy valve to a 36-37 since even trying to get to a 38 has the cutter hitting the chamber wall. This is probably a good thing anyway and just more work. The seat is machined/ blended now to 36 and I also have a 36mm valve to run a flow test. The final diameter is more likely going to be 36.5 to 37mm.

Finally adding the Intake to the test continued to push down any improvements. Its super predictable. If you are at 195 it will fall to 177 with intake
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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

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

So... Exhaust flows pretty good with no pipe or manifold. This is with the new beryllium-free copper seat and a 36mm Ferrea valve. The previous owner had done some minor port work which will require comparing to stock exhaust flow from another head.

What isn't shown is how the flow collapses with Exhaust Manifold. I put it on and tested only at max lift. Flow went from 154 down to 127 which is actually preferred with what the Intake does to flow. Flow ratio is a bit high with Intake mounted. The idea this whole time is really the right idea. Just work the Intake

_________________
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 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

Weird stuff going on down low at .1" lift but after that dip it moves air efficiently. Can't explain the dip? Wondering now that the seat is done if a valve back cut will help? I keep talking about it but haven't tried.

Here are two graphs. No bone stock exhaust flow shown yet, just the ported head with unknown exhaust work by PO.

The one graph shows the efficiency of the port vs stock intake which correlates with the crossover you see in the flow graph where the stock briefly beats the ported version. Literally how close to a straight port do these two compare which Cedric pointed out a while back. The closer to "1" you are the better

Thin Red is ported exhaust. Also this is NO INTAKE and NO EXHAUST MANIFOLD and also showing non-turbulent ported Intake data. In other words the "best of the best". Oddly the Intake helped the upper end turbulent behavior of the ported head. I pulled a bit over 180 with Intake which was better at the top than when port goes turbulent. That was a first.

Finally, vertical lines are the respective .25D points (.25 * Valve Diameters)

_________________
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 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

ahhh, pressure recovery. That is the issue

New rabbit hole for me to go down even though its what I thought I had covered from the start. hmmm, time to think
_________________
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 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

That felt good. One itch scratched and scratched well

Just wanted to be sure that the chamber modifications didn't hurt pressure recovery. The whole idea of the chamber shape was to carry on the valve seat angles like a nozzle as the valve opens. My worry was that I went too far out with the chamber. So I used clay to fill in that area a bit and shaped it really nicely.

Well data says it hurt rather than helped and very evenly too. At all the lift points the flow was hurt. Few cfm lost everywhere and it went turbulent earlier. Yesterdays test also had turbulence rearing its ugly head again. All this just because I finalized the seat.

This is a fast port
_________________
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 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

I have to laugh at myself sometimes. Actually looking at tables of data I've written shows clearly that the .1 lift point has been stable at this lift for a long while now. Why it starts strong, dips, and then goes stronger afterward is weird but we carry on....

String tested the port today and it shows much better stability than before. Its not perfect but its no longer crazy. Nice thing is that it reaches higher velocity after .1" and is more stable than before

Waiting on machine to open up so I can try a 30deg back cut on intake valve
_________________
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

gegge · Joined: 27 Jul 2007 Posts: 1124 Location: Sweden

I just love to read this! "Pressure recovery" does feel goood.
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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

Fifty50Plus · Posted: Sat May 06, 2023 12:18 pm Post subject:

Mike, sorry this might be a dumb question. I just told my machinist to do a 5 angle valve job on my latest 924 race head (still not allowed to do anything beyond port matching). Oh yes, 924 NA head. Am I wasting his time?
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

Fifty50Plus · Posted: Mon May 08, 2023 9:18 am Post subject:

Yes, it's and NA head on an NA engine. SCCA has allowed us to lighten the engine components and bump the compression to 11:1 but chopped some lift off the cam for H-Production. It's now restricted to .425 lift but the cam profile can be changed. Dema Elgin has done some work on them that changes the lobe centers as well as increasing the duration. I've noticed a bit more mid range torque when driving his cam in my old IT-B (9.5:1 compression) but am hoping the compression bump will help lap times. Another kicker is that the stock throttle body must be used so it feels like the engine runs out of air above 6200 RPM or so.
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

Mike9311 · Joined: 14 Dec 2004 Posts: 1678 Location: Chicago-ish

MikeJinCO · Posted: Tue May 09, 2023 9:48 pm Post subject:

In Vizard's book on the BMC A engine he found the width of the intake valve seat to be very important to low lift flow. For it a width of .060 to .065. On the exhaust side a slight rounding of the exhaust valve edge helped the exhaust flow.
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)