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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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 Posted: Tue May 09, 2023 11:55 pm Post subject: |
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| MikeJinCO wrote: | | 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. |
Thanks Mike
Wish I could find my book. Its somewhere and just when you want it 
Yeah, looks like I am pretty narrow. Just over 1mm at 0.043"
I feel like I lost the low lift at .1" lift once I cut a bit more of the seat angle above the 45 deg. It is a 39 deg and then the chamber. Almost wondering if the 39 directs it more into chamber wall even though its not much different
Its just 0.1" where I lose a tiny bit of velocity. Just that one point?? And it isn't even that much loss. Then it gains nicely thereafter
Thanks Mike, I'll look at other cutters to see if there is something close. Makes sense venturi / nozzle wise
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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 |
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MikeJinCO
Joined: 08 Jun 2010
Posts: 1236
Location: Maysville, Colorado
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| Posted: Wed May 10, 2023 3:54 am Post subject: |
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I have no idea if that applies to any other motor. He gave price dimensions for that motor, I believe many times thevalve seat is too wide.
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Mike
'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild) |
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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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| Posted: Wed May 10, 2023 6:22 am Post subject: |
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| MikeJinCO wrote: | | I have no idea if that applies to any other motor. He gave price dimensions for that motor, I believe many times the valve seat is too wide. |
I agree as well
As I think about it throughout the day, it makes sense in that the path the air flows out at low lift would stay in the smallest section a bit longer with a slightly wider seat. My seat is rather small at the 45 so as the valve lifts, the smallest section between the 45 of the valve and 45 of the seat opens up fast. Maybe too fast in that I lose the valve-to-seat venturi too fast. It then immediately recovers after .1" lift as the next throat venturi comes into play.
Just ordered a 45 only cutter just to get something on the way even though I could just try my old Neway cutter to expand the 45 a tad
There is a lot going on trying to bend the air and then eject it out past the valve smoothly, without losing speed, which I am intentionally trying slow locally at the short side radius (SSR), and then accelerate again at the seat / valve area. I start at almost 80% efficient, then drop to 70%, then bump up slightly as I pass 0.1" , roughly 72%. Then it falls as expected until 0.413" when it then gains again as port bias comes into play
I'm probably pushing the modern design idea too hard with such a small margin
Thanks much for giving me something to think about and try!
One more note. In all this I have played with various levels of depression. From over 28" (35 ish) to a lot less. The only time I have seen a real difference so far is at 0.05" lift. Really low depression yields a bit higher flow only at 0.05" (valve just off the seat) but once at 0.1" a change doesn't seem to matter.
This is really a study in low lift flow in general. The big boys call us RV cam guys for a tow rig with our low level lift   Anything up to .4 to .5" is low to them
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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 |
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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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| Posted: Sat May 13, 2023 8:11 am Post subject: |
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Sometimes being oblivious might be a good thing. Or as I tell my kids... 'the more you know, the more you will realize the less you really know'
I keep scratching itches and it only generates questions
increased 45 deg seat which takes the top cut away. Resulted in lower off the seat flow through mid-range lift but had an interesting side effect
It was a turbulence reducer. Any residual turbulence at the high end disappeared. Would just go up
Interesting test though! Thanks MikeJinCo
_________________
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 |
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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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| Posted: Tue May 16, 2023 11:49 pm Post subject: |
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Ok, I am moving on with this head. I feel like it isn't exactly were I think it could be but more material removal isn't answer.
The next 931 head will likely be a 40mm since the biased flow efficiency pivot would happen at lower lift keep the flow efficiency higher throughout. With a 40mm the flow efficiency would start improving, after going down, at .394" lift rather than .413"
Same with a NA especially since its already offset toward cylinder center by 1.2mm vs 931 intake valve. The NA just might be the monster in the closet
If I do another 42mm offset head, I would change some things slightly with all that was learned. Its hard to compare to all the other heads out there with our lift levels being so low. Our lift window is all but ignored as 'low lift flow' by the general community. The ideas are the same but its important that you ignore comparing numbers.
I have a decent idea, or two, whats happening at .1" lift. I mean I literally know (slight loss in velocity even though over all its higher everywhere else). Will apply what was learned moving on
Finally I owe some testing for Cedric and Fifty ....and me of course because I want to know too
_________________
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 |
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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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| Posted: Sun May 21, 2023 1:50 am Post subject: |
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I am glad I did all this so far but this is getting frustrating. Yesterday I made yet one more mold and while that was curing I ran the stock head again to get finer values at every 0.50" lift point (1.25mm) ...then everything went sideways
The stock head had better numbers yesterday, so to compare an apple to an apple, I pulled the mold on the ported head (it was now cured) and tested the ported head. This is minutes apart
Ported head performed as it had in the last test except one or two points down low it was actually worse, oddly worse. The stock head was beating it down low and the stock head had higher flow numbers than it had way back when first tested. This is the exact head? Never had discrepancies I couldn't explain until now. The data has been backing itself up nicely every retest of ported until now. Even installed a non-ported intake on stock head and values where within 1/2 cfm at each point.
This has been the itch I have had now in the depth of my mind... that I went too far porting wise back 10 pages or so on this thread.
Software shows what I am seeing. efficiency down on ported head until .2-.250" lift, or halfway through the curve. I lose up to 20-25% only to gain it back up top. Not at all the goal
Bottom line is I am really going to switch gears hard now. Stock head with 40mm and a mild clean up until I can figure this out with more time.
_________________
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 |
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Beartooth
Joined: 05 Apr 2022
Posts: 239
Location: Roberts, MT
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| Posted: Sun May 21, 2023 3:39 am Post subject: |
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I've gotta say, I've learned a lot following you through this process. There's definitely not a pile of CFM on the table with these heads like there is with old American iron, but I'd think with all the work and research you've put in that you'd be seeing better numbers across the board. You definitely hit it right on the "RV cam," but of course, it's not so much an RV cam given the valves sizes. A small V8 like Ford's 302 has 1.78" intake and 1.46" exhaust valves (and it's undervalved if you want to rev it), compared to 1.57/1.29. That's 25% more intake valve area, and stepping up to a fairly typical 2.02" valve jumps you to 50% more area. Not opening a 2" valve at least .5 inch leaves a lot of flow on the table, where a 1.6ish" valve has probably stopped gaining flow at .5"
Anyway, I wonder if there's some "Ah-ha!" discovery that'd pull the gains you'd expect out of the work you've done. Also, I wonder what the dyno would say; sometimes the flow bench doesn't tell all... I'm curious how you'd build a head for a typical performance street 924 based on what you've discovered. If it were me and I were going so far as custom valves and all, I don't think I could resist going a bit bigger on valve head diameter and smaller in the stem. Of course, the 924 engine architecture is facing multiple bottlenecks, and at some point you're doing more work for less gain than sorting out an engine swap. That said, I think most of us are old and wise enough to know that engine swaps are easier said than done; we'd just like to be able to put some money into the head with reasonable assurance of another 10-20 HP (and maybe more, depending on supporting mods). I think you've done a great job exploring the possibilities here; I really appreciate your effort to share it, even if it's proving to be kind of frustrating. That's how most of my projects go!
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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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| Posted: Sun May 21, 2023 7:27 am Post subject: |
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| Beartooth wrote: | I've gotta say, I've learned a lot following you through this process. There's definitely not a pile of CFM on the table with these heads like there is with old American iron, but I'd think with all the work and research you've put in that you'd be seeing better numbers across the board. You definitely hit it right on the "RV cam," but of course, it's not so much an RV cam given the valves sizes. A small V8 like Ford's 302 has 1.78" intake and 1.46" exhaust valves (and it's undervalved if you want to rev it), compared to 1.57/1.29. That's 25% more intake valve area, and stepping up to a fairly typical 2.02" valve jumps you to 50% more area. Not opening a 2" valve at least .5 inch leaves a lot of flow on the table, where a 1.6ish" valve has probably stopped gaining flow at .5"
Anyway, I wonder if there's some "Ah-ha!" discovery that'd pull the gains you'd expect out of the work you've done. Also, I wonder what the dyno would say; sometimes the flow bench doesn't tell all... I'm curious how you'd build a head for a typical performance street 924 based on what you've discovered. If it were me and I were going so far as custom valves and all, I don't think I could resist going a bit bigger on valve head diameter and smaller in the stem. Of course, the 924 engine architecture is facing multiple bottlenecks, and at some point you're doing more work for less gain than sorting out an engine swap. That said, I think most of us are old and wise enough to know that engine swaps are easier said than done; we'd just like to be able to put some money into the head with reasonable assurance of another 10-20 HP (and maybe more, depending on supporting mods). I think you've done a great job exploring the possibilities here; I really appreciate your effort to share it, even if it's proving to be kind of frustrating. That's how most of my projects go! |
Thanks for the encouragement and you hit an interesting point with the RV cam/valve size comparison. Its like i'm scaling the entire system which I already noticed with the port volume. Your comment makes sense and I wasn't really seeing the whole comparison
My only thoughts right now are that I did something to the throat venturi when I finished the valve seat which set it down more effectively taking some of that away. This would also lower the short side radius distance to seat which might not be so good. The other thought is that the valve shape might not be the best for this application. It is a motorcycle valve technically. Would be cool to try something more tulip shaped if I could find something
My thought process the last few weeks was that my velocity was rather high at the top. To deal with that strategically, I added some port volume. It might have affected the lower lift region.
This is a much harder process than I originally thought. My two biggest porting achievements prior to this were on a Chevy 383 and Buick Grand National which are pretty darn standard examples American V8 style porting. Both turned out awesome. Ducati 748 heads too but the head design is so far away from something like this 924. I only mention all these so you can see where my brain is at.
This whole .25Diameter thing has me thinking that a 40mm should also work quite well even though like you said, the urge is there to go bigger.
Back to the throat area right below the seat angles. I made the ratio the same as stock which was 90% of valve diameter (somewhat racy really). Now wondering if something like 88% and a longer section of it at that diameter would have been better
_________________
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 |
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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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| Posted: Wed May 24, 2023 4:36 am Post subject: |
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Couple of thoughts as I continue my progress.
My last test was the first time my graph resembled gegge's with the hump. In particular the stock blue line but in my case the ported version. This is a clear indicator of turbulence. In my case the port went from quiet to loud and any lift after that point had a slightly lower flow number. ...The hump
Also the stock head with intake only had issues down low in the first 3-4 lift points when flow was steady. Once it went turbulent the flow numbers matched without intake
I take this to mean my ported head is at steady flow with intake higher in the lift curve. The flow numbers with and without intake only match when it finally goes turbulent
still working on things plus I received my 9mm pilot for testing seat work on other heads. I am suspecting my seat work will make it worse but let us see what happens
_________________
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 |
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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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| Posted: Wed Jun 07, 2023 11:39 pm Post subject: |
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Update:
I have been trying several port modifications with clay to see if there are dead flow areas, direct flow, and reduce unnecessary port volume with hopes that it might affect very low lift flow (right off the seat as valve opens). All of these have not really done much of anything. In a way surprising
For example, one test was to revisit the adding of a valve guide contour.
All this has caused an immediate shift in my process. This head will not be abandoned but it requires more time to work this all out properly.
I have already pulled another head I have that I can hopefully do just a basic run through. It needs to be skimmed due to its previous rough life. Almost looks like the PO had a head gasket go.
If this then gets up and running I will have something to compare it to and will allow me to sort the other fuel system mods etc. Might even dyno the car if it runs well enough. Then, ideally, if this offset valve head is ready, do a swap and test only a head change
_________________
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 |
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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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| Posted: Fri Jun 23, 2023 7:13 am Post subject: |
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I seriously have issues. Stuck valve in my tractor had me straightening push rods until they broke just to keep going. Couldn't take it anymore so I ordered a new head cheap
...And you know what happened next Seriously though. Just a quick job to clean it up. There were casting burrs everywhere. No testing. Too small as well so it was kind of hard to get in there
_________________
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 |
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Cedric
Joined: 27 Aug 2004
Posts: 2658
Location: Sweden
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| Posted: Fri Jun 23, 2023 7:43 am Post subject: |
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Haha, it do look a bit ugly though, a quick clean up surely help a little:) At least mentally it will feel better 
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1980 924 Turbo
www.instagram.com/garagecedric/ |
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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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| Posted: Fri Jun 23, 2023 11:05 pm Post subject: |
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| Cedric wrote: | | Haha, it do look a bit ugly though, a quick clean up surely help a little:) At least mentally it will feel better |
Thats it exactly "mentally it will feel better"
_________________
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 |
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Mike9311
Joined: 14 Dec 2004
Posts: 1698
Location: Chicago-ish
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| Posted: Thu Jan 04, 2024 9:19 am Post subject: |
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Comment on above post: tractor ended up having more power It no longer bogged while doing the same or harder work. Glad I took the time to amuse myself
Anyway, things have been going on in the background. Originally I was machining the 6mm valve stem groove using a smaller radius tool on a CNC and never on a real stem up to this point. One issue that really played over and over in my head was surface finish. I never was happy and was frustrated to think I had to come up with a post process to improve the groove finish. The easy way is to polish while turning but that places polishing grooves (small scratches really) in the wrong orientation to the stem. Its like placing "please break here starter grooves". I thought of things like micro shot peening and/or polishing radially with a small tool so lines would be on same axis as stem. I disliked all these ideas just because it is extra work
Then I made the smartest move by researching and then purchasing other tooling which took forever. First, figuring out what I wanted followed by what I could actually get which had me buying from all over and then waiting. Still smart because surface finish is no longer an issue. I also believe the groove surface will be burnished in compression similar to peening a few seconds after the motor starts for the first time as long as the finish is decent to begin with and it really is...
Oh...the other problem was work holding a valve since you want to have the stem held close to where you cut the groove so its nice and rigid. The issue is the valve head. Your fixture has to hold the valve so the head can be "inside" the chuck with accuracy and repeatability. This was finally figured out so I could do it on a real valve and it was moved to a manual process away from the cnc. This picture shows the groove in a test valve that was already grooved so I could compare fit and finish. Worked so nicely and certainly worth all the trouble. I geek out on stuff like this so I had to share plus you all have to know I am still going to finish this!
_________________
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 |
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Mclaren924
Joined: 13 Oct 2021
Posts: 198
Location: California
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| Posted: Fri Aug 09, 2024 5:51 pm Post subject: |
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any news on the insanity?
_________________
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 |
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