High Flow, Low Cost, 8V Cylinder Head Project
03-21-2015, 07:38 PM
#121
I think this confirms what Jon Milledge has said, no reason to really go more than 48mm on a 104mm bore. I also saw this on my flow bench. I think especially when you can get 48mm valves for $29/each. Just my opinion. The reward past 48mm is minimal at best. The cost goes up dramatically and the valves just get heavier. If you want much more flow than 250cfm then the 16V head starts to really make sense. In my mind the beauty of the 8V head is fairly good performance at a bargin price. If cost is not really a consideration then the 16V head is the way to go.
I don't disagree that the 4 valve is much better but more complicated and the velocity is better in the 2 valve head which is the main reason I believe my 2 valve engines will make excellent power.
03-21-2015, 07:52 PM
#122
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Well the 52 mm is flowing around 275 cfm, which is quite a lot more, the 52 mm valves I used weigh less than the 45 mm factory intakes and a lot less than the factory 48 mm intakes. The other head I have, if you read the whole thread used 48 mm in a 100 mm bore as a comparison flowed just under 250 cfm but the head was ported before and the current porter did complain about some of the workmanship.
I don't disagree that the 4 valve is much better but more complicated and the velocity is better in the 2 valve head which is the main reason I believe my 2 valve engines will make excellent power.
I don't disagree that the 4 valve is much better but more complicated and the velocity is better in the 2 valve head which is the main reason I believe my 2 valve engines will make excellent power.
03-21-2015, 08:18 PM
#123
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I think this confirms what Jon Milledge has said, no reason to really go more than 48mm on a 104mm bore. I also saw this on my flow bench. I think especially when you can get 48mm valves for $29/each. Just my opinion. The reward past 48mm is minimal at best. The cost goes up dramatically and the valves just get heavier. If you want much more flow than 250cfm then the 16V head starts to really make sense. In my mind the beauty of the 8V head is fairly good performance at a bargin price. If cost is not really a consideration then the 16V head is the way to go.
03-21-2015, 08:50 PM
#124
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03-21-2015, 10:07 PM
#125
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I believe it was around 2007. Some of us shared some emails with Corleone and he told us that this is what JM told him. He said they discussed it extensively. He told us JM did a lot of testing looking at 48mm, 49mm, and 50mm valves and that 48mm was always better.
03-22-2015, 07:59 AM
#126
To reach the same inlet valve area of a stock 968 head (using 39mm intake valves) we would need a 55mm single intake valve (!). This plus JME's experience about the 48mm being the largest size that may be used suggests to me it's probably going to be even more cost-effective to build right away a 16V engine than spending a fortune on major port work, aftermarket valves & springs and a suited camshaft. Both set ups will require an aftermarket intake to make the most of the top end, too.
03-22-2015, 12:29 PM
#127
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I am living this nightmare right now! The giant valves in my head were simply too big even with my giant bore. We all thought with the 106.5 mm bore it would work, but it didn't. At least not where I wanted it. We are starting over now and going all out. Nothing but the best going into this head now. Hopefully we can make it special and not just expensive! Just the new Titanium valves and BeCu seats cost more than most complete worked heads.
03-22-2015, 01:25 PM
#128
I am living this nightmare right now! The giant valves in my head were simply too big even with my giant bore. We all thought with the 106.5 mm bore it would work, but it didn't. At least not where I wanted it. We are starting over now and going all out. Nothing but the best going into this head now. Hopefully we can make it special and not just expensive! Just the new Titanium valves and BeCu seats cost more than most complete worked heads.
The quoted 350 cfm is at or around 0.650" lift. I have achieved 305 cfm at 0.500" lift with 2.10" valve in a 4.060" bore and got to peak flow at 315 cfm for that port. However it does depend on the port work as I did another port that flowed 292cfm at 0.500" and flowed 325 cfm at 0.650". You only have to look at Harley heads and their flow numbers to realise this is doable but you need all the key ingredients.
03-22-2015, 02:44 PM
#130
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Yes referring to a very large valve 951 head. I am not familiar with the differences in the 928 heads.
This app crashes every time I try to add a picture. This is like the 10th time I have typed this. I hate this App. The powers that be who refuse to fix this issue should be fired!
This app crashes every time I try to add a picture. This is like the 10th time I have typed this. I hate this App. The powers that be who refuse to fix this issue should be fired!
03-22-2015, 03:06 PM
#132
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The bore size you are referring too is very similar to mine but you are using a 53.34mm intake? How did you achieve such giant lift without coil bind? It took tons of research for Shawn to locate good valves to allow for .550 and still keep correct seat pressure. How far did you move inward??? Which exhaust valve did you chose and what kind of numbers there? Getting it in without getting out doesn't help much.
03-22-2015, 04:08 PM
#133
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With enough money you can do a lot of amazing things.
03-22-2015, 04:20 PM
#134
The bore size you are referring too is very similar to mine but you are using a 53.34mm intake? How did you achieve such giant lift without coil bind? It took tons of research for Shawn to locate good valves to allow for .550 and still keep correct seat pressure. How far did you move inward??? Which exhaust valve did you chose and what kind of numbers there? Getting it in without getting out doesn't help much.
Easy question first, the exhaust flows very well, you will need to look up some of my flow tests, I don't have them on my iPad. There can be a big difference in flow figures on the exhaust side, I normally get them to use a flow pipe which is bent 90 degrees
Well on the coil bind issue, the first set of springs I bought were for my 0.550" lift cams and they were from the Ford modular engine using beehive springs from Comp Cams. To go bigger and raise the roof enough I have welded the spring seat recesses up and will either add a sandwich plate between the head and the cambox. It would be around 10 mm thick. 5 mm for raising the roof the other 5 mm for extra travel on the springs.
I may just get custom billet cam boxes made with bigger bearing journals or modify the design somewhat to include bearing caps so that I don't need such large bearing diameters and add extra height into this cam box design. The belt length is a non issue as I am not using the factory oil pump and this allows me to gain some extra length without penalty. I realise this aspect of bespoke design is not for everybody....
The other thing I am looking at us using GT3 radiused lifters which are hydraulic and only weigh 30 grams. This way I don't need to look at constantly adjusting lash.
Before this work can be done I need to get the two engines back together that are the more simple builds and be able to put that aside as I have parts everywhere.