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| 300WHP Supernatural 3.XX Coming Soon! (Page 42/54) |
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La fiera
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MAY 29, 12:54 PM
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| quote | Originally posted by Blacktree:
Just out of curiosity, what's the static compression ratio? |
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According to my calculations taking every detail made to the heads and short block into account it is 11.58:1 exactly. Its a huge difference from the calculated dynamic compression of 15.99:1 which is the product of the compression test results divided by atmospheric pressure. The 3.4L also had the same difference in dynamic compression being much higher than the calculated static compression.
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fishsticks
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MAY 29, 01:18 PM
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| quote | Originally posted by La fiera:
According to my calculations taking every detail made to the heads and short block into account it is 11.58:1 exactly. Its a huge difference from the calculated dynamic compression of 15.99:1 which is the product of the compression test results divided by atmospheric pressure. The 3.4L also had the same difference in dynamic compression being much higher than the calculated static compression. |
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Would you mind showing your math on this? I don't believe DCR can be higher than SCR, since it's a function of stroke and cam timing. Atmospheric pressure doesn't really come into play since it would be a variable depending on where you are, and DCR doesn't change once calculated.
What did your combustion chambers CC out to once you were done working the heads? Curious as I think you said your pistons are above deck at TDC now. DId you have to cut valve reliefs?
Are you giving up on pump gas and turning this into an E85 only ordeal?
This is an excellent starter on DCR for those who are unfamiliar.: http://cochise.uia.net/pkelley2/DynamicCR.html
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La fiera
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MAY 29, 08:21 PM
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| quote | Originally posted by fishsticks:
Are you giving up on pump gas and turning this into an E85 only ordeal?
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I haven't use gasloline in years. Wait, I get E85 at my local gas station, so it is pump gas right!? 
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fishsticks
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MAY 30, 11:05 AM
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| quote | Originally posted by La fiera:
I haven't use gasloline in years. Wait, I get E85 at my local gas station, so it is pump gas right!? |
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We used to have an E85 pump up here. But the station shut down. 
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Blacktree
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MAY 30, 12:16 PM
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| quote | | Originally posted by La fiera: According to my calculations taking every detail made to the heads and short block into account it is 11.58:1 exactly. |
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Wow. The difference between the cylinder pressure and SCR is impressive! Heads and intake for the win!
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Notorio
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MAY 30, 01:33 PM
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Fishsticks, thanks for posting that. It actually makes a lot of sense. I'd love to see a timeline laid out showing a cylinder's pressure over time, when valves operate, piston position, pulse width of the injected fuel and spark. It would help to see the variables we can play with on that timeline for engines like ours with fixed valve timing. I don't know if I agree that there is No Compression until the intake valve is fully seated but it does highlight that at least Some of the compression stroke is wasted, early in the cycle.[This message has been edited by Notorio (edited 05-30-2021).]
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fishsticks
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MAY 30, 06:09 PM
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| quote | Originally posted by Notorio:
Fishsticks, thanks for posting that. It actually makes a lot of sense. I'd love to see a timeline laid out showing a cylinder's pressure over time, when valves operate, piston position, pulse width of the injected fuel and spark. It would help to see the variables we can play with on that timeline for engines like ours with fixed valve timing. I don't know if I agree that there is No Compression until the intake valve is fully seated but it does highlight that at least Some of the compression stroke is wasted, early in the cycle.
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There are a lot of moving parts in that timeline, especially when you factor in things like cam overlap vs engine RPM. I'm not an ME, just a guy who's built a lot of engines, so the calculus involved in generating that is a bit beyond me.
It's interesting to see the various methods camshaft manufacturers have used to manipulate the intake charge. Example:
Comp XER lobes open relatively gradually, but then slam the valve shut very quickly to try to start building compression ASAP.
Ultradyne/Lunati Voodoo lobes open the valve extremely fast to maximize use of the intake stroke on heads that flow well at high lifts, but close the valve much less abruptly than Comp XER lobes.[This message has been edited by fishsticks (edited 05-30-2021).]
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Notorio
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MAY 30, 11:38 PM
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| quote | Originally posted by fishsticks:
There are a lot of moving parts in that timeline, especially when you factor in things like cam overlap vs engine RPM. I'm not an ME, just a guy who's built a lot of engines, so the calculus involved in generating that is a bit beyond me.
It's interesting to see the various methods camshaft manufacturers have used to manipulate the intake charge. Example:
Comp XER lobes open relatively gradually, but then slam the valve shut very quickly to try to start building compression ASAP.
Ultradyne/Lunati Voodoo lobes open the valve extremely fast to maximize use of the intake stroke on heads that flow well at high lifts, but close the valve much less abruptly than Comp XER lobes.
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Very interesting!
La Fiera, you've mentioned that you get custom grinds for these builds. Can you tell us about these kinds of decisions you are making? Is there software that can simulate the results given a set of variables?
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Will
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MAY 31, 08:24 AM
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| quote | Originally posted by fishsticks:
Comp XER lobes open relatively gradually, but then slam the valve shut very quickly to try to start building compression ASAP.
Ultradyne/Lunati Voodoo lobes open the valve extremely fast to maximize use of the intake stroke on heads that flow well at high lifts, but close the valve much less abruptly than Comp XER lobes.
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The Comp lobe might work better with a long rod (or small port) flat tappet engine at high RPM while the Lunati lobe might work better with a short rod roller cam big port engine with a carb.
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fishsticks
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MAY 31, 10:56 AM
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| quote | Originally posted by Will:
The Comp lobe might work better with a long rod (or small port) flat tappet engine at high RPM while the Lunati lobe might work better with a short rod roller cam big port engine with a carb. |
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Yep. Lunati cams seem to have a stronger vacuum signal at similar durations and (usually) make a touch more torque. They're a bit rougher on valve springs though.
I've heard of people seeing accelerated valve seat wear from some of the more aggressive Comp lobes, which makes sense.
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