But your sure that it couldn't have more?
If it is lower could it be made better with more?
Moderator: Team
But your sure that it couldn't have more?
True but that doesn't really explain the other example in my post of the EMC engine with the cam degree optimized and dynoed tested.David Redszus wrote: ↑Tue Feb 11, 2020 6:57 pmMaybe not. A change in lash will produce a change in IVC. How much did the lash change affect IVC?Some food for thought, on this engine the only change made was tightening the valve lash from about .030 intake and exhaust to .026/.028 there by increasing only the seat numbers
A change in IVC will change compression pressure and compression temperature.
How much did compression pressure and temperature actually change?
How does compression pressure and temperature change with engine speed?
Compression pressure alone, has no effect on required octane.
Ignorance screams loudly when cranking pressure is correlated to octane requirement.
Two fuels with the same octane numbers may not provide the same detonation protection.
You're missing the point. IVC is important, but so are about 30 other parameters, and they all work together.
On this, we agree 100%. That's why I'm one of the few cam companies to list the actual seat duration, not some arbitrary "Advertised" duration.
Or in other words a BBC with a stock length rod and a Pontiac with a stock length rod, with the same stroke (ex 3.75") and same IVC have different DCR and cranking compression.CamKing wrote: ↑Thu Feb 13, 2020 9:30 am
You're missing the point. IVC is important, but so are about 30 other parameters, and they all work together.
DCR is useless, because it doesn't take into account most of the parameters that control the engine's power curve.
You can't base iny formula off of 5% of the information.
What the optimum IVC point is, can depend on many other parameters. Change one other parameter, and the optimum IVC changes.
Change the size of the port, and the optimum IVC changes.
Change the altitude you're running at, and the optimum IVC changes.
Change the IVO, and the optimum IVC changes.
Change the rod length, and the optimum IVC changes.
The rod length would have to change by a very large amount to make any difference in IVC.Change the rod length, and the optimum IVC changes.
DCR does not determine IVC. The optimized IVC (considering Mike's parameters) will determine the DCR.Or in other words a BBC with a stock length rod and a Pontiac with a stock length rod, with the same stroke (ex 3.75") and same IVC have different DCR and cranking compression.
Stan
David,David Redszus wrote: ↑Thu Feb 13, 2020 11:36 amThe rod length would have to change by a very large amount to make any difference in IVC.Change the rod length, and the optimum IVC changes.
DCR does not determine IVC. The optimized IVC (considering Mike's parameters) will determine the DCR.Or in other words a BBC with a stock length rod and a Pontiac with a stock length rod, with the same stroke (ex 3.75") and same IVC have different DCR and cranking compression.
Stan
But DCR is only a ratio not an actual pressure. DCR coupled with inlet conditions at IVC, will determine
compression pressure and temperature. That's what is useful to know and important for performance.
Cranking pressure is not very useful since it does not reflect actual conditions at operating engine speeds.
That's where in-cylinder pressure measurement becomes so very important.
I understand that, it just seems like the more people can learn about the cause and effect of these things that the better choice they can make before even ordering parts.CamKing wrote: ↑Thu Feb 13, 2020 9:30 amYou're missing the point. IVC is important, but so are about 30 other parameters, and they all work together.
DCR is useless, because it doesn't take into account most of the parameters that control the engine's power curve.
You can't base iny formula off of 5% of the information.
What the optimum IVC point is, can depend on many other parameters. Change one other parameter, and the optimum IVC changes.
Change the size of the port, and the optimum IVC changes.
Change the altitude you're running at, and the optimum IVC changes.
Change the IVO, and the optimum IVC changes.
Change the rod length, and the optimum IVC changes.
StanStan Weiss wrote: ↑Thu Feb 13, 2020 12:15 pmDavid,David Redszus wrote: ↑Thu Feb 13, 2020 11:36 amThe rod length would have to change by a very large amount to make any difference in IVC.Change the rod length, and the optimum IVC changes.
DCR does not determine IVC. The optimized IVC (considering Mike's parameters) will determine the DCR.Or in other words a BBC with a stock length rod and a Pontiac with a stock length rod, with the same stroke (ex 3.75") and same IVC have different DCR and cranking compression.
Stan
But DCR is only a ratio not an actual pressure. DCR coupled with inlet conditions at IVC, will determine
compression pressure and temperature. That's what is useful to know and important for performance.
Cranking pressure is not very useful since it does not reflect actual conditions at operating engine speeds.
That's where in-cylinder pressure measurement becomes so very important.
That is an interesting conclusion to draw from what I posted. That DCR determines IVC.
"DCR coupled with inlet conditions at IVC, will determine compression pressure and temperature." So if inlet conditions and IVC are the same and DCR / Dynamic stroke is different due to rod length. Is there not a change in compression pressure and temperature?
Stan
Right dynamic compression for what, IVC? Probably so.
Interesting to hear you say that. I always felt like something was being overlooked or ignored in the @ 0.050 duration numbers.CamKing wrote: ↑Thu Feb 13, 2020 9:35 amOn this, we agree 100%. That's why I'm one of the few cam companies to list the actual seat duration, not some arbitrary "Advertised" duration.
All my calculations for designing a cam for a given application, are based off of actual seat duration.
Basing calculations off of .050" durations is nowhere near as accurate, because there's too many variables that effect .050" duration.