Modified & Simplified VE Calculator! - I need some input!
#42
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Originally Posted by DanZ28
I get 10.06 with the +.007 and 10.39 with -.007", so that looks correct to me.
You will have Less compression with a positive number (in hole) and more with a negative number (out of hole).
Dan
You will have Less compression with a positive number (in hole) and more with a negative number (out of hole).
Dan
#43
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Originally Posted by DanZ28
To clarify more, you should use the negative number for stock blocks.
#44
Originally Posted by pianoprodigy
How so? If we use a negative number, the compression comes out to 10.4:1. Stock LS1 compression is 10:1, correct? Is another figure wrong? I don't think so.
Dan
#45
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Originally Posted by DanZ28
I believe stock is 10.1 to 10.2 area. So something is wrong with the calculator. Stock pistons come out of the hole -.007". If you use the calcultor like it is using a positive number for a negative number, how are you going to calculate pistons that are positive or in the hole?
Dan
Dan
Just to be clear for you and everyone, I did not modify anything with J-Rod's calculations. I just made it "pretty" and simplified.
As far as I can tell, deck height is used to calculate clearance volume which according to J-Rod's description (which is just hidden on my calculator) is:
Clearance volume = 0.7853982 x bore2 (squared) x deck height
If you have a negative number (meaning piston is out of the hole), you would have a negative clearance volume. I'm not exactly sure what that means. I believe that would mean that because the piston is sticking out a bit, you are losing some clearance volume. Alternatively, if there is a positive deck height (piston is still in the hole), you would have a positive clearance volume.
Someone just needs to clarify exactly if this is correct. I believe all of the other figures are correct.
#46
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Originally Posted by DanZ28
I get 10.06 with the +.007 and 10.39 with -.007", so that looks correct to me.
You will have Less compression with a positive number (in hole) and more with a negative number (out of hole).
Dan
You will have Less compression with a positive number (in hole) and more with a negative number (out of hole).
Dan
If this is unecessarily confusing, I can modify the formula by multiplying by negative 1.
#47
I used this calculator as well http://www.rbracing-rsr.com/compstaticcalc.html.
I get the same exact SCR as I do with yours/J-Rods calcultor when I enter a positive deck height as well as the negative with that calcultor. So, either stock motors have 10.4 CR or both calculators are wrong. You can't reverse it and make it come out right for both the positive and negative numbers.
I know this is based off of J-Rod's, but it would be nice if we can figure out where the discrepency is so it's accurate .
Dan
I get the same exact SCR as I do with yours/J-Rods calcultor when I enter a positive deck height as well as the negative with that calcultor. So, either stock motors have 10.4 CR or both calculators are wrong. You can't reverse it and make it come out right for both the positive and negative numbers.
I know this is based off of J-Rod's, but it would be nice if we can figure out where the discrepency is so it's accurate .
Dan
#48
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Originally Posted by DanZ28
I used this calculator as well http://www.rbracing-rsr.com/compstaticcalc.html.
I get the same exact SCR as I do with yours/J-Rods calcultor when I enter a positive deck height as well as the negative with that calcultor. So, either stock motors have 10.4 CR or both calculators are wrong. You can't reverse it and make it come out right for both the positive and negative numbers.
I know this is based off of J-Rod's, but it would be nice if we can figure out where the discrepency is so it's accurate .
Dan
I get the same exact SCR as I do with yours/J-Rods calcultor when I enter a positive deck height as well as the negative with that calcultor. So, either stock motors have 10.4 CR or both calculators are wrong. You can't reverse it and make it come out right for both the positive and negative numbers.
I know this is based off of J-Rod's, but it would be nice if we can figure out where the discrepency is so it's accurate .
Dan
#49
What are you using for gross duration on the stock cam?
Also, here is some food for thought on DCR.
Remeber, don't get hung up on just one thing.
Repeat after me...
Combination, combination, combination
Also, here is some food for thought on DCR.
DCR is widely considered to be an accurate barometer of knock resistance (e.g., “up to 8-1 DCR can be used with XX octane”, &c.).
This is not true, and not safe, since (in a high compression motor with its DCR reduced by late intake closure) after the early low-pressure period expires (at the beginning of the torque curve) actual combustion pressure will be at least as high with the bigger cam than it was previously - even though the DCR is lower, and therefore suggests that lower octane is safe. However, in a motor with 14-1 static CR the gas pressure at its torque peak is not at all reduced by a very late intake closing point, although the (lower) DCR may indicate that 92 octane &c. is sufficient.
Since the knock will only occur at high speeds it may not be audible, and will reduce power (lower MPH) even if no damage can be detected. In my opinion, the power sometimes gained by retarding spark in high gear is actually an attempt to recover some of this loss - but would be better served by reducing the static ratio slightly.
DCR is a curve or slope of cylinder (not combustion) pressure, with Position 0 (the absolute low end) at cranking speed, then a small rise to idle speed, then another rise to the capture point &c. After this point (and especially near the torque peak) the static CR becomes more important, since approximately the full stroke length and nominal swept cylinder volume (or more, depending on VE) is captured and compressed at (below, at, or above) the nominal static ratio, regardless of the intake closing point.
Any cam will determine the “slope” (or rate of rise) of the DCR curve. A long-duration cam with its attendant late intake closing point will have a high degree of rise, a mild cam less, &c. A longer cam will also extend (stretch) the range of RPM that the slope covers, sometimes over several thousand more RPM.
The static ratio determines the height of the cylinder pressure line at Position 0 (cranking speed). With high static ratio the entire curve is higher, with the curve's upward intensity being governed by the intake closing point.
It's possible to design a DCR that looks promising, but will not provide any more power, by assuming that there is no limit to either static ratio or intake closure - and, of course, neither is true. Some motors cannot turn fast enough (due to stroke length, weak valve gear, high reciprocating weight, &c.) to reach their capture point if the intake closure is too late, and will produce more power with more conservative cam timing. A motor with limited static ratio (flathead) must conserve cylinder pressure by limiting intake closure for the same reasons.
Another error in use of DCR calculations for low-speed power prediction lies in the fact that a smaller volume of mixture being compressed to a higher ratio. Even though the pressure gauge reading taken during cranking or idling is higher, the total of cylinder pressure times the actual mixture volume captured may still be lower (compared to the original milder cam and moderate compression ratio).
To sum up: DCR a useful tool, but widely perceived to be of greater worth than can be supported by physics.
This is not true, and not safe, since (in a high compression motor with its DCR reduced by late intake closure) after the early low-pressure period expires (at the beginning of the torque curve) actual combustion pressure will be at least as high with the bigger cam than it was previously - even though the DCR is lower, and therefore suggests that lower octane is safe. However, in a motor with 14-1 static CR the gas pressure at its torque peak is not at all reduced by a very late intake closing point, although the (lower) DCR may indicate that 92 octane &c. is sufficient.
Since the knock will only occur at high speeds it may not be audible, and will reduce power (lower MPH) even if no damage can be detected. In my opinion, the power sometimes gained by retarding spark in high gear is actually an attempt to recover some of this loss - but would be better served by reducing the static ratio slightly.
DCR is a curve or slope of cylinder (not combustion) pressure, with Position 0 (the absolute low end) at cranking speed, then a small rise to idle speed, then another rise to the capture point &c. After this point (and especially near the torque peak) the static CR becomes more important, since approximately the full stroke length and nominal swept cylinder volume (or more, depending on VE) is captured and compressed at (below, at, or above) the nominal static ratio, regardless of the intake closing point.
Any cam will determine the “slope” (or rate of rise) of the DCR curve. A long-duration cam with its attendant late intake closing point will have a high degree of rise, a mild cam less, &c. A longer cam will also extend (stretch) the range of RPM that the slope covers, sometimes over several thousand more RPM.
The static ratio determines the height of the cylinder pressure line at Position 0 (cranking speed). With high static ratio the entire curve is higher, with the curve's upward intensity being governed by the intake closing point.
It's possible to design a DCR that looks promising, but will not provide any more power, by assuming that there is no limit to either static ratio or intake closure - and, of course, neither is true. Some motors cannot turn fast enough (due to stroke length, weak valve gear, high reciprocating weight, &c.) to reach their capture point if the intake closure is too late, and will produce more power with more conservative cam timing. A motor with limited static ratio (flathead) must conserve cylinder pressure by limiting intake closure for the same reasons.
Another error in use of DCR calculations for low-speed power prediction lies in the fact that a smaller volume of mixture being compressed to a higher ratio. Even though the pressure gauge reading taken during cranking or idling is higher, the total of cylinder pressure times the actual mixture volume captured may still be lower (compared to the original milder cam and moderate compression ratio).
To sum up: DCR a useful tool, but widely perceived to be of greater worth than can be supported by physics.
Repeat after me...
Combination, combination, combination
#50
Stock duration is 202/210, but were talking SCR not being accurate.
Yes alot of things factor into your DCR, mainly SCR and valve timing. the calculator is just a nice tool to use to see how everything adds up.
Your right, combination is where it's at and don't get hung up on DCR so much.
Yes alot of things factor into your DCR, mainly SCR and valve timing. the calculator is just a nice tool to use to see how everything adds up.
Your right, combination is where it's at and don't get hung up on DCR so much.