Cam Experts: Lobe Separation Angle?

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middleagecrisis said:
Does someone have the formula to figure out the DCR using this cam:
1176: 230/236 (.050), LC: 106 (Intake), 114 (Exhaust), Lift (1.5) .488(I)/.491(E), LSA listed as 110
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I randomly chose the Wallace calculator and got about 7:1 assuming 64 deg intake closing ABDC based on the XE274 cam. I'm not overly familiar with this metric but I don't think 7"1 is good for a na motor. I think this llustrates why cam mfg recommend minimum compression ratios.
 
B3422w5 said:
Track results and dyno results can and usually do differ.
My car that I mentioned earlier in the thread ran within half a mile per hour with the 106 or 112.
But the 106 was way way quicker. All the other incrementals were better.
Roughly tenth and a half difference.
I will always place track results way above dyno numbers.
I can pretty much guess, pretty darn close what any typical small block bracket car will make on the dyno if I have the combo particulars.
But I am often easily fooled by what a given car actually runs.
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You're describing much better average torque production ALA Enginemasters competition results. No surprise to me really what you experienced. J.Rob
 
DCR...about as useful as a sunroof in a submarine. Takes NO account of port flow/port efficiency which affects the amount of air taken in by the cyls...
 
Advancing/retarding the cam would shift the whole LSA and IC/EC, correct? For example, 2 degrees advanced would have the effect of moving a 106 IC/114 EC, 110 LSA cam to 104 IC/112 EC, 108 LSA? Am I thinking this correctly?
 
RustyRatRod said:
What's the difference between the two?
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Effective compression ratio is measured from the time the intake valve closes to TDC. I have to do the math again but I think my engine is 12:1 measured but it’s only 9:1 effective compression ratio.

DCR changes with load, VE, temperature and such.
 
fishmens67 said:
DCR never changes, it's set, cylinder pressure is the only thing that changes. The two are not the same
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Again, what does DCR tell you? If it's "dynamic" it means it changes with outside influences.

I haven't seen any math where DCR is a part of it. Doesn't mean they aren't out there but I've never seen them. I have seen several that use ECR. I use one that does.
 
Newbomb Turk said:
Effective compression ratio is measured from the time the intake valve closes to TDC. I have to do the math again but I think my engine is 12:1 measured but it’s only 9:1 effective compression ratio.

DCR changes with load, VE, temperature and such.
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Understood. Thank you. Then, clearly, effective is most important.
 
RustyRatRod said:
Understood. Thank you. Then, clearly, effective is most important.
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That depends on who you ask. I also don’t get excited about cranking compression either except in the fact that as cranking compression goes up, the tuning window gets smaller.

If someone isn’t into tuning and keeping a close eye on stuff then a lower cranking compression is a good idea.

What I’ve never seen is a correlation between cranking compression and detonation.

I’ve had over 200 psi not rattle (but you had to make sure the tune up was pretty close or it would rattle) and I’ve had 160 psi rattle like crazy.

That was GM garbage though. You have to work pretty hard to get even a decent small block Chrysler to rattle.
 
Newbomb Turk said:
That depends on who you ask. I also don’t get excited about cranking compression either except in the fact that as cranking compression goes up, the tuning window gets smaller.

If someone isn’t into tuning and keeping a close eye on stuff then a lower cranking compression is a good idea.

What I’ve never seen is a correlation between cranking compression and detonation.

I’ve had over 200 psi not rattle (but you had to make sure the tune up was pretty close or it would rattle) and I’ve had 160 psi rattle like crazy.

That was GM garbage though. You have to work pretty hard to get even a decent small block Chrysler to rattle.
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Yeah, I had a 360 in a 65 Valiant years ago that had 210 PSI and it never once rattled on pump premium once I got everything tuned. It did, however RUN better on 112 leaded Cam 2.
 
Newbomb Turk said:
That depends on who you ask. I also don’t get excited about cranking compression either except in the fact that as cranking compression goes up, the tuning window gets smaller.

If someone isn’t into tuning and keeping a close eye on stuff then a lower cranking compression is a good idea.
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AJ ain't gonna like that line lol


Isn't cr more important for effect on expansion ratio ?
 
273 said:
AJ ain't gonna like that line lol


Isn't cr more important for effect on expansion ratio ?
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It’s part of it.

The HIGHER the unfired cylinder pressure, the higher the power.

The LOWER the unfired cylinder temperature, the higher the power.

Higher unfired cylinder pressure requires LESS timing (the opposite of why you want vacuum advance at a cruise) and that means less negative work. Until you get to the point where you are using more work to compress the unfired fuel/air than you gain on the work side.

The extra help from a greater expansion ratio is a nice bonus.
 
I think when most people refer to dynamic compression ratio, they're referring to the actual calculated compression ratio from the point at which the intake valve closes. I know when I've used DCR calculators in the past, that exactly what they're calculating - with no inputs for load, VE, or temperature.

Sounds like that's the same as effective compression ratio? Seems more like semantics, or maybe people simply using incorrect terminology.
 
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