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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: BSB67]
#885003
12/21/10 11:53 PM
12/21/10 11:53 PM
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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
OP
Taking time off to work on my car
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OP
Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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Quote:
Which is it, Wallace calculator and 0.050" (lobe) or 0.006" (valve)?
Wallace doesn't say, so I threw something together to see what made sense (to me, at least). I plugged in the same combination into Engine Analyzer Pro 3.3, which uses .050" input specs and derives seat duration from those based on cam type selected and actual & designed lash settings. The EA Pro 3.3 instructions say the seat durations (after lash) it calculates are crank degrees valve is opened at least .003" over base circle. (That's an odd way to describe it, IMO.)
As a result, the intake duration # that EA Pro 3.3 comes up w/ for the street roller cam above picks up 3-4 degrees over the SAE .006" # which, in this case, is 301 vs 298. I plugged all the #s into the Wallace calculator using an intake closing of 76.5 ABDC based on 301 seat duration installed on 106 ICL and it cranked out a DCR of 7.83. For comparison, EA Pro 3.3 says the DCR for that combination is 7.79... pretty darn close.
IMO, the closer you can get to the real seat duration & intake valve closing point w/ the Wallace calculator, the more accurate the DCR calculation will be. I don't think a duration # at .050" has any validity with the Wallace calculator after seeing this.
FWIW, the predicted cranking psi for Wallace (154) and EA Pro 3.3 (197) aren't even in the same ballpark. I'd ignore that completely at this point.
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: moper]
#885004
12/22/10 01:02 AM
12/22/10 01:02 AM
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Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
64Post
master
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master
Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
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Quote:
The only problem I have in using pressures as the indicator is a cylinder's pressure is dependant on the quality of parts, and machining, plus altitude, and those to me are hugely different from build to build when talking about different shops. I suppose it comes down to either empirical testing, or the "best guess" of a calculator...lol
Jim's empirical testing seemed to support the finding of the Wallace; that's why I brought that thread up.
I'm acutely aware the effect of altitude has on a build. When I built my motor for 6000 ft altitude I added about 2 points (10cc domes) of static compression to bring the cylinder pressure close to sea level standards. I roughly used the 4%/1000 ft. rule.
I then experimented with different intake closing points to bring my cranking/dynamic up to a comfortable level. I don't remember where my dynamic was, but I wanted my cranking pressure at about 185 psi; it tested out at 184-187 psi. So I was happy with the results.
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: BradH]
#885005
12/22/10 01:06 AM
12/22/10 01:06 AM
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Joined: Feb 2005
Posts: 4,318
Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,318
Prospect, PA
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Quote:
Quote:
Which is it, Wallace calculator and 0.050" (lobe) or 0.006" (valve)?
Wallace doesn't say, so I threw something together to see what made sense (to me, at least). I plugged in the same combination into Engine Analyzer Pro 3.3, which uses .050" input specs and derives seat duration from those based on cam type selected and actual & designed lash settings. The EA Pro 3.3 instructions say the seat durations (after lash) it calculates are crank degrees valve is opened at least .003" over base circle. (That's an odd way to describe it, IMO.)
As a result, the intake duration # that EA Pro 3.3 comes up w/ for the street roller cam above picks up 3-4 degrees over the SAE .006" # which, in this case, is 301 vs 298. I plugged all the #s into the Wallace calculator using an intake closing of 76.5 ABDC based on 301 seat duration installed on 106 ICL and it cranked out a DCR of 7.83. For comparison, EA Pro 3.3 says the DCR for that combination is 7.79... pretty darn close.
IMO, the closer you can get to the real seat duration & intake valve closing point w/ the Wallace calculator, the more accurate the DCR calculation will be. I don't think a duration # at .050" has any validity with the Wallace calculator after seeing this.
FWIW, the predicted cranking psi for Wallace (154) and EA Pro 3.3 (197) aren't even in the same ballpark. I'd ignore that completely at this point.
I agree that actual closing point (actual seat timing) would seem to make the most sense. But I have read it both ways, and not just in this thread. When I plug in my intake closing (at 0.006" valve lift) the DCR is 7.6 and 148 psi. However, the engines seems to actually be on the edge of detonation with 93 octane, and blows 185 psi. Plug in the 0.050" numbers and its 8.8:1 and 180 psi. 
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: BSB67]
#885006
12/22/10 05:18 PM
12/22/10 05:18 PM
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Joined: Feb 2003
Posts: 12,675
Columbia, CT
moper
I Live Here
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I Live Here
Joined: Feb 2003
Posts: 12,675
Columbia, CT
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Like anything else, the less amount of generalization you have, the better the prediction vs result. I think the ".050" inputs are more general as a result of that, and Wallace and EA Pro use the clearer defined parameter.
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: moper]
#885007
12/22/10 09:57 PM
12/22/10 09:57 PM
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Joined: Feb 2005
Posts: 4,318
Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,318
Prospect, PA
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Quote:
Like anything else, the less amount of generalization you have, the better the prediction vs result. I think the ".050" inputs are more general as a result of that, and Wallace and EA Pro use the clearer defined parameter.
I'm not sure what you mean by generalization. Do you mean the accuracy of the inputs? My .050" input into the Wallace calc. appears to give a result that more closely reflects reality.
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