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Some Dynamic CR calcs... 93-octane friendly?
#884981
12/21/10 11:21 AM
12/21/10 11:21 AM
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Val-haul-ass... eventually
BradH
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Do these Dynamic CR values really indicate how well the particular combinations would handle 93-octane fuel? 1. Assume closed-chamber heads w/ .040" quench. 2. Dynamic CR calcs using http://www.wallaceracing.com/dynamic-cr.php3. Intake Closing calculations using SAE duration (.006” valve lift) The street roller cam to be used in my 448 w/ 11.0 CR: 298/304 on 108 + 0 ==> Intake Closes at 77 ABDC ==> 7.78 DCR 298/304 on 108 + 2 ==> Intake Closes at 75 ABDC ==> 7.94 DCR The solid flat-tappet cam used in my 452 w/ 10.8 CR: 302/302 on 108 + 2 ==> Intake Closes at 77 ABDC ==> 7.64 DCR 
Last edited by Blew My Budget!; 12/21/10 11:32 AM.
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: BradH]
#884982
12/21/10 11:42 AM
12/21/10 11:42 AM
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Joined: Feb 2007
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U.S.
moparniac
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You know how I feel about this  I think static is overplayed to a point and dynamic is more what it's about!!! And you know I like to race on pump gas!! I'm no pro at all but real world experience don't count to some around here!
Mopar Performance
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: BradH]
#884986
12/21/10 12:25 PM
12/21/10 12:25 PM
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Joined: Oct 2003
Posts: 7,506
Az
Crizila
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How do you know that using .006" for a closing event is correct? Many cam suppliers these days are using .050" for opening and closing events and don't give any numbers at .006". Don't think the calculator tells you what to use - or gives you a conversion?
Fastest 300
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: Performance Only]
#884987
12/21/10 12:25 PM
12/21/10 12:25 PM
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Joined: Jan 2003
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BradH
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First, more details on the two cams:
COMP Xtreme Solid Street Roller
298/304 @ .015", 260/266 @ .050", .016" lash
COMP XX Solid Flat-tappet
298/@ .020", 266 @ .050", .020" lash
Re: the duration #s... SAE duration is measured as .006" valve lift after lash. You can figure out where on the cam lobe this maps to by then dividing that point by the rocker ratio.
Example: (.016" lash + .006" lift) / 1.5 = .0147" lobe lift. In this case, since COMP's Xtreme street rollers advertised durations are rated at .015" lobe lift, they're virtually the same as the SAE duration when using that lash value.
You need to use a realistic estimation of the seat-to-seat duration to determine where the valve is actually closing. The effects of lash and the various rates of acceleration from where lobes are rated for "advertised" duration vs. .050" #s cannot be ignored. I can think of two cams where the .050" are virtually the same, yet their .020" durations are quite different as are their lash specs:
- 302, 266, .608" (1.5), .026" lash
- 294, 267, .609" (1.5), 016" lash.
The SAE durations between the two cams are about 5 degrees different... and it's the 294 @ .020" cam w/ the .016" lash that's the larger of the two (305 vs 300). There's no way to "see" that difference from comparing only .050" values.
Last edited by Blew My Budget!; 12/21/10 12:42 PM.
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: moparniac]
#884990
12/21/10 02:32 PM
12/21/10 02:32 PM
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Joined: Feb 2003
Posts: 12,675
Columbia, CT
moper
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I use the KB-Silvolite calculator for mine. That uses the intake closure at .050. My guess is just like advertising numbers for cams that removes some of the variables associated with the modern cam lobe shapes. I also think quench is critical and I set it this way: Bores over 4.10 I set quench at .035-.040. For smaller than that it's .030-.035. Knowing that...I use 8.75:1 dynamic with aluminum heads and a tight quench as a maximum for pump 93/10%ethanol as I get in the northeast. For iron closed chamber with good quench that drops to 8.5:1, and with open chambers I don't like to go over 8.25:1. I have not had any tuning/ping/detonation issues with pump 87/10% ethanol on any engine regardless of chamber or design using 8.25:1 as a max.
IMO, for what you have. It's low. But I build steet engines and if you're into revving well beyond 6K I think it's important to keep the dynamic figure down a little from my maxes. That's because it's my opinion that the dynamics of the whole intake/burn process change as rpms rise and the intake tract gets more efficient (pressure waves). I feel there will be more resulting pressure in a cylinder once the efficiency gets up past 90%. The compression ratio never changes. But the amount of intake charge occupying that space does go up. Just my opinion there tho.
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: BradH]
#884992
12/21/10 03:17 PM
12/21/10 03:17 PM
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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
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Taking time off to work on my car
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Taking time off to work on my car
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You know what's really sad? That I can search Google for stuff like this thread and come up w/ another Moparts.com thread from only a couple of months ago that sounds "a lot" like this one. Is it just me (or even because of me?), or is this place turning into a broken record? 
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: moper]
#884993
12/21/10 03:24 PM
12/21/10 03:24 PM
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Joined: Jan 2003
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Val-haul-ass... eventually
BradH
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Quote:
...I use 8.75:1 dynamic with aluminum heads and a tight quench as a maximum for pump 93/10%ethanol as I get in the northeast.
We've got the same shi... I mean stuff... here.
Quote:
IMO, for what you have. It's low. But I build steet engines and if you're into revving well beyond 6K I think it's important to keep the dynamic figure down a little from my maxes.
I'm hitting close to 7000 RPM in the traps already w/ the old combination. It'll probably pick up a couple hundred revs assuming I find some more power in the future.
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: BradH]
#884994
12/21/10 05:05 PM
12/21/10 05:05 PM
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Joined: Dec 2008
Posts: 1,200
UK
602heavy
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Quote:
You know what's really sad? That I can search Google for stuff like this thread and come up w/ another Moparts.com thread from only a couple of months ago that sounds "a lot" like this one.
Is it just me (or even because of me?), or is this place turning into a broken record?
...i guess guys will repeat themselves if they feel the info is correct , were you looking for something more than what was posted two months ago?...just saying not trying to be funny. 
Intake valve closure is just part of the puzzle when considering which fuel to use , lots more variables. 
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: BradH]
#884997
12/21/10 06:33 PM
12/21/10 06:33 PM
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Joined: Feb 2007
Posts: 6,295
U.S.
moparniac
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Challenger 4.150 stroke 248/254 @ 50 11.12 static --- 8.56:1 dynamic Intake Valve Closes ABDC - 69 Dart 4.250 stroke 269/269 @ 50 11.0 static --- 9.07:1 dynamic Intake Valve Closes ABDC - 60.5 both raced on pump fuel with no pinging or signs of detonation in either setups... however I have never caught air better than 2400DA and that was with the chally... those dynamic number are figured above are at altitude so crappy air the dynamic is lower yet and I would have started to watch the dart closer in "good cool air"! you can see the dur @ 50 is a good bit higher on the dart "which higher duration bleeds of more cylinder pressures making pump gas friendly" but look at the timing events between the 2! the dynamic is "worse" on the dart and the timing event is much lower! my new setup on the dart will have more static and less dynamic than previous setup! and oh yea! my cam will have higher Intake Valve Closing ABDC than before on the dart also... just sharing my data is all!
Mopar Performance
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: BradH]
#884998
12/21/10 07:04 PM
12/21/10 07:04 PM
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Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
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Another member (toward the bottom of the page -- https://board.moparts.org/ubbthreads/show...=1&fpart=2) actually checked his combo first then input the combo into the Wallace calculator using the .050" number. The Wallace was accurate to less than 1 psi. So as far as that calculator goes it seems to be pretty accurate @.050" ICA.
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Re: Some Dynamic CR calcs... 93-octane friendly?
[Re: 64Post]
#884999
12/21/10 07:37 PM
12/21/10 07:37 PM
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Joined: Feb 2003
Posts: 12,675
Columbia, CT
moper
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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
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: 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
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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
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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: 4,316
Prospect, PA
BSB67
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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
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Columbia, CT
moper
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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: 4,316
Prospect, PA
BSB67
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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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100% - and I've got broken pistons to prove it 
. It's all about how much of a margin for error you want to leave on the table. I've heard some horrendous numbers (IMO) coming from this sight ( reads expert builder )that I wouldn't even consider for a build. One bit of info that cam Mfg'ers are giving out more often these days is suggested cranking Cyl press. Although my Dynamic CR ( best I can figure ) is 9.7:1, my cylinder cranking pressure is about 20psi above what my cam Mfg recommends for that cam, so I DO NOT run pump gas.
