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Some Dynamic CR calcs... 93-octane friendly?

Posted By: BradH

Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 03:21 PM

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.php
3. 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

Posted By: moparniac

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 03:42 PM

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!
Posted By: Performance Only

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 03:47 PM

your in the 89 octane safe zone with those numbers.
Posted By: moparniac

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 03:49 PM

Dram do you agree 9.00 is about the limit for 93? Always enjoy your expertise around here!!!
Posted By: Performance Only

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 04:15 PM

i think it's a close approximation. there's other factors involved. rushed for time right now. i'll visit this one again later.
Posted By: Crizila

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 04:25 PM

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?
Posted By: BradH

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 04:25 PM

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.
Posted By: BradH

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 05:10 PM

Quote:

I think static is overplayed to a point and dynamic is more what it's about!!!


From what I've been able to find discussed here and elsewhere (SpeedTalk.com, etc.), I think they they both need to be taken into account.

As the RPMs rise and the engine becomes more efficient, it's going to transition from operating under the lower DCR to conditions where the actual static CR takes over. The idea that you can use a big static CR w/ low(er) octane fuel and "crutch it" with a long duration cam only holds up to a certain point, at which time that big CR is still going to make itself known.

And if I knew those limits and points, I wouldn't be posting questions like this.
Posted By: moparniac

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 06:06 PM

I hope my HEMI grind cam helps out my new cause!!
Posted By: moper

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 06:32 PM

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.
Posted By: Crizila

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 06:42 PM

Quote:

Quote:

I think static is overplayed to a point and dynamic is more what it's about!!!


From what I've been able to find discussed here and elsewhere (SpeedTalk.com, etc.), I think they they both need to be taken into account.

As the RPMs rise and the engine becomes more efficient, it's going to transition from operating under the lower DCR to conditions where the actual static CR takes over. The idea that you can use a big static CR w/ low(er) octane fuel and "crutch it" with a long duration cam only holds up to a certain point, at which time that big CR is still going to make itself known.

And if I knew those limits and points, I wouldn't be posting questions like this.

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.
Posted By: BradH

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 07:17 PM

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?
Posted By: BradH

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 07:24 PM

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.
Posted By: 602heavy

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 09:05 PM

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.
Posted By: dannysbee

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 09:18 PM

Thats why it is called Hot Rodding, sometimes you just don't know the answer till you try it. It is not an exact science. You just push it to the limit then back off a hair.
Posted By: Twin Turbo Mower

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 09:32 PM

I ran 11.8 static/ 9.11 dynamic with 210 cranking compression before. But that was with 93 octane no ethonal. Quench was .038. Was my old 511 with a comp extreme solid roller 248/254 @ 050.
Posted By: moparniac

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 10:33 PM

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!
Posted By: 64Post

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 11:04 PM

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.
Posted By: moper

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/21/10 11:37 PM

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
Posted By: BSB67

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/22/10 01:02 AM

General question here: Which is it, Wallace calculator and 0.050" (lobe) or 0.006" (valve)? This will certainly give you different results.
Posted By: quick77rt

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/22/10 03:25 AM

Here is a good link, not all mopar but performance V8 related.

Opinions differ....but read if you wish..

http://www.empirenet.com/pkelley2/DynamicCR.html
Posted By: 602heavy

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/22/10 03:39 AM

Are we working backwards here?.......would it not be better to calculate DCR with regard to the camshaft being used then build the motor off the calculated SCR?.................most shelf hydraulic grinds tend to be around 28*/30* from .006 to .050 (intensity) which puts these calculators a little out of whack , a fair # for solid grinds would be around 18/20 (intensity)

Posted By: BradH

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/22/10 03:53 AM

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.
Posted By: 64Post

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/22/10 05:02 AM

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.
Posted By: BSB67

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/22/10 05:06 AM

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.
Posted By: moper

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/22/10 09:18 PM

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.
Posted By: BSB67

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/23/10 01:57 AM

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.
Posted By: 64Post

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/23/10 04:05 AM

Exact/absolute data is always preferable to assumptions/ambiguities.

For example, Comp's Camquest program (if you have faith in such programs) allows you to input head flow data. For MCH Eddys, flow is 325 cfm @ .600 lift and, to keep it simple, you're going to run a .600" lift cam. That in itself doesn't give an actual indication how the head flows at lower lifts and can skew the HP/TQ figures. Or, you can input individual flow values at increments of .100" lift. This gives the program more parameters to work with to arrive at an accurate figure (hopefully).
Posted By: BSB67

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/23/10 04:57 AM

Of course, but I'm not sure how that relates to the DCR calc. What are the assumptions or ambiguities associated with the Wallace calc, and/or input data?
Posted By: moparniac

Re: Some Dynamic CR calcs... 93-octane friendly? - 12/23/10 11:18 AM

Does anyone else have some proven setups like I posted on pump gas? I think chip and Jimmy race on pump gas also ... Maybe there grinds are a secret
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