DCR vs SCR vs Octane

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May 16, 2007 | 08:53 PM

RomulusSmallBlock

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DCR vs SCR vs Octane

i am curious about this subject as many ppl are. i figured that i could gather some data from a sample group and plot the data to see what kinds of interesting things i get. i will post my finding here so that you can see them too. i will let collecting of data run for about two days, and once it's over i will process it and present my findings.

so to help me out i would like a few things from you

what is your DCR?
what is your SCR?
what temp does your engine operate at?
bore and stroke?
what octane you use without any issues?

May 17, 2007 | 08:24 AM

MISERICORDIA

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This sounds kindof interesting. I won't have my setup put together for a while but if this thread is still around when I get it working I'll post some results.

May 17, 2007 | 08:28 AM

BIG_MIKE2005

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From: Skiatook, OK

Hopefully PREDATOR-Z will chime in. He helped me with my calculations on this.

May 17, 2007 | 11:20 AM

RAACCR

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11.36:1 SCR
8.97:1 DCR
160's highway, 170's around town
Stock LS1 bore & stroke
93 octane (in hot & humid South Florida)

May 17, 2007 | 11:25 AM

KCS

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From: Conroe, TX

Quote:

Originally Posted by RomulusSmallBlock

Dema Elgin and David Vizard did a bunch of research on this a while back. There's a snipit of it in Pat Ganahl's How to Build High Performance Rat Motors, but I'm sure an internet search would turn up more info. I highly doubt they used any Gen III/IV engines in their research, but I'm sure it would still apply.

May 17, 2007 | 11:28 AM

jmm98LS1

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From: KS

Wow...8.97 DCR on pump gas

.....awesome.

May 17, 2007 | 12:24 PM

RAACCR

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Quote:

Originally Posted by jmm98LS1

Wow...8.97 DCR on pump gas

.....awesome.

Daily driver, in a hot climate, and with relatively aggressive timing, too. 0.033" quench certainly helps, but I believe the generally accepted standards are overly conservative.

Last edited by RAACCR; May 17, 2007 at 12:29 PM.

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May 17, 2007 | 02:47 PM

RomulusSmallBlock

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Quote:

Originally Posted by RAACCR

11.36:1 SCR
8.97:1 DCR
160's highway, 170's around town
Stock LS1 bore & stroke
93 octane (in hot & humid South Florida)

actually 93 with this setup isn't shocking it's perfect as in it fits the trend lines to the "T". so far i have 14 peoples engines.

i have graphs if someone tells me how to post them it will be done. i made trend lines for both and as soon as i figure out how to do a trend surface for 3D plots i will post that data (i think is more promissing)

DCR vs Octane trend line: f(x)= -.0252x^2+3.915x+59.906
x is DCR and f(x) is octane

SCR vs Octane trend line: f(x)= -.0631x^2+3.3908x+62.85
x is SCR and f(x) is octane

what i found to be interesting are engines that when using the trend lines for both DCR vs Octane and SCR vs Octane that their Octane usage was the same.

example:

DCR= 7.68 and SCR= 9.11 its octane requirement is 88.5. RAACCR's engine is an other good example of this too. the LS1 the i built requires 91 for both as well (purely accidental). hower, i was doing this research to help a build on a old school 388 chevy for my friend. i purposely made the DCR and SCR requirements the same (89 octane).

what makes this interesting is that its DCR complements its SCR. it kind of begs the question: does this complementation improve HP and torque?

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May 17, 2007 | 05:18 PM

Ryan02SS

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From: Lake Anna, VA/ Fairmont, WV

10.8-1
8.64-1
Stock gauge always stays around 210*
Stock bore and stroke
93 octane, no problems..

May 17, 2007 | 08:22 PM

#10

ProjecT 9

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From: Houston

11.43:1
8.66:1
right below 210
stock B&S
93

May 18, 2007 | 12:52 AM

#11

warp_6

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From: Moorpark,Ca

11:1
8.4:1
180-190
91 Cali gas

May 18, 2007 | 01:24 AM

#12

DONAIMIAN

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From: NW Houston, TX

Everyone keep in mind that if you have a 99+ car your stock temp gauge is useless.

May 18, 2007 | 01:29 AM

#13

RomulusSmallBlock

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The time limit i posted it up, so here are the findings.

The finding for DCR vs Octane

Aluminum and Iron combined

Iron only

Aluminum only

The findings for SCR vs Octane

Aluminum and Iron combined

Iron only

Aluminum only

Last edited by RomulusSmallBlock; May 18, 2007 at 01:43 AM.

May 18, 2007 | 05:23 AM

#14

ProjecT 9

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From: Houston

Quote:

Originally Posted by DONAIMIAN

Everyone keep in mind that if you have a 99+ car your stock temp gauge is useless.

so does it tend to read high or low?

May 18, 2007 | 05:42 AM

#15

The Alchemist

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From: Doylestown PA

Quote:

Originally Posted by ProjecT 9

so does it tend to read high or low?

Neither, the temp gauge reads, COLD, Up to Tempt, and HOT. It will be in the cold range up to about 130 degrees, then from 140-220 it will be striaght up/down and read up to temp, and I've never had my engine above 205 degrees to see when it goes hot.

Back to the topic at hand, my SCR is 11.27, and DCR is 8.88 and can run 91 or 93 without a problem. I do run a lot of timing though, I max out at 27 degrees but mostly it's 24-26 degrees. Most tuners will tell you that too much timing will only hurt but doesn't help much. The difference between running 24 and 28 degrees might be 2-4hp, but as soon as you get knock, it will pull lots of timing anyway. So a safer tune of 24-26 degrees is better.

I ran a 160-tstat last year for the power tour because I was in stop and go traffic all week long and never saw temps above 175. I've since switched back to the stock t-stat and hover right around 190. Gotta realize that our motors like to run hotter because it helps to burn cleaner and make more power. I saw no difference in performance running 20 degrees colder temps and my mileage went down 2 mpg.

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