Is my DCR too high?

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Dec 7, 2008 | 11:24 PM

frito1

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From: Ottawa, KS

Is my DCR too high?

My old 346 specs. Is this too high for 91 pump? Patrick G's spec sheet said I would be at 8.51:1 DCR and like a dummy I didn't check.

And what my #7 piston looks like now...

Here is the new 6.0 L76 DCR I was getting ready to assemble

Looks like I better use a GM MLS gasket cause this gets worse than I had before

Dec 8, 2008 | 12:09 AM

5.3LJimmy

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From: Napoleonville, LA

I don't think you are using the correct intake closing angle. Just throwing your numbers in my calculator with a 112LSA and 110ICL(which gives a 70 degree closing angle) I get a DCR of 8.58 for your 346. I know this is not accurate, but 61 degrees cannot be right.

Post all of the specs of your cam.

Dec 8, 2008 | 05:20 AM

frito1

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From: Ottawa, KS

231/235, .617/.620

valve timing @ .050"

open int: 4 BTDC
open exh: 52 BBDC
close int: 46 ABDC
close exh: 2 ATDC

ICI @ 111

LSA 113

Dec 8, 2008 | 06:15 AM

macca33

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From: 60 mi SE of Melbourne, Australia

Comp LSL lobes?

By my calculations, with a stock gasket thickness, it ought to be around 8.3:1 DCR - not too high at all.

Cheers,

Macca

Dec 8, 2008 | 10:16 AM

5.3LJimmy

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From: Napoleonville, LA

You need to use 71.5 degrees for your intake closing angle.

Dec 8, 2008 | 11:13 AM

Patrick G

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You can't use duration at .050". You have to use duration at .006". The DCR on your cam build sheet was correct. Most DCR calculators are mis-used and/or inaccurate. Sorry for your loss, but I don't think it stemmed from your DCR being too high for the fuel.

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Dec 8, 2008 | 12:25 PM

PREDATOR-Z

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From: BFE

I agree with Patrick, probably tune related (too lean).
Wha was your SCR and what plugs did you use?

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Dec 8, 2008 | 04:34 PM

frito1

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From: Ottawa, KS

Quote:

Originally Posted by macca33

Comp LSL lobes?

By my calculations, with a stock gasket thickness, it ought to be around 8.3:1 DCR - not too high at all.

Cheers,

Macca

Yes sir, LSL lobes. I was using a .041" gasket so with that it would be around 8.5:1 DCR I'd say.

Quote:

Originally Posted by 5.3LJimmy

You need to use 71.5 degrees for your intake closing angle.

Hmm.. that's not what my chart was asking for. I thought it was wanting intake closing point ABDC @ .050" plus 15 degrees. Maybe it's a bad calculator. Do you have a link to what you are using?

Quote:

Originally Posted by Patrick G

Well, I will give you all the info/data that I have. I would like to get to the bottom of this before I go back together. I was hoping I was on to something (wasn't pointing fingers, I just need to know what to fix). Thanks

Quote:

Originally Posted by PREDATOR-Z

I agree with Patrick, probably tune related (too lean).
Wha was your SCR and what plugs did you use?

SCR is 11.33:1 Plugs used were TR6. Tuner had it dialed at 12.9:1 AFR. Then he riched it up at the track to 12.5:1 AFR to see if it would pick up any. Notta. I thought I was plenty covered.

Quote:

Originally Posted by 1BADAIR

did that happen NA or on spray?

NA all the way. I would hope I would be a little faster than 11.35 on spray

Dec 8, 2008 | 04:57 PM

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Patrick G

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From: Victoria, TX

Any chart that asks for duration at .050" then asks you to add 15 degrees is a crap calculator. Cam lobes vary too much between .006" and .050". Go to the Advance Tech section of LS1Tech and look in the stickies. J-Rod has a calculator that is badass. Best one I've seen. You'll need to know your cam's duration at .006" though. LSL lobes are easy because their duration at .006" is 50 degrees larger than the duration at .050".

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Dec 8, 2008 | 05:02 PM

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Shawn MacAnanny

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I'm drunk but thats a sweet pic

Dec 8, 2008 | 05:15 PM

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dlove

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From: Fort Worth

check your rod length, it is needed for DCR. and I have also know to use advertised duration.

with that I get 8.36 DCR

http://www.projectpontiac.com/ppsite...nt/view/16/30/

Dec 8, 2008 | 06:03 PM

#13

vsocks1

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Ok..can someone confirm the DCR on my cam - I don't know how to use the calculator correctly either!
Engine is stock LS6 bore using GM MLS Gasket, heads are TFS 215's milled to 61 cc with the following cam specs:

Gross Valve Lift .595/.579
Duration at .006 281/289
Valve timing intake: 6 BTDC 46 ATDC
exhaust: 54 BBDC 2 ATDC
Specs are for cam installed at 110 intake centerline

Duration at .050 232/236
Lobe Seperation 113 +3

Dec 9, 2008 | 08:54 AM

#14

voda1

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From: Cedar Rapids, Iowa

I got 11.06 static and 8.39 dynamic with .054 gasket and .006 deck.

Dec 9, 2008 | 09:08 AM

#15

5.3LJimmy

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From: Napoleonville, LA

The DCR calculator I use is linked at the bottom of this page: http://cochise.uia.net/pkelley2/DynamicCR.html

There is also some good reading on that page and the other links on it. If you've got time you may want to read through it.

Dec 9, 2008 | 09:22 AM

#16

on2

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Search for the Piano Prodigy calculator. Very easy to use. I don't know if it lets you input LSL lobes though.

Dec 9, 2008 | 10:08 AM

#17

vsocks1

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From: Belgium, WI

Quote:

Originally Posted by voda1

I got 11.06 static and 8.39 dynamic with .054 gasket and .006 deck.

Thanks! That is more inline with what I origonally calculated. Somehow trying to use the one in the beginning of this thread I came up with a DCR of over 9....

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Is my DCR too high?

Is my DCR too high?

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