Thread: 355 street build. DCR, SCR, octane, quench, confusion

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building my 355 vortec. L31 block. want to run 87 if i don't give up alot of power, 89 octane if possible, 91 only if absolutely neccesary. confused.

4.03 x 3.48 on 5.7 rods
64cc vortec iron heads
12cc pistons with 4 valve relief and dish
.035 or .04 gasket
.015, .01 or .00 deck
zz4 cam info follows

Seat-to-seat (@.004)
I: 24 BTDC, 66 ABDC
E: 75 BBDC, 28 ATDC
Cam installed advanced(+) / Retarded(-) 0.0
True IVO 24.0------True EVO 75.0
True IVC 66.0------True EVC 28.0
True ECA 113.5
--------Intake Duration 270.0-----Exhaust Duration 283.0
Intake Centerline Angle 111.0----Exhaust Centerline 113.5
-Lobe Centerline Angle 112.3
Valve Overlap 52.0
@ .050
Intake Valve Timing 222.0-----Exhaust Valve Timing 227.0
Intake Centerline 111.0-------Exhaust Centerline 113.5
Cam Lobe Centerline 112.3

stock vortec injection with wait4me or black bear PCM tune.
stock TC
daily driver

factors i'm considering include

quench. prefer .035-.045 but getting .04 -.05 depending on combination of deck and gasket. .04 quench combo gets my SCR up to 9.6 while .05 quench is only 9.4. factory quench figures to be .056.
i'm dealing with 4VR+Dish style pistons with no d-cup styles available thru this builder. I'm not sure is quench height is affected by dish, seems it would be.

SCR. many combinations of gasket and deck allow me to get 9.35-9.45 and one allows me to get 9.6. every calculator i ran came up with same numbers. want it pump gas friendly above all, low octane/10% ethanol would save me even more.

DCR. oh boy... no two calculators agree. some want ABDC at .05 and some want ABDC advertised. some want ABDC at .05 plus 15. WTH?? i know i want DCR to be between 7.5 and 8.5 with lower being less likely to detonate. what claculator and cam figure to use? what numbers do you get?

Cranking Pressure. new to me. am told between 170 and 180 is good. too high is bad. too low gives up power.

Overall. I want good, reliable power. Primary concern is detonation when I run pump gas of 87-89-91 octane. Help me put this together, please.

Posted similar question to another board and got the below feedback. Does this jive with the gospel of Techinspector and Denny? i've been reading and searching and reading some more. Looking for closure on this. Help!!


""OK. With an IVC of 66 and the above specs:

SCR-9.62
DCR-7.62
Dynamic cranking pressure: 149 psi

Should be fine running 87 octane. Just be sure the IVC is in fact 66.

I used a quench of .04 (.01 deck, .030 gasket).

SCR by itself does not mean anything. DCR is calculated by using the intake valve closing point. The earlier the intake valve closes on the compression stroke of the engine, the more air gets compressed so you have a higher DCR.

Smaller cams will close the intake valve earlier and larger cams will close the intake valve later. Had you used a bigger cam with a larger IVC your DCR would be below 7.5 and you would need to increase your SCR to get it above 7.5. That's why I said SCR by itself does not mean anything.

Your DCR should be between 7.5 and 8.5. Yours is at 7.62 which is at the bottom of the recommended range. The higher you go with your DCR the higher the octane must be.""

Cranking pressure should not exceed 165 psi for operation on pump gas according to Crane Cams.

You may have shot yourself in the foot with your piston choice. If there is no large flat area on the crown to mate up with the underside of the head, then proper squishing of air/fuel across the chamber at TDC could be a problem. Here's a 12cc D-Cup from Keith Black that has the proper configuration. See the large, flat area on the right side of the photo. If your pistons have only a thin ring of crown material around the perimeter of the piston, there may not be enough area to form proper squish.....
http://kb-silvolite.com/performance....tails&P_id=155

A tight 0.035" to 0.045" squish is one of the best ways to prevent detonation, but again, there must be enough material to form a good squish.

At zero deck with a 0.040" gasket (8.65cc's with 4.100" bore), 12cc pistons and 64cc heads, the SCR will be 9.59:1

With 5.7 rods, 3.48" stroke, 9.59:1 SCR and the intake valve closing at 42 degrees ABDC @0.050" tappet lift, the DCR will be 8.103:1 and should support the use of cheapo pump gas, assuming the squish is right and the ignition system is optimized for the combination.

thanks tech!

i looked at those pistons. ran the KB calculator. ended up with numbers a little different than yours. if i add .005 to deck/gasket height i come down .1 in DCR and SCR. see below. the KB calc 7.6 DCR makes me feel alot better. How did you arrive at 8.1 ? piston face design doesn't seem to affect SCR or DCR, they are all about volumes, but i bet it effects spark and flame propagation. Am i getting too wrapped up in this? is a few tenths SCR or DCR really going to matter in my app? my main concern is detonation and the impact DCR and SCR have on it as well as trying to get a good quench. these three things aren't playing nice with each other. LOL.

ENTER YOUR DATA CALCULATED DATA
Cylinder Head Volume (cc) Cylinder Head Vol
(cubic in.) 03.904
Piston Head Volume (cc) Piston Head Vol
(cubic in.) 00.732
Gasket Thickness (in.) Swept Volume
(cubic in.) 44.389
Gasket Bore (in.) T.D.C. Volume
(cubic in.) 05.226
Cylinder Bore Diameter (in.) Gasket Volume
(cubic in.) 00.462
Deck Clearance (in.)
Note: Neg. nubmer above deck, Pos. number below deck Deck Volume
(cubic in.) 00.128
Stroke (in.) STATIC COMPRESSION RATIO 09.494

OPTIONAL DATA
Rod Length (in.) Adjusted Stroke (in.) 02.674
Intake Closing Point (degrees)
ABDC @ 0.050 lift plus 15 degrees DYNAMIC EFFECTIVE COMPRESSION RATIO 07.527

Posted by thebigblue:
"How did you arrive at 8.1 ?"

727.35cc's plus 64cc's plus 8.65cc's plus 12cc's = 812
64cc's plus 8.65cc's plus 12cc's = 84.65
812 divided by 84.65 = 9.59:1 SCR

In the KB calculator, enter 9.650 compression ratio, enter 3.480 stroke, enter 5.700 rod length, enter 57.000 intake closing point (intake valve closes at 42 degrees ABDC @0.050" tappet lift. Add 15 to that and enter 57.000 into the calculator).
Result: 8.103:1 DCR.

"my main concern is detonation and the impact DCR and SCR have on it as well as trying to get a good quench. these three things aren't playing nice with each other."

The numbers work out fine. Cut the block decks to square them up and achieve zero deck height. Use a 0.040" gasket. The only thing that concerns me at this point is the configuration of the piston crown. If you don't have enough squish pad on the piston, you've shot yourself in the foot.