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Discussion Starter · #1 ·
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
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.
 

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I've been looking into a similar combo.

I've decided that it may be worthwhile to use a piston that can take full advantage of the "dual" quench pads of Vortec heads.

Whether this can be done w/a dish, D-cup, or whatever- I believe there's gains in power and/or octane sensitivity to be had.

It would seem that a piston w/a "reversed" dish (as compared to the combustion chamber) would be the ideal in this case. But whether or not such a piston is available off the shelf, I do not know.

AFA "cranking pressures" go, there's some leeway- I've heard of engines that pump close to 210 that run fine on pump gas, others have struggled w/180. It seems there's a lot to that whole deal- and not a small part of it is in the cam.
 

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Discussion Starter · #3 ·
unless d-cup is a HUGE advantage over regular 12cc 4VR+dish i'm not gonna do it. i have my reasons. i ran the diamond racing SCR calculator and came up with friendlier numbers than the hand calculations i did using lunati formula's. it's a more specific calculator and sometimes dif was as much as 0.1:1 CR lower than lunati hand calculations.

i'm cool with 9.4:1 on 87,89,91 octane. 9.6:1 makes me nervous even though quench is better. the DCR issue has me in fits.

someone put my combo together! Please!
 

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What is the IVC for the zz4 cam? Can't come up with an accurate DCR without it. DCR is not a rule of thumb when it comes to figuring out if your combo will work they way you want it to. It's can be used as a good reference however. There are a lot of factors that will dictate whether your combo will work as you want it to or not (VE, chamber shape, cooling system, iron vs aluminum, etc.).

For an accurate DCR calculator do a search for Pat Kelley's calculator.
 

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ZZ4 Cam Specs:

112 LSA
109 IC/115 EC
208/221 @ .050"
.474/.510 with a 1.5 rocker

I don't recall where this came from, I must've trusted the source or I wouldn't have bothered to cut/paste them- but you might want to verify it just the same.
 

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cobalt327 said:
ZZ4 Cam Specs:

112 LSA
109 IC/115 EC
208/221 @ .050"
.474/.510 with a 1.5 rocker

I don't recall where this came from, I must've trusted the source or I wouldn't have bothered to cut/paste them- but you might want to verify it just the same.

To get an accurate DCR you need the valve timing events. Specifically the IVC (Intake valve closing in degrees). You will not be able to get an accurate DCR without it.

Read this:
http://www.empirenet.com/pkelley2/DynamicCR.html

Toward the bottom you can download the calculator for DCR but you need the valve timing events. Either way it's good reading for you original question.
 

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thebigblue said:
after alot of digging around IVC = 66

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).
 

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Discussion Starter · #9 ·
all the zz4 cam specs i could find.

http://www.clubhotrod.com/forums/showthread.php?t=39545

so, the 9.62 SCR is alright? defies the general CR x 10 = octane but then so many rules of thumb go out the window anymore.

what characteristics of this build indicate 9.62 is alright? it is iron heads, vortec efi, etc.

is it better to go for optimum quench even if it means raising compression? i've read that reducing compression can increase detonation.

any idea on expected TQ and HP ??
 

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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.

I plugged in the specs in Dyno2003 and came up with the following #'s:
Peak HP: 390 @ 5500 rpm
Peak TQ: 410 @ 4500 rpm

I used a single plane intake and 600cfm carb with large tube headers. Those numbers look high to me though.
 

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Discussion Starter · #11 · (Edited)
excellent!

any word on how my vacuum will be affected compared to stock?

should i worry about cranking pressure being low? am i giving anything up?

those numbers do look a little high. i'll be using stock vortec mpfi, say roughly 17-19lb equivalent poppets, and summit 9016 shorty headers with 2 into 1 exhaust existing a 3" tailpipe.

Thanks!
 

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I am running an aluminum headed 383 stroker with a CC XE274H cam. '0' decked block, 0.041 head gasket, 12cc dish pistons, 35* timing all in by 2600rpm plus 16* vacuum advance.

Static CR is 10.3 and Dynamic CR is 8.2.

Has been running fine on 89 octane for a couple of years.
 

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I am running a Vortec head combo.

10.63:1 SCR
7.9:1 DCR (using Pat Kelley's calculator)

I run locally available 93 octane. This is an engine in my dragster. It went 9.83 @ 131MPH with stock parts (with the exception of the crappy cam and a PP air gap dual plane intake).

I have read a lot of stuff saying DCR is important and others saying it aint worth your time investigating. Me? I don't know what to think.
 

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thebigblue said:
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
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.

Not to get too excited about DCR calculators, these things are black boxes inside of which we have no idea what's really going on. The simplistic approach is to say that because of reverse pumping, some portion of the intake mixture is being pushed by the piston back into the intake track and out the carb. Hence mixture stand off for this and other reasons. And they pontificate that this is somehow proportional to when the intake valve closes. Therefore, the mixture density in the cylinder is reduced by some fraction of less than what could be obtained if the cylinder could/would breath till it was full of mixture at atmospheric pressure. Then the density, or pressure, would simply be the SCR times atmospheric pressure and the Dynamic Compression Pressure Ratio would be equal to the Static Mechanical Compression Ratio.

However, and it's a big "however"! The DCR is as dependent upon RPM, perhaps more-so than just when the intake valve closes. This is because the incoming mixture has mass and velocity. Mass times the velocity gives an inertial weight to mixture. At low RPMs this inertial weigh is low and the rising piston can easily push the incoming charge backwards, a condition that would be accentuated by a late closing valve resulting in the DCR being less than the SCR in terms of pressure. But as the RPMs increase, so does the velocity of the mixture and times its mass the mixture begins to get rather, shall we say, porky. There is a point in rising revs where it resists being pumped out of the cylinder and will in fact continue to rush into the diminishing volume of the cylinder against the efforts of the rising piston. At this point the density in the cylinder is increasing and therefore the DCR is going up. On top of this general effect with increasing RPM, the velocity in the intake system is also controlled by the size/volume of the ports, valves, plenum volume and carb size as well as RPMs. So one can see that these one size fits all calculators are either missing the ability to be sensitive to a lot of missing information about your engine, or are making some pretty substantial assumptions about it.

As far as clearance to the quench deck is concerned, don't loose track of the fact that going over TDC on the exhaust stroke, the inertia of the piston and rod will take up all the rod clearance and that has to be added to the length of the piston and rod assembly which is eating away your safety margin keeping piston crown and head deck separated. Also, the piston is twisting sideways as it takes up the thrust clearance of the skirt, thus allowing a side of the crown to come closer to the head. This is not to even take in consideration for things stretching from inertia or the formation of hard deposits on the top of the piston and bottom of the head. You need to be sure to provide structural clearance for which with a steel rod and nominal production clearances .040 inch is considered to be minimally adequate. You can buy a lot of gasoline for what it costs to fix a collision between the piston and the head.

Bogie
 

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oldbogie said:
Not to get too excited about DCR calculators, these things are black boxes inside of which we have no idea what's really going on. The simplistic approach is to say that because of reverse pumping, some portion of the intake mixture is being pushed by the piston back into the intake track and out the carb. Hence mixture stand off for this and other reasons. And they pontificate that this is somehow proportional to when the intake valve closes. Therefore, the mixture density in the cylinder is reduced by some fraction of less than what could be obtained if the cylinder could/would breath till it was full of mixture at atmospheric pressure. Then the density, or pressure, would simply be the SCR times atmospheric pressure and the Dynamic Compression Pressure Ratio would be equal to the Static Mechanical Compression Ratio.

However, and it's a big "however"! The SCR is as dependent upon RPM, perhaps more-so than just when the intake valve closes. This is because the incoming mixture has mass and velocity. Mass times the velocity gives an inertial weight to mixture. At low RPMs this inertial weigh is low and the rising piston can easily push the incoming charge backwards, a condition that would be accentuated by a late closing valve resulting in the DCR being less than the SCR in terms of pressure. But as the RPMs increase, so does the velocity of the mixture and times its mass the mixture begins to get rather, shall we say, porky. There is a point in rising revs where it resists being pumped out of the cylinder and will in fact continue to rush into the diminishing volume of the cylinder against the efforts of the rising piston. At this point the density in the cylinder is increasing and therefore the DCR is going up. On top of this general effect with increasing RPM, the velocity in the intake system is also controlled by the size/volume of the ports, valves, plenum volume and carb size as well as RPMs. So one can see that these one size fits all calculators are either missing the ability to be sensitive to a lot of missing information about your engine, or are making some pretty substantial assumptions about it.

As far as clearance to the quench deck is concerned, don't loose track of the fact that going over TDC on the exhaust stroke, the inertia of the piston and rod will take up all the rod clearance and that has to be added to the length of the piston and rod assembly which is eating away your safety margin keeping piston crown and head deck separated. Also, the piston is twisting sideways as it takes up the thrust clearance of the skirt, thus allowing a side of the crown to come closer to the head. This is not to even take in consideration for things stretching from inertia or the formation of hard deposits on the top of the piston and bottom of the head. You need to be sure to provide structural clearance for which with a steel rod and nominal production clearances .040 inch is considered to be minimally adequate. You can buy a lot of gasoline for what it costs to fix a collision between the piston and the head.

Bogie
Bogie, wouldn't the DCR be more dependent on RPM rather than the SCR? You make a good point about the effects of the inertia of the mixture at low and high rpms. I think that these calculators give a general idea of where you stand with the combination of parts you have chosen. For example if you see that your DCR is 9.5 you might have to rethink your plan.

Also Pat Kelley gives an explanation and the formulas he uses for his calculator in his article. This is the reason why I like his calculator more than the rest.
 

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nick8 said:
Bogie, wouldn't the DCR be more dependent on RPM rather than the SCR? You make a good point about the effects of the inertia of the mixture at low and high rpms. I think that these calculators give a general idea of where you stand with the combination of parts you have chosen. For example if you see that your DCR is 9.5 you might have to rethink your plan.

Also Pat Kelley gives an explanation and the formulas he uses for his calculator in his article. This is the reason why I like his calculator more than the rest.
Yeah, I fixed it, my typing has a hard time keeping up with my thinking, I usually catch those but not always sorry for the confusion.

Bogie
 
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