What SCR/DCR are you running?

[laxplayermjd]

I think this would be a very useful post to be stickied.

What SCR and DCR are you running in your stroker?
What Quench are you running?
What Grade fuel are you using?
What size injectors?
What AFR mods?
And Do you have any piging?

Im looking roughly at these specs...SCR ~ 10 DCR ~ 7.4
About ready to send block to machine shop do deck height machining is still open. It will definitely have some take off. Id prefer not to spend more money on dishing pistons but it may have to be done. Do you think these numbers could be run on 93 octane???

[lafrad]

I'm planning on running a
10:1 SCR,
8.2-ish DCR,
.038" quench.

Don't have injectors picked out yet.
Don't know the fuel. expecting 91/93, hoping for 87... probably 89.

I have a PSC MAP piggyback that I will be installing to get the fuel trims +/- 5% across the board... hopefully that also can get WOT close enough too.

[gradon]

You'll be fine with those #'s la, and the psc will be able to keep the trims w/in +/-5% and make WOT 12.8:1 if you have at least 24# injectors.
Mine right now is 10:1scr, 8.57dcr(too high, so a lil pinging before OL), .063" quench: .051" 9076pti Fel-pro HG and .012" deck clearance--I thought I ordered the Victor Reinz .043"), LT1s at 25.5#, and a Adj map set to 6.0V(accidentally got water in the psc and blew it).

[RAPTORFAN85]

SCR=9.4 DCR=8.0
.048 quench with .005 dech height and .043 Victor gasket
I run 93 oct. for piece of mind but it will run 89 no prob. 87 with little ping.
rated 24lbs. injectors that flow somthing like 24.6lbs.
No AFR mods but I do have an AFR gauge and everything seems to be happy

7.4 DCR should run on premium no problem. Why do you want your static comp. so high?

[lafrad]

SCR=9.4 DCR=8.0
.048 quench with .005 dech height and .043 Victor gasket
I run 93 oct. for piece of mind but it will run 89 no prob. 87 with little ping.
rated 24lbs. injectors that flow somthing like 24.6lbs.
No AFR mods but I do have an AFR gauge and everything seems to be happy

7.4 DCR should run on premium no problem. Why do you want your static comp. so high?

My problem, is I want good quench (I run 0.030" in my HEMI), and also want Hypereutectic pistons. The combo's available for that leave me with the 10:1 CR.

If I could get the DCR down into the high 7's without running a MONSTER cam... I would.

[laxplayermjd]

Thats just approx what i calculated as im not really planning on dishing pistons unless its a must. With those numbers i was using OEM cam.SCR ~ 10 DCR ~ 7.4
Cam choice is still in the open. Possible luncati cam or mopar performance cam. Lunati cam gives me about SCR 10.1 DCR 8.8. I will be running this on a renix and will make a map adjuster. Looking at .062 Quench or less. Can be lowered with the gasket and some more decking. I sent the block out, he said atleast .010 needs to be decked off. Looking to get it back then measure to see if i should take more off for better quench.

As far as SCR vs DCR,, can SCR be disregarded as long as DCR is about 8.5 can run 93???

[PolloLoco]

As far as SCR vs DCR,, can SCR be disregarded as long as DCR is about 8.5 can run 93???

SCR doesn't mean much, if any at all. It's the real compression, aka DCR, that really matters. Nothing is being compressed until the cylinder is sealed shut and that's when DCR is measured. SCR measures the geometry of the engine. So yes, your ultimate goal should be a set value for DCR, which from what I've read 8.5 is about as high as you want to go and run on pump gas. I'm shooting for 9.5 but I'll be running E85.

[RAPTORFAN85]

SCR doesn't mean much, if any at all. It's the real compression, aka DCR, that really matters. Nothing is being compressed until the cylinder is sealed shut and that's when DCR is measured. SCR measures the geometry of the engine. So yes, your ultimate goal should be a set value for DCR, which from what I've read 8.5 is about as high as you want to go and run on pump gas. I'm shooting for 9.5 but I'll be running E85.

You are correct sir

Dynamic comp. is the working comp. of the engine. Thats what you want to pay attention to.

[dwg86]

Using tha calculator, I am coming up with 9.24 SCR and 7.75 DCR. I don't know it will run yet...It's not installed.

[PolloLoco]

Attached is a nice little gem that I found on Wikipedia that may help us visual learners.

Ideally the 180° between "2" and "1" would be your compression stroke, and this leads to the SCR. In reality the yellow region "B" is your compression stroke, and this leads to the DCR. Notice how the yellow region is less than the 180° between '2" and "1?" It will always be this way. The intake valve closes after bottom dead center, as show by green region "A" passing the "2" mark. The compression, SCR and DCR, will always end at the "1" mark, top dead center, because the piston then moves down and expands the combustion chamber volume.
Now to make this diagram even more realistic the red region "C" should be adjusted to reflect the spark timing. Move it left of "1" and your timing is advance and to the right of "1" and your timing is retarded. Yes, "C" can overlap "B" and many times in real engines it does.
This picture also shows valve overlap. The blue region "D" occurs at the same time as the green region "A" indicating that the intake and exhaust valves are both open at the same time.

[laxplayermjd]

Well im down to getting set on a piston dish. Im looking at 22CC 677cp piston..

My numbers calculate as follow.

SCR 9.6
DCR 8.58
Quench .043
Zero Deck clearance.

Will this work out well for 93 on my renix?

[eastin82]

i hope so im going to use the sp 677cp30 dished to 23cc with the comp cam 68-231-4 im coming up with 9.49scr and 8.3 dcr if i use .044 head gasket.

[SilverXJ]

I'll let you know what fuel I can run as soon as I sort out all the other little issues with my stroker.

[Cheromaniac]

You'll need to use a DCR calculator to find out the DCR of your engine, so I'm curious as to what intake valve closing point you're all entering. The 0.050" lift closing point, the advertised at-the-seat closing point, or something in between? The results will differ quite a bit.

[mendelmax]

I'm also curious about one effect- we do know, that in theory, the DCR is dependent on the closing angle at 0", since this is when no air can leave the chamber.

But on the other hand, the lobe profile also plays a role, because I think we can all agree, that with minimum valve opening, the opening area is too small, to let the air escape at certain revs, and the compression begins. So this is the case, that makes all our calculations imprecise to some point. I mean some identical setups may work differently, since they use different lobe profile, regardless of identical advertised closing point...