SCR vs DCR

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805moparkid

805moparkid

Slant and AFX Guy
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ok so this is a new variable that i have come across... i know that a big cam bleeds off compression and what not so i started looking...

and well im not sure i like what i found...

here are the specs on my motor
3.480 bore
4.120 stroke
6.700 rod
.157 in the hole
3.510 bore head gasket .020 compresses
44cc chambers
cam's IVC is 67 (adv) and 51 ( @ .050)
cam is .475 valve lift 246 @ .050 106LSA installed @ 102

now the program i use to figure compression and what not says i have 9.96:1 SCR... good... i just went onto wallace and it said its 235.12ci and a 8.95 compression! based on this my DCR is like 7.6!

now i need to be a little closer to 8.5 to 9 DCR...

am i just missing a step or what? thanks guys...
 
a dcr of anything upwards of 8.5 will be race gas only. I thought you had a street strip car.
 
daredevil said:
a dcr of anything upwards of 8.5 will be race gas only. I thought you had a street strip car.
Click to expand...

this is from over on .org

Post subject: Yes it is... (Mon May 30, 2011 1:37 pm) Quote: Is 11:1 doable on pump gas?

If you pick a fair duration and watch the overlap event, and use the DCR calculator, then adjust the timing/distributor recurve. It's very doable...I ran a 10.3:1 engine that would run on plus (with a few degrees of timing adjustment I could use regular or super, depending on race or daily driving).

The DCR calculator can subjectively show you what grade gas you may need to use with your build... (general rule of thumb 7-8DCR=regular, 8-8.5=plus/super, 8.5ish-9+=higher octane, there are some other variables that will move the rule around a bit).

While I was out of country, I had a dry erase board that I doodled and tweaked an 11.5:1 long rod build that worked out to using plus/super
(I think the day Rob Simmons visited my office, he thought I was translating some ancient Sumerian performance texts...LOL)

-D.Idiot
 
this is what i got





COMPRESSION RATIO CALCULATOR
Static and Dynamic Compression Ratio

(Considers Cam Timing and Rod Ratio)


ENTER YOUR DATA CALCULATED DATA Cylinder Head Volume (cc) Cylinder Head Vol (cubic in.) 2.684 Piston Head Volume (cc) Piston Head Vol (cubic in.) 0.000 Gasket Thickness (in.) Swept Volume (cubic in.) 39.187 Gasket Bore (in.) T.D.C. Volume (cubic in.) 4.371 Cylinder Bore Diameter (in.) Gasket Volume (cubic in.) 0.194 Deck Clearance (in.)Note: Neg. nubmer above deck, Pos. number below deck Deck Volume (cubic in.) 1.493 Stroke (in.) STATIC COMPRESSION RATIO
9.965
OPTIONAL DATA Rod Length (in.) Adjusted Stroke (in.) 3.168 Intake Closing Point (degrees)ABDC @ 0.050 lift plus 15 degrees DYNAMIC EFFECTIVE COMPRESSION RATIO
7.893
 
if your not running big/big intake valves then mill the head a tad

or try a diif cam profile

I would mill the head....big HP comes from high comp.
 
I dont understand what you dont like about it. Do you like paying for high octane. You could always run a shorter duration camshaft to raise the d r
 
805moparkid said:
DYNAMIC EFFECTIVE COMPRESSION RATIO
7.893
Click to expand...

How's your hearing, Ed?

I hear "OPPORTUNITY KNOCKS 101"!!!!

I hear a short block SCREAMING for a turbocharger.... no changes except for maybe a different cam (less duration.)

Want to pick this thing up to mid tens in ONE FELL SWOOP???:hello1:

Food for thought; you already have 90-percent of what you'd need....

120+ mph, 500 HP.... Most 340s will be in your rear view mirror...

Think about it. Lord knows, there are lots of people on here who would help you with advice/info, etc....

Just sayin'...
 
USAJon said:
if your not running big/big intake valves then mill the head a tad

or try a diif cam profile

I would mill the head....big HP comes from high comp.
Click to expand...

well im thinking the cam might be a tad to big so im feeling out all directions

daredevil said:
I dont understand what you dont like about it. Do you like paying for high octane. You could always run a shorter duration camshaft to raise the d r
Click to expand...

already run premium...

Bill Dedman said:
How's your hearing, Ed?

I hear "OPPORTUNITY KNOCKS 101"!!!!

I hear a short block SCREAMING for a turbocharger.... no changes except for maybe a different cam (less duration.)

Want to pick this thing up to mid tens in ONE FELL SWOOP???:hello1:

Food for thought; you already have 90-percent of what you'd need....

120+ mph, 500 HP.... Most 340s will be in your rear view mirror...

Think about it. Lord knows, there are lots of people on here who would help you with advice/info, etc....

Just sayin'...
Click to expand...

i was wondering when you would hit me up! i kow i can and will on another engine... im just luv making NA power... its not even the power but the best you can do whit that it is...
 
805moparkid said:
well im thinking the cam might be a tad to big so im feeling out all directions



already run premium...



i was wondering when you would hit me up! i kow i can and will on another engine... im just luv making NA power... its not even the power but the best you can do whit that it is...
Click to expand...


Am I THAT predictable? LOL!!!

I only have anough money for 1 car at a time, and the current one may be the last, so my thinking is sort of skewed that way. but for crying out lond, this setup is PERFECT (forged pistons.rods, low compression, ported head, etc.) if you'd just bolt a Buick turbo onto a stock exhaust manifold, you would IMMEDIATELY forget all about trying to make horsepower, normaly-aspirated.

If there were a decent head for a 225, I could see your point, but this making HP with a 170 cylinder head is just such an uphill battle...

But, there's not... and 200 cfm on the intake for a 39 cubic inch cylinder will never get the job done.

The Chevy V8s with that size cylinders routinely use heads that flow 300+.

Just sayin'....

Be good to yourself... give it half a chance. Yes, boost is addictive... :hello1:
 
Bill Dedman said:
Am I THAT predictable? LOL!!!

I only have anough money for 1 car at a time, and the current one may be the last, so my thinking is sort of skewed that way. but for crying out lond, this setup is PERFECT (forged pistons.rods, low compression, ported head, etc.) if you'd just bolt a Buick turbo onto a stock exhaust manifold, you would IMMEDIATELY forget all about trying to make horsepower, normaly-aspirated.

If there were a decent head for a 225, I could see your point, but this making HP with a 170 cylinder head is just such an uphill battle...

But, there's not... and 200 cfm on the intake for a 39 cubic inch cylinder will never get the job done.

The Chevy V8s with that size cylinders routinely use heads that flow 300+.

Just sayin'....

Be good to yourself... give it half a chance. Yes, boost is addictive... :hello1:
Click to expand...

i dont have forged rods or pistons
 
805moparkid said:
well im thinking the cam might be a tad to big so im feeling out all directions]


Since it's pretty much a foregone conclusion that your static compression is not going to work all that well with anything resembling a high-horspower cam, you can either change the cam, the pistons, or both, if you want to run anywhere down in the 11's (without putting your motor in a lighter chassis).

Add up the total cost (including gaskets, cam, valvetrain components, etc.) for this change, and when you get a viable total, see how it compares with the cost of a turbo setup that would NOT include pieces that you ALREADY HAVE ON/IN the motor, such as your existing, 4bbl intake manifold, your converter, rear end, pistons, rings, cam. valve springs, rockers, etc....

Doesn't leave much to buy, other than the exhaust manifold with a turbo flange welded to it, and the intake (cold) plumbing, a wastegate, and a blowoff valve, if you want one, along with changing your carb to blow-thru jetting, etc.

Tom Wolfe bolted a Buick turbo on his bone stock 225 '70 Dart with a 2bbl and went 12.95 @104.... You'll go a LOT faster than that.

You probably can do this cheaper than fixing the compression/cam issues of your normally aspirated motor.

Maybe not, but I'll bet it will be close...

I'll shut up, now.... :)
Click to expand...
 
805moparkid said:
well im thinking the cam might be a tad to big so im feeling out all directions



already run premium...



i was wondering when you would hit me up! i kow i can and will on another engine... im just luv making NA power... its not even the power but the best you can do whit that it is...
Click to expand...

91? with that you prolly can run 87-89...I run 91 with 8.3-8.4
 
74Burntorange said:
91? with that you prolly can run 87-89...I run 91 with 8.3-8.4
Click to expand...

is this an iron head motor? just trying to keep apples to apples...

im going to finish this round of tricks and then get my roller rockers 1.6's (.540 lift)

re-tune and dyno it, track it...

then im gonna play with cam timing to see what might be hiding in there as far as cyl pressure and DCR...
 
805moparkid said:
is this an iron head motor? just trying to keep apples to apples...

im going to finish this round of tricks and then get my roller rockers 1.6's (.540 lift)

re-tune and dyno it, track it...

then im gonna play with cam timing to see what might be hiding in there as far as cyl pressure and DCR...
Click to expand...

YUP RHS head with 34 total timing, DC3 the guy with a green cuda is also running 87-89 with iron but magnum heads so might have something to do with it.
 
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