well theres another thread here that got me trying to figure out my dcr and while doing that i was studying my cam card and comparing it to some other cams. now my head hurts. naturally the newb has questions.

First question, whats the difference between my cam and a GM847 going to be in the powerband?
engine: 383, if i need to get more specific than that let me know
heads: stock LT1 castings with LE3 headwork that flow...
.100 65/57
.200 132/108
.300 195/142
.400 239/165
.500 268/179
.550 272/183
.600 272/188

my cam:
242in / 248ex
.587" / .578" w/ 1.6 rr's

GM847 cam
234in / 242ex
.574" / .595" w/ 1.6 rr's

vlv event / my cam / gm847
int v o / 15 btdc / 10 btdc
int v c / 47 abdc / 44 abdc
exh v o / 54 bbdc / 58 bbdc
exh v c / 14 abdc / 4 abdc

as far as I can tell...
my cams intake valve opens 5 degrees sooner and closes 3 degrees later
my cams exhaust valve opens 4 degrees later and closes 10 degrees later

are there any good sites that have tutorials for figuring out what changes what and why involving cams? For some reason I have become fascinated with cams and really want to learn more, and Im actually understanding things now.

on to my next question... dynamic compression ratio. After reading the other thread I gathered up all this information:
ICL: 106
LSA: 108
advertised duration: 304 degrees intake, 314 degrees exhaust
.050 duration: 242 intake, 248 exhaust
rod length: 5.7"
head gasket thickness: mr gasket 5716 .026"
piston in hole depth: I have no idea! block isn't decked. I'll try and measure it as closes as possible tomorrow
head CC's: 58cc
type of piston: type? SRP forged
CC's in valve relief: 14cc or 16cc, Im not quite sure.

Is that all that is needed? Anyone have a good semi-educated guess as to what my deck height is? or better yet what my dcr is?
when I ran all my info in THIS DCR calculator I get:
isn't 9.0:1 dcr about the limits of pump gas? does that mean I will I have to run race gas? I may be off with the 11.0:1 c/r, I tried 10.5:1 and still got 9.36:1 dcr. I gotta be doing something wrong here! If tonight the planets are aligned and I am right, could I advance or retard the cam to help out a bit?

and since Im asking questions that are difficult/hard to answer... how long will my 10 bolt last with 400+ rwhp, why can't I keep my wheels clean, and when will I get a girlfriend and stop being obsessed with my car (these questions dont need to be answered)

I need sleep

 

Ya need to use the advertised duration numbers to figure DCR not the @50 numbers. Your DCR is not as high as you figured with the @50 numbers. WILD GUESS you are below 8.5,but do it with the advertised numbers and see.

 

What 1racerdude said re: your calculation error. There is no way to "guess" at your deck height except that if the block has not been decked, the block deck will be at ~9.025" (stock height). You can use this number to estimate your piston deck by subtracting the rod length, piston compression height, and 1/2 the stroke.

That is one "healthy" cam for a street car. It may not make enough vacuum to run the brakes in stop and go traffic and will like a pretty loose converter.

Rich

 

I had both on there just to make sure, the site says to use duration at .050
HERE is my cam card if that helps.

I also didnt mean deck height, but how far the piston sits in the cylinder bore at top dead center. Im pretty sure the block isnt decked. not 100% though.

As for it being a healthy cam, I sure hope so! this car wont be a street car too much longer. gas prices are finaly to the point that they offset the cost of a econobox beater I can remember filling my 68 bonneville's gas tank with 20+ gallons of gas and spending less money than with a 15 gallon tank today...

 

Using a 383 with 6.0 rod,flat top's with 4CC valve relief,54CC chambers,and .020 in hole for deck height( some are more,some are less) and your listed set up.
Your static is 12.56
Your dynamic is 8.86
Ya are good to go with a GOOD tune and cooling,and 92 octane

 

Larry got you covered here....


WE NEED TO MAKE A STICKY ABOUT DCR AND THAT YOU DON'T USE THE .050" IVC!!!!

Bret

 

Ya got that right...maybe one day people will understand.. I ain't holding my breath though.

 

hmm, that looks great I wish I would have went that way.
I dont have flat top pistons with 4cc valve reliefs, theyre 16cc dished I believe
I dont use 6" rods, theyre 5.7"
guess I shouldnt have left out that information. stupid me.

however, knowing that I could get away with that kind of compression ratio with this cam makes me feel like buying new pistons for the engine. If I keep my 5.7" rods and get SRP flat top pistons with 5cc reliefs would that yield roughly the same dcr?

Thank you guys alot, I REALLY wish I would have done more research prior to purchasing the bottom end for this engine. I'm trying to learn more here. wish I had half the knowledge you guys do.

 

DCR is related to STATIC Compression and IVC.

Static is around 10.6:1 and DCR is now 7.6:1, try your calcs with a IVC of 77*

Bret

 

awesome! got the same numbers you did.

question: where did that IVC of 77 degrees come from?

 

Easy way to get it....

Take the Advertised Duration..... 304
Minus the .050 ..... 242

= 62

Divide that by 2

= 31

add that to the ICL @ .050 = 78

I just use a simluator to get close so I don't have to look up the number but that's the easy way by hand to do it.

Bret