rustynutz

i'll try posting this here since there's been no response elsewhere.
i'm confused with the proper dcr calculation. i've been trying to use this calc due to seeming less complex than others. i get lost when cam talk comes into the discussion. still learning here folks.

http://www.kb-silvolite.com/calc.php?action=comp

for figuring dcr w/ this calc, the require this: Intake Closing Point (degrees)
ABDC @ 0.050 lift plus 15 degrees. others here have stated using the closing degrees abdc at .006" in place of. is this right? yes i've been searching/reading and still can't get clarification which is why i'm posting. i appologize in advance to the seniors in this forum that may feel this is too much a newb ?

i've attached my cam card and all my specs. can someone help a brother out and give me some sort of confirmation that the dcr i've come up with is in fact fairly accurate? engines is literally appart awaiting re-assembly as we speak. nows the time for any changes.

head cc = 66.3
piston head volume = 0
gasket thickness = .045
gasket bore = 3.910
bore = 3.898
piston out of hole = -.007
stroke = 3.622
rod = 6.098
if my intake valve @ .006 closes at 67.5*
then my dcr should = 8.261
and my scr should = 10.605

does this look accurate? if not, why.

what is a stock ls1 dcr????????? 7:1?

5.3LJimmy

iTrader: (10)

Your calculations are correct. Using a different calculator I get 8.25.

Ragtop 99

iTrader: (7)

I use the calculator found in this thread:

https://ls1tech.com/forums/advanced-engineering-tech/394937-updated-valve-event-dcr-scr-header-length-spreadsheet.html

vettenuts

iTrader: (4)

Use a different calculator. Comp uses 0.006", Crane uses 0.004", which is essentially the seat timing and the values you should use in the calculator. I don't like using the 0.050" numbers and adding a fixed value to them as it may not properly account for ramp rate. For example, my current cam has a 216 duration at 0.050 and the new cam I bought is 224 at 0.050 so one could assume that the seat duration would be more for the 224. In actuality it is less as the ramp rate is faster so the DCR numbers for my new cam are actually more than for my current cam even though my current cam has less duration at 0.050".

Die Grinder

I would love to know why there is so much discussion of "DCR" in the LSX world and who started it. Outside of here, the only people that concern themselves with it are OEM engineers that try to predict detonation resistance at low rpms under relatively high loads.

5.3LJimmy

iTrader: (10)

I am certain that OEM Engineers are not the only other people concerned with DCR. A simple google search for dynamic compression ratio will easily prove that. Ever wonder why camshaft manufacturers recommend a certain compression ratio with their cams? I bet it's to keep the DCR up. I'm not sure who started the DCR discussion in the LSX world, but the reason why is obvious. After that google search try reading a few of the results. With all due respect, and remember I'm saying w/ all due respect. While you are at it apply those new reading skills to help you avoid making pointless and mindless posts in the future.

Die Grinder

At the risk of barratry, let me pose this question. If you were given the task of designing engines for a: (1)passenger car. (2)sports car. (3)Formula 1 car, would your DCR formula give you predictable results for all three? Would it enable you to establish throttle body size and plenum volume? How about intake runner length and intake and exhaust valve area? RPM range? Exhaust pipe diameter and length? Or perhaps these things are not worth considering?

Can I just "GOOGLE" my next combination?

5.3LJimmy

iTrader: (10)

keep reading

Die Grinder

That is a very concise answer from someone with a thorough command of the principles at hand. I appreciate your furthering of my education in this matter. I am in your debt.

5.3LJimmy

iTrader: (10)

I suggested you keep reading because it seems to me that you went from the topic of calculating DCR to Volumetric Efficiency. The formula one car really does not fit into the realm of discussion here as it runs on race fuel, which is what most people are trying to avoid by using the DCR calculations. I see now that you weren't looking for someone to tell you why the LSX world is so concerned with DCR, you were just looking for a pissing match. If you really feel the need to **** any further please do so by PM as there are now 2 of us needlessly posting in this thread.

Die Grinder

rustynutz, I apologize for hijacking your thread. I actually would like to know what rpm range you operate in. It seems you have an interesting application for the venerable LS1. Please elaborate on what it is you do.

PREDATOR-Z

DieGrinder, you seem well versed so, post the explanation of DCR and what effect doest it have in a 4 stroke engine.
in other words, tell us exactly why it is insignifcant IYO with regard to the LSx?

BIG_MIKE2005

iTrader: (116)

Well i guess your SCR & DCR isn't important if you don't care about your engine. Any damn fool can slap parts together without consideration of the end result, but that doesn't mean it'll work. Properly calculating your SCR/DCR will help your engine not only perform better with the proper combo, but run better overall.

You cant just slap a combo together, end up with really high compression & expect to run pump gas. Only a total damn idiot would do that & thats why its important to know exactly where you sit in these areas. It's just flat out stupid to not worry about these things, especially when you get into crackin open the motors & internally modding them.

rpmauto

iTrader: (14)

Just thought i would put my .02 in. I am a ASE certified master tech, i own my own repair shop, and although i only get to work on a few (my own and 7 or 8 buddies) "fun cars" Have built several performance engines until i started lurking around this site i had never heard of dcr. I would like to know more about it. I will do a google search. I am building a 402 for my 98 and dcr is not of any concern to me, (maybe, until i read more) Why is it so important?? everybody is talking about it, but not much real info on it.

rpmauto

iTrader: (14)

On engines we built, we would always know what the scr and end cr would be, I just want to know more about dcr.

Thorny

iTrader: (14)

Of the engines you've built, you've been lucky Seriously, DCR problems are rare on most builds because most large duration cams will have the intake valve close when the piston is further up the cylinder on the compression stroke, which bleeds off compression. To run into problems with DCR you have to be running a small cam with milled heads, something that doesn't happen all that often. EDIT: or be running low octane or low quality fuel

Using SCR will get you close to where you want to be, but DCR is much more accurate since it measures the actual ratio by taking valve events into consideration.

IMHO, you hear so much about it on this site because everyone is wanting to squeeze every available pony out of their motor. Having the proper DCR is vital because it defines the limits of the fuel you can run in the engine without having problems with detonation. When you're trying to get as much power as possible, it pays to know the limits of the fuel you'll be running and figure your DCR accordingly.

rpmauto

iTrader: (14)

Thank you Thorny, that is what i wanted to know in a nutshell, I just have not had the time to research it. I wonder why i never heard about that in any of my classes, I also took engine machinist classes when i was in college, and never a word was said about dcr. Very interesting that is why i like this site, once you weed through the crap there is a ton of useful info.

PREDATOR-Z

Nice one Thorny, well said,.

I hope DieGrinder reads this.

Die Grinder

Proponents of Dynamic Compression Ratio purport that if you plug cylinder size, engine speed, comp ratio and valve events into a formula, that you will generate a meaningful peak cylinder pressure expressed as DCR, and that there is some number which you can not exceed without likely damage from detonation.

Viewed this way, you would say that these formulas would be accurate predictors of power would you not. Of course that would mean that those complicated engine simulation programs ranging in cost from hundreds, to tens of thousands of dollars used by the OEM's are not necessary.

The reality is formula's like this are far too simplistic to be of any value. Would your limiting DCR be the same for an open chambered cast iron headed, iron block engine like a big block Mopar or BBC as it is for an aluminum headed, aluminum block LS1? Would you say you could tolerate a higher DCR with a looser converter or taller gears?

If DCR calculations are so valuable to wring every last ounce of power out of your engine as Thorny claims, then they should also tell you what would be the best course of action to lower a dangerously high DCR. Would you lower your compression ratio? Would you change cams? Lower your coolant temperature? Reduce spark advance? Or perhaps try a different DCR calculator?

Damian

iTrader: (89)

I agree with Die Grinder. People are getting their boners waaaay too stiff these days trying to get the "perfect" DCR.

Motors aren't making any more power (especially the 346's) while trying to get perfect DCR than the others who aren't concerned with it. I made 460+ rwhp 4 yrs ago on old parts with a 346 and never gave one crap about calculating DCR.

Unless you're running crazy compression levels, save your time and energy towards something else.