seawolf18

iTrader: (18)

Im trying to figure out my dynamic and static compression ratios with my new head and cam combo. I bought a set of PRC stage 1 LS6 Heads from TSP. The heads are decked .015. I was planning on using stock head gaskets. My cam is a Comp custom grind 228/232 .588/.592 lift on 112 LSA + 4 advanced ground in. The other cam specs are. The motor is a stock cubed LS1.

0.006 0.050 0.200
277 228 149
281 232 153

Thanks for the help.

Sean Collins

Does anybody have the helmholtz action model in the DCR calculations ? experience says that the cam should work Good.

seawolf18

iTrader: (18)

I keep hearing about thease compression spreadsheets, but can never find one.

Sean Collins

I have been reading up on how everybody else calculates DCR here and i am highly concerned. The design of the ls1 ls6 ls2 intake manifolds is a Plenum ram or basically is a helmholts resonance runner. DCR calces are fine and dandy but of more critical concern then the DCR ( it does affect TQ output) is cylinder filling.You can have whatever compression ratio you want but if you don't fill the cylinder then you wont make any power. Now the DCR is handy in making a combo more efficient but it should be kept in mind that the engine is a complex wave action machine. Without considering all the variables doing all of you cam estimation based on DCR is like a blind man painting.

There are sevral Variable that need to be added to the DCR model and honestly there should be a thurough model done for each intake manifold. What interesting however is that the intake manifold dynamics change with displcement so now we need a class of calculations that will again have to be modified with cylinder head volume.

To no leave anything on the table here Rod angularity and piston velcotiy will have an affect on the DCR and helmholts wave action in the intake runner.

Guys please stop looking for a striaght answer on this. Yes DCR is a handy tool but there are sevral other variable that may contribute more to it then one might think.We could calculate the DCR but without knowing the Ramcharging effect in the runner for a given cylinder head and intake combo on a fixed displacement DCR will go out the window.

Here what i can tell you. don't be affriad to buy more then one camshaft.If you don't want to experiment find a good running combo and emulate it. the fast guys are fast becuase they have conveinetly taken the time to try 10-20 cams and see which one works best. You can get close but using a dynomometer will show you how well it is or isn't working.humps in the power curve are a good sign that cam timing is wrong.

trey04gto

iTrader: (4)

Here yah go... I used this one as well http://www.race-cars.net/calculators...alculator.html

slow trap

iTrader: (22)

i figure you have between 10:8-10:85 scr but no idea on dcr.unfortunately the calculator i used is no longer available. maybe one of the gurus will step in and help.

seawolf18

iTrader: (18)

Im trying to figure out the highest compression I can run on pump gas around here. The bad thing is, I only can find 91 octane.

Sean Collins

Stay with 10.1:1 if 91 octane is all that is aviable. I dont put much fiath in DCR due to aforementioned post.

PREDATOR-Z

Man, where do you come up with these answers? 10.1:1 on 91 octane??
You can run stock 10.9:1 LS2 in Cali with 91 Octane.
SCR is not the relative factor in detonnation but DCR is.

DCR is important and will make a huge difference in the overall combo. This has been proven by quite a few of us around here. Optimize DCR/quench/SCR and that can be worth a lot of power on the table.

seawolf18

iTrader: (18)

Thats what im trying to do Optimize my DCR/quench/SCR, so I don't leave a bunch of power on the table. Basically I need to know what thickness head gasket to get.

PREDATOR-Z

with stock gasket assuming your piston is .007 out of hole:

11.09 SCR and 8.69 DCR,

Not bad with a good tune, just run a set of TR6 1 step colder plugs.

seawolf18

iTrader: (18)

Thank yo sir. Looks like stock gaskets for me.

Sean Collins

Wild how ignorant people are to the intake manifold playing around with cylinder filling. You can calculate DCR to death but if you don;t know how the manifold behaves with the dylinder head then all you are doing is geussing at best. Hopefully i will have found some calcs to correct for the manifolds effects on DCR until then everybody is just geussing..

PREDATOR-Z

CA,
Ignorant? comming from someone that says stick with 10.1:1 on 91 octane??
Look at the majority of my posts on DCR and you'll see the magic (~) sign that means aproximate.
We are sooo ignorant, that by paying more attention to those little details some of us are able to squeeze 20+rwhp from cams that otherwise just don't dish out.
Maybe the cams you are using have the wrong VEs for the flow potential of the FAST you are using, and i'm sure you know that VEs play a role in DCR as well.
Is FAST ultimate, certainly not, the design of the intake itself is a crutch on airflow. But it is a definite improvement on the other GM intakes.
24x/24x on 10.1:1 LS1 is overcammed, the intake, which ever you decide to put on will not resolve that issue no matter how you look at it. ((11.0:1) as well for that matter)
As a matter of fact, 24x/24x 115 (what you consider wide lsa) would need serious compression to put out the numbers it should make.
Take a look at the T-Rex for exemple, 110 LSA 108 ICL, why? for VEs good looks, no! but a byproduct of the tighter LSA/ICL is an increase in DCR.
Too early a IVC will push the peak power capability of that cam way beyond the airflow potential of the FAST design, but slap that 24x/24x 115 in with a sheetmetal tuned runner intake, then spin this sucker to neverland and you'll get numbers that you only dream of.
However this is beyond the average setup most of poeple here would ever use.

So please, I asked you where you get your theories from (meaning facts and numbers, not just talk), and the best you lash out is an insult?

Here read this, I think it will help
https://ls1tech.com/forums/generation-iii-internal-engine/163744-camshaft-discussion-cfm-requirements-rpm.html

seawolf18

iTrader: (18)

PREDATOR, What do you reccamend for a pushrod length? You da man when it comes to cam set ups

Sean Collins

Thoerys ??? Facts ??? DCR is alot of hype. Yes its not a bad formula but it is designed around a single plane intake manifold. It needs correcting for the intake manifold filling model. Yes DCR might be relative but everyone seems to negate the intake moanifold runner.

PREDATOR-Z

For your info the calculator (Excel spreadsheet) is custom an caters for manifold runners (LS6).
It also gives me an idea about exhaust primary header length needed etc..
It is not a Yahoo calc

Dynamic Compression a lot of hype? OMG, I better leave this discussion at that.

PREDATOR-Z

you'll be fine with 7.400 or 7.425s with stock gasket.

Sean Collins

I am not going to continue to argue with an internet quarter back engine builder.

PREDATOR-Z

Well, that is settled then

However for the poeple who wish to understand what we are arguing about, this is a small article that easily defines the importance of DCR and the role it plays in a motor.

It is "Lehman" enough for most to understand, even an "internet quarterback like myself"

http://www.kennedysdynotune.com/Dyna...ion%20Tech.htm