1SLwLS1

iTrader: (6)

I have been on a learning frenzy these past couple of days just thinking about the dynamics of the LS1.

So what makes more torque/power? I am guessing it is a combination of increasing DCR and VE. From what I can tell SCR is useless in these terms, other than some calculators use SCR when some fields are omitted.

I have used this DCR calculator and the VE text calculator posted up on this website and get different numbers.

So, to confirm what I wanting to compare...

Stock Cam 01-02(0.006 calcs referenced from here assuming same ramp rates)
............................ 0.006 0.050
Intake Duration......... 282 197
Exhaust Duration....... 286 207
Lobe Sep Angle......... 116 116
Intake Center Line..... 116 116
IVC (ID/2 + LSA)-180.. 77

MS4 Cam
............................ 0.006 0.050
Intake Duration......... 289 239
Exhaust Duration....... 291 242
Lobe Sep Angle......... 111 111
Intake Center Line..... 110 110 (With 1 degree advance ground in - installed straight up)
IVC (ID/2+LSA)-180-1.. 74.5(From 1 degree advance ground in)

241 Head CC 66.67cc
799 Head CC 64.45cc
Stock Bore 3.898"
Stock Stroke 3.622"
Stock Rod Length 6.098"
MLS Crushed 0.054" or 0.052" - depending on who you ask
Deck Clearance -0.006"(Negative for distance protruding from deck)
Gasket Bore 3.910"
Stock Piston Head Volume 0.000"

From the DCR website, I get...

Stock(with stock MLS gaskets) SCR 10.309:1
Stock(with stock MLS gaskets) DCR 7.371:1

Current setup changes, MS4 cam, 799 heads(64.45cc), stock MLS gaskets

Now SCR 10.590:1
Now DCR 7.752:1

From the Quick and Dirty

Stock(with stock MLS gaskets) SCR 10.171:1
Stock(with stock MLS gaskets) DCR 7.278:1

Current Setup

Now SCR 10.443:1
Now DCR 7.648:1

The difference b/w Stock SCR and DCR is 2.938:1 and with current setup 2.838:1 which is due to the IVC 2.5 degrees sooner, from DCR website calculations.

Now my power increased to ~420rwhp and ~390rwtq with a slipping clutch. I do not have a stock VE to compare to. I have done some searching, but it is mostly talking about volumetric efficiency and not stock volumetric efficiency at random RPM levels. I will calculate mine this weekend and post up data to confirm my calculations. If I would have to guess, stock VE is in the range of 75%. I have no clue what mine is now, but will calculate using MAF reading, IAT readings, and RPMs at various ranges through WOT.

Now to modify my current setup, find a head, something like a PRC 215, to increase VE, maybe, that would keep stock valving locations, due to low P2V clearances, and have a CC of 58cc and advance the timing 2 degrees to give me a IVC of 72.5, which, according to the website DCR calculator, would yield a SCR of 11.507:1, DCR of 8.557:1 and Quick and Dirty of SCR of 11.331:1, DCR 8.432:1.

Does all of this sound somewhat accurate, will I have problems with advancing the cam and and the intake valve opening too soon in the exhaust stroke?

Thoughts, comments, suggestions, corrections?

1SLwLS1

iTrader: (6)

no one?

1 FMF

iTrader: (1)

have you read these?
http://www.empirenet.com/pkelley2/DynamicCR.html
http://www.epi-eng.com/piston_engine..._yardstick.htm

DCR is just SCR and it is can be meaningless and oftentimes is taken out of context or used to draw incorrect conclusions.

SCR = [volume when piston @ BDC] / [ volume when piston @ TDC ]
DCR is the same deal as SCR except you don't use volume when piston @ BDC, instead you use volume when the intake valve closes... either at 0.050, at 0.006, or completely closed. The rationale here is because the intake valve is open on the upstroke, which can be anywhere from 10 degrees to 40 degrees of crankshaft rotation, you lose cylinder pressure because it is expelled back through the intake as the piston moves upward. That being said, DCR is always less than SCR and DCR is nothing more than a mathematical attempt to quantify... something. You cannot conclude that higher or lower DCR makes more or less torque/power because DCR has no correlation to cylinder pressure- it's cylinder pressure which makes torque, and it's torque at whatever rpm is your power. At low rpms you want a smaller intake duration cam because you will lose cylinder pressure through an open intake valve on the upstroke, which means higher DCR. However at high rpms, the cylinder will keep filling even though the piston is on the upstroke and the intake valve is open because the air/fuel charge has kinetic energy and it overcomes the force resulting from the piston on the upstroke to a certain point, which is why the intake valve closing point is the most important value of the cam, so in this case you may have a much lower DCR but because of rpm's you will have higher cylinder pressure resulting in more torque/power. That is the fundamental part, now you add in valve overlap- when the intake valve opens before the piston has reached TDC on the exhaust stroke- which basically helps airflow into and out of the cylinder. Because the intake valve opens before piston at TDC on the exhaust stroke, does exhaust get pushed up into the intake? Does the intake charge if it's coming in go right out the still open exhaust valve? How long does the exhaust valve stay open on the downward intake stroke? All these variables affect the BMEP for that resulting compression and power stroke, and is what influences the magnitude and shape of the curve when you plot torque vs rpm.

This is not dynamics of just the LS1, it's for every internal combustion engine that has a piston and valves. And once you square away the cam specs, then you factor in your intake and exhaust setup and how well or how bad they flow which will either help or hurt. The basic idea there is velocity is more important than volume, which is why you don't just go buy the intake with the largest plenum and intake runners and look for the biggest exhaust headers thinking they will flow the most air and make the most "cylinder pressure".

1SLwLS1

iTrader: (6)

I have read the link including the DCR before, but not the BMEP link. To maximize BMEP, a middle ground must be determined between flow and velocity.

For example, an engine that has intake/heads/exhaust flow rates greater than needed, compromises intake and exhaust velocity, due to the fact that the larger port sizes will have a slower velocity to move the same amount of air compared to smaller ports.

Velocity is directly related to momentum via mass, and inertia is the resistance to change of said momentum. So, if velocity is high, inertia will be greater, and therefor force more air into the engine. If there is more air into the engine, the cylinder pressure will increase and create a large BMEP, correct?