Ok tell me if my calculations are correct, I was trying to figure the DCR on the stock LS2 cam from the spreed sheet posted earlier, and being that there is no 204 on the chart I did some simple math and with a 0 advance on the timing on the stock cam with a 116lsa I came up with 8.72 DCR for the stock cam and motor, is that correct???

The cam that I am considering is at 8.51 DCR and thats with + 4 degrees ground in, I assume that is such a small difference that it would not be noticeable at idle through 3k rpm.

At what point do you begin to notice a drop in DCR?

 

I think you'd be very close on the stock DCR from what I was able to calculate with the closest available Comp lobes, which produced an 8.5. The stocker, having even less duration than the smallest cam on there, will deliver a higher DCR.

I believe the conventional wisdom is that you want to be as close to 8.5, but that down to 8.0 is fine. Most of the cams I looked at, even the "big" 230 ish ones, will give you 8+ as long as you eep the LSA tight. You pay in drivability, of course (referring to the 230s ones). Charlie Tuner indicates he has no problem getting the G5X1 to run near stock if the 114 LSA is selected. But that's about the limit, it seems.

 

DCR is strictly a function of the Intake Closing Angle. The later the intake closes, the lower the DCR. Advancing a given cam will increase the DCR. As a rule, longer duration cams will lower the DCR as they make the intake close later.

I made up a fairly elaborate MS Excel spreadsheet which among other things calculates the DCR but you have to know the bore, stroke, piston dome/dish volume, deck clearance, compression height (position of the wrist pin in the piston), head gasket thickness, rod length, cylinder head combustion chamber volume, and the camshaft information (intake closing in particular). I would upload it but I'm not sure how!

Dave

 

Yeah I have already used it, someone posted it yesterday and I was able to play around with it to figure out what the stock DCR is and what different cams would do to DCR.

I want a cam that still feels like the stock cam at idle and in low end power. I plan is to eventually go with a S/C so I want a cam that will work well with procharger, and still maintain stock like driveability. Here is what I have come up with using the DCR spread sheet.

218/226 .565 .572 116 LSA + 4 advance

From my calculations this will make great power down low with the 4 degree advance, the high LSA for good idle and won't bleed off under boost, and the intake duration is low enough not to effect the DCR too much over the stock cam. Most tuners I have spoken with recomend atleast 6-8 more degrees on the exhaust and the exhaust doesn't effect the DCR. I know that with the 4 degrees I will lose some up top but I am much more concerned about driveability. I plan to make 650rwhp with a conservative tune anyways and I believe I can easily do it with this cam. I have truly become a believer that a bigger cam doesn't mean better, specially on FI.

 

 

Several tuners I have spoken with are consistent in saying they can get a 228/232 114LSA cam to idle and run near stock. Basically, as long as you have 114 LSA, you are fine. The 116 kills your DCR but adds little to idel quality.

These days, it's all in the tune.

 

Here's some data to help you out...

 

"Quick and Dirty Cam/SCR/DCR Calculator Spreadsheet
Modified and Simplified by PianoProdigy - PianoProdigy@gmail.com"
"Values that are green are standard stock LS2 values (if only swapping a cam, leave them alone).
The blue values are calculated and thus, are not editable. Compression values are orange (not editable)."

0.006 0.050 0.200
Intake Duration - ID (first number) 271 218 136
Exhaust Duration - ED (second number) 279 226 143
Lobe Center Angle - LCA (also known as LSA) 116 116 116
Intake Centerline - ICL (LSA - degrees of advance e.g. 114+2 = 112) 112 112 112

Intake Valve opens - IVO 23.5 -3 -44 BTDC (- indicates ATDC)
Intake Valve closes - IVC 67.5 41 0 ABDC
Exhaust Valve Opens - EVO 79.5 53 11.5 BBDC
Exhaust Valve Closes - EVC 19.5 -7 -48.5 ATDC (- indicates BTDC)
Exhaust Centerline - ECL 120 120 120
Overlap 43 -10 -92.5 degrees

Bore 4
ST = Stroke 3.622
RL = Rod Length 6.098
Number of cylinders 8
Deck Height (how much pistons come out of the hole) -0.006
Piston Dome or Dish (- for a dome + for a dish) 0
Compressed Head gasket thickness 0.06
Cylinder Head Chamber Volume 64

Static Compression Ratio 10.93 :1
Dynamic Compresion Ratio 8.51 :1
Rod to Stroke Ratio 1.68 :1
Bore to Stroke Ratio 1.10 :1


On the calculations that I found on this spread sheet shows the DCR at 8.51 with the + 4 advance. Is my chart off? If you are able can you email me your spread sheet to bjpgf@hotmail.com Thanks for your help in posting that info.
I noticed on the stock LS2 sheet it said the LSA was 118.5? I believe it is 116 but I could be wrong.

 

Man I don't know about getting that cam to idle like stock, it's a + 2 overlap and I have never heard any car with a cam like that sound like stock, specially with a 114 lsa. Maybe with a 117.

A good tune does make all the difference, being that I am going SC I want to have the higher LSA to prevent bleed off and for idle quality. I may look at going with a 115 +4 with 218/224, will see.

 

Now THIS is a thread with some great info. Thanks for posting.

 

 

For you that is best indeed. As far as tuning, Charlie (who posted above) is one of the guys promising he can tame that 228/232 114 no problem. Seriously, I know very little about this art, but I think these guys can really fine-tune the VE tables to get these to run.