By my calculations, the stock DCR of the '05+ LS2 motors is 8.62:1. This is very high, considering the LS1/LS6 motors all were around 8.25:1, give or take.

1) Can someone please confirm the DCR of the LS2?

2) How the heck can it run so high of a DCR from the factory - traditional "assumptions" were that anything over 8.5:1 and good gas was a must. (Unless you really had your system setup optimized; ie, proper quench, etc.... Which the stock setup falls shy of doing so)

3) What's the highest DCR someone here has successfully run on an LS2 on 92+ non-oxygenated pump gas with NO KR?

4) Would you judge that a DCR of ~8.8:1 on an LS2 to be safe with 92+ octane (tuned)? Thinking of a 212/218 cam on a 114 or 116 LSA with ~+2 or +4 degrees advance, *and* also tightening up the quench with a thinner HG.... Leaving the heads unmilled (otherwise DCR goes thru the roof 9+ if milled heads and a thinner HG)....

5) Assuming that AFR 205 heads are thrown onto the motor with the cam... With AFR's improved runner design and combustion chamber shape, how much more DCR can the AFR heads tolerate OVER the stock 243 heads? (I am in a discussion with Tony M about this, but also curious to hear others' thoughts...)

6) Generally speaking, would it be better to run a higher DCR and less timing advance, or a more moderate DCR and increase timing?


My ultimate goal would be to run the 212/218 cam on a 116 LSA +4 degrees advance, milled AFR205 heads .012" for 64cc chambers, and a .045" HG thickness.... But the DCR for this is a whopping 9.00:1. Not sure I can even think of approaching this with pump 92+ (normally 99% of the time its 93) octane.

This would be on my Trailblazer-SS (4600# weight), stock stall converter of 2100rpm, shift points at 1-2 6500rpm, 2-3 and 3-4 at 6400rpm. Looking for incredibly stocklike idle, better low-end torque, but a cam that doesn't wheeze out of power on the top-end. Stock intake and exhaust manifolds w/ stock cats. Stealth H/C setup, sort-of.


Thoughts and opinions?!

TIA!

 

Your info is incorrect. Stock LS1 '97-00: stock DCR is 6.97:1.

Need to run the numbers on the LS2, but I'm sure that it's more in the mid 7s for DCR. What figures are you using? You have to use the duration at .006" and not the duration at .050" to compute DCR.

 

Welp, I suppose I better post my calcs... I have tried this on The "VE Calculator" and the "DCR Calculator" programs found from links on here. Where are they (my calcs) incorrect?


LS2 Cam (at .050"): 204/211 .525" 116 LSA
LS2 Cam (at .006"): 259/266 116LSA

.006 Specs:
-----------
LSA: 116
ICL: 116
IVO: 13.5
IVC: 65.5
EVO: 69
EVC: 17
ECL: 116
Overlap: 30.5

Bore: 4.00"
Stroke: 3.622
Rod Length: 6.098
Deck Ht: -0.006 (out of hole)
Piston Dish: 0
Compressed HG Thickness: 0.060"
Cylinder Head Volume: 64.5 cc's

Static Compression Ratio: 10.86 (rounded 10.9, exactly what GM Advertises)
Dynamic Compression Ratio: 8.60

And by using the same calcs above (and adjusting for the LS1/6's 3.90 bore, head volume, and cam specs), I've come up with DCRs for ALL LS1's / LS6's to be anywhere from 8.21 up to 8.36. All also came up with the proper SCR for each as well.

Where do I have it so far off to affect the DCR that much?? I'm not even CLOSE to calc'ing a stock DCR in the ~7 range, for any config...

 

For comparison, here's my calcs for the '97-00 LS1:

(Using JRP's camdoctor data)
LS1 Cam (at .050"): 199/209 .525" 119 LSA
LS1 Cam (at .006"): 253/263 119 LSA

.006 Specs:
-----------
LSA: 119
ICL: 119
IVO: 7.5
IVC: 65.5
EVO: 70.5
EVC: 12.5
ECL: 119
Overlap: 20

Bore: 3.90"
Stroke: 3.622
Rod Length: 6.098
Deck Ht: -0.006 (out of hole)
Piston Dish: 0
Compressed HG Thickness: 0.054"
Cylinder Head Volume: 66.67 cc's

Static Compression Ratio: 10.2
Dynamic Compression Ratio: 8.15


Now, my numbers came out slightly different this time, mainly because I neglected to lookup the proper HG thickness & make the proper adjustment to the VE Calculator program to include the overbore volume on the HG. But, those *slight* adjustments will only change the DCR *maybe* .15, max...

Where am I screwing up??

 

Your duration at .006 is way to fast.

Here's the stock '98-00 F-body cam:
................................ 0.006 0.050 0.200
Intake Duration - ID 284 199 113 Stock Cam intake
Exhaust Duration - ED 289 210 118 Stock Cam exhaust
Lobe Center Angle - LSA 119.5 119.5 119.5
Intake Centerline - ICL 119 119 119

Intake Valve opens - IVO 23 -19.5 -62.5 BTDC (- indicates ATDC)
Intake Valve closes - IVC 81 38.5 -4.5 ABDC
Exhaust Valve Opens - EVO 84.5 45 -1 BBDC
Exhaust Valve Closes - EVC 24.5 -15 -61 ATDC (- indicates BTDC)
Exhaust Centerline - ECL 120 120 120
Overlap........................ 47.5 -34.5 -123.5 degrees

Here's the '02 Z06 cam:
02 Z06 cam.................. 0.006 0.050 0.200
Intake Duration - ID 270 204 166.6
Exhaust Duration - ED 275 218 178
Lobe Center Angle - LSA 117 117 117
Intake Centerline - ICL 117.4 118.9 118

Intake Valve opens - IVO 17.6 -16.9 -34.7 BTDC
Intake Valve closes - IVC 72.4 40.9 21.3 ABDC
Exhaust Valve Opens - EVO 74.1 44.1 25 BBDC
Exhaust Valve Closes - EVC 20.9 -6.1 -27 ATDC
Exhaust Centerline - ECL 116.6 115.1 116
Overlap......................... 38.5 -23 -61.7 degrees

 

Cool - thank you. It still puts the LS2 around a 8.0-8.1 DCR, but still better than what I was originally calculating!

That answers questions 1 and 2....

Now, whom can help with Questions 3, 4, 5, and 6?

 

how about a ls6?

 

'02+ LS6 Cam... Stock DCR is 7.90:1

Q's 3,4,5, and 6 anyone?

 

Top for the night... Surely there's some folk out there "in the know" that can help...!