Scooby, do you think there could be any advantage in advancing or retarding one of the cams in a stock motor?

 

JEFFROE, i'd try both cams. i don't know what size turbo you're going to use and how you want your DS setup. i'd try the stock cams, then try retarding the intake cam 1 tooth, then try the web cams. you'll have to decide which setup you like better, based on lowend power and upper RPM power. maybe someone will test the web cams w/turbo and give their opinion soon.

mystereid, there might be a slight improvement in upper RPM power if you retard the stock intake cam one tooth, but you also lose a little on the bottom.

 

ScoobyDFW, I've found out the same thing you have about stock cams. It just seem like I loose too much on the bottom end with big cams. If I want more power, I just crank the wastgate down. I almost like a stock cam better. How much boost are you running and what is your static compression?

 

Scooby, I think advancing the intake 1 tooth would increase overlap and loose low end. Retarding it should help the low end.?? How many teeth do these cam gears have? how many degrees are we talking from one tooth?

 

Doctorturbo, I run 8:1 static compression. Boost can be set anywhere. I run 17-20psi normally on methanol, can go up to 25-30psi, but clutch and head sealing become tricky, and +8 swingarm becomes too short.

mystereid, The gears are 17 teeth at crank and 34 teeth at cams. I think when you rotate a cam one tooth it is 21.2 crankshaft degrees (360/17).

The stock timing is roughly (with stock head gasket):
I. Duration = 242
E. Duration = 242
Lobe Center= 105
Advance = 1

CAM TIMING (Calculated):
I. Open 17 BTDC
I. Close 45 ABDC
E. Open 47 BBDC
E. Close 15 ATDC
Overlap 32 degrees

PERCENT OF STATIC COMPRESSION (Calculated):
% Compression= 85.36%

ENTER STATIC COMPRESSION:
S. Compression = 9.70 to 1

DYNAMIC COMPRESSION (Calculated):
D. Compression= 8.279 to 1

ESTIMATED CRANKING PRESSURE
ENTER DATA
Atmosphere pressure = 29.9 "HG
Cylinder Leakdown = 2 %

CALCULATED PRESSURE Result:
Cranking Pressure = 212.7 psi

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With the intake cam retarded one tooth (stock head gasket):
I. Duration = 242
E. Duration = 242
Lobe Center= 115.5
Advance = -9.5

CAM TIMING (Calculated):
I. Open -4 BTDC
I. Close 66 ABDC
E. Open 47 BBDC
E. Close 15 ATDC
Overlap 11 degrees

PERCENT OF STATIC COMPRESSION (Calculated):
% Compression= 70.34%

ENTER STATIC COMPRESSION:
S. Compression = 9.70 to 1

DYNAMIC COMPRESSION (Calculated):
D. Compression= 6.823 to 1

ESTIMATED CRANKING PRESSURE
ENTER DATA
Atmosphere pressure = 29.9 "HG
Cylinder Leakdown = 2 %

CALCULATED PRESSURE Result:
Cranking Pressure = 170.0 psi


From what I've read, every 10 degrees of duration (5 degrees added at both ends of each cam) moves powerband up 500RPM (more overlap). Retarding both cams 4 degrees move powerband up 200RPM.

Since we are only changing the intake cam, I'm not 100% sure. But when I tested advancing the intake cam 1 tooth, the lowend was great but the topend fell off quickly. The opposite was true when I retarded the intake cam 1 tooth. You can see from the above that the cranking pressure (lowend) was down when retarding the intake cam 1 tooth. See below for advancing the intake cam 1 tooth - cranking pressure is up (more lowend).


With the intake cam advanced one tooth (stock head gasket):
I. Duration = 242
E. Duration = 242
Lobe Center= 94.5
Advance = 11.5

CAM TIMING (Calculated):
I. Open 38 BTDC
I. Close 24 ABDC
E. Open 47 BBDC
E. Close 15 ATDC
Overlap 53 degrees

PERCENT OF STATIC COMPRESSION (Calculated):
% Compression= 95.68%

ENTER STATIC COMPRESSION:
S. Compression = 9.70 to 1

DYNAMIC COMPRESSION (Calculated):
D. Compression= 9.281 to 1

ESTIMATED CRANKING PRESSURE
ENTER DATA
Atmosphere pressure = 29.9 "HG
Cylinder Leakdown = 2 %

CALCULATED PRESSURE Result:
Cranking Pressure = 242.0 psi

The Excel spreadsheet is availble here: http://users.rcn.com/alokaeng/swfiles/dcomp.xls