Speed Pro CS165R L71 Factory Cam Specs to degree the cam

[Thomas N.]

[Richard G.]

Re: Speed Pro CS165R L71 Factory Cam Specs to degree the cam

Possible this will help answer your question?

https://www.lunatipower.com/how-to-degree-a-cam

Rick

[Thomas N.]

Re: Speed Pro CS165R L71 Factory Cam Specs to degree the cam

Rick:
Thanks for the information.
If you look at step 10 on the Lunati degreeing the cam it tells you to compare your readings of degrees at BDTC to what is on the cam card. I'm trying to derive those numbers from the specs I've listed above to see if I am where I should be.

[Joseph S.]

Re: Speed Pro CS165R L71 Factory Cam Specs to degree the cam

Tom, I have a card. Here are the specs @.050 Intake & Exhaust are both .306 Gross Lift at Cam with 242 degrees duration. I can send you a photo if you need it.

Joe

[Duke W.]

Re: Speed Pro CS165R L71 Factory Cam Specs to degree the cam

Hi:
exhaust lobe center 120, intake lobe center 108, and overlap 98.

As ground and installed with a standard timing chain the inlet lobe point of maximum lift (POML) is 108 deg ATDC. I don't know what you mean by "degree the cam", but if you want to verify that the cam is indexed per the spec, determine the crank angle at .180" to .250" lift on both the opening and closing flanks and the POML is halfway in between. Below about .160" the lobe is asymmetrical.

If the inlet/exhaust lobes are within a degree or two of 108 ATDC/120 BTDC it's okay. If you've never done this before suggest you pick at least three lifts to make the measurements and look for consistent results.

Duke

[Thomas N.]

Re: Speed Pro CS165R L71 Factory Cam Specs to degree the cam

Joe/Duke:
Thanks for your inputs.
I was getting hung up on that the lobe center equates to POML.
I was expecting to see something like inlet@108 degrees ATDC, and exhaust @120 degrees BTDC.
I'm trying to verify that the cam is what it should be, and checking valve to piston clearances also while I'm at it.

[Duke W.]

Re: Speed Pro CS165R L71 Factory Cam Specs to degree the cam

I use the term POML because most lobes are asymmetrical (Duntov cam is the one OE exception I know of as its lobes are symmetrical). The closing event is more gentle than the opening event to keep the valve from bouncing off the seat at high revs, so the actual "centerline" of the lobe is not coincident with POML.

A useful formula to know is (IPOML + EPOML)/2 = LSA

I've never quite figured out what "straight up" means. Cams are designed/manufactured with specific IPOML/EPOML/LSA like 108/120/114 for the L-72/71 cam. The L-46/82 cam is 114/114/114 ground as designed. I think this means "straight up", and hot rod slang would describe the L-72/71 as having 6 degrees of advance "ground in". I'm an engineer, so I use actual data (numbers) not vague slang expressions to specify important characteristics.

About ten year ago when I was designing a couple of custom SB cams I visited a small cam grinding shop that was fairly local to me to investigate having them manufacture the cam. We discussed both available lobe masters he had and making a master to my specs. When I asked about indexing he said he couldn't tell me how the finished cam would be indexed... I would have to "degree it in". I thanked him for his time, and left the shop shaking my head in amazement wondering how they had stayed in business so long.

Duke