How to Guide: Degreeing Cams on 6G72 w/ Pictures

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Originally Posted by J. Fast

I think you and McCoy are saying the same thing Grasso. If you set to 110 centerlines you will not have the same valve timing as if you set your cams to stock centerlines and then adjusted the valve timing to +1, -3. You both are reitierating that MFR and OEM specified centerlines may not always be were you want peak power output. We're free to change the centerlines as a matter of preference and performance.

You did make a valid point regarding what works for one may not work for all. If I recall Chris is also not running a traditional I to E lift ratio so his results are also going to be skewed from the norm. Each setup is unique.

When it comes down to it you really cant make any blanket statements about what cam timing is ideal becase the real intention of the adjustment is to control the air to fuel ratio. That all changes when you increase or decrease temperature, humidity, and barometric pressure.

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You talking about me? If so, how's that?

-Chris

Exactly!
If I fell ambitious one day I'll check as my motor is still out of the car.

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Originally Posted by Ninja Performance

So Bob,
You used the Adjustable cam gears set at 0 to degree the cams and find out how "off" they were either due to the manufacturer or the mill on the heads etc? Then added that difference to the adjustable gears?

If so, I am still wondering if the gears are perfect, if they are not 0 when set to 0, then I wonder how "off" the cams would have been if you used OE cam gears to find where they needed to be set.

Not that it would matter.
Just would be interesting to know.

-Chris

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Originally Posted by Italo Grasso

I guess I missunderstood, i see your cam gears adjustments but that really doesn't tell me much in terms of in/ex CL only tells me you had to compensate for given head/block decking and cam grinding offsets....What i'm saying is the stock CL's for our cars is 109.5 in/106.5ex so that is zero, if you put them at 110 they are further seperated then stock and lastly if you put them at +1, -3 then they should be 107.5 in/100.5 ex. For some reason no one is willing to confirm these numbers which is odd to me...

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Not sure if this upload will work but here's a cam algorythm I came up with. You can enter in the durations for your exhaust and intake cams and the advance or retard (retard will be negative advance) and it will spit out your overlap. You can also make adjustments to the cam timing and it will give you the revised centerlines :)

Attachment 4855

For clarification the lobe separation angle for the stock cam profile is 108 degrees. The stock intake cam has a duration of 251, the stock exhaust cam has a duration of 247. There's 1.5 degrees of advance on the stock duration.

When you enter in those values into my calculator with a lobe separation angle of 108 the resultants are:

Intake lobe center 106.5
Exhaust lobe center 109.5
Degrees overlap 33

There's your confirmation.

You can use the calculator to find the new lobe centers. Just enter in your gear adjusted advance numbers in the lower red tables.

I pulled the data for the stock cam profiles from here: Stealth 316 - 6G72 DOHC-Turbo Head Info

Quote:

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Originally Posted by J. Fast

Not sure if this upload will work but here's a cam algorythm I came up with. You can enter in the durations for your exhaust and intake cams and the advance or retard (retard will be negative advance) and it will spit out your overlap. You can also make adjustments to the cam timing and it will give you the revised centerlines :)

Attachment 4855

For clarification the lobe separation angle for the stock cam profile is 108 degrees. The stock intake cam has a duration of 251, the stock exhaust cam has a duration of 247. There's 1.5 degrees of advance on the stock duration.

When you enter in those values into my calculator with a lobe separation angle of 108 the resultants are:

Intake lobe center 106.5
Exhaust lobe center 109.5
Degrees overlap 33

There's your confirmation.

You can use the calculator to find the new lobe centers. Just enter in your gear adjusted advance numbers in the lower red tables.

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Hey J-fast.. Think your intake and exhaust lobe centers are switched...

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Originally Posted by Italo Grasso

Hey J-fast.. Think your intake and exhaust lobe centers are switched...

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Good catch... I enterd in 1.5 advance... Should have entered -1.5

Looks like this when you make the adjustment in the calculator

Specifications:
Intake duration 251
Exhaust duration 247
Lobe separation 108
Advance -1.5

Calculations:
Intake open BTC 16
Intake close ABC 55
Exhaust open BBC 50
Exhaust close ATC 17
Intake center 109.5
Exhaust center 106.5


Thanks for catching that for me!

When you play with intake cam timing, couldn't that affect your ignition and/or injector timing as well, since the ecu is using the cam sensor (and crank) for ignition/injector timing...maybe it would just affect the 1st gens with cam/crank in one? I'm not an expert by any means, just thought it could be fudging with other things.

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Originally Posted by familyMAN

When you play with intake cam timing, couldn't that affect your ignition and/or injector timing as well, since the ecu is using the cam sensor (and crank) for ignition/injector timing...maybe it would just affect the 1st gens with cam/crank in one? I'm not an expert by any means, just thought it could be fudging with other things.

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Inconsequential on a 1st gen, the CAS is adjustable, you would simply set the ignition timing to spec and be done... With 2nd gen style, the ignition is triggered from the crank sensor position. As long as you don't send the CMP out of phase enough to screw up the cylinder ID, (like a tooth or more when it starts dropping coils) the only consequence could be a small variation in injector timing, which is not a big deal at all...

I have to say, it's extremely refreshing to see intelligent discourse regarding fundamental engine parameters on a 3/S forum. It's not usually the norm. I need to start threads more often. Thanks everyone for the contributions.

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Originally Posted by Italo Grasso

Take a look at the BC Cam Card, the note states set to "0" and then tune from there for best result, well 0 is 109.5 in/106.5 ex for us....BC could have reccomended 1XX in/ex but that wouldn't be zero (0) on our cars...Just to clear up any confusion here is the math from the BC Cam card to show the BC cam "0" is the same as our cars ((180+7+31)/2)=109 CL intake ; ((180+1+33)/2)=107 CL ex...

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Is this why, when I asked 3SX how I was going to degree my 264/272 cams that I bought from them if they don't supply a cam card. They said just degree them as Stock?
Jeff:coo3l: