Insufficient PTV, now what?
It probably is 61cc. The porting TSP/PRC did likely opened up the chamber a bit, so the milling got it back down to 61cc. Normally, a 5.3L head starts off at 61cc, so cutting off .017" would have made it about 58cc.
It seems like the cam was meant for smaller engines and making max torque, like maybe in a truck application, hence the early IVC. Just retarding the cam 4 degrees would still be conservative enough to maintain very good low end power and extend the RPM range a bit too.
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Speedtigger and KCS, you guys are making alot of sense, thank you very much for your input and everybody else who has commented. It does seem odd that this cam is so advanced. After reading what other people have done, I think I would be fine with .060" PTV clearance on the intake. If the same change in clearance applies to the exhaust, I would still have .126" on the Exhaust PTV if I retard 4 degrees.
Another advantage of retarding 4 degrees is I would decrease the dynamic compression slightly. I am afraid that I might be prone to detonation with the current cam phasing.
Another advantage of retarding 4 degrees is I would decrease the dynamic compression slightly. I am afraid that I might be prone to detonation with the current cam phasing.
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The general cam spec page actually lists this cam as 4.8 -5.7. The next set of cams says all out power for 5.7-6.2. I like my cam choice Gagliano so I have decided to retard it 4 degrees and see where I am with PTV. I ordered a Cloyes 9 way adjustable timing set form Texas Speed and will try again this weekend. I like the way you are thinking KCS.
I have done some dynamic pressure calculations, and my dynamic compression will go from 8.908 with the cam in its current 5 degrees advanced position to 8.625 if I retard the cam 4 degrees for a net 1 degree advance. I think dynamic compression of 8.625 on an LS-1 should be pretty safe on 93 octane.
I would retard it. A 223 intake duration at 107 IVC is too damn early. And your DCR of 9:1 is going to take a very careful tune on 93.
Retarding it and thus lowering the DCR, will give you more clearance, provide more overall power, and make it safer on 93. All pluses.
Retarding it and thus lowering the DCR, will give you more clearance, provide more overall power, and make it safer on 93. All pluses.
Good news, I installed my new Cloyes adjustable timing set at 4 degrees retarded, and I now have a minimum of 0.070" PTV clearance at 10 degrees ATDC. I checked every degree between 5-15 ATDC and 0.070" was the least. Texas Speed and others had said 0.060" on the intake is good, so I am above that. On the exhaust side, my minimum was 0.112" 10 degrees BTDC, so I lost a little there, but I am comfortable with that number. I was actually surprised how much just 4 degrees makes.
I measured my new Intake Valve Centerline at 110 degrees, so that made sense since I am probably +/- 1 degree off.
Thank you so much to all of you that commented and provided advice. It was very helpful and now I feel like I have a much better understanding of this engine.
I measured my new Intake Valve Centerline at 110 degrees, so that made sense since I am probably +/- 1 degree off.
Thank you so much to all of you that commented and provided advice. It was very helpful and now I feel like I have a much better understanding of this engine.
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