LS2 LQ4 PTV clearance question
Thread Starter
Cruising
Joined: Aug 2020
Posts: 12
Likes: 0
From: Hamilton, ON Canada
LS2 LQ4 PTV clearance question
I need some help, I am putting a set of 862 heads milled down 0.015 to 58.85cc on my Lq4 block so with stock dished pistons I expect about 10.7:1 compression ratio. I would like to put a Comp cam 54-459-11 (231/239 with .617 lift), 113 LSA) in but I see some others online that suggest aggressive cams like this may not be installed without replacing pistons due to no valve relief? How do I calculate the valve clearance to ensure the stock dished pistons will be ok?
Pro
Joined: Jul 2004
Posts: 713
Likes: 61
From: Waterford CT
Valva clearance
Rather than try to calculate clearance, measure it using the stock cam, before you spend money on a new cam.
1. Place a wad of modeling clay (available at Walmart) on one piston.
2. Oil the face of the valves so they won't stick to the clay.
3. Bolt the head down with two bolts at the test piston, using no gasket.
4. Turn the motor over by hand.
5. Take the head off and measure the thickness of the clay that was squeezed by the valves.
Now you know how much additional lift you can tolerate. The lack of a gasket provides some margin for error. This will tell you if there any chance that what you have now will work with your cam choice, or you have to change pistons, or pick another cam.
1. Place a wad of modeling clay (available at Walmart) on one piston.
2. Oil the face of the valves so they won't stick to the clay.
3. Bolt the head down with two bolts at the test piston, using no gasket.
4. Turn the motor over by hand.
5. Take the head off and measure the thickness of the clay that was squeezed by the valves.
Now you know how much additional lift you can tolerate. The lack of a gasket provides some margin for error. This will tell you if there any chance that what you have now will work with your cam choice, or you have to change pistons, or pick another cam.
