No PTV clearance on LQ4?
03-06-2014, 07:35 AM
#41
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I'm using stock 317 heads. I was toying with the idea of putting my stock 241 heads on it (not 243 ls6) because it'd bump the compression w/ same size valves but they all said to stick with the 317's cuz the air flow is more important than compression.
Called Comp 3 times and basically they only said I must have something wrong cuz there shouldn't be any PTVC problems blah blah blah....... well its hard to ignore numbers
Anyway, we'll see I guess
Called Comp 3 times and basically they only said I must have something wrong cuz there shouldn't be any PTVC problems blah blah blah....... well its hard to ignore numbers
Anyway, we'll see I guess
03-06-2014, 08:57 AM
#42
I was advised by Martin@Tick to still check PTV on my custom cam with a LQ4 motor.
Why? Although the pistons are dished and with the larger chamber heads DO have lower compression...the DISH itself does not extend all the way across the top of the piston.
Radial clearance is the issue here. you have plenty directly under the valve because of the dish...it's the edges of the valve that are coming too close...
FWIW my combo MAY end up being TEA CNC 241's and a martin cam on a LQ4 shortblock. I don't ANTICIPATE any PTV issues but you can be damn sure i'll be checking to be safe.
Why? Although the pistons are dished and with the larger chamber heads DO have lower compression...the DISH itself does not extend all the way across the top of the piston.
Radial clearance is the issue here. you have plenty directly under the valve because of the dish...it's the edges of the valve that are coming too close...
FWIW my combo MAY end up being TEA CNC 241's and a martin cam on a LQ4 shortblock. I don't ANTICIPATE any PTV issues but you can be damn sure i'll be checking to be safe.
03-06-2014, 10:17 AM
#43
TECH Apprentice
Remember when checking valve to piston depending on the stroke and rod length Min. clearance on the IN takes place 9 Degrees ATDC and 9 Degrees BTDC on the EX. When you check VTP Loaded meaning with the springs you are going to run and Unloaded meaning test or light spring depending on the set up stiffness of your valve train your measurements can very as much as .025 to .045 so on the IN you could have .01 with checking springs and .045 with the springs you are going to run. On a cam like this with 1.7 RR every one crank degree the valve is moving around .006 so going from 108 to 110 will give about .012 more VTP. If the stroke is 3.622 the piston will be down .029 at 9 degrees. I thought this may help.
