Piston Valve Reliefs
- Thread starter LxVert
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stangster50
New Member
i have gt-40x heads which have 1.94's and had to cut bigger reliefs to clear.... it hit outer edge... depends on heads too/cam...
I'm also running 1.94s but with a .542 lift on stock pistons with no problems. It has a lot to do with the heads themselves and the orientation of the valves in relationship to the reliefs, also the lift and duration.
StinkinLincoln
Member
fords2fast4u
Founding Member
well, in order to know what's the max size valve you can run on a given piston, you'd have to know a lot more than the size of the valve reliefs... and even then, it still has to be checked to make sure.
By that I mean that if you're trying to figure out a way to determine how big of valves you can run on a given/existing piston, you're just going to have to go off other people's combo's to know of a ball park estimate. Things like cam profile (lift, duration, advance/retard, and lobe seperation all play in here), head gasket thickness, chamber size/milling, distance in and out of the hole the piston comes, and how hot you're going to run it (power adder/ N/A). Basically, no, there is no formula. Only a few rules of thumb to guide you.
First, from the start, max lift on a stock block and heads is "around" .544"
If you have aftermarket pistons, and they're any good, they'll "fit" a 2.02 intake valve np, with respect to valve diameter... depth into the relief that the valve will clear is then up to the lift and zero deck/in/or out of the hole the piston travels. (as you can see by the guys already posted, stock pistons don't clear a bigger valve with much lift, the reliefs just aren't big enough and you have to cut them)
Twisted Wedge head's valves are in a different position than most and usually require special pistons, so if you're thinking TW heads, consider that.
You need about .080" clearance on the intake valve and .10" on the exhaust, which can only really be checked by claying it, which i do without a head gasket, just to make sure... and on the engines i've built its been really close most of the time, but with the head gasket thickness, there's np.
Anytime you build, always check it before you bolt it together! Nothing like missed tolerances in the longblock...
I hope that helped
By that I mean that if you're trying to figure out a way to determine how big of valves you can run on a given/existing piston, you're just going to have to go off other people's combo's to know of a ball park estimate. Things like cam profile (lift, duration, advance/retard, and lobe seperation all play in here), head gasket thickness, chamber size/milling, distance in and out of the hole the piston comes, and how hot you're going to run it (power adder/ N/A). Basically, no, there is no formula. Only a few rules of thumb to guide you.
First, from the start, max lift on a stock block and heads is "around" .544"
If you have aftermarket pistons, and they're any good, they'll "fit" a 2.02 intake valve np, with respect to valve diameter... depth into the relief that the valve will clear is then up to the lift and zero deck/in/or out of the hole the piston travels. (as you can see by the guys already posted, stock pistons don't clear a bigger valve with much lift, the reliefs just aren't big enough and you have to cut them)
Twisted Wedge head's valves are in a different position than most and usually require special pistons, so if you're thinking TW heads, consider that.
You need about .080" clearance on the intake valve and .10" on the exhaust, which can only really be checked by claying it, which i do without a head gasket, just to make sure... and on the engines i've built its been really close most of the time, but with the head gasket thickness, there's np.
Anytime you build, always check it before you bolt it together! Nothing like missed tolerances in the longblock...
I hope that helped
Lets not forget that max lift occurs when the piston is on its way down the cylinder...the bigger issue here is duration. Theoretically you could grind a cam with .800 lift if you had a super short duration....it wouldn't make any sense but it would be possible to run a retarded amount of lift on stock valve reliefs if the duration allowed it to work..
Block is just a simple stock 302 just cleaned up .030
Piston Specs:
Bore (in): 4.030 in.
Bore (mm): 102.362mm
Piston Style: Flat top, with four valve reliefs
Piston Material: Hypereutectic aluminum
Compression Distance (in): 1.605 in.
Piston Head Volume (cc): +8.00cc
Wrist Pin Style: Press-fit
Pin Diameter (in): 0.912 in.
Piston Ring Thickness: 5/64 in. x 5/64 in. x 3/16 in.
Cam Specs:
Intake Duration at 050 inch Lift: 221
Exhaust Duration at 050 inch Lift: 225
Duration at 050 inch Lift: 221 int./225 exh.
Advertised Intake Duration: 275
Advertised Exhaust Duration: 279
Advertised Duration: 275 int./279 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.499 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.510 in.
Valve Lift with Factory Rocker Arm Ratio: 0.499 int./0.510 exh. lift
Lobe Separation (degrees): 112
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash: 0.000 in.
The reason i'm asking this is because i'm trying to figure out what heads to go with. With the pistons being aftermarket I didn't know if they would already have larger reliefs. For cylinder heads i'm torn between TrickFlow Twisted Wedges, 185 AFR's, or Tri-States.....
ls1beater4eva
New Member
i had to just barely clean up the very edge of the valve relife on the stock pistons on a friends car when he put alum heads on, what brand piston are you running?
strtrcr50
New Member
Trick Flow said:
Trick Flow has moved the valves and they are 2.02/1.6, but you can run stock pistons within reason. According to Fox Lake, you can run a tfs stage 2 cam on stock pistons with no modifications.
Fox Lake said:
ls1beater4eva
New Member
well im sure your speed pros cant be that different from the ones i had in my old 306 about a year ago , i run another set of these tristate heads i have forsale on them they had the same valve size just smaller intake runners they were 190's
There is a bit of missleading information going on in this thread.
Lift and duration are part of the equation but only to the extent that in a OTS cam they can typically be related to ramp rates. The important part is the valve events as the cam is installed in YOUR engine (intake open, exhaust close) and the ramp rates. None of the specs you listed give that information. Even at that the ramp rates are never listed with cam specs so you can only guess what the lift at TDC will be.
I have a motor here with a custom cam that is very mild, 214/224 @.050 and I have ZERO PTV cleareance on the intake with the same pistons you are running.
Now there are some published specs out there like a TFS1 and TW heads working with an 86 piston and other people may have been able to run certain combo's but you have to check for yourself. The bottom line is those pistons do not have a relief to accomodate a 2.02 valve. You'll have to measure PTV, don't use the clay method in this case, and be prepared to cut the reliefs.
As far as picking a head don't use your piston type to make the choice. Pick a head based on your goals and intended use of the motor. Even if you have aftermarket pistons (your's are stock replacements) you can cut the valve relief for a TW head. Many pistons out there have reliefs to accomodate both heads.
Lift and duration are part of the equation but only to the extent that in a OTS cam they can typically be related to ramp rates. The important part is the valve events as the cam is installed in YOUR engine (intake open, exhaust close) and the ramp rates. None of the specs you listed give that information. Even at that the ramp rates are never listed with cam specs so you can only guess what the lift at TDC will be.
I have a motor here with a custom cam that is very mild, 214/224 @.050 and I have ZERO PTV cleareance on the intake with the same pistons you are running.
Now there are some published specs out there like a TFS1 and TW heads working with an 86 piston and other people may have been able to run certain combo's but you have to check for yourself. The bottom line is those pistons do not have a relief to accomodate a 2.02 valve. You'll have to measure PTV, don't use the clay method in this case, and be prepared to cut the reliefs.
As far as picking a head don't use your piston type to make the choice. Pick a head based on your goals and intended use of the motor. Even if you have aftermarket pistons (your's are stock replacements) you can cut the valve relief for a TW head. Many pistons out there have reliefs to accomodate both heads.
ls1beater4eva
New Member
isky makes a tool that works great for notching pistons and saves alot of extra money of having to fly cut pistons, u can buy it or rent it they do both.
They do but are out of stock on the tool for a 2.02 valve. They say it is 30 to 60 days until they restock.
This place Lindy Tools has a tool that they sell. It's instock and ships the next day after ordering.
ls1beater4eva
New Member
looks like ill be buying another one through them instead so i can finish a friends motor . dont ever lend one of these out for some odd reason they never come back.
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