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Discussion Starter #1
I just finished measuring my p-v, and came up with 0.040" on the intake and over 0.100" on the exhaust. The intake side seems a little thin, what kind of clearances whould I have there? It's on a 351w, with tfs track heat heads and speed pro pistons L2446F30.

Trevor
 

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Yikes - you're gonna have to change something. You need at least .080" on the intake and .100" on the exhaust. You could retard the cam a bit to help on the intake side, but that's gonna reduce the exhaust side and you're already at the minimum. I suspect you're gonna have to either change the cam to one with a bit less duration/overlap or longer LSA, or get the tool and fly cut the pistons. At least you measured - good for you. Most folks just crank it up and go. Some are fine; some don't go far.
 

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Is the engine on a stand? The short block has to go along with the heads. No idea what it costs. I'd guess a couple a hundred.
 

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If you take the pistons to them and ask them to increase the current piston relief, or mark where you want it, the cost is less than $100 for all 8 pistons.
 

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Do the TFS heads have the valves arranged in the same way the current piston reliefs are cut? Are they called Twisted Wedge (is that TFS?) because the chambers are 'twisted' relative to most heads? Sorry for the elementary questions - I don't know anything about your piston model numbers either. It may not be as simple as enlarging the existing reliefs with a dremel. i guess you know better than us whether you have a valve size to relief size issue, and relief depth issue or a complete misalignment of valve angle to relief angle.

There is a tool that is designed to be inserted through the valve opening - it sits in the guide so it's at exactly the same angle as the valve - you put your drill on it and turn it and it cuts a relief in the piston. You calculate how much you think you need to cut based on your clearance measurements. Cut a little less than that, pull the head, remove tool, reinstall the valve and measure again. Once you get your depth determined, then you can cut all the rest at the same depth without remeasuring.
 

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Discussion Starter #9
My heads are acutally the track heat heads. I was just joking about the dremel ;-) (I'm not going to be taking a dremel to $400 pistons). I just bought the tool from isky cams, only a 130 bucks. I figure thats about the same price as a shop doing it, but this way i can charge my buddies to do theirs.
 

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Actually, if the reliefs are in the right place, opening them up to a bit of a larger diameter can be done with a Dremel -- or at least I of folks that have done it. Right tool for the job and all that, but sometimes we make do with what we have. Sounds like you've got it under control.
 

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Discussion Starter #11
Naw, the reliefs are about a 1/4 off. The pistons have a 13cc dish, and where the dish end (rectangular in size), is where I'm having the clearence prob. I've heard of guys dremeling their pistons with no ill effects, but I'm gonna be spinning the motor around 7g and I want to keep it all balenced. If they were just stock pistons I might try that.
 

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Discussion Starter #16
dammit! I didn't see that. I wonder if I could just use it once send it back and see if they send me the rest of my money back? Ah **** it, with the shipping charges it's almost worth buying it.
 
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