dreamer1q

I have a few guesses, but I am not 100% sure why this is something you would want to do yourself, instead of buying the piston precut.'

http://www.forcefedhighperformance.com/tech_Isky.htm

Stephen 87 IROC

Good article

I had some pistons flycut a few years ago. You can misjudge your cam choice and get too much lift even when using a longer rocker ratio. It's a lot cheaper to have the valve notches cut deeper into the pistons than it is to buy new pistons.

At $500-$700 for race pistons, a couple of hundred dollars to have them flycut is better than buying new pistons or living with a smaller lift cam.

kmook

I was looking at converting a Gen1 SBC head over to use it on a stock bottom end LT1, and with the 2.08 (or 2.125 cant remember) intake valves and big lift, i was going to probably need to use that isky tool on the stock pistons.

Stephen 87 IROC

My current block is even notched for big valves however I'm not using big enough valves to need the clearance. The top of the cylinder is notched to clear the bigger intake valves. My BBC only uses 2.19 intakes and the notches in the block are good enough to clear 2.30 valves. My new aluminum heads only have 2.25 intake valves. It's nice how the BBC valves are canted. They don't open straight down but actually open angled into the center of the cylinder moving the head of the valve away from the cylinder walls. You can't just take a piston and guess the angle of the flycut.

That Isky tool eliminates that guesswork because it uses a valve guide to determine the correct angle. You just need a scrap (or partially scrapped head) to use with the tool. I like how that tool works. It takes the guesswork out of knowing the angle and center of the valve when having them flycut out of the block. Hand a bare piston to a machinist to have it flycut and he can only guess if it's going to be done right.

One problem I can see is having to get at those rear cylinders under the cowl. An angle drill or angle adaptor will probably have to be used. Just love how they stuff the engines under the cowl now.

At least when I bought my JE race pistons, they have deep enough pockets that I'll have no problems with whatever cam I decide to use. Problems start to occur when people start milling heads and stuff.

The rule of thumb says you should have minimum 0.060" piston to valve clearance on the intake and 0.100" on the exhaust. Any less than that and you risk smaking a valve into a piston.

dreamer1q

Thanks for the info guys. I appreicate it.

Mindgame

Just be careful not to weaken the piston by cutting the pockets too deep.

-Mindgame

dano73327

Its not too hard to set up a piston for fly cutting on a mill if you know what you are doing. Any competent machinist should be able to do that job without any real guess work. That Isky tool does work if you are in a pinch or just don't care that much about having it done the proper way.

While you can order pistons from JE or any other good manufacturer and tell them the valve sizes and the specs of your cam and they should be able to give you pistons with notches machined with more than enough clearance but if you are building a race engine and want to keep all your clearances minimized to keep up your compression then you will need to mock up the assembly and find your p to v both radial and vertical and machine accordingly. For the average person building a street engine shelf pistons will work or a little touch up with the isky tool but thats pretty much a backyard fix.