Z28M6TT

Cliffs: Gonna be running a prc 5.3 head and need to flycut. Can I use a 241 head for the cutting?



Iv'e been searching for an answer to no avail, but maybe someone lurking may have the answer to this question...

Does anyone know if there is a difference in the valve placement on a 241 head vs a 5.3 head (specifically a prc 2.5 5.3 head with 1cc milled off). I'm wondering because I recently found out a need to flycut ~.050 for intake and exhaust, and even though I'm using the Lindy cutters I rather use the stock heads and not worry about accidentally nicking a seat on the new head.

I'm thinking the valve placement between the two different heads is the same since they are both factory 15 degree heads that use stock rockers; so the geometry should be the same. Also, it seems when most people rent a flycutting setup it just comes with a generic LS1 head and they don't think about it.....

The only difference I see with my setup would be the height of the valve in relationship to the deck, with the .040 gaskets (.011 thinner then stock) and .006 milled from the head (1cc). But with a 15 degree head, dropping the head .017 closer to the piston would only move the valve horizontally ~.0046 horizontally (assuming I can still do high school math).

Thanks in advance guys.

bww3588

iTrader: (49)

You will be fine with the junk head. If I recall, the prc heads have a 2.02 intake valve, versus the 2.0 intake valve of the stock 241. The valve centerline is the same and the lindy cutters usually cut a 2.08 or so relief in the piston. Which will still give you .003 clearance on either side of the larger 2.02 valve.

Z28M6TT

Okay thanks, confirmation of the valve centerline being the same is what I needed. Yea PRC uses 2.020/1.575 valves. When I ordered the cutters from lindy I got a 2.120 for the intake and 1.675 for the exhaust, that way I'll have .050 radial clearance which seems to be the recommendation. I think the ISKY cutter people normally use for the stock bore ls1's is 2-1/8 (2.125) so i don't think the cutter will be too big. Anyone that can definitely say they used the ISKY 2-1/8 cutter with no issues as far as cutting too close to the edge of the piston?

M1SERY

your build similar to mine, I cut mine .095intake and 0.15 exhaust, but I took one of my 5.3 heads a part to do mine, but I also milled .024 off of mine . you will be surprised by how much it wakes the little engine up , should net you around 30hp at wheels , take ur time and use a lots of grease around the piston to keep the shaving from in between the block and piston , if you have done this before u already know , just throwing that out there good luck