Stock LS1 head going to 317's
 

I just bought some new 317 castings, I'm going to clean them up a bit and would like to keep my CR (9.5-1) the same as my stock ported heads. Do I need to have them shaved and how much? I was thinking that the cumbustion chamber was larger on the LS6 heads but I wasn't sure, can someone help me out here? Thanks.
Wolfee

Combustion chamber volume on the 317's is usually 71-72cc. I'm not sure what your piston dome volume (valve notches) is, if any. I think your c/r will be a bit higher than 9.5:1. Either way, I don't think you need to mill the heads.

We've ported a bunch of Raptor heads and are now doing head work for some rather large motorcycle companies involved with Supermoto programs. They really respond to head work.........

Good luck,

Richard :)

The 317's are for the 6 litre. If your going to bolt them on a 5.3 you'll have to run the larger 6.0 gaskets or else your stock gaskets will br hanging into the chamber, also consider that the chamber will now be overhanging the cylinder bore. We've run this combo with the chambers welded up to bring the chambers down to 66 c.c. so there was no comp. loss and had great results. one thing milling your heads, it will take about .007 to get one c.c. back so if you want your same comp. your talking about milling over .040, that's getting scary. We make great power with the std LS1 small chamber heads mildly ported, was there anything wrong with yours to make you want to switch ?

The stock heads were junk from the time I got them, I've put way to much money in the stock ported heads I bought off a list member and now one of the valve seats broke and fell into my basically brand new shortblock and took out the piston and cracked the block along with seriouslt screwing up the head. I figured I'd make the swap to the LS6 head on my 5.7 and help the flow. Maybe I shouldn't have though, did I make a mistake buying the 317 castings and should I have just bought a set of stockers and bolted them on without porting which I don't have the money to do right now?
Wolfee

IMO do a light cleanup in the valve bowls and have a proper valve job done. Install and enjoy the boost.
If your budget allows, I've got a new Stage 2 CNC port program thats selling for $1300 per pair exchanged. Stainless valves, ti retainers, dual springs etc.


Good luck,

Richard :)

Unfortunately I can't afford the $1300 but where will this put my CR? I was going to be 9.5-1 with the stock heads but I don't know where I will be with the 317's. Can you help me out?
Wolfee

BTW, I don't know if you've heard of them but Schnitz racing out of my home town done the port and polish on my Raptor head. Ryan just won his first NHRA pro stock bike race in Columbus last weekend. The Raptor is just scary fast, seriously!

If you were calculating 9.5:1 with a 67 cc chamber I believe that your going to loose some compression with the swap. Since I'm not at the shop right now, I'll make an off handed guess that your CR will most likely be around 9.0:1 with the addition of the 317's. If you mill the heads between .025"-.030" you should get back to your target 9.5:1 cr. I'll double check your cr when I get to the shop in the morning and repost.

Yes, I've heard of Schnitz Racing. Thery're gaining a whole lot of respect from some of us on the west coast. Your Raptor must peg your Smile 'O Meter.........

Good luck with your build up.

Richard

I'll look forward to hearing back Richard, thank you Very much for all the help.
Wolfee

BTW, My goal when bought the Raptor new in 03 was to have it scare me everytime I ride it, I'm happy to say I've accomplished my goal. It's by far not the first thing I've had too, mostly street bikes before this and this thing is just insane. I'm going to take it to the 1/4 mile pretty soon to see what it does.

Working backward here, I'm guessing that your dish volume in the piston is around 7.5cc. That would get you to 9.5:1 cr. Recalculating for a 317 chamber (I'm using 72cc) I show that your cr will drop to almost 9.0:1. I usually allow .0065" with a flat surface mill per cc, so it looks like .0325" will get you back to 9.5:1 cr. Angle milling isn't needed here. Your intake manifold should't have any fit issues either.
I would suggest having at least one chamber on each head cc checked before you do any milling. One cc should change your cr approx. .9 of a point in compression.

Good luck,

Richard