Doing research on the forum about cam/head installs I came across the word fly-cutting a couple of times. What is this about? It seems to be involving piston/valve interference...perhaps, no one ever explained it really. Is this cutting your own valve reliefs in the pistons????

I am getting some stock ported heads w/stock rockers but using a XE-R cam. I was also planning on milling the heads to get a little more comp.

So, what is flycutting, and will I need to do it?

 

Yes.

As far as when it is necessary, you have to take all your cam lobe and valve train geometry into consideration, coupled with how much you are milling the heads, to determine what your final piston:valve clearance is. If you do need to do this I'm pretty sure it means you will have to disassemble the heads, and use a drill/grinder through the valve port. I'm pretty sure the back two are going to require the engine being dropped or moved somehow.

I would really get advice from a pro on this, so hopefully one of the tuners will step in and be more authoritative on this.

Good Luck!

 

Ok, I want to avoid this. Here are the cam specs
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Cam Style Hydraulic roller tappet
Basic Operating RPM Range 2000 to 7000 RPM
Intake Duration 050 inch Lift 224
Exhaust Duration 050 inch Lift 230
Advertised Intake Duration 273
Advertised Exhaust Duration 279
Intake Valve Lift with Factory Rocker Arm Ratio 0.581
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.588
Lobe Separation (degrees) 114
Intake Valve Lash (in) 0.000
Exhaust Valve Lash (in) 0.000
Grind Number LS1 XER273HR
_________________________________

If anyone else has then cam, could they chime in and say if they were able to mill their heads and how much before fly-cutting is necessary.

 

We had to flycut the pistons for intake valve clearance on the last h/c job we did with the LGM X3 cam and AFr 205's milled .040". No problem doing it on the car. We used a set of used LS1 heads so as not to screw up the new AFR's.

 

I'm guessing that cam will fit with no problem, BUT CHECK your clearance when you install it! With most larger cams there is no way to be 100% sure they will fit until you check. Everything plays into the clearance, and no two engines are made exactly the same. With that said, the 114 LSA will help your clearance, it will be better than a 112LSA cam. I just installed a 230 duration .592 lift cam on 112LSA and it was really close, so I cut the pistons just to be sure. Fly cutting in the car is pretty easy, lot of extra work but not really hard to do. Here is what your pistons will look like when done. Those little cuts in the top is the notches your cutting, the factory pistons are completely flat on top.



Here is the tool you use. It looks a lot like a valve but has those wavy cutters on the top. You just remove the valve and stick this tool in the hole, put the head back on the engine and turn the cutter and push it down on top of the piston. It only takes slow lite pressure on the tool to cut. The tool has a stop on the shaft which will hit the top of the valve guide to limit the depth of cut. You can use any head, but like patches said, I wouldn't recommend you use AFR heads to cut pistons. I bought a used set of LS1 heads cheap to do my cutting. You can rent the tool from some of the shops, LG is one of them, they ship you the tool and used head.



On the rear most cylinders you will need a 90 degree drill to turn the cutter. Again slow turning lite pressure is all that is needed. I didn't like this drill, it was too fast but did the job OK.

 

with Patches and Speedy. I would also like to add that the head you use should have the seats cut out to fit the notching tools because they are much thicker than stock valves and won't sit square on the deck without clearancing the seats. If you want to do this, pm me, I have a head all set up and the tools and can help you out.
My guess is you won't need to notch them unless you have the heads milled more than .030" or are using a thin, less than .052" head gasket and light milling. Also, the advance the cam is installed at will make a difference, and the size of the valve wil also play into account. Textbook p/v is .080" intake and .100" exhaust. You want a little more on the exhaust because the piston is chasing the exhaust valve up the chamber. One last suggestion is, do a lot of homework on valve train geometry and using the correct length pushrods. There is a great thread on LS1Tech.com in the LS1 Internals forum at the top titled Cam Guide. It's a sticky and it will have tons of info for you to peruse.

 

Thanks guys, I feel much more confident doing this now, I thought this was done free-hand with a template, that's why I was nervous about doing it.

Were you able to clean up inside the piston easily enough afterwords. It does make me nervous thinking about possibly getting metal shavings down around the rings.

Im probably going to get the heads milled .025~.030 if I am going to do it.

I do see the stock head gaskets are .055 though, are there thinner ones available for the LS1, that would be cheaper in the end for me than milling a set of heads that do not need it.

 

Great post speedy!

What did you use to get your pistons so clean?

 

I used a shop vac and sucked the shavings out of the exhaust port when I did the intake and vice-versa with the exhaust. Then I lifted the head carefully and used the shop vac again at the bottom of the cylinder and also on the surface. With the cylinder all cleaned up the shavings didn't stick to anything. Fel-Pro, Mr. Gasket and Cometic make thinner head gaskets. I am using .040" Cometics. I am using a thin Cometic primarily for a tighter quench, but a little boost in CR is always welcome. You have to be careful with thinner gaskets though. On the LS1 the piston actually comes out of the hole, anywhere from .003" to .009". I measured mine and they were out .004" - .005". That gave me a .035" - .036" quench height. You probably shouldn't go tighter than that. Piston rock and rod stretch could mean contact at high rpms. Your best bet would be to measure your piston to deck height after you get the old heads off and have cleaned up the deck. Some guys have measured .008" out and went with Cometic .045" gaskets. My theory is that pre 2001 LS1's were ~.004" out and post 2000 LS1's were .008" out. Remember, as far as P/V is concerned, milling and thiner gaskets are the same, so a .012" mill and stock .052" gaskets is the same as .040 gaskets and no milling. Also, 97-98 heads have a notch on them that prevents an MLS gasket like the Cometics form sealing, so if you have a set of those you will have to go with .052" graphite gaskets.

 

I was told the same thing too, that was why I bought used LS1 heads and not cut up my LS6 heads. But after I got the tool I wonder why they were made like they were. I chucked the tool up in my lathe and ground a 45 on the rear of the tool and it fit into the head below deck level without touching the head! Worked great! You do have to grind because those tools are HARD! Also don't let the tool get hotter than you can touch, you don't want to make it softer with too much heat. Also, be sure you don't cut the back down into the ribs on the front or the may break off. You can see on this intake cutter I didn't even have to get close to the cutting ribs. I did both the intake and exhaust tools and they both work great on a stock head. I wonder why Isky don't make the tools like this to start with? Maybe so we won't use our good AFR heads to cut pistons?

I cut my notches without a gasket under my stock head since the AFR heads were cut .042 figured it would be about right.

 

Thanks

On the pistons I used a little brake clean, a little rag, and a lot of finger

 

It really is pretty easy to do. It is a lot more work putting the head on and taking it off so many times but it's not really hard work. I have some really good tips for keeping your engine clean if you have to go this route. I'm still guessing you won't need to notch but if you do it's not too bad. My AFR heads were milled .042 and I used the factory .054 gaskets. I thought about .040 gaskets but they cost so much more and I was already getting high on compression. You should only have to do the intake side, normally you will have plenty on the exhaust. I cut both while I was there cutting, I can fit a pretty big can in there now!

Now that you know how easy it is to cut your pistons, you might as well get a BIG cam!

Good luck,

 

What, 224/230 .581/.588 114 LSA not BIG enough?

I had the LT4 hot cam on my old LT1 Vette and I thought it was decent enough at 210/228 .535/.525 112 LSA

 

Just have ET send you milled heads like they did me. When you bend every valve in them you can see on the pistons where exactly they hit so you know where to flycut

 

These guys are giving you some good advice, but there are a few things I would add. Recess the piston .040, cover it with duck tape, and put on the old gasket. The duck tape keeps the cuttings from getting in between the piston and cylinder wall. It is best to remove the duck tape from where the cutters are cutting. Recessing the piston and using the old gasket compensates for the intake valve cutter protruding from the deck of the head.

 

Nah.. you wont need to flycut with that small cam... lol..



I just did mine... really not hard. The time is spent on moving the cutter from cyl to cyl and putting th head on each time. I didnt' use a gasket while cutting. I found that spray carb cleaner works WELL on the pistons. MUCH better than brake cleaner on the carbon... Also.. I put a bunch of grease on top of the pistons while cutting. it catches pretyt much all the shavings and prolly helps out the cutting.. worked great.

DIRTY BEFORE CLEANING


CLEAN BEFORE CUT


AFTER


CLOSEUP