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Flycutting Mayhem

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Old 12-01-2005, 09:43 AM   #1
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Question Flycutting Mayhem

Hello Everyone,

I've searched, and searched, already put up a couple posts about this and have found to answer thus far.

Simple question, actually couple questions:

With 2.055/1.57 valves on a LS6 head with stock height/MLS GM Gasket....

1. What is the maximum distance that the stock pistons can be flycut?

2. What is the deck thickness of the stock pistons?

3. Is there any formula or calculation that can be used to figure the distance required to flycut in order to fit any particular cam based on valve sizes/lifters/duration/lift/pushrod length/ect...

Any help would be greatly appreciated as I've not found any answer anywhere, nor recieved any answer in the Internal engine sections!!

Thanks!
Adrian
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Old 12-01-2005, 10:23 AM   #2
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A friend of mine is running .630" lift without any flycutting and slightly milled LS1 heads. Unless you have a very extended duration cam you may not need flycutting.

If you're set on valve reliefs to have a "non-interference" valvetrain, then the answer is simply to cut as deep as you dare into the piston.
If you float valves/lifters, or break a spring, then you're going to need all the room you can get.
If this makes you nervous about piston integrity, then you'll want aftermarket pistons cast with reliefs.

If you're caught in the middle of these two choices, then the only way to find out for sure is to mock up the engine and test it. There is no calculation that is more reliable than a real-world test.

Sorry if I had a stock piston on hand I'd measure it for you. I'm sure someone else on here does have.

On a side note, if the heads are angle milled you don't need to go as deep into the piston.

Last edited by white2001s10; 12-01-2005 at 02:33 PM..
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Old 12-01-2005, 12:03 PM   #3
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You know I've never thought of an angle mill before....but the only downside I can see is that the holes for the heads (bolts, pushrods, ect..) will have to be realigned which would pose a big problem. But thanks for the info...really appreciate it.

Does anyone have any information on angle milling heads?

Also, does anyone have any stock pistons that they can measure the stock deck thickness, and suggest what a safe amount of flycutting would be?

Thanks in advance!
Adrian
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Old 12-01-2005, 03:49 PM   #4
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I wouldn't worry about how deep I could go. I would just cut what you need and thats all. Unless your thinking your going to have to go really deep.

I just did a set in a Vette a few weeks ago. The cam was from LG and they suggested .070. That was enough for this cam and room for a bigger cam down the road.
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Old 12-01-2005, 03:56 PM   #5
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Thanks! Thats some good info there.

But I would still like to know the deck thickness of those pistons, and how far down it would be "safe" to dig, on a N/A motor, and then a 100 shot motor, so I can see the difference.

Thanks!
Adrian
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Old 12-01-2005, 04:29 PM   #6
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Yeah I know, it would be nice to know. I have a couple cars (engines) to do the pistons in, in a month or so. If no one post it up I will have a set coming out of a Vette around the end of this month I'll measure their thickness then. But I'm sure someone allready has a set laying around.
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Old 12-01-2005, 07:32 PM   #7
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The piston is very thick in that eyebrow area. On the order of 400 thou thick, and then some.

Ring lands break before the flycut will ever pose an issue, even on spray.

I have cut .125 deep reliefs in my personal engines, and sprayed a 150 shot on top of them. They still run today with no failures.

Typically, most cams need 80 thou cut for more than adequate clearance.

However, that is not to say that it shouldnt be checked. We know our cams/ cam/heads packages and know what to cut in order for any of our cams to work. If you say you have a 650 lift cam, that tells me nothing about clearance.

Most assemble the engine with the head/gasket in place with a few bolts tight. Put clay on the top of the piston, and as you rotate the engine over, it will smush the clay.

The indentation that the valve leaves will tell you how much clearance you have. Make no mistake with the hydraulic lifters, and pump up, lash, ect. There are good writeups about this procedure here.

As for having a non-interference setup, that would require one big valve relief
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Old 12-01-2005, 11:33 PM   #8
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Quote:
Originally Posted by Louis
The piston is very thick in that eyebrow area. On the order of 400 thou thick, and then some.

Ring lands break before the flycut will ever pose an issue, even on spray.

I have cut .125 deep reliefs in my personal engines, and sprayed a 150 shot on top of them. They still run today with no failures.

Typically, most cams need 80 thou cut for more than adequate clearance.

However, that is not to say that it shouldnt be checked. We know our cams/ cam/heads packages and know what to cut in order for any of our cams to work. If you say you have a 650 lift cam, that tells me nothing about clearance.

Most assemble the engine with the head/gasket in place with a few bolts tight. Put clay on the top of the piston, and as you rotate the engine over, it will smush the clay.

The indentation that the valve leaves will tell you how much clearance you have. Make no mistake with the hydraulic lifters, and pump up, lash, ect. There are good writeups about this procedure here.

As for having a non-interference setup, that would require one big valve relief
Thanks for the great reply....couple of questions again.

1. is there any calculations that gives you the lift of the valves based on the degree of the cam using the cam specs.....such as duration, lift at .05 or .004, overlap, or cam advance ect...

2. When using the good ol' mock-up method, how many times would you have to completely rotate the engine to insure that the lifters have "pumped-up" ect.. twice?

3. Do you have any links to those writeups that you're talking about...I haven't been able to find them

Thanks a lot!
Adrian
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Old 12-02-2005, 07:05 AM   #9
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Comp Cams has a pretty good write up on checking for valve clearance.
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Old 12-02-2005, 08:27 AM   #10
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1. No because the ramps vary so much.

2. Mocking up is the best method, but turning the engine over several times will actually make the lifters bleed down. There are weaker springs available to make this operation go more smoothly.
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Old 12-02-2005, 10:41 AM   #11
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Willyfastz, thanks for the spot, i'll check it out.

white2001s10, for all of us who don't know, what exactly does it mean for the lifters to "bleed down"?
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Old 12-03-2005, 08:44 AM   #12
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The best way is to use mock up springs. You just take the heavy springs out and install the Mock up springs and do the test. You can use clay or a dail indicator to check clearance
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Old 12-03-2005, 01:18 PM   #13
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Make sure you have ZERO preload on the lifter with the soft spring. If you have preload, it will open the valve with the soft spring, as opposed to preloading the lifter. This automatically takes away from your PTV starting with the valve anywhere from 20-80 thou open. Remember, 10 thou of preload is 17 thou that the valve would open with a soft flowbench style spring.
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Old 12-05-2005, 01:07 AM   #14
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To make this as simple as possible, since i've never done this before...should I just cut .125 deep relief for both the intake and exhaust, then mock up the engine, rotate it once with the new cam/heads/pushrods, ect..., and if for some reason it still doesn't clear, just get a smaller cam? I think that would be the best idea for me, because I know you have to be VERY strict with measurements, and since well....I've never even taken a head off before, i'd much rather take away more then enough, then to not take away enough because I screwed up the measurements. I'll be pulling my engine too, so this process might be a little easier.

What do you guys think?

Regards,
Adrian
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Old 12-06-2005, 11:48 AM   #15
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Any thoughts? Or is my idea just really stupid?

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Old 12-06-2005, 12:05 PM   #16
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Quote:
Originally Posted by Haans249
To make this as simple as possible, since i've never done this before...should I just cut .125 deep relief for both the intake and exhaust, then mock up the engine, rotate it once with the new cam/heads/pushrods, ect..., and if for some reason it still doesn't clear, just get a smaller cam? I think that would be the best idea for me, because I know you have to be VERY strict with measurements, and since well....I've never even taken a head off before, i'd much rather take away more then enough, then to not take away enough because I screwed up the measurements. I'll be pulling my engine too, so this process might be a little easier.

What do you guys think?

Regards,
Adrian
I would never generically cut reliefs because compression is precious. I run ls1 heads milled .035" stock valves, .040" MLS gaskets, with a 231*/237* .595" .605" on a 112* LSA with no reliefs and i turn true 7000rpm
LSA is what plays biggest part in PTV on these engines, a 110* LSA loses a good bit of ptv over a 112* or 114* cam. Dont cut reliefs until you mocked up motor with your heads and cam the way you are going to run it.
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Old 12-06-2005, 01:28 PM   #17
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Well, i have 61cc heads (unmilled LS6 deck height) and the MLS gaskets, so that should put me at about 10.9-10.8 compression. With those notches, what sort of compression loss would I be looking at (.1-.2 or less? because those notches MIGHT add like .5cc's to the total volume) And with that loss in compression, what sort of power loss will I be looking at as well? I'm just trying to weigh the negatives vs. the main positive...reducing measurement error and guaranteeing fit!

Thanks!
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Old 12-06-2005, 08:16 PM   #18
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My chambers are 62cc and my compression is 11.2 to 1.
You would give up like a 1/2 a point or more, this would prolly be 10 hp but also affects gas mileage and throttle response/idle quality. Check your clearances than grind notches if you dont have say .080"/.100" intake and exhaust ptv clearances.You run into trouble with aftermarket larger valves with there thicker margin area.
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Old 12-06-2005, 09:56 PM   #19
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Quote:
Originally Posted by LSwonderfull
My chambers are 62cc and my compression is 11.2 to 1.
You would give up like a 1/2 a point or more, this would prolly be 10 hp but also affects gas mileage and throttle response/idle quality. Check your clearances than grind notches if you dont have say .080"/.100" intake and exhaust ptv clearances.You run into trouble with aftermarket larger valves with there thicker margin area.

Ok thank you, that is very helpful. I'll check and notch to make sure I have that .080/.1 clearances for my valves. Now the biggest question...which I believe to be quite the confusing one is, how do I go about doing this?

If we know that i'm going to have some collision with the p and v, then how is "claying" going to be effective because the first pass on there isn't going to give a good estimate because isn't the clay going to be cut all the way through? So, am I going to have a make an initial cut first...and then check?

Is there a write up anywhere that explains this process?

Thanks again everyone for your help so far,
Adrian
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Old 12-08-2005, 05:38 AM   #20
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Quote:
Originally Posted by Haans249
Ok thank you, that is very helpful. I'll check and notch to make sure I have that .080/.1 clearances for my valves. Now the biggest question...which I believe to be quite the confusing one is, how do I go about doing this?

If we know that i'm going to have some collision with the p and v, then how is "claying" going to be effective because the first pass on there isn't going to give a good estimate because isn't the clay going to be cut all the way through? So, am I going to have a make an initial cut first...and then check?

Is there a write up anywhere that explains this process?

Thanks again everyone for your help so far,
Adrian
You are not sure there is going to be interference, you havent mentioned cam size yet, this could have sufficient clearance depending on cam duration, lift and LSA.
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Old 12-08-2005, 05:38 AM
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