6.9 decked .05 bored .40 over want to run boost!!

[ah1988ford]

just got my block back from the machine shop got it decked, bored, freeze plugs and oil plugs. I want to run my ats 085 turbo setup. do I need to shave the pistons to run 10-12 psi of boost? I saw on r&d performance he shaves pistons. I want my motor to last a long time after the rebuild with turbo LoL

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[Thewespaul]

Leave your pistons alone unless you want to run a cam with higher lift/duration. You need head studs to run that boost through a 6.9 and that’s about it.

 

[david85]

+1, you already have everything you need. Just make sure there is no valve to piston interference, and you're good to go. Even 15 PSI should be safe with studs.

 

[no mufflers]

Wouldn't it be a good idea to shave the Piston since it was decked?

 

[Thewespaul]

Not if the machine shop stayed within spec for what they can take off, but usually this isn’t the case. Be sure and check your valve to piston clearances with the head gasket in place, this will tell you if you need your pistons shaved. If you use a felpro gasket they are slightly thicker so you may be able to avoid additional machining costs that way.

 

[ah1988ford]

Not if the machine shop stayed within spec for what they can take off, but usually this isn’t the case. Be sure and check your valve to piston clearances with the head gasket in place, this will tell you if you need your pistons shaved. If you use a felpro gasket they are slightly thicker so you may be able to avoid additional machining costs that way.

How do I check valve to piston clearance? do I just make sure they don't touch? I am new to engine building it's my first motor still learning.

 

[DrCharles]

Usually checked with a strip of modeling clay on top the piston, coated with oil to keep it from sticking to the valves. turn it over by hand, remove the head and then you can measure the thickness of the compressed clay.
In general exhaust valves are closest a few degrees before TDC (the piston is chasing it as it closes) and the intake valves a few degrees after TDC (valve is already opening before the piston starts down).

 

[Hydro-idi]

Like mentioned, you will be fine if the shop went by the book in regards to specs, which I’m pretty sure they did if it was a reputable shop.
Maybe you can call them just to verify, but you don’t need to shave pistons unless you got a hot cam in it.
You can safely run about 13 lbs boost before the compressed turbo air gets super heated. After about 13 psi, you’ll need an intercooler to regain efficiency. Sounds like a fun build!

 

[david85]

If you really want to be 100% sure, then torque the heads down with real head gaskets in place and modelling clay on the pistons. Then remove the heads and check the clearance. This means wasting a set of head gaskets but at least then you know for sure what your running clearance really is.

 

[Macrobb]

For the pistons, there is a spec on how far they can come out of the block at top dead center. For the heads, there is a spec on the valve recession clearance, from the bottom of the valve to the bottom of the head. Using a stock cam, as long as those two are within spec, you should be fine. If you have to machine the pistons, shoot for the small end of the spec(more clearance). With the valves, shoot for the high end(more clearance)

You wan to run headstuds on a 6.9 so you can run boost. A stock pump only needs a max of around 10-12 to fully clean up with the fuel screw maxed.

 

[genscripter]

Piston deck protrusion spec is 0.010-0.031 for the IDIT.

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From here.

 

[icanfixall]

Piston deck protrusion spec is 0.010-0.031 for the IDIT.
Very good pic showing how ALL idi pistons come up out of the block. This is a 7.3 piston too. Those recessions in top of the piston ARE NOT valve cutouts either. they are called Richardo cups and have a lot to do with combustion.

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From here.

 

[IDIBRONCO]

I'd be willing to bet money that if your block was decked .050", then it's NOT in spec. Also, in order to eliminate excessive "play" from your lifters, you need to modify an old one or two. I used two so that I could check both valves on one cylinder at a time. On mine, I removed the upper retaining clip, removed the "push rod plate", removed the inner parts, then I used some 3/16" ( if I remember right) washers inside to make take up the inside space and make it so that it will not collapse under valve spring pressure.

 

[Lootenny]

If you really want to be 100% sure, then torque the heads down with real head gaskets in place and modelling clay on the pistons. Then remove the heads and check the clearance. This means wasting a set of head gaskets but at least then you know for sure what your running clearance really is.

You can reuse the head gaskets as long as they are not heat cycled. Torquing them down to Clay the piston will not ruin them.


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[david85]

You can reuse the head gaskets as long as they are not heat cycled. Torquing them down to Clay the piston will not ruin them.


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My machinist advised me that only after the engine heats up, are sealers in the gaskets released to the deck surfaces.

I actually did have to reposition the heads when my engine was still on the stand. The heads were only freshly torqued down and not sitting for several days, weeks or months. Several years on, the gaskets are still holding. I wasn't 100% sure on advising others to do the same because I still took a risk. How big a risk was it? Apparently not very big.