6.9 IDI Build

WarNose

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I'm building a 6.9, so I may as well start a thread right? Plans are:

6.9 bored .020 over
Head Studs
Type4 cam
Comp Cams 910 springs
All new valve train parts
Stock ATS 093 Turbo
IP undecided
Intercooler plans for the near future

Goal for this motor: To reliably pull a small toy hauler through the mountains at 65 MPH without having to worry about overheating or high EGTs.
 
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WarNose

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I'm going with Mahle forged pistons. I'm wondering if I should buy them destroked .010. The block deck checked out good so it will be a stock deck height. The heads will be milled .005. Since I'm using the higher lift cam, milling the heads and boring the block, I think I should go with the destroked pistons. Am I on the right track?
 

Thewespaul

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What are your goals and plans to use the engine for? I personally wouldn’t destroke an engine that isn’t just a toy, these IDIs really need compression to start well. 5 thou isn’t much, and using the fel pro gaskets you will gain extra thickness over the stock gaskets. Check your valve to piston clearances and recess the valve instead of taking meat off the pistons. The Mahle pistons are not forged, they are a cast aluminum/steel alloy
 

WarNose

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What are your goals and plans to use the engine for? I personally wouldn’t destroke an engine that isn’t just a toy, these IDIs really need compression to start well.

I'm not looking to hot rod the motor. I just want to reliably pull a small toy hauler through the mountains at 65 MPH without having to worry about overheating or high EGTs.
 

Thewespaul

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That’s what most guys are after, I think you are setup well to achieve that goal. Like I said try to avoid taking meat out of the pistons if at all possible and you should be good. Looking forward to seeing it come together!
 

WarNose

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The Mahle pistons are not forged, they are a cast aluminum/steel alloy

Oh I was under the impression that they are forged. It seems like forged pistons aren't available for this motor then. Would hypereutectic pistons be better for a couple of hundred less?
 

Thewespaul

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From what little data there is on the idi piston composition, I believe it’s close to a 4032 alloy, which is around 11% silicone content, which is very close to what would be considered a hypereutectic piston, just slightly less silicone. The aftermarket pistons available do not seem to be different in composition from oem, so I don’t think there is a performance advantage going with a pricier option, although I have not explored them myself to prove otherwise.
 

WarNose

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I'm leaning towards a Moose Junior pump. I'm hoping that I will be able to tow through the mountains with it until I am intercooled, without generating too much heat.
 

icanfixall

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Many time coolant getting out of control is because the radiator is plugged or the fan clutch is worn out. Now very seldom do we see the lower radiator hose has lost the spring that keeps it from sucking closed. Also always use only the motorcraft factory thermostat. It starts to open at 192 degrees and is fully open at 212 degrees. If you choose to replace the radiator be sure you get the 3 or 4 row with at least 13 fins per inch. Unless you buy the Rodney Red aluminum. That will keep anything cool.
 

WarNose

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I just picked up a Moose Junior pump and ARP studs, both still unused, from a fellow member for a nice price. Gotta love this site.
 

WarNose

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What are your goals and plans to use the engine for? I personally wouldn’t destroke an engine that isn’t just a toy, these IDIs really need compression to start well. 5 thou isn’t much, and using the fel pro gaskets you will gain extra thickness over the stock gaskets. Check your valve to piston clearances and recess the valve instead of taking meat off the pistons. The Mahle pistons are not forged, they are a cast aluminum/steel alloy

Maybe I'm overthinking this and I'm being overly worried about piston to valve clearance. But the destroked pistons with an original thickness head gasket would give about the same compression ratio as a stock height piston with the thicker head gasket. And with the desroked piston I would still be able to switch to the thicker Fel Pro head gasket if I absolutely needed to. The way I understand it, these pistons are not shaved but rather the pin is moved up higher in the piston, making the piston height lower.
 

Macrobb

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You still have lower compression ratio - you want to keep as much compression as possible, for good cold start performance.
The "decompressed" pistons are designed so you can skim-cut the block when rebuilding it. That's what the .010" is for.

For piston-valve clearance, you recess the seats to get the clearance you need. Don't thin out the valves - thickness there is important. The seats, however, have plenty of meat on them, and .030" or so isn't going to hurt them.

Now, realistically, .010" of decompression piston/head gasket wise won't make a huge difference.
I ran with an experimental double-thickness gasket for a while... it was *not* a good idea - Cold starting was a pain, lots of smoke when cold; I literally had to advance the IP like a whole extra tooth just to get it to start cold, and then had to deal with that advance hindering me when running and warm.
It was also, as you might expect, relatively gutless down low. Once you get boost, it really doesn't matter what else is going on(and that includes rings worn to the point of failure), you *will* make power; but in the idle-1600 range, that's where you need to keep compression for best performance.
 

WarNose

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My machinist is not happy installing the Comp Cams 910 valve springs. He thinks they are much too stiff. Do you all use new retainers and keepers when installing these springs. He would really be much happier if I let him install the original springs.
 
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