Shaving OEM pistons to use with 5.956 351w rod?

92bird

Registered User
Planning a rebuild, need to keep costs down. Power output expected to be 350 rwhp. Originally I was looking for a set of '94-'95 SC rods with new Sealed Power OEM relacement pistons (supposed to be slightly stronger than OEM ford pistons, and they have a coated skirt).

However, the Eagle 5.956" I-beam rods are lighter, just slightly longer, and stronger than SC rods. Same big end bore and same pin diameter.

So I was thinking why not use them along with the new sealed power pistons with about .030 shaved off the top? My deck height is 9.222 (shaved .010).

Has anyone ever done this, or thought of doing this?

I don't plan on running nitrous, and will tune safely.

Only reason for current rebuild is that last time I didn't overbore the block (just a good hone) and used OEM ford rings (loose ring gaps), which suck.. I have a ton of blowby now after 20k hard miles at over 300rwhp. I'm thinking some .030 over pistons with total seal gapless rings should fix that.

Jeramie
 
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I would think a factory oem type piston will not be thick enough to cut...And if it isnt a forged piston forgetabout it...Factory is a hyper..not forged
 
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I would think a factory oem type piston will not be thick enough to cut...And if it isnt a forged piston forgetabout it...Factory is a hyper..not fprged

Not quite accurate. The cast pistons are already dished so you would only be taking stock of the raised portions which will not materially affect the strength or thickness of the crown. The only thing I would be concerned with is that by cutting the tops you are effectively putting the rings closer to the fire. This is a good practice for an NA motor but questionable on a blown application. My biggest thing would be keeping a safe tune on it. The raised compression from the shallower dish would also be helpful, especially at your altitude.
 
I have long rods with forged stock style pistons cut for the extra rod length. So far so good. My compression ratio is 9.89 to 1
 
Thanks for the info guys. I haven't weighed the stock rod/piston combo yet, but I'm sure this would be a bit lighter. The ESP SIR rods weigh only 570 grams.

I really think I'm going to try this.

Personally, I think the forged piston thing is overrated, unless you plan to run NO2 or have a questionable tuner.. I do have a local person who is tuning for me, and we now have a wideband o2 to keep tabs on it.

Summit Racing has the Sealed Power coated skirt pistons in a .030 overbore for $29.99. And I can get press fit pin versions of the Eagle rods to re-use my wrist pins for $269 for a v8 set.

I figure this setup will be slightly stronger than the stock 89-93 setup I've been running, and at 345.5 rwhp, some wheel hop here and there, and a powershift or two.. I haven't broken them yet. I'm a firm believer in only using what you need.

The lighter rotating assembly and a full balance will compliment my new rev-happy cam profile. I already have the aluminum flywheel, BHJ, and aluminum pullies.

Jeramie
 
Thanks for the info guys. I haven't weighed the stock rod/piston combo yet, but I'm sure this would be a bit lighter. The ESP SIR rods weigh only 570 grams.

I really think I'm going to try this.

Personally, I think the forged piston thing is overrated, unless you plan to run NO2 or have a questionable tuner.. I do have a local person who is tuning for me, and we now have a wideband o2 to keep tabs on it.

Summit Racing has the Sealed Power coated skirt pistons in a .030 overbore for $29.99. And I can get press fit pin versions of the Eagle rods to re-use my wrist pins for $269 for a v8 set.

I figure this setup will be slightly stronger than the stock 89-93 setup I've been running, and at 345.5 rwhp, some wheel hop here and there, and a powershift or two.. I haven't broken them yet. I'm a firm believer in only using what you need.

The lighter rotating assembly and a full balance will compliment my new rev-happy cam profile. I already have the aluminum flywheel, BHJ, and aluminum pullies.

Jeramie

The Sealed Power pistons will come with pins and locks so you can run a bushed or pressed rod. Your choice. The Sealed power pistons are a little lighter than the OE ones as well so it should work out fine. You will also note that the stock assembly is underbalanced from the factory so you may not even need to rebalance the crank unless you want to.
 
Make sure your machinist is o.k. with the shaving. While cast, the pistons are of high silicon content and thus fairly hard. It'll take a slightly different approach to machine the top down than a forged piston.

As dave said, the pistons come with pins and locks, so just make sure the small end of your eagle rods is appropriate.

tim, I bet your pin placement was moved for the longer rods with the dish of the piston kept the same. That's usually how you fit a longer rod while keeping all other things equal.
 
The Sealed Power pistons will come with pins and locks so you can run a bushed or pressed rod. Your choice.

Really? Awesome.. I would rather run a full floating design. That's cool..

Not sure who/where I would have them machined yet.. I'll have to do some looking around locally.

Jeramie
 
Mike I really dont know, I know the pistons are shaved to the point where there is almost no eyebrow left for the valves. Like everything else i have done I would probably do it differant next time. The higher compression is nice off boost. It pulls nice. when I got the forged pistons I was not thinking of nitruos. Now I am glad i got all the HD stuff in the engine.
 
Maybe dave can pipe up on what he found when he pulled his XR7 motor apart. I seem to recall he may have posted that the top ring lands on his over 400rwhp stock lower end motor still had decent looking pistons in it when he tore it down. Those stock cast pistons are very tough, but nice and slippery. If they weren't quite so brittle they would be great high performance pistons.

It's just that when they fail or a valve drops onto them, they make a mess out of the whole engine. Forged pistons just don't usually create that kind of mess when things let loose, thus saving a block.

found dave's post on his block
http://www.sccoa.com/forums/showthread.php?t=80954
 
What is a safe amount to bring the piston above deck without smacking the valves? I've got .010 off the heads, with a .520 lift cam and 60cc chambers, stock valves..

Trying to avoid taking more material off than I have to. I've ran this idea by a few hardcore engine guys and they think its a pretty cool idea on the cheap.

Jeramie
 
I always thought the Sealed Power Pistons were forged. Are they not? Who makes a good forged pistons .030" overbore for the SC?

Jeremie in theory I think what you want to do is a good idea. I just don't know what it's going to be like in the real world. I've never done it so I can't say whether or not it's a good idea or not. But I follow where you're going with this and I would think shaving them so slightly isn't going to matter.

Keep us posted on how this turns out.
 
Thanks for the info guys. I haven't weighed the stock rod/piston combo yet, but I'm sure this would be a bit lighter. The ESP SIR rods weigh only 570 grams.

The factory rods weigh in at about 720 grams each.

Arent the Hyper pistons Coated ? So would shaving them remove some of that outer layer ? The Hyper pistons have certain thermal characteristics and expand to a specific size when they reach operating temperatures, so Id imagine this could affect the way they might react in the engine environment. Forged might be a different situation, but I dont really know, Im just thinking ..

- Dan
 
Post #12 in this thread has a fairly reliable number.
http://www.sccoa.com/forums/showthre...highlight=deck

I had things machined for .0010 above deck.. Haven't assembled things yet but when I do I'll be checking things very closely.

Thanks! I was looking for that exact same post, I remember reading it before but couldn't find it in my search.

Main problem I have is, I don't trust that my block was machined exactly .010 I asked the machine shop that did the work 5 years ago and he said they may have "fly cut" it first. Not sure what he means by that, but I know the block surface was pretty bad from the factory. When we assembled it I remember it seemed like the stock piston was "zeroed" which would indicate more like .020 taken off. But I never measured it. Before I machine anything, I think I'll tear down the engine and measure each cylinder with a dial indicator to see how far the piston comes up. That should tell me if it was machined strait too. Then at that point I will only mill one piston down and test fit it with putty in the dish to see if the valves clear the shallower dish. If all is well, I can then cc the new shorter piston dish and figure out my compression ratio.

If it turns out my block's deck height is too short to work (trying to avoid machining too much off the pistons), I will have to look into getting a spare block, or just say "screw it" and spend the $$ for some custom pistons.

I'll keep you all updated.

Thanks for all the input,

Jeramie
 
The factory rods weigh in at about 720 grams each.

Arent the Hyper pistons Coated ? So would shaving them remove some of that outer layer ? The Hyper pistons have certain thermal characteristics and expand to a specific size when they reach operating temperatures, so Id imagine this could affect the way they might react in the engine environment. Forged might be a different situation, but I dont really know, Im just thinking ..

Thanks for the weight info.

The hyper pistons are coated, but only on the side skirts. Its to help make them more "slippery" from what I understand.
 
Well that makes sense that they would be coated on the outsides.

I wrote it down, but I believe the pistons were about 670 grams each ( Sealed power, Hyper type ) .. not sure about the stock pistons, or the wrist pins.

- Dan
 
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