Piston Clearance

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Drg racr

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I was checking clearances on my 360. My crank was already turned .010 recently, so I think just a fresh set of bearings will do it. But, I checked the pistons, and they're like a quarter inch down the more or more at TDC!! And these are flat tops, .030 over. Is that normal? No wonder the compression is so low on the 360.
Any advantages to running dome pistons?
 
Did you actually measure this or just "look" at them? If what you say is true, something is seriously wrong. What all have you changed, crank, pistons, etc? Sounds like your crank grinder swapped your crank for a de-stroker and didn't bother to tell you!!!
 
Sounds like you've got a set of low compression pistons.

I measured a set of flat tops that I put into my 318 to begin with and they were a touch over .150" in the hole at TDC.

They are made for heavy vehicle/ industrial use.

If you want your engine to run good: Throw them in the trash and buy a good set. They aren't exactly cheap, but affordable and worth the money, if it's a high performance build. You'll be disappointed if you keep them in, if you are building this engine to run fast.

I don't like to break bad news, but I've been down this exact road.
 
I just looked up the Silvolite replacement slugs...apparently, they would be about .110" in the hole for a blueprint height of 9.6"...damn-that is pretty low.
 
Well, my buddy didn't believe me either. So he came over and brought his measuring instruments with him. He checked my mic and found that somewhere along the way I messed it up. It was .130" off. He then mic'd my clearance, and found it to be .125" below deck. Still sounds high, but I'm used to zero deck motors when they're rebuilt. Sorry for the alarm, but that's what I get for not checking my tools!!:banghead:
 
Yea.

Silvolite is the low buck brand, owned by United Engine, who also owns Keith Black, which is their race application and high performance application brand cast piston. They also own Icon, which is the name they use to hock their forged units.

130 is in the 7:1- 7.5:1 range
 
Everybody is off because the factory block height roll ranges are very off and quality control is a joke. I have had KB-107's down the hole .020.
The crank being ground doesn't destroke it. I extreme my high doubt you have a destroyed crank. In a MAJOR WAY!

If your that far down the he then you have replacement pistons designed for a low 8-1 ratio.
 
The only reason the crank would be changing anything, is if someone stroke corrected the grind, which is a custom machining request that not all crank shops do and that kind of work is not common.

undersize crank cut to clean up the journals make up the material loss in undersize bearings.

107s in .020? Hmm... I've got a set of 167s that are .011" which is what they spec.
 
Nothing wrong with these pistons, but I doubt they're for a hi-po application. Might swap them for some forged ones. Still thinking of domes, especially if I have to run my current heads. If I zero deck the block, that's a lot of metal to grind off.
 
The 318 flat tops I had were exactly .154"... It's coming up on 1/4" Looks gross to the naked eye.

What is this engine going in?
 
Most aftermarket domes bring them up to 11:1 with a typical X or J head, some 10.5:1 with the right gasket and no deck work.
 
rumblefish360 said:
]Everybody is off because the factory block height roll ranges are very off and quality control is a joke.[/U] I have had KB-107's down the hole .020.
The crank being ground doesn't destroke it. I extreme my high doubt you have a destroyed crank. In a MAJOR WAY!

If your that far down the he then you have replacement pistons designed for a low 8-1 ratio.
Click to expand...

Quoted for the truth. Have seen the deck heights off as much as .030 on the same block. .120 down the hole is on par for replacement pistons.
 
It's going in my 69 Barracuda weekend racer. I'm trying to build a 360 on a reeeaally tight budget. The motor has already been rebuilt, but to stock specs. I think the pistons are Speed Pro units, which some claim to be around 9.5/1 with a smog head. I'm doubting that. I'm guessing with my 1051's, it'll put the compression around 8.2/1.
 
Those are good gaskets.

I'm running them.

If you want some more squeeze, plan to go with a set of magnum heads, especially with those pistons.

If you want to use an open head, you can with those pistons, but don't expect much.

If those pistons have valve reliefs, don't forget to add CC to the volume on those for CR.
 
I guess it really depends on how much power you want to make or how fast you want to go?

If the engines in good shape as is, just cam it for the low compression.....Decent lift and a mild to moderate duration. If you want to run brackets, just tune it nice and clean with the carb/timing and let it run what it runs. Lot's of win light's can be had that way.

If you want to make more power and go faster, then a piston change is in your future.....That's why the KB's are so popular.
 
Good idea on the cam.

Advance the thing 3-4 degrees and it will help bring up cylinder pressure, even though your initial static compression ratio won't be as high as it could be.

In the end, dynamic compression is what matters. Build cylinder PSI to build power. You can do it a lot of ways.
 
67Dart273 said:
It does if that's what the machinist did to it.........lol
.
Click to expand...

Sometimes, I'm not sure if your screwing with me or your just simply on drugs with the cmenta you make. Considering what he said...
 
Now if I run the magnum heads, say the '88-'91 heads, I can run my old intake, right? I know a guy that has some 340 heads, if he'll sell them. he's been sitting on them for years.
 
Most machine shops if any good will bore the motor as per the piston set installed. Get a zero deck height piston and have the same shop correct the problem. They bored it. Then take some cranking pressure out with Heads or gastkets or camshaft choice. You can lower the compression if its to high easier then you can raise it if its to low.
If they are good slugs you bought. You can through some boost to it.
 
Back in the day you had two choice, stock pistons that were figured with a "blue printed eng."( so the compression was lower then what was stated)

OR, you had a 11:5 piston that was based off a non blue printed eng. and you got your 11:5 compression.

Now a day, there a lot of ways to get compression between 8:1 and 11:5....or higher for that matter.
You just have to do the math to figure it out.:cheers:
 
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