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Ok Heres the situation. Lets say you have a 96 Cobra with all the Boltons including longtubes. Your making only 310RWHP and you have no plans of going blower,nitrous or any other major mods. Your engine has high miles and its time for a rebuild.

Wouldnt it be a waste going forged pistons and rods? With forged pistons you have the large piston/wall clearances and the forged clatter/piston slap. If a cast piston will surely take the HP because it has been taking it all along on a stock part... Would one be better off with a cast piston vs forged even if they cost the same?

I know when I was into Shelby Dodges we ran Mahle Cast pistons and they took 20+ PSI of boost with no problems, does Mahle make a cast DOHC piston??
 

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Not sure but if your only running 310 rwhp and dont plan on going with any boost or nitrous, just get the hyperuetectic pistons. Better than cast not quite as strong as forged. Thats what came stock anyway.
 

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Get a set of CP pistons....no piston slap.
 

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SLVR01COBRA said:
Get a set of CP pistons....no piston slap.
piston slap??? please elaborate. I have diamond forged 10.5.1 pistons & eagle rods, and i've never heard 'piston slap' from the motor ... please educate me...
 

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The point is if you have the motor apart, you might as well put the good parts in because the cost of labor is high. You don't want to have to do it again.

Besides, you never know if you will get the power adder bug :)
 

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blacksnake305 said:
piston slap??? please elaborate. I have diamond forged 10.5.1 pistons & eagle rods, and i've never heard 'piston slap' from the motor ... please educate me...
yeah me too:)
 

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Chris - Some of the earlier forged motors had piston slap. They sounded rather diesel-like, which isn't the case anymore. I remember a vid clip of a guy who had a forged motor before a lot of places started doing any internal work on mod motors and it didn't sound good.

SSHEL-B - You shouldn't have this problem now. I've heard forged setups in person and haven't heard the slap.

I think once more people started getting into the mod motor they figured out what was causing these problems and over time have corrected them. If I was paying the same price, i'd sure as heck get the stronger ones.
 

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hell no u don't want cp pistons.

they are about the most expensive and strongest piston out there. that would be a total waste of cash.

i got a set of barely used JE .020 over flat top pistons that i would sell ya much cheaper then any new ones. they are in great shape, are quiet and are good for NA applications.

[email protected] if you are interested.

Piston slap occurs because forged pistons expand more compared to hyper pistons. Since the engine builder must account for this, the piston ends up being slightly too small for the bore when they are cold. So before the engine warms up, the piston rocks around in the bore causing the diesel type noise. Once the engine is warm, you should not hear anything like that.
 

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I wonder the same thing as I will stay NA and may have to rebuild some day. A question: Isn't the hyper piston lighter than a typical forged one?

Not as strong to be sure - but if one is staying NA and out of detonation, then I would think lighter is better as it reduces reciprocating mass. Assuming they ARE lighter?

-Dave
'01 Cobra coupe
 

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Another question:

Should you be concerned about getting stronger internals if you are going with a higher compression rate (such as 10.5 - 11:1)?
 

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higher compression will make detonation easier and forged pistons are just better at handling detonation. It isn't neccessary but yes it would be better.
 

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There are many companies that sell forged pistons that would be suitable for n/a applications. If you are going into the motor go with forged pistons. Do NOT mess around with cast or stock pistons. If I had an NA street car I would go with 11.1 slugs and shroud the valves to reduce the compression just a tad. Or if you have a means of adjusting the tuneup I would go with 11.5 slugs and run less timing for pump gas, more timing with race gas. If you are into reducing recipicating mass theres a lot you can trim off the crankshaft. It still wont give you more than 5 to 10 rwhp and isn't the least expensive mod (mallory is very expensive).

As for cast pistons you can't say there aren't strong in a blanket statement. Cast pistons are used in 2000-2002 Suburu STI's and they handle 20 pounds of boost without any problems. The cost difference between cast and forged isnt worth going with cast when you can get nice forged pistons.
 

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the 'piston slap' commonly assosiated with forged pistons in all engines is due to the fact that forged pistons have a much greater expansion coefficient then any cast piston. therefore, when the engine is cold, the pistons will have shrunk down a bit, and once warmed, will be up to specified size. a cast piston is extremely rigid, and a 'hyperutectic' cast piston, is basically a cast piston, but using a special process, i forgot the ratios, more silicon is mixed into the material then would be a eutectic, or perfect mixture, of silicone and aluminum, is even more rigid and has that much lower thermal expansion properties. This rigidity makes ita great piston for any stock motor, and really, even higher horsepower engines. the only true advantage of a forged piston is overall ability to take abuse with great resistance to cracking/breakage. A bit of a knock or ping will be absorbed into the 'softer' , less rigid, and more forgiving material.

Now that you know the differences, i would agree with most of the statements ... that u never know when the power adder bug will get you, and your going to want to get blown on a daily basis. Under these boost conditions, either while or before tuning is done, u will be much safer with the forged pistons, due to their forgiving construction, and it wont cost you a tremendous amount more now while building the engine.

just my 2 cents plus a couple bucks
 

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blacksnake305 said:
piston slap??? please elaborate. I have diamond forged 10.5.1 pistons & eagle rods, and i've never heard 'piston slap' from the motor ... please educate me...
if you never heard it, then you dont have it...;)
 
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