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Any drawbacks to using forged pistons?

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Old 02-13-2007, 08:11 PM
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Originally Posted by Irocss85
and yes, forged pistons will make more noise when cold due to thermal expansion. basically the forged pistons will grow as they heat up and not rock back and forth like they will when cold.
My LS6 sounds like a diesel when it's cold so a little knocking would be nothing new.


Let's talk brand for a second, what does everyone like?
Old 02-13-2007, 08:20 PM
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go with a reputable brand. diamond, je, wiseco etc. i am sure there is differences but for what i would be using them for i doubt its anything i would notice
Old 02-13-2007, 09:44 PM
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Originally Posted by jub jub
Forged it is.

Will there be any HP loss over cast pistons?
i have forged pistons on my 346......thas why imma step up the comp a lil with a head swap
Old 02-13-2007, 09:59 PM
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I just built my engine using manley rods and diamond pistons,the engine is quieter with the diamonds,no knocking.
Old 02-13-2007, 10:47 PM
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I used the Speed Pro forged pistons on my L98 build up. They came from the factory coated. They are quiet on start up. No piston slap.

Now my 2000 Tahoe is another story on start up. I can hear the piston slap on it.
Old 02-14-2007, 07:17 AM
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Originally Posted by streetlegalls1
I just built my engine using manley rods and diamond pistons,the engine is quieter with the diamonds,no knocking.
Originally Posted by 1989GTA
I used the Speed Pro forged pistons on my L98 build up. They came from the factory coated. They are quiet on start up. No piston slap.

That's good to hear!
Old 02-14-2007, 07:40 AM
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Last year I decided to have my block forged, because of its piston slap noise.

I'm no mecanic so I had LPE do the work, they used JE pistons, made out of 4032 hi-silicon forging material. Im told, this metal doesnt expand much, so these pistons can be installed with a tighter clearance...meaning less noise at cold start-up as compared to other type of forged materials.

Anyway, all I can say is the car sounds nice & mean at started, cold, warm or hot! No slapping at all.
Old 02-14-2007, 08:08 AM
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Originally Posted by Michael02hawk
Last year I decided to have my block forged, because of its piston slap noise.

I'm no mecanic so I had LPE do the work, they used JE pistons, made out of 4032 hi-silicon forging material. Im told, this metal doesnt expand much, so these pistons can be installed with a tighter clearance...meaning less noise at cold start-up as compared to other type of forged materials.

Anyway, all I can say is the car sounds nice & mean at started, cold, warm or hot! No slapping at all.
In your original block, were you plagued by the notorious "tick" even after the engine came up to normal operating temp? The reason I ask is, I have the problem and have never been able to pin-point the noise. I have always just assumed it was excessive piston to bore clearance. Another reason I want to switch to a forged block with 3.905 pistons.
Old 02-14-2007, 08:16 AM
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i used mahle forged pistons in mine and there is no piston slap or knocking (however the car has only 1000 miles on the motor os far).

but stated by another user, my pistons dont expand as much so the clearance can be tighter to avoid piston slap.

i saved some money and built my motor from the oil pan up.
Old 02-14-2007, 09:15 AM
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My original 346 had noticable piston slap when cold. My forged 346 has no piston slap at all. Diamond pistons.
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Old 02-14-2007, 09:41 AM
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Also, forged pistons are typically lighter than their cast counterparts because it requires less material to make a significantly stronger and more durable piece.
Old 02-14-2007, 11:34 AM
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New modern forged pistons hardly make any noise over a stock piston if set up correctly. They are light years above the 60's-70's era forged slugs. I've had great results with Speedpro forged pistons in my marine engine builds. Have never had a problem and we run WOT for over 5 mins at times.
Old 02-14-2007, 11:51 AM
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Originally Posted by jub jub
In your original block, were you plagued by the notorious "tick" even after the engine came up to normal operating temp? The reason I ask is, I have the problem and have never been able to pin-point the noise. I have always just assumed it was excessive piston to bore clearance. Another reason I want to switch to a forged block with 3.905 pistons.
Yup, the stock engine was loud at cold start-up, got better when up to temp, but still had a ticking.
Old 02-14-2007, 11:52 AM
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So, only negligable power loss and no added noise.

Do they use oil? There was another (long) thread asking this but I can't remember the end answer. I'm thinking about attempting to rebuild my engine myself and I might spring for some forged pistons, but will probably keep the stockers if they look really good.

EDIT: And, by the way, my 109,000-mile '99 LS1 has never made any of this noise people are talking about, other than a very little valve train "sewing machine" noise.
Old 02-14-2007, 12:38 PM
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Originally Posted by Sharpe
Do they use oil? There was another (long) thread asking this but I can't remember the end answer.
I remember that thread. I believe the answer was that most of the stroker engines used more oil due to less piston control with a longer stroke. I will keep the stock bore and stroke so that shouldn't be an issue.

Well, I'm starting to get a good feeling now about going forged. Kind of makes all warm and fuzzy inside.



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