Rebuild with forged internals vs. rebuild with stock internals?
11-14-2014, 03:26 PM
#11
Thread Starter
Join Date: Nov 2014
Location: Alabama
Posts: 9
Well, sort of. The stock pistons are hypereutectic, which just means that they are a high silicone content cast piston. The high silicon content has two benefits and one major draw back. The benefits are that it has high scuff resistance and low thermal expansion. This allows manufacturers to set the piston to wall clearance very tight and the piston will take very little wear over a long service life. The major detractor is that the silicon is never evenly distributed through the piston. High concentrations of silicon through the piston make it brittle, and any engine detonation often results in the piston shattering. This sends shards of metal through the engine, quickly destroying everything else.
A forged piston has much lower silicon content and a much more even grain structure because of the forging process. This makes it much stronger. The trade off is that the low silicon content means greater thermal expansion. Thus, the piston to wall clearance must be greater, especially when cold. This results in some piston noise on cold start and you should not drive the engine hard until it reaches operating temperature. However, that doesn't mean you can't drive it at all until it warms up. I've also never heard of the requirement to wait till a warm forged engine cools before restarting it.
The scuff resistance is also less, so the pistons will not last as long, although coatings can mitigate this.
However, forged pistons do not shatter like hypereutectic pistons under detonation. Their ring lands are also much stronger, thus forged pistons can handle much higher power levels.
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A forged piston has much lower silicon content and a much more even grain structure because of the forging process. This makes it much stronger. The trade off is that the low silicon content means greater thermal expansion. Thus, the piston to wall clearance must be greater, especially when cold. This results in some piston noise on cold start and you should not drive the engine hard until it reaches operating temperature. However, that doesn't mean you can't drive it at all until it warms up. I've also never heard of the requirement to wait till a warm forged engine cools before restarting it.
The scuff resistance is also less, so the pistons will not last as long, although coatings can mitigate this.
However, forged pistons do not shatter like hypereutectic pistons under detonation. Their ring lands are also much stronger, thus forged pistons can handle much higher power levels.
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11-14-2014, 03:38 PM
#12
2nd Gear Member
Join Date: Apr 2014
Location: IL
Posts: 335
No, with proper maintenance and oil change intervals/quality, you should have no problem getting 100K out of a forged engine. Try to get pistons with a coating on the thrust faces (Manley and most other quality manufacturers will have this) as that mitigates the wear.
11-14-2014, 05:46 PM
#13
Thread Starter
Join Date: Nov 2014
Location: Alabama
Posts: 9
Are the parts I was quoted for good quality? Sealed Power forged pistons and Eagle forged h beam rods? I am going to reuse my stock crank.
11-15-2014, 08:14 PM
#14
6th Gear Member
Join Date: Aug 2007
Location: MO/ Born and raised in Louisiana
Posts: 10,696
Hey Soldier, I was looking at your page with your build details. It looks like you are running forged 11 cc pistons at .030 over on stock 42cc heads? Do you know for sure what compression ratio you have, and how much pressure are you able to run with the blower on what octane? I ask because my son's 2002 GT is getting 11cc .020 over forged Manley pistons as we are deciding on 38cc (11.75:1 if the calculator I used is correct) or 44cc (10.67:1) TFS heads. Down the road, he may want to supercharge it. The 38cc heads would rule that out, but it may be possible to go with a low PSI 44cc combo.
11-15-2014, 08:27 PM
#15
2nd Gear Member
Join Date: Apr 2014
Location: IL
Posts: 335
On the plus side, I went on Trick Flow's website and they have a build that is nearly identical to what he will have. It made 408HP! I think his compression ratio will be slightly higher with the .020 over bore compared to that build, so there is no doubt he will have plenty of ponies.
I also got him a used steering wheel pulled from a 2003 Cobra. It arrived the other day and looks brand new. The leather wheel in his car is worn down to the metal at the top after 143K miles. This is his birthday present (he turns 20 at the end of the month). I ordered a tool from Amazon to pull the wheel and it will be here next Friday. Now I have to decide if I want to install it and show him or wrap it up and let him install it later.
I just did a compression calculator with updated info specific to the deck height, head gasket bore diameter, and compressed head gasket height. I got ~10.49:1 with the 44cc heads, which should allow for a low pressure supercharger later on.
11-15-2014, 08:31 PM
#16
2nd Gear Member
Join Date: Apr 2014
Location: IL
Posts: 335
Sealed Power and Eagle are both well known performance brands. I've heard some debate as to whether Eagle are Chinese parts, but then what isn't these days?
11-15-2014, 11:36 PM
#17
Thread Starter
Join Date: Nov 2014
Location: Alabama
Posts: 9
So you believe those parts would make for a good strong short block? If I'm spending all that money I don't want to get cheaply made parts that won't be reliable.
11-16-2014, 12:08 AM
#18
2nd Gear Member
Join Date: Apr 2014
Location: IL
Posts: 335
They will certainly be stronger than the originals. You would have to ask the seller what power level they are good for and then figure out what your power goals are. The absolute upper limit for the stock cast crank is 600HP.
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11-16-2014, 08:41 AM
#19
6th Gear Member
Join Date: Aug 2007
Location: MO/ Born and raised in Louisiana
Posts: 10,696
Hey man i went the route of building a short block and as stated earlier had issues. After three days the block had major detonation. If I had to do it all over again, I would have went with the route that I am going with now and just buy a new forged shortblock already built. I would suggest MMR. Those guys have excellent customer service and an excellent warranty. I bought my 900 for 2800 bucks shipped to my door. The price may seem kinda steep but once you start buying the internals for your block, machine work, installation of the block etc, you'll looking at close to 2 grand if not more. Also MMR has layaway so that's also a perk.
11-16-2014, 02:05 PM
#20
Thread Starter
Join Date: Nov 2014
Location: Alabama
Posts: 9
Hey man i went the route of building a short block and as stated earlier had issues. After three days the block had major detonation. If I had to do it all over again, I would have went with the route that I am going with now and just buy a new forged shortblock already built. I would suggest MMR. Those guys have excellent customer service and an excellent warranty. I bought my 900 for 2800 bucks shipped to my door. The price may seem kinda steep but once you start buying the internals for your block, machine work, installation of the block etc, you'll looking at close to 2 grand if not more. Also MMR has layaway so that's also a perk.