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Old 01-26-2011, 09:44 PM
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Choosing pistons

Hi,
Okay, I am working out the parts for the bottom of my 383 Chevy build, and I am considering 2 different pistons. I would like your thoughts on them, good or bad.

Keith Black IC734-030
or
Sportsman Racing Products 138103

Both are forged pistons with 1/16 1/16 3/16 rings
The SRP is a dish piston with a 16 cc dish, and a 1.125 comp height, which will give me a comp ratio of 9.8.
The KB is a step dish piston with 18.6 cc dish and a 1.130 comp height for a comp ratio of 9.6.
The deck will be machined down to keep the quench at .040, no matter the piston I go with.
The heads I am considering have a 64 cc chamber.
The comp ratio difference is pretty small, so I doubt there would be a big difference in peak torque and HP. My thought is the step dish would have better quench effect. I have heard good and bad things about both KB and SRP.
The SRP bore clearance is tighter at .0025 to .0035 then the KB's at .0035 to .0045.
The SRp costs a little more, but not all that much.

So, what are your thoughts.

Thanks,
Michael

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Old 01-26-2011, 10:17 PM
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Both of those Pistons are actually a D-Dish or Inverted Dome.
I'd try to stay close to 9.5Cr to inable using cheaper lower octane fuel.
A friend of mine has a 383 w/Vortecs & Bowl type Dish Pistons & about 9.8Cr, it needs 93 octane for best performance but, will run on 87 w/timing retarded slightly. With the D-Dish you should be able to run lower octane & optimal timing with the correct Cam.
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Old 01-27-2011, 12:02 PM
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I am running those sportsman pistons in my 383 engine. Very happy with them! Good quality and like you said, can run them a bit tighter than other forgings! Imho get the srp sportsmans, they are made by JE pistons.
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Old 01-27-2011, 12:59 PM
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Quote:
Originally Posted by mbaldwin
Hi,
Okay, I am working out the parts for the bottom of my 383 Chevy build, and I am considering 2 different pistons. I would like your thoughts on them, good or bad.

Keith Black IC734-030
or
Sportsman Racing Products 138103

Both are forged pistons with 1/16 1/16 3/16 rings
The SRP is a dish piston with a 16 cc dish, and a 1.125 comp height, which will give me a comp ratio of 9.8.
The KB is a step dish piston with 18.6 cc dish and a 1.130 comp height for a comp ratio of 9.6.
The deck will be machined down to keep the quench at .040, no matter the piston I go with.
The heads I am considering have a 64 cc chamber.
The comp ratio difference is pretty small, so I doubt there would be a big difference in peak torque and HP. My thought is the step dish would have better quench effect. I have heard good and bad things about both KB and SRP.
The SRP bore clearance is tighter at .0025 to .0035 then the KB's at .0035 to .0045.
The SRp costs a little more, but not all that much.

So, what are your thoughts.

Thanks,
Michael
Both are good, the KB is made from a more traditional material 2618, good, strong stuff but expands and contracts more than eutectic aluminum so it requires a looser clearance which then requires some engine warm up time to establish ring seal and eliminate skirt banging. The SRP is a high silicon eutectic alloy, these have almost the same strength as the 2618 material but is more brittle, they don't expand and contract as much 2618 with heat cycles this allows them to be run with a tighter clearance which provides better ring seal and doesn't batter the skirts when they are cold, so you can wail on these without having to warm them up. I've used both except for the extra care and feeding the 2618 alloy needs on start up I have otherwise found them to be pretty close. If this is going to be a street engine I think the SRP's would be easier to live with from the standpoint of being able to just start-up and go. Racing I think the SRPs are less prone to seizures from over heating or sudden temp changes but will not tolerate detonation as well as the KBs. SRP offers a Napier second ring, these are great for a racing engine as they really take the oil off the walls and that helps keep it out of the combustion chamber, on the street I think this ring runs the upper wall too dry resulting in more wall wear than is desireable.

Bogie
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Old 01-27-2011, 09:01 PM
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Thanks for the thoughts. I am still undecided, but it is not like I have to make a choice right this second. The plan is to stuff the 383 in a 81 Monte Carlo for a toy, not a daily driver, but not for a competitive racer, just something to have fun with.
Thanks again, I am sure I will have more questions.

Michael
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