hypereutectic vs. forged?
01-04-2003, 01:09 AM
#16
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Location: MI
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if they are so terrible why are they offered 9 times out of ten in the majority of engine buildups out there?
i'm all for having the strongest one can get, but if they are that "cheap" why would they be put in engines that are expected to see some mileage?
it seems like it's a rather rabid debate, those who have forged say you must have them while everyone else says you can get by without them....which is it? if your not building a race motor and you strictly want a good running street setup what's wrong with the hyper?
i'm all for having the strongest one can get, but if they are that "cheap" why would they be put in engines that are expected to see some mileage?
it seems like it's a rather rabid debate, those who have forged say you must have them while everyone else says you can get by without them....which is it? if your not building a race motor and you strictly want a good running street setup what's wrong with the hyper?
01-04-2003, 02:55 AM
#17
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Join Date: Jul 2000
Location: MD
Posts: 520
Forged and Hyper are 2 ends of the scale and both have their advantages and disadvantages.
Forged pistons only real advantage is the incredible amount of abuse they can take before failing. Many can be completely deformed and messed up without catastrophic failure (not taking out the block, head…) and in general, because they don’t break easily they are much more forgiving of going lean or extreme detonation when running a power adder.
Their disadvantages are that they don’t tend to be as dimensionally stable so they can expand much more from cold to hot then others so they have to be fit in the bores slightly looser, possibly causing cold start piston slap, blow by (emissions), hurting gas mileage…
Hypereutectic are the opposite, their silicon matrix makes them very dimensionally stable, allowing even tighter clearances then with normal cast pistons. It also makes them much more wear resistant… While this also gives the piston comparable strength to forgings, they loose toughness, they area very brittle and are not tolerant of any force that tries to deform them (they crack/shatter rather then deform).
Forgings are actually denser, so assuming that the pistons were otherwise identical they would be marginally heavier, but in the real world, piston design plays a much bigger factor on ultimate weight, so it doesn’t make a difference.
As has been said, good hypereutectic is probably the best choice for all applications with the exception being if someone is going to run a power adder. For that matter, if your power adder is going to stay perfectly tuned all the time (no detonation…), then they’d be fine there also, but once you see any significant detonation then a forging is better (some argue that in that situation plain cast is even better/more forgiving then hyper...)
Forged pistons only real advantage is the incredible amount of abuse they can take before failing. Many can be completely deformed and messed up without catastrophic failure (not taking out the block, head…) and in general, because they don’t break easily they are much more forgiving of going lean or extreme detonation when running a power adder.
Their disadvantages are that they don’t tend to be as dimensionally stable so they can expand much more from cold to hot then others so they have to be fit in the bores slightly looser, possibly causing cold start piston slap, blow by (emissions), hurting gas mileage…
Hypereutectic are the opposite, their silicon matrix makes them very dimensionally stable, allowing even tighter clearances then with normal cast pistons. It also makes them much more wear resistant… While this also gives the piston comparable strength to forgings, they loose toughness, they area very brittle and are not tolerant of any force that tries to deform them (they crack/shatter rather then deform).
Forgings are actually denser, so assuming that the pistons were otherwise identical they would be marginally heavier, but in the real world, piston design plays a much bigger factor on ultimate weight, so it doesn’t make a difference.
As has been said, good hypereutectic is probably the best choice for all applications with the exception being if someone is going to run a power adder. For that matter, if your power adder is going to stay perfectly tuned all the time (no detonation…), then they’d be fine there also, but once you see any significant detonation then a forging is better (some argue that in that situation plain cast is even better/more forgiving then hyper...)
01-04-2003, 08:47 AM
#18
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Join Date: Jun 2001
Location: SW Michigan
Posts: 304
So it would be safe to say that the Hyper can give a better ring seal. And that the same piston design, the Hyper will be lighter. I am checking this because I am trying to build the MAXIMUM HP with a stock engine. Stock type (flat top 4 valve relief .040 over) pistons. Stock cam and valvetrain. ported intake, gasket matched heads. And some oil control things. Probably a canton pan with an additional crank scraper.
This is a rules requirement thing.
Basically any power that can be made through machine work is legal. No head porting though.
This is a rules requirement thing.
Basically any power that can be made through machine work is legal. No head porting though.
01-04-2003, 12:47 PM
#20
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Location: MD
Posts: 520
Is this the basically stock LT1 that was asked about in another thread for autox or something?
from what you're describing I'd go with hypereutectic. I'd probably polish all the sharp edges on their tops as well as in the chambers, set the deck height to 0 and use a gasket in the .035" range.
from what you're describing I'd go with hypereutectic. I'd probably polish all the sharp edges on their tops as well as in the chambers, set the deck height to 0 and use a gasket in the .035" range.
01-04-2003, 01:10 PM
#21
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Location: Tx
Posts: 128
I think the KB Hypereutectic piston is an excellent piston for most naturally aspirated street engines and will even work well with mild nitrous and boost.
Weight comparisons:
The KB (3.75/ 6"/ 4.030/ 2-valve relief) weighs 425 grams. That's 10 grams more than a JE Pro Flat-top and 46 grams less that a comparable SRP forging. At less that $30 a piece, they're an excellent value.
Not the best piston for every situation but considering the fact that most are building 400-450 rwhp naturally aspirated engines, they're a smart buy.
Chuck Riddeck
Progressive Race Engine Development
Weight comparisons:
The KB (3.75/ 6"/ 4.030/ 2-valve relief) weighs 425 grams. That's 10 grams more than a JE Pro Flat-top and 46 grams less that a comparable SRP forging. At less that $30 a piece, they're an excellent value.
Not the best piston for every situation but considering the fact that most are building 400-450 rwhp naturally aspirated engines, they're a smart buy.
Chuck Riddeck
Progressive Race Engine Development
01-04-2003, 05:03 PM
#22
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Join Date: Jun 2001
Location: SW Michigan
Posts: 304
Originally posted by WS6 TA
Is this the basically stock LT1 that was asked about in another thread for autox or something?
from what you're describing I'd go with hypereutectic. I'd probably polish all the sharp edges on their tops as well as in the chambers, set the deck height to 0 and use a gasket in the .035" range.
Is this the basically stock LT1 that was asked about in another thread for autox or something?
from what you're describing I'd go with hypereutectic. I'd probably polish all the sharp edges on their tops as well as in the chambers, set the deck height to 0 and use a gasket in the .035" range.
Any draw backs to .040 over? In this situation I would think not. Also do you think strength is a problem considering 3000-6200 rpm for about 45 seconds about 6 times per weekend on average. Should be fine I would think.
Is 6200 a safe RPM limit? I could get away with some light CM pushrods. Would they help at all?
Thanks for all the help!!
01-04-2003, 06:37 PM
#23
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Location: MD
Posts: 520
I don’t think that strength will be a problem. My just about stock LT1 seemed happiest when shifted right at 6400 (datalogs always showed 6375, which is the highest output that I could get, with the rev limiter set at 6400, which I rarely hit), and it doesn’t seem any worse for it.
The problem is that you want to keep the quench distance right around .035” +/- .003”, above that you’ll loose compression, but will also have more of a tendency to have pockets that result in detonation, below that you start getting too close for comfort for head/piston contact.
The Impy gaskets are thinner, if I remember correctly, .028 or .029”, but they are designed for a iron on both sides of them (same expansion/contraction rates). I thought that the factory aluminum head gaskets are in the .038” range (again, don’t quote me but I know I’m close), and the common felpros that people use are around .041”. With the felpros (assuming that the #’s are all correct, like I said, I know I’m in the right range but I may be a few 1/1000’s off, I just haven't worked on anything GM for a little bit, so I haven't bought any headgaskets for a while) I would seriously consider setting the deck height at about .005” above the deck.
The problem is that you want to keep the quench distance right around .035” +/- .003”, above that you’ll loose compression, but will also have more of a tendency to have pockets that result in detonation, below that you start getting too close for comfort for head/piston contact.
The Impy gaskets are thinner, if I remember correctly, .028 or .029”, but they are designed for a iron on both sides of them (same expansion/contraction rates). I thought that the factory aluminum head gaskets are in the .038” range (again, don’t quote me but I know I’m close), and the common felpros that people use are around .041”. With the felpros (assuming that the #’s are all correct, like I said, I know I’m in the right range but I may be a few 1/1000’s off, I just haven't worked on anything GM for a little bit, so I haven't bought any headgaskets for a while) I would seriously consider setting the deck height at about .005” above the deck.
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