Pistons specs question for 340 build

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33IMP said:
Now THAT i can agree with! I did say earlier that actual MEASUREMENTS will be required if you want the calculations to be right. He cant just plug in numbers.
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But that's why "just pluggin in numbers" is dangerous. THAT'S the point I'm trying to make here. You need to plug in the RIGHT numbers.
 
Now im curious. Ive got a thirty year old trw catalog that lists dome volume, and valve relief volumes, but i dont remember exactly how, and its 200 miles away.
 
33IMP said:
...so i assumed the -5 and -16 were both minus'ing chamber volume.
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Yes so did I, but they are ADDING to the volume, not taking away, so the CR goes down. I didn't know that the other manufacturer uses a positive for theirs, seems like there's no standard for that yet. As you say (and I didn't know until you said it) the 5 is 5cc for the valve depressions and 16 is for the dish. The only minus value should relate to the CR, but it's not, so it seems strange they use it for cc
 
pishta said:
I think that "CROWN CC" is a rarely used measurement of the volume of the eyebrows, not the piston material. in the 4595 specs, the volume is actually 5 cc's of material REMOVED from the piston face... anyone else would state that's a -5cc
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Yes that makes sense.
 
But it does make sense that if you remove material from a piston it would be stated as a negative value. I think the calculators for CR need the +ve values as it's CR that is going to be the end result and increasing volume decreases the CR.

But anyway, not wanting to sound like a broken record (and yes I grew up as a school kid buying Alice Cooper and Led Zep records for $4 each...), I'm hoping that someone reading this thread knows if the DSS Racing pistons are lighter than the popular KB Hyper's. I have read that the DSS are rated as on the heavy side for a forged. And I know the KB's, even though technically a cast piston , are lighter than the stock ones. But I need some numbers hopefully and I don' know why manufacturers don't post the weight of their pistons in their specs - well maybe the top dollar ones do but I haven't seen any weights for shelf pistons.
 
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70Hardtop said:
Yes so did I, but they are ADDING to the volume, not taking away, so the CR goes down. I didn't know that the other manufacturer uses a positive for theirs, seems like there's no standard for that yet. As you say (and I didn't know until you said it) the 5 is 5cc for the valve depressions and 16 is for the dish. The only minus value should relate to the CR, but it's not, so it seems strange they use it for cc
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Well, there IS a standard and I can tell you what it is.

When you actually SIT DOWN and manually figure compression ratio using formulas, instead of online calculators, you must use the positive and negative numbers as I outlined. If you reverse that, your results will not be correct. That's why I make the argument. If you use the online calculators, just make sure which way they use those figures and that you are entering them correctly.
 
70Hardtop said:
But it does make sense that if you remove material from a piston it would be stated as a negative value. I think the calculators for CR need the +ve values as it's CR that is going to be the end result and increasing volume decreases the CR.

But anyway, not wanting to sound like a broken record (and yes I grew up as a school kid buying Alice Cooper and Led Zep records for $4 each...), I'm hoping that someone reading this thread knows if the DSS Racing pistons are lighter than the popular KB Hyper's. I have read that the DSS are rated as on the heavy side for a forged. And I know the KB's, even though technically a cast piston , are lighter than the stock ones. But I need some numbers hopefully and I don' know why manufacturers don't post the weight of their pistons in their specs - well maybe the top dollar ones do but I haven't seen any weights for shelf pistons.
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Where the confusion comes in is that ultimately we're not talking about the piston at all. We're talking about volume. So in that sense, taking away from the piston adds to volume and must be looked at with a positive number when making calculations. Conversely, when a piston takes away volume, such as a dome, you must use a negative number when making calculations. That's not debatable. That's math and math doesn't lie.

Now, if you're using calculators that calculate that backwards, like evidently the Wallace calculator does, then you have to use the numbers like you're saying. But with a standard formula for volume you'd be backwards.
 
33IMP said:
Now im curious. Ive got a thirty year old trw catalog that lists dome volume, and valve relief volumes, but i dont remember exactly how, and its 200 miles away.
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I can just about guarantee you that catalog uses negative numbers for domes and positive for dishes, just like the two Speed Pro examples I posted, since the Speed Pro is essentially the old TRW pistons using the same part number.
 
Anything above the crown is +cc, anything under it is -cc. Think of it like a flat top box and use that to determine what the calculator is asking. Is it combustion chamber volume at TDC, cause a dome is gonna give you a smaller chamber volume and higher CR. A TRW forged 340 is gonna have some extra dome on top, +cc. A cast Dodge 360 is gonna have a dish, -cc. even a flat top with valve reliefs is gonna be a small - number just like a dish. We can beat this sideways but ultimately its what the calculator is asking in whatever terminology they use. If your still questioning the input value, put in an exaggerated value and watch what the calculator does with it l. You'll know which way to go from there.
 
Piston to deck relationship.......A negative number means that the piston is above the deck. i.e. reducing the combustion chamber volume. That's my story and I'm sticking to it!:lol:
 
pishta said:
Anything above the crown is +cc, anything under it is -cc. Think of it like a flat top box and use that to determine what the calculator is asking. Is it combustion chamber volume at TDC, cause a dome is gonna give you a smaller chamber volume and higher CR. A TRW forged 340 is gonna have some extra dome on top, +cc. A cast Dodge 360 is gonna have a dish, -cc. even a flat top with valve reliefs is gonna be a small - number just like a dish. We can beat this sideways but ultimately its what the calculator is asking in whatever terminology they use. If your still questioning the input value, put in an exaggerated value and watch what the calculator does with it l. You'll know which way to go from there.
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Nope. We'll agree to disagree on this. Look at an actual written formula for figuring compression and you'll see what I mean. It's all about letting something else do the work for you, instead of figuring it out on your own. Simple as that, really.
 
CFD244 said:
Piston to deck relationship.......A negative number means that the piston is above the deck. i.e. reducing the combustion chamber volume. That's my story and I'm sticking to it!:lol:
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Yup. You got it!
 
70Hardtop said:
But it does make sense that if you remove material from a piston it would be stated as a negative value. I think the calculators for CR need the +ve values as it's CR that is going to be the end result and increasing volume decreases the CR.

But anyway, not wanting to sound like a broken record (and yes I grew up as a school kid buying Alice Cooper and Led Zep records for $4 each...), I'm hoping that someone reading this thread knows if the DSS Racing pistons are lighter than the popular KB Hyper's. I have read that the DSS are rated as on the heavy side for a forged. And I know the KB's, even though technically a cast piston , are lighter than the stock ones. But I need some numbers hopefully and I don' know why manufacturers don't post the weight of their pistons in their specs - well maybe the top dollar ones do but I haven't seen any weights for shelf pistons.
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DSS forged pistons were a few grams heavier than ICON forged pistons when I asked DSS directly two years ago. That makes them heavier than hypereutectic pistons for the same application, which is typical of most shelf pistons in a similar price range. They are not designed as an ultralight piston for really exotic engine builds.
 
@70Hardtop, i would just call DSS and ask for the weight for the part # you want. I cant find a tech line phone number however.
Considering you are in Australia, i would just e-mail them the part# you want, and ask.
 
33IMP said:
@70Hardtop, i would just call DSS and ask for the weight for the part # you want. I cant find a tech line phone number however.
Considering you are in Australia, i would just e-mail them the part# you want, and ask.
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I agree.
I emailed them. It was only two or three days and they sent a detailed response for piston, pin, and pin clip weights.
 
Thank you, and just to add to that, I saw on Summit looking at Sportsman Racing pistons, they have in the notes down the bottom of some piston specs: "gram weight" 462g. So that's a good start for a comparison.
 
33IMP said:
i would just call DSS and ask for the weight for the part # you want. I cant find a tech line phone number however.
Considering you are in Australia, i would just e-mail them the part# you want, and ask.
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Yes I will probably try either calling or emailing. Now I know what some US$850+ pistons weigh (see prev post) I can start comparing.
 
Bobzilla said:
I agree.
I emailed them. It was only two or three days and they sent a detailed response for piston, pin, and pin clip weights.
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Good news! Are you able to share the weights please - the flat top FX1 if you have that w/gudgeon and /w clips. Although I suppose the pin could be considered like a wheel, as 'unsprung weight' ?
 
Gudgeon pins are anything but, unsprung weight! They are a huge part of the reciprocating weight. You need to know the pin (gudgeon) weight of the new pistons to compare to stock.
(As an example, in my old TRW book, 440 pistons, and their pins, are the heaviest in the book. 225 gram pins! I have some old dome maxwedge pistons that are 1100+ grams with pins.)

And yes i remember you are dealing with a small block. Physics still applies.
 
When they sell pistons they list the piston dome + or dish - , they are not selling you compression, that is what the calculator (and your heads) determines. They have no idea what your head volume is nor do they care. That's probably why they sell pistons with the - dish and the + dome and the compression calculator asks for this value inverted as it is determining compression.

^^ my stroker cast pistons were so mismatched (MP castings by ?) that I had to take weight out the pins to get the heaviest one down to the 2nd lightest one. I actually added a zip of MiG wire to the lightest one inside the pin to get 3 grams. They were all over the place, maybe even 2 batches.
 
RustyRatRod said:
...and that number must be turned positive when figuring for compression. Unless the calculator does it for you.

Yall can post up all the links you want, that doesn't make them right.
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just posted the link cause they show how much they weigh , sory to offend you
 
Nat said:
just posted the link cause they show how much they weigh , sory to offend you
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Offended? Hardly. It's a good discussion with correct information everyone needs to know.
 
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