Pistons specs question for 340 build

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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.
Yes, now I think about it - silly me, even the big end area is reciprocating mass. I suppose I was thinking it was just as much a part of the conrod as it is the piston. But it's adding to the conrod, so it's part of the piston mass that the conrod has to move. Those figures for the 440 pistons and pins are huge compared to the SRP weight of 462g. But it's good because I'm starting to get an awareness of weights now. I know the old TRW forged were pretty heavy (even though they could take huge punishment) and that stopped a lot of racers of the day using them.
 
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.

That's very interesting, almost horrific (from an engine builder's view) but not a good advertisement for MP. if that's what they were.
 
just posted the link cause they show how much they weigh
I can't see where you posted it, I will look at previous posts maybe you edited one? Thanks in advance.

EDIT: Ok I see it now !
 
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

I've just edited this post due to my later post showing the UEM pistons further down which is the opposite of what you said. From this discussion the + or - refers to the amount of material added to or subtracted from the piston (crown) in total flat top form. So it's crown volume. Couldn't be simpler. But it seems this is in conflict with what some manufacturers have. With dome showing a negative (-ve) value and dish or reliefs as a positive (+ve) value. Which is what I saw from the start and was wondering why...
 
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Just had a look at the PDF that Nat posted the link to. That has now given me a very good idea of weights. The Mahl PowerPak piston range goes from 470g to 512g. The heaviest one being what my engine is: standard stroke 340 + 0.030. So that SRP forged I mentioned previously at 462g is quite light. If there is only a few grams difference between the KB Hypers and the DSS FX1 (ie if the KB's are bit lighter) I might still buy the DSS. They also offer a ring package as well.
 
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Yes, now I think about it - silly me, even the big end area is reciprocating mass. I suppose I was thinking it was just as much a part of the conrod as it is the piston. But it's adding to the conrod, so it's part of the piston mass that the conrod has to move. Those figures for the 440 pistons and pins are huge compared to the SRP weight of 462g. But it's good because I'm starting to get an awareness of weights now. I know the old TRW forged were pretty heavy (even though they could take huge punishment) and that stopped a lot of racers of the day using them.
Nope, big end of the rod is rotating, (along with the rod bearing and oil). The small end of the rod, piston,pins, clips, and rings, are reciprocating.
And my ross dished for my 440 stroker are almost 400gr lighter than thosd maxwedge pistons.
 
Nope, big end of the rod is rotating, (along with the rod bearing and oil). The small end of the rod, piston,pins, clips, and rings, are reciprocating.

Ah, you made me look it up - I never actually knew what reciprocating meant in a mechanical sense. Although I knew the internal combustion engine converted up and down motion into rotary motion. "Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth linear motion. The two opposite motions that comprise a single reciprocation cycle are called strokes". Courtesy Wikipedia.

But I shouldn't digress from the original post.

Thanks for all answers and contributions.
 
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I just had a look at the KB pistons site (they are made by UEM) and their protocol is opposite to what people are talking about here and what I thought would be correct. See the three pictures as well as the link below if interested, you can clearly see that the domed pistons are given as a -ve value and the dished and valve relief pistons are +ve value.

KB AUTOMOTIVE - KB Automotive Hyper

KB Pistons 1.jpg


KB Pistons 2.jpg


KB Pistons 3 (hemi).jpg
 
Just had a look at the PDF that Nat posted the link to. That has now given me a very good idea of weights. The Mahl PowerPak piston range goes from 470g to 512g. The heaviest one being what my engine is: standard stroke 340 + 0.030. So that SRP forged I mentioned previously at 462g is quite light. If there is only a few grams difference between the KB Hypers and the DSS FX1 (ie if the KB's are bit lighter) I might still buy the DSS. They also offer a ring package as well.
Mahle are really good pistons use them on my last 340 build DSS MAKE SOME GOOD PISTONS AS WELL using them on my stroker build , they custom made me a set if -13 cc dished pistons and they all weigh in at the exact same weight 635grams , they were made and delivered in 3 weeks . Either way thy are both quality pistons
 
Mahle are really good pistons use them on my last 340 build DSS MAKE SOME GOOD PISTONS AS WELL using them on my stroker build , they custom made me a set if -13 cc dished pistons and they all weigh in at the exact same weight 635grams , they were made and delivered in 3 weeks . Either way thy are both quality pistons

Thanks for the tip and the weight. I'm just about to try and call up UEM to see if they have a weight for the KB 340 piston. I checked Mahle on Summit Racing but they are too expensive for me.
 
Thanks for the tip and the weight. I'm just about to try and call up UEM to see if they have a weight for the KB 340 piston. I checked Mahle on Summit Racing but they are too expensive for me.


Piston weight is not a big deal. Neither is pin weight. 90 grams on piston won’t ever show up. Ever. Pin weight is the same. A heavy pin comparatively will not make or take one HP. Unless you are trying to match piston weights all this is just an exercise in futility.
 
I just had a look at the KB pistons site (they are made by UEM) and their protocol is opposite to what people are talking about here and what I thought would be correct. See the three pictures as well as the link below if interested, you can clearly see that the domed pistons are given as a -ve value and the dished and valve relief pistons are +ve value.

KB AUTOMOTIVE - KB Automotive Hyper

View attachment 1715775232

View attachment 1715775233

View attachment 1715775234

Look at the Wallace link I posted as well. What you say is "standard across the board" is actually "backwards across the board". I don't know at what point in time it came to be used in such a fashion, but it's wrong as wrong can be.

Any "good" grammar school geometry student will tell you the same thing.
 
I called up both UEM (who make KB Hypers) and DSS Racing and was surprised I got straight onto the right tech guy in each case within 2 minutes. Both guys were really helpful and friendly and went and weighed some similar pistons. Both were within 5g of each other, at around 580 +/- 10g + 132g pin so that's interesting.

I'll probably get the DSS Piston & rings package $750 since I know they're made in the USA. I'm not sure where UEM gets the KB's made but if it's not USA I could probably guess.
 
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I called up both UEM (who make KB Hypers) and DSS Racing and was surprised I got straight onto the right tech guy in each case within 2 minutes. Both guys were really helpful and friendly and went and weighed some similar pistons. Both were within 5g of each other, at around 580 +/- 10g + 132g pin so that's interesting.


The difference is in the ring pack. The KB’s use the 5/64-3/16 ring pack and the DSS use a 1/16-3/16 ring pack. The thinner ring pack is way more important than piston and pin weight.
 
The difference is in the ring pack. The KB’s use the 5/64-3/16 ring pack and the DSS use a 1/16-3/16 ring pack. The thinner ring pack is way more important than piston and pin weight.

Damn right it is. WAY less friction.
 
The difference is in the ring pack. The KB’s use the 5/64-3/16 ring pack and the DSS use a 1/16-3/16 ring pack. The thinner ring pack is way more important than piston and pin weight.
Thnks, That'a also interesting, I didnt realise that but I would have noticed sooner or later when ordering rings. Well that's definitely made my mind up for the DSS pistons.
 
Thnks, That'a also interesting, I didnt realise that but I would have noticed sooner or later when ordering rings. Well that's definitely made my mind up for the DSS pistons.

I'd also recommend low tension rings, too. You'll never notice a difference in oil consumption, but the benefit in reduced friction is really good.
 
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' ?
DSS said their 6350-4060 piston was 574 grams. The pin was 146 grams. The clips are 4 grams for one pair (one piston set).
 
DSS said their 6350-4060 piston was 574 grams. The pin was 146 grams. The clips are 4 grams for one pair (one piston set).

That's interesting because I spoke to DSS as well as UEM (who make the KB HyperEutectics) and both gave me almost identical weights which are different from yours but arrive at the same weight (720 +/- 3g). They told me around 588g for the piston and 131g for the pin. They said that the piston will vary according to castings as well as oversizes.
 
Just missed out on a bargain here, see below picture. JE Pistons (SRP) Flat top with the 5cc valve reliefs in the size I need 4.070 from PitStopUSA in Idaho, half price at US$546! But they don't ship internationally and they don't accept payment from outside USA either. Also I called them up and they only have one set left. Dang! Oh well, just letting people here know in case they can use them, grab them at that price!

JE SRP Pistons Sale.jpg
 
Summit has these for that same price so maybe that's a normal price but they don't have them in 030 over. Will have to see if they can order them

Edit: One and a half hours later, I have called up Summit and they did a special order SRP Forged Flat top for me from the manufacturer - piston and rings set $546.47.
 
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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.
My 1989 TRW catalog shows a 2295 dome piston as 13.1/12.1 cc. No plus or minus.
It shows a 2266 as "flat head" (no cc rating) cause its a flat top with no reliefs.
It shows a 2355 (six pack, four relief flat top) as minus 7cc.
It shows 2399 (my 454 chevy piston, small dome, with an exhaust valve relief) as 13.8 cc. (No plus or minus)
All of these are in a column marked "effective dome volume".
 
My 1989 TRW catalog shows a 2295 dome piston as 13.1/12.1 cc. No plus or minus.
It shows a 2266 as "flat head" (no cc rating) cause its a flat top with no reliefs.
It shows a 2355 (six pack, four relief flat top) as minus 7cc.
It shows 2399 (my 454 chevy piston, small dome, with an exhaust valve relief) as 13.8 cc. (No plus or minus)
All of these are in a column marked "effective dome volume".

And that's correct. What's getting lost and dazed and confused is, we're talking about two different things. Piston volume is not the same as chamber/cylinder volume. That's where the problem is.....and it should never have been measured like that. They should have measured pistons in the same manner as chamber and cylinder volume, but somewhere along the way somebody glommed up the works tryin to be "smart".
 
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