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.
Pistons specs question for 340 build
- Thread starter 70Hardtop
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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.
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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Put your numbers in this calculator and see what happens.
Compression Ratio Calculator - Wallace Racing
Compression Ratio Calculator - Wallace Racing
Then this one.
Compression Ratio Calculator
No fair cheatin. Enter your numbers JUST like you have been everywhere else in each one.
Compression Ratio Calculator
No fair cheatin. Enter your numbers JUST like you have been everywhere else in each one.
33IMP
Well-Known Member
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.
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 AUTOMOTIVE - KB Automotive Hyper
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
448Scamp
Running Free
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.
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.
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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448Scamp
Running Free
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.
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.
Bobzilla
Well-Known Member
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!
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.
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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33IMP
Well-Known Member
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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