quick question about pistons

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diymirage

diymirage

HP@idle > hondaHP@redline
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is there such a thing as a drop in high compression piston ?
I really don't want to spend the money on a new bottom end right now but I am considering slapping some fresh pistons on there
ive read up on it and there seem to be some nice options out there that might bump the compression ratio on my old 360 up a tad but all of those seem to be lighter then the stock units and I really don't want to go through the hassle of having to rebalance everything

and what is the deal with piston rings nowadays (and why did that sound like jerry Seinfeld?) do they not include them with the pistons anymore?
has it been so long since I rebuild something 4 stroke?
 
You can change to a lighter piston with no ill effects.
 
(don't have the link) but I read one thread where you (among others) were talking about the KB107s and the whole rebalancing issue came up

so, if I want too I could install a lighter piston without needing to rebalance?
 
In theory a domed piston would raise the compression ratio, but in practice it's rarely done because of valve clearance issues -- there's no way to test clearance "on the shelf" -- everyone's motor is different. Plus, most performance builders are putting in a big cam or high-ratio rockers, and can't afford to give up any clearance. This is also why aftermarket pistons are lighter -- for performance -- they figure you want to optimize everything. This also explains the piston rings -- there are many types and brands, and people want to optimize their build to their price point.

The one exception would be if the factory offered two versions of the same motor; for example: the 273 2bbl with 9:1 CR and the 4bbl with 10.5:1 CR. The high compression pistons would be a straight swap, although you would probably also want the matching cam to take advantage.

If you really just want some extra CR, it would be simpler to plane the heads and manifold -- you wouldn't have to get into the bottom end at all.
 
yeah, ill most likely just let it be for now (maybe once I can afford the stroker kit ill worry about it)

I did have the heads looked at and shaved 8thou
(they had been worked on before so who knows how much has been removed before)
 
I don't think it would hurt a thing to use just lighter pistons. I would do it in a second and have with no trouble. I am sure others will be along to tell me how stupid I am but I wouldn't sweat it.

All that said, since you will be tearing the engine that far apart, what's to stop you from a rebalance? Money? While it would be better to do it, it's not necessary. I am sure the forum geniuses will disagree.
 
yeah, money is a big factor, this is rolling and rolling

im not sure how to price it out
pistons are roughly 300 ok, I can afford that
but now I need rings, what 50?
rob bearings, while im in there I might as well replace the mains , theres another 50
now I need to have it rebalanced...I don't know what that runs but the price tag keeps going up up up


at some point the wifey is going to wonder where all our money is going
 
If money's tight why not leave it alone or make other smaller changes to exterior stuff? Compression in and of itself doesn't do that much, and if it's a 360 the pistons are pressed on the rods. So you'll have removal and mounting costs in there too.
Personally I'd leave it alone if it was 6:1 unless I was going to internally balance it when the pistons were replaced. You can stick a cam in it, or pull the heads and mess with compression with the gaskets or milling if you wanted to for similar money.
 
Man, I know there are a lot of race scientists on here, but I have always felt that a set of pistons was matched closely enough in weight that you would never notice. If you are worried, weigh each one before installing it, I believe this is part of the blueprinting process. I installed a set of Keith Black flat tops in my 340 because I had old school dome pistons in it and wanted a more streetable engine that would run on todays gas. I have experienced no problems, but My engine isn't "blueprinted " either. It is a street car engime.
 
diymirage said:
yeah, money is a big factor, this is rolling and rolling


at some point the wifey is going to wonder where all our money is going
Click to expand...


That's when you pick something she spends money on and tell her it is her "uncontrollable spending" LOL!!
 
Bad Sport said:
Man, that snowball is getting bigger. :poke:
Click to expand...

no kidding, I should have been a politician, I don't know how I talked myself into taking the heads off so I could actually see the piston

if I ever go back to a vanity plate that's what it will be "snoball"
 
hey, at least you're only into gaskets at this point. It's when the pistons come out of the bores that things really get ugly...lol.
 
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