Piston upgrade without honing?

[Xjas]

I am helping a mate wind up his 09 WRX, the car has only 45000km on it and we have tossed up doing a piston upgrade as the stockers are only good to around 220rwkw.

I am wondering if anyone out there has done a piston swap on any engine without honing, either with new rings or reusing the old ones, and how did it go?

I know its not an LS engine but bores, rings and pistons are basically the same regardless of make.

[duke5700]

So your going to the effort of pulling the engine and putting in $1000 pistons, but you want to use 2nd hand rings and not hone the bores... Come on.

[Soopy]

Subaru engines are finiky at the best of times. Don't half ass it or you'll be doing it all over again very shortly.

[Xjas]

So your going to the effort of pulling the engine and putting in $1000 pistons, but you want to use 2nd hand rings and not hone the bores... Come on.

The flat four in a WRX is a bit different to a V8, you dont really strip the engine down much to get the pistons out, there are plugs in the ends of the block, you remove the plugs the pull out the gudgeon pin and then pull the piston out leaving the bottom end together (with the heads off obviously),
So a piston swap is really only a weekends work, splitting the block halves is a lot more work.

I have heard of guys doing it with only delivery kays on the car but not to cars that have 40 odd thousand on them.

[duke5700]

I still reckon your keen.. very keen.

I was under the impression they had toothpicks for rods, not pistons issues.

[Xjas]

I still reckon your keen.. very keen.

I was under the impression they had toothpicks for rods, not pistons issues.

I agree its a risk, thats why I'm asking if anyones tried it.

I think the 2 litre motors might have had weak rods but the 2.5 litre (in the 09s) are know for ring land failures rather than rod issues.

[Soopy]

EJ257's have pistons made from butter.

Some people do replace the pistons without honing, but then the same people try and run 20psi through the standard turbo and wonder why the IAT's are 5000c.

[Xjas]

EJ257's have pistons made from butter.

Thats basically why I'm thinking of changing them, I can get a CP forged piston kit for $500, I'm thinking it may be worth the risk of changing them now rather than melting a ringland because of a bad tank of fuel and having to strip it to sleeve the block.

[Soopy]

Its certainly a smart idea, just do it properly.

[gaz05]

Thats basically why I'm thinking of changing them, I can get a CP forged piston kit for $500, I'm thinking it may be worth the risk of changing them now rather than melting a ringland because of a bad tank of fuel and having to strip it to sleeve the block.

I certainly wouldnt do it, what about weights, piston to bore clearance, etc ??? foolish idea really.

PS: Forged pistons melt too.

[Xjas]

I certainly wouldnt do it, what about weights, piston to bore clearance, etc ??? foolish idea really.

PS: Forged pistons melt too.

Piston weight is not an issue so long as all pistons weigh the same as it is a horizontally opposed engine so the piston weights counter each other somewhat. I can still measure the bores to check the piston bore clearance is ok and I know forged pistons melt, just not as quickly as the factory ones.

Thanks for your input.

[lowhsv]

Get on rexnet plenty of good info on there very helpful too

[gaz05]

Piston weight is not an issue so long as all pistons weigh the same as it is a horizontally opposed engine so the piston weights counter each other somewhat. I can still measure the bores to check the piston bore clearance is ok and I know forged pistons melt, just not as quickly as the factory ones.

Thanks for your input.

Why ask?? go ahead and do it... not your engine.

[DukeZ]

lol just half ass it...why not....just dont wonder why it shat itself in 2000km hahaha



this thread is a piss take yer???

[Xjas]

Why ask?? go ahead and do it... not your engine.

I'm not sure whats with the negative comment...?

I asked a question, people have responed, I have answered others and yourself with facts as best I can in the spirit of starting a discussion on the subject, I am taking on board everyones comments in the hopes of making the right decision which at this poist appears to be leave the stock pistons in for now and keep the tune conservative until time and dollars permit a full build, but that doesnt mean we cant still discuss the pro and cons of the idea, while you and others have said its a bad idea no-one has yet said the have seen someone do just that and the engine failed for _______ reason, which was what I originally asked.

[DukeZ]

i built afew of these in my time and ive seen MANY people try to do the job half assed...seen them melt bearings detonate pistons bend rods bend valves etc etc the list goes on... im not saying that it doesnt happen on motors done properly...but for the sake of saving a little bit of coin now is it worth the risk of having to do it all properly a 2nd time and end up costing urself more than it would have in the first place....but its ur move so feel free to do what u like that is just my personal experince
:)

[Xjas]

i built afew of these in my time and ive seen MANY people try to do the job half assed...seen them melt bearings detonate pistons bend rods bend valves etc etc the list goes on... im not saying that it doesnt happen on motors done properly...but for the sake of saving a little bit of coin now is it worth the risk of having to do it all properly a 2nd time and end up costing urself more than it would have in the first place....but its ur move so feel free to do what u like that is just my personal experince
:)

Thank you for posting something constructive, it isnt really a question of dollars, I had just read that people had done and thought I ask the question, if I was set on it already I wouldnt have asked in the first place.
Looks like we'll go with the initial plan of exhaust, headers, intercooler and tune shooting for 200-220rwkw and then do the pistons later as part of a rebuild for 270+rwkw.

[SirNemesis]

So, I can't really comment on experience as I've never tried this, or even really thought about it. Thinking about it now though, lets look at the negatives.

Fitting new pistons (and I'd expect new rings) without honing can/(will?) result in poor ring seal, which would result in more blowby. More blowby would increase the amount of oil in the combustion chamber, which would lower the octane rating of the fuel and theoretically increase the chances of detonation.

Sounds like by introducing a forged piston here, you are still adding other risks that might not have happened otherwise.

[Xjas]

Fitting new pistons (and I'd expect new rings) without honing can/(will?) result in poor ring seal, which would result in more blowby. More blowby would increase the amount of oil in the combustion chamber, which would lower the octane rating of the fuel and theoretically increase the chances of detonation.

So how long can an engine run before it need to be rehoned when fitting pistons, the car has 45000kms so I dont know how glazed it would be but how long can an engine run before it is glazed enough that the rings wont bed in, if you run a new engine on a dyno for an hour and then change the piston and rings (for whatever reason) do you have to rehone the bores then? what about of the engine runs for a few 100kms or a few 1000, just curious really...

[SirNemesis]

Well they say rings should be bedded in after 1000-2000k's right? I personally wouldn't change anything without honing after that point. I'm no expert by any stretch of the imagination, but I wouldn't be doing it.