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Discussion Starter #1
Hi

I am currently running 15psi, with stock 9:1 pistons and rods. I have a good IC, fuel computer and water injection, so am running a fairly cool intake charge.

I understand I am likely living on borrowed time with the rods....but what about the pistons? I have a spare very low mileage motor, and the pistons etc look new, so I am thinking of just doing the rods. If I did that, I would not have to rebore the cylinders (just hone), so I would probably save about $700 total on my build. (money is a bit tight now)

Is this a good idea?... anyone with opinions or hard experience?

thanks
Greg
 

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Stock pistons can work just fine assuming everything else is in proper working order (intake temps, fuel and oil pressure, proper AFRs, EGTs and detonation controlled, etc.) The biggest problem with stock pistons is their weight. How high rpm do you want to rev? People have done what you're doing on stock bottom ends and been fine but there are no absolute, definitive answers to what will make your motor "bulletproof" so to speak as there are too many variables involved. However, stronger rods will provide an additional measure of protection.
 

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Two comments:

1: If money's tight and you can't afford to rebuild an engine right, turn down the boost on the one you can't afford to break. Don't cheap out on rebuilds. :)

2: What boost level are they good for? How much fuel do you have? I've always been convinced that with the right amount of fuel and the proper rings, you could use marshmallows for pistons and it wouldn't matter. An exaggeration of course, but you get the idea.
 

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The rings are the issue. They will wear out. How long it will take is the question. I ran my stock 1.8 for 60K before the rings went south on me.
 

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In comparison, on my Non-Miata, i got 10K before the rings went, and took a ringland out when they moved in the groove, and the piston cracked. No detonation, nothing like that... just 10k miles and then "you know, i shouldn't use 4qts of oil per tank of gas..."
 

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Discussion Starter #7
all well grounded and good advise ... thank you

Braineack -I can tell you are a man of few words :lol:

So, since I don't plan on running higher than stock RPM, I am now thinking of holding off on the build until I have more cash.

One thing mentioned that I have not done is measure my EGT's. I am currently running 12-12.5 AFR on 94 octane fuel with as much timing as possible without knock. Come spring time, I plan on doing some work at the dyno to dial fuel and timing in more closely. In the meantime, I need to read up on EGT's and how that ties in to the picture.

Greg
 
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