2.5 sti build help needed hybrid build
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This is a discussion on 2.5 sti build help needed hybrid build within the Builds forums, part of the Tech & Modifying & General Repairs category; Hello guys, I just had a few questions to ask, I got me a sti2.5 block wich I bored out ...

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    Lightbulb 2.5 sti build help needed hybrid build

    Hello guys, I just had a few questions to ask, I got me a sti2.5 block wich I bored out 0.20 over so def need 100 mm pistons, what is the best compression ratio to use on a hybrid build? I'm using a stock wrx head which I'm going to throw on a cometic head gasket, I'm getting that head honed and machined also any suggestions???

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    Subaru Newb MainFrame's Avatar
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    There is no "best" compression ratio. It depends on what you're using the car for, and what fuel you plan on running. If you have good 93 octane readily available, I would shoot for around 9:1 for a daily driver.

    My best suggestion is to be sure your builder has a good reputation with hybrid Subaru engines.. I've seen so many poorly executed builds it's ridiculous.




    (I'm a little uneasy about your build already since you said you already bored the cylinders so now you will need 100mm pistons.. you're doing it wrong. What you should do is mic the walls to see how much you will need to take off, then you order pistons for that size. AFTER you get the pistons, you decide which piston will go where, carefully measure each specific piston, and bore the cylinder for that piston.. not the other way around.)

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    I totally understand what your saying i would do the exact same thing, i just got the block like that it was bored and honed, i measured my cylinder wall i get 99.99 in every cylinder

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    Subaru Newb MainFrame's Avatar
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    You can go ahead and put it together and just hope you end up with decent piston to wall clearance. People use drop in pistons all the time. You can't get your ptw clearance just right, but it will still work.

    You certainly don't want to go over 100mm, that's asking for a cracked cylinder. I made the mistake of going straight to 100mm before, and after rebuilding the block three more times it was all used up. Now I'm back down to 99.54mm with a different set of case halves.

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    Hopefully my piston to wall clearance should be good enough, there is no way I would go over 100 mm lol I read threads on how easy you can crack the cylinder just have to find me a decent set off pistons, I already got Manley rods with acl bearings and a heat treated sti crank

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    Subaru Newb MainFrame's Avatar
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    CP pistons are decent a decent off the shelf option. They're tough as hell, but a little on the noisy side. You can get pistons from Arias with an off set wrist pin that will reduce piston slap quite a bit, but they are custom order.

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    How much do they cost is there a good site to get them since it will be a custom order, and yea I heard that cp pistons are little bit noisy to It wasn't my option for cp,

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    Subaru Newb MainFrame's Avatar
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    My Arias pistons were $586.56, plus $120 for coating. You can order them from AriasPistons.com, but you'll probably have to call and tell them exactly what you want.

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