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Old 03-03-09, 03:58 PM   #1
tomcat7810
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Default ? about built motor

hey i have an 07 sti and i recently put mahle pistons in it due to a broken ring on the stocks. all i have is drop in pistons and arp head studs. when i first start it up it has a slight slap, i think this is cold start piston slap because it goes away once warm. this has been occuring since i have got it built so if you guys could just let me know what u think it is?
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Old 03-03-09, 04:18 PM   #2
Flycaster
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Default Re: ? about built motor

Cold slap it is.
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Old 03-03-09, 05:18 PM   #3
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Default Re: ? about built motor

If you don't already have some catch cans or a air/separator I would put something on. You are probably getting some blow-by during the cold starts. Hopefully you are letting it warm up at idle and not driving down the road with the pistons slapping. I guess at idle blow-by would probably not be an issue, but a good A/O separator is a good idea on a STI.

Forged pistons are usually noisy on cold start ups, so your car has teh clap... I mean the slap.
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Old 03-03-09, 06:55 PM   #4
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Default Re: ? about built motor

Quote:
Originally Posted by tomcat7810 View Post
hey i have an 07 sti and i recently put mahle pistons in it due to a broken ring on the stocks. all i have is drop in pistons and arp head studs. when i first start it up it has a slight slap, i think this is cold start piston slap because it goes away once warm. this has been occuring since i have got it built so if you guys could just let me know what u think it is?
I had drop in cp pistons then it blew up at 2,000 miles on my last engine at a diffierent backyard shop hope whoever build did it right never just do drop in pistons just build it up fully the first time

Last edited by SUPERLOUDSTI; 03-03-09 at 06:58 PM.
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Old 03-03-09, 07:00 PM   #5
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Default Re: ? about built motor

ok good.. well sounds like i should put on a a/o separator. i noticed the crawford ones are pretty pricey. is their any other options out there?
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Old 03-03-09, 07:01 PM   #6
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Default Re: ? about built motor

Quote:
Originally Posted by tomcat7810 View Post
ok good.. well sounds like i should put on a a/o separator. i noticed the crawford ones are pretty pricey. is their any other options out there?
Ixiz Concept Air/Oil Separator

InnovativeTuning.Com

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Old 03-04-09, 03:20 AM   #7
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Default Re: ? about built motor

I also have Mahle forged drop-in pistons. Slap at start-up is the price to pay to have pistons that will take much more abuse than the stockers...
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Old 03-04-09, 10:59 AM   #8
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Default Re: ? about built motor

Quote:
Originally Posted by SUPERLOUDSTI View Post
I had drop in cp pistons then it blew up at 2,000 miles on my last engine at a diffierent backyard shop hope whoever build did it right never just do drop in pistons just build it up fully the first time
You broke Cp pistons I mean I know of a ej25 engine running 800whp with cp without problems. I run CP forged pistons on my built engine and they slap around when cold but it quiets down once warmed up... then the cams make noise

Ixiz A/O separator is what im getting when I decide its necesary.
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Old 03-04-09, 02:18 PM   #9
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Quote:
Originally Posted by bluedemon_II View Post
You broke Cp pistons .
Yeah, I just read that too. I've only heard of one forged piston (and it was a Cosworth) that blew apart in one of our cars...it was at 550whp on the dyno, with an injector/rail failure causing an instaneous, catastrophically lean AFR at full boost. Moreover, I've never read about any land failures in a STi using a 2618 CP.

True, some guys complain about high oil usage using drop in pistons, but a piston failure? Interesting. SUPERLOUDSTI: what do you mean by it "blew up?" If you have a picture of that piston, we'd sure like to see it.

[edit] I'm not calling BS here - I'm genuinely curious.

Last edited by Flycaster; 03-05-09 at 11:11 AM.
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Old 03-05-09, 04:12 PM   #10
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Default Re: ? about built motor

WOW! same here... i had a crappy tuner and had my afr at 13.x at WOT
I had some serious detonation, but the cp pistons took it like a CHAMP!
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