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Old 05-09-2012, 12:34 AM   #1
Wagun
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Default Hybrid - new pistons vs. machining heads

Anyone tried these pistons http://www.ebay.com/itm/ws/eBayISAPI...tchlink:top:en
vs. machining the 2.0 heads? It seems to me to be a better alternative to machining the heads since these pistons will be stronger than stock.
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Last edited by Wagun; 05-09-2012 at 12:51 AM.
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Old 05-09-2012, 02:23 PM   #2
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Bump, no one has tried these pistons instead of sending their heads to EqTuning and waiting 3 months?!?!?!
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Old 05-09-2012, 03:45 PM   #3
RexWagonWA
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Default Pistons vs. Heads

My hybrid has both. My pistons may be slightly different, but they are the JE pistons made for hybrids.

The head machining works well. It allows you better flow and cuts down on detonation hot spots. The are lots of hybrid Subarus without machining in the Pacific Northwest that need frequent rebuilds. My motto is do it right the first time. Avoid multiple rebuilds, as that gets expensive.

The folks at AndrewTech are getting good results without machining. I do not know what they are doing. But we have no idea if you are near Maryland.

GLWYB
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Old 05-09-2012, 06:21 PM   #4
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Thanks!
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Old 05-10-2012, 12:01 PM   #5
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Quote:
Originally Posted by RexWagonWA View Post
My hybrid has both. My pistons may be slightly different, but they are the JE pistons made for hybrids.

The head machining works well. It allows you better flow and cuts down on detonation hot spots. The are lots of hybrid Subarus without machining in the Pacific Northwest that need frequent rebuilds. My motto is do it right the first time. Avoid multiple rebuilds, as that gets expensive.

The folks at AndrewTech are getting good results without machining. I do not know what they are doing. But we have no idea if you are near Maryland.

GLWYB
Wouldn't doing both lower the static CR to lower than an STi? Not to mention making a hybrid build more expensive.....
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Old 05-10-2012, 02:43 PM   #6
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^And kinda defeats the purpose of getting these pistons in the first place
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Old 05-10-2012, 04:08 PM   #7
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I'm doing a hybrid build on my 02 REX and I did a lot of research on this subject and yes I agree on doing it right the first time. My heads are at ASF Machine getting the chambers matched to my 2.5 block. The Block was built by S&R Performance with CP Pistons. My turbo is a custom built 18G by TurboChargers.com and I will be running Crower 264 Cams. The goal is not to have the highest WHP I can get but to have a reliable fun street car does what I want it to do. I will be starting a Build Thread soon to cover all that I have done and more on what a good build is all about.
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Old 05-10-2012, 04:08 PM   #8
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you can machine the head to bring the combustion chamber out like the 257 or simply flare out the sides to allow better airflow and reduce the sharp edge hanging in the chamber
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Old 05-10-2012, 04:28 PM   #9
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Quote:
Originally Posted by FuJi K View Post
simply flare out the sides to allow better airflow and reduce the sharp edge hanging in the chamber
can you elaborate on this or possibly show some pics on what you mean here?
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Old 05-10-2012, 04:46 PM   #10
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Quote:
Originally Posted by wrxhard

can you elaborate on this or possibly show some pics on what you mean here?
flare it out! EJ205 head



reduce over hands in the chambers. stock EJ205 head on a 2.5L block



stock 257 chamber on 2.5L block
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Old 05-10-2012, 06:32 PM   #11
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I see no difference in the amount of material "overhang" on the sides with the 205 heads and the amount of overhang present with both 205 and 257 heads at the top and bottom of the chambers. If JE pistons are designed to compensate for the extra material using the 205 heads and bring the CR back to 8.5:1, then why do the machining?

Seems the only benefit would be to "unshroud" the valves for a little more flow.

Anyone have any flow bench data on the benefits of unshrouding the valves?

FYI, I exchanged emails with the folks at AndrewTech: they don't use special pistons and they don't machine the chambers, so how come they don't have a lot of engine failures? I suspect because they do proper engine tuning right after the install.

Last edited by Wagun; 05-10-2012 at 06:39 PM.
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Old 05-10-2012, 08:28 PM   #12
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Quote:
Originally Posted by Wagun View Post
I see no difference in the amount of material "overhang" on the sides with the 205 heads and the amount of overhang present with both 205 and 257 heads at the top and bottom of the chambers. If JE pistons are designed to compensate for the extra material using the 205 heads and bring the CR back to 8.5:1, then why do the machining?

Seems the only benefit would be to "unshroud" the valves for a little more flow.

Anyone have any flow bench data on the benefits of unshrouding the valves?

FYI, I exchanged emails with the folks at AndrewTech: they don't use special pistons and they don't machine the chambers, so how come they don't have a lot of engine failures? I suspect because they do proper engine tuning right after the install.


ARE YOU BLIND!?
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Old 05-10-2012, 08:58 PM   #13
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What he said!
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Old 05-10-2012, 08:59 PM   #14
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Quote:
Originally Posted by TechMJ
What he said!
Are you Blind? LoL
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Old 05-10-2012, 09:00 PM   #15
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You can plainly see the differences in the pics posted by FuJi K

Last edited by TechMJ; 05-10-2012 at 09:12 PM.
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Old 05-10-2012, 09:03 PM   #16
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I'm just going to post my own experience regarding "hybrids". The bottomline is that no they won't blow up if you don't get the heads machined etc.

Cliff Notes - If your Tuner doesn't suck and isn't lazy, your hybrid shouldn't blow up.

The only thing that will make a difference is the tune that you put on the hybrid motor. I've run my hybrid motor for 60K miles using everything from a gt52 to a 35R.

My personal opinion is as follows:
1) hybrids have a higher compression ratio - which means you probably shouldn't run as much timing if you want your motor to last
2) With the higher compression ratio, you probably can't run as much boost - but for most people they are already octane limited by 93 pump
3) So assuming you run a bit less timing a couple less pounds of boost, you will probably make a bit less power. BUT
4) People want MOAR power! - so either they a) tell their tuner "I want dyno numbers" or b) their tuner is lazy doesn't feel like changing their tunes and maps, doesn't really compensate for the higher compression etc and gives them a tune that on the road will detonate more - and then bye bye motor
5) does chamber matching make more power? probably - can't hurt - could it be "safer" - maybe
6) I've gone to multiple tuners over the years and ONLY 1 tuner harped about getting the heads machined - and his tune was by far the worst tune - (damn car misfired on the way home from the tune..) coincidence? perhaps, but bottomline my motor is still together after 60K miles (using a different tuner of course)
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