#80573, "RE: Pictures of OEM SRT-4 internals." In response to Reply # 0
Domes aren't necessarily good. Especially when they just drop the piston so that it sits below the deck to compensate for the dome, which they only did to make a non-interference motor. I'd like to hear your version of why they are so good, other then "they are cheap and hold a lot of power."
#80575, "RE: Pictures of OEM SRT-4 internals." In response to Reply # 1
Originally posted by Ducking_Fumbass Domes aren't necessarily good. Especially when they just drop the piston so that it sits below the deck to compensate for the dome, which they only did to make a non-interference motor. I'd like to hear your version of why they are so good, other then "they are cheap and hold a lot of power."
I said nothing about why the piston is so good. Nor am I inferring it. I am only saying that when I opened the box I expected to see a relatively flat piston with valve reliefs.
#80596, "RE: Pictures of OEM SRT-4 internals." In response to Reply # 5
They're still cast, and that makes me uncomfortable. I don't care how much power they've taken in an SRT4, we don't drive SRT4's.
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#80598, "RE: Pictures of OEM SRT-4 internals." In response to Reply # 1
Originally posted by Ducking_Fumbass Domes aren't necessarily good. Especially when they just drop the piston so that it sits below the deck to compensate for the dome, which they only did to make a non-interference motor. I'd like to hear your version of why they are so good, other then "they are cheap and hold a lot of power."
moly coated ring lands to prevent micro welding of the top ring land, full floating pins, moly coated skirts. cast or not they can handle the cylinder pressures of 500+hp...so whats the problem? if the shoe fits, wear it.
the ramp is a design so that the a/f charge mixes more as it hits the ramp, its not such a great idea with it being lower than the deck but they dont have detonation problems so the ramp works out just fine.
badass pistons, i got a set for like 102$ on ebay and turned around and sold them for 225, lol
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96 Black ESi 91 Red TSI AWD (RIP) 02 WRX
"turnin wrenches for nine hours in the pouring rain, just to get the beast up and running again"
Aerospace Certified TIG welder for Precision Castparts in Portland, OR.
#80599, "RE: Pictures of OEM SRT-4 internals." In response to Reply # 6
Originally posted by DarkOne They're still cast, and that makes me uncomfortable. I don't care how much power they've taken in an SRT4, we don't drive SRT4's.
Absolutely...
The SRT-4 PCM will control the boost and timing also to limit the load on the pistons... If you put them in a motor with our PCM... haha, who knows what will happen!
Also, the reason they made the pistons with the raised dome, but dropped down into the block is to maintain a nice consistent distance from the top of the piston to the top of the combustion chamber...
#80604, "RE: Pictures of OEM SRT-4 internals." In response to Reply # 8 Sep-15-04 08:24 AM by turbo8u
Originally posted by MrSlick The SRT-4 PCM will control the boost and timing also to limit the load on the pistons... If you put them in a motor with our PCM... haha, who knows what will happen!
the srt-4 that dynoed 500+whp on stock internals i DOUBT was using the stock boost control. the boost and timing are general, and besides....who's in control of your motor lee? the pcm? or your megasquirt, lol
control your own timing and fuel, but these pistons and rods will handle 500+hp, regardless of pcm.
"CFD analysis and dyno testing showed that the ski-jump-shaped dome on the piston was desirable for performance, so compression ratio was reduced to 8.1:1 by decreasing the piston compression height to lower piston position in the cylinder. Both versions are Mahle eutectic castings with Mahle Grafal skirt coating, but the turbo version also has a hard-anodized top ringland, a moly-coated 1.2mm top ring and has a shorter skirt, contributing to the 335-gram weight."
so as you can see, the reason the piston is dropped down in the bore farther...is its just another way to drop compression.
edit:
"the "ski ramp" piston dome encourages tumble in the cylinder, which improves idle stability and light-load performance. The best wide-open throttle performance, though, usually comes from a piston that comes as close as possible to the flat edges of the combustion chamber (called quench pads). The gas trapped between the piston and the quench pads gets squished out, flying directly into the flame kernel where combustion is starting. This added turbulence speeds flame propagation and reduces the chance of knock. Of course, a taller piston would raise compression, so the ski ramp would have to be replaced with a dish, but that's do-able."
-scc
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96 Black ESi 91 Red TSI AWD (RIP) 02 WRX
"turnin wrenches for nine hours in the pouring rain, just to get the beast up and running again"
Aerospace Certified TIG welder for Precision Castparts in Portland, OR.
<--This is our god... god decides our fate. We shall not upset our god. God can and will ruin our lives if we were to upset him.
