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09-09-2022, 02:14 PM | #1 |
Scooby Newbie
Member#: 501606
Join Date: May 2019
Chapter/Region:
NESIC
Location: Maine
Vehicle:2005 Impreza WRX STi |
Are My Heads Worth Porting?
Please take a look at the back of this valve seat and let me know if you would still try to port this.
Looks like Subaru missed the mark on aligning the intake valves on this head. All of the valve seats are off center by about 1 mm. This makes for a big ridge that would require me to eat deeply into the valve seat to correct. I am new to porting and was hoping to take on this project as a minimalistic blend without changing the port diameters and shape too much. Is this a big deal? Would you send it? Thoughts/feelings?
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Last edited by Wes7143; 09-09-2022 at 03:01 PM. |
09-09-2022, 03:33 PM | #2 |
Scooby Specialist
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i saw similar on my heads and am in a similar thought process...i dont think personally that it would hurt to blend it down as the valve seat is higher...but others may join in and verify!
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09-09-2022, 03:35 PM | #3 |
Scooby Specialist
Member#: 273868
Join Date: Feb 2011
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MAIC
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looks like an intake port
are those d25? |
09-09-2022, 03:41 PM | #4 |
Scooby Newbie
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Location: Maine
Vehicle:2005 Impreza WRX STi |
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09-10-2022, 12:17 AM | #5 |
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that's a baby lip. I've seen worse! Open the throat up a little. I've blended it back like a venturi if the shift was really bad.
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09-10-2022, 06:47 AM | #6 | |
Scooby Newbie
Member#: 501606
Join Date: May 2019
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Vehicle:2005 Impreza WRX STi |
Quote:
This article has a good example. Looks like they took a pretty significant cut. Are there any guidelines available for how much of a throat diameter increase is too much for stock size valves? If I wanted this 1mm lip to go away completely, I would have to have the throat diameter increased by 2mm. Last edited by Wes7143; 09-10-2022 at 06:56 AM. |
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09-10-2022, 12:53 PM | #7 |
Scooby Newbie
Member#: 501606
Join Date: May 2019
Chapter/Region:
NESIC
Location: Maine
Vehicle:2005 Impreza WRX STi |
I did some quick measurements and math on what my throat/valve ratios would be if I had the machine shop increase the throat diameters by 2mm. I included the possibility of 0.5mm and 1mm oversized valves.
My exhaust valvetrain will need the same treatment. Core shift of about 1mm there too. The internet tells me that 85% throat/valve is ideal for a street car and 90% throat/valve is ideal for a high RPM race car. But I'm sure getting rid of these harsh valve seat lips is more important than the theoretical ideal throat/valve ratio. Here's the nerdy math table. Grey cells are the OEM values. |
09-12-2022, 04:32 AM | #8 |
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Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
Do not put oversize valves in a dohc engine. The valves are to close. One miss shift and the valves will touch.
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09-12-2022, 07:54 AM | #9 | |
Scooby Newbie
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Vehicle:2005 Impreza WRX STi |
Quote:
The bigger issue here is getting rid of these valve seat lips though. I may or may not need oversized valves after opening the throats up. I would love some input from someone who has done this before and can recommend a course of action. |
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09-12-2022, 04:37 PM | #10 |
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09-12-2022, 04:49 PM | #11 | |
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Quote:
we spoke about all this i think |
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09-12-2022, 05:08 PM | #12 |
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Member#: 515308
Join Date: Jun 2020
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Lil epoxy or weld the gap up then port.
I think 1mm on ex valve never hurt anyone |
09-12-2022, 05:58 PM | #13 | |
Scooby Newbie
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Quote:
We didn't talk about these particular heads because I just tore them down and got my first look at these seats. Plus, it's important to post here so the next person googling around for what to do when they have a head with core shift can see the discussion and solutions. There's not a lot out there that I am able to find, so let's put it in this thread. My big problem with smoothing out this lip by hand is that it will make the seat shape all funky. This lip is 1 - 1.5 mm tall. Here is an artist's interpretation of what the seat will look like if I just blended the transition without cutting into the 45. Only 1 of the 2 heads has this problem too, so keeping flow equal will be hard. Having the machine shop open up the throats with a plunge cut during the valve job seems to be the way that the spec miata guys solve this problem. Here is an article showing an example I got the snippit about oversized valves running hotter from this Headgames Motorworks video. |
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09-17-2022, 04:55 PM | #14 |
Scooby Newbie
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Join Date: May 2019
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I ended up finding a better manufactured D25 head locally. Much easier than trying to work with a head with this much core shift.
For anyone in the future with a core shifted head like mine, Dave from Headgames Motorworks advised me against increasing the throat size or trying to smooth the affected area by hand. He recommended just leaving it since it would do more harm than good to the head's flow to try to fix it. |
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