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Old 06-25-2020, 09:46 PM   #1
tehnation
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Default Aftermarket vs oem valves

Rebuilt my motor, come to find out one of the heads are cracked, so its back at the machine shop. Its got manley forged internals and bc stage 3 cams and springs, goal is to be able to spin to 8k rpm. I have b25 heads.

Something tells me I should put in aftermarket valves now that its at the shop again because I regretted not doing it the first time. I don't know a good or recommended brand. I was thinking of getting at least exhaust valves.... I'm not to up to date on the subject. No idea of what material or brand is better.

Any helpful info would be appreciated. I search for valves and all I get are posts on bovs ... I need to order something quick, so I don't really have time for much research.

I'm willing to invest like $350-400 for both intake and exhaust.

GSC, BC, Supertech or ???
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Last edited by tehnation; 06-25-2020 at 09:53 PM.
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Old 06-25-2020, 09:49 PM   #2
benflynn
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Bigger valves? If not then why?
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Old 06-25-2020, 09:56 PM   #3
tehnation
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can oem valves take the abuse of 450-500awhp @ 8k rpm? I know exhaust valves are prone to getting burnt. I'm beating this motor like I stole it....
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Old 06-25-2020, 10:10 PM   #4
tehnation
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I think when the motor was built, I was under the impression that the stock valves were good enough.... not sure why I think differently now?
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Old 06-26-2020, 08:01 AM   #5
tehnation
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I think I will go with manley, page 9,

http://www.manleyperformance.com/sc/...ortCompact.pdf

or BC

https://briancrower.com/makes/subaru...lvetrain.shtml

Figured I would use whatever brand is already in my build. manley pistons and rods, bc cams and springs.

any thoughts or comments?
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Old 06-26-2020, 11:15 AM   #6
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OEM valves will take the abuse. The main reason to go aftermarket is the +1 sizing.
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Old 06-26-2020, 04:11 PM   #7
rtv900
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Quote:
Originally Posted by tehnation View Post
can oem valves take the abuse of 450-500awhp @ 8k rpm? I know exhaust valves are prone to getting burnt. I'm beating this motor like I stole it....
a hp figure or an rpm isn't the issue
oem valves can take a million hp if it is going to be street use
only on a track will they see the duration of high heat to burn
nobody burns valves on the street unless they have major tune issues which is a totally different story

2nd, oem valves can handle 92 million rpm, until they start to float way before even 8000 rpm
so you either go lighter or heavier springs or both, and then your cam needs to handle the springs, etc
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Old 06-26-2020, 05:03 PM   #8
tehnation
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thank you for pulling me back down to reality!
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Old 06-28-2020, 07:13 AM   #9
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Quote:
Originally Posted by rtv900 View Post
a hp figure or an rpm isn't the issue
oem valves can take a million hp if it is going to be street use
only on a track will they see the duration of high heat to burn
nobody burns valves on the street unless they have major tune issues which is a totally different story

2nd, oem valves can handle 92 million rpm, until they start to float way before even 8000 rpm
so you either go lighter or heavier springs or both, and then your cam needs to handle the springs, etc
i just burned my cylinder 2 exhaust valve with 350whp on a stock engine with methanol... i didnt even blow the stock clutch or ringlands... it was a fricken valve. replace them when doing the heads.
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Old 06-28-2020, 08:43 AM   #10
KillerBMotorsport
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I'd do GSC on a lower dollar build. They will not go out of round or tulip like the OEM valves. We always replace OEM valves on anything more than a refresh just because the longevity of the OEM valves is not as good once the power/boost starts climbing.
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Old 06-29-2020, 07:58 AM   #11
rtv900
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Quote:
Originally Posted by blckholehurican View Post
i just burned my cylinder 2 exhaust valve with 350whp on a stock engine with methanol... i didnt even blow the stock clutch or ringlands... it was a fricken valve. replace them when doing the heads.
ok, so a stock engine with methanol, which means it isn't even close to stock
perhaps you had a tune issue and fried it
Because really, what were you doing on the street to cause that?
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Old 07-01-2020, 02:25 AM   #12
blckholehurican
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Quote:
Originally Posted by rtv900 View Post
ok, so a stock engine with methanol, which means it isn't even close to stock
perhaps you had a tune issue and fried it
Because really, what were you doing on the street to cause that?
Normal daily street driving, pulls on to the freeway, random pulls here and there, lots of easy highway miles. No top speed runs and nothing anyone on this site would consider abuse. The engine itself is totally stock. Original owner 2016 Sti with full bolt on's, running a cobb 20g. It blew at nearly exactly 160,000 kms. All mods done at 110,000 kms. Clearly not a tune problem as it lasted 50,000 kms with no knock at all... Most people beat the piss out of there engines and destroy the pistons or bearings and never experience an exhaust valve burn but guess what... the stock exhaust valves will still burn... There is a reason GSC makes an optional super alloy exhaust valve, its because even their stainless exhaust valves (which are better than stock) still burn. change them.
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Old 07-01-2020, 09:29 AM   #13
rtv900
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Quote:
Originally Posted by blckholehurican View Post
Clearly not a tune problem as it lasted 50,000 kms with no knock at all...
^interesting conclusion here

clearly not a tune problem (just because you had no auto ignition which is one single issue) but you did burn a valve on the street, which kind of means you had a tune issue and excessive EGT's

I'd bet you modded things to utilize methanol and lost control of EGT's
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Old 07-01-2020, 09:56 AM   #14
BlackFighter
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I would agree with rtv. I can not imagine a stock exhaust valve burning at those powers all on its own. There have been people pushing 500whp on stock valves with abuse and no issues. Unless it was a defective valve from the dealer that was getting damaged overtime and just eventually failed.
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