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Intake & Exhaust Valves (Is There Such A Thing As To Big 

 

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 Post subject: Intake & Exhaust Valves (Is There Such A Thing As To Big
Posted: Sat Nov 06, 2004 9:33 pm 
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Hi Guys,
Just wondering im running a AU XR6 head with oversized exhaust and intake valves im just wondering could this be what my power loss problem is im also running JMM Race Series Extractors and Dev3HL Cam. Opinions Please?
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Spider
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Posted: Sat Nov 06, 2004 9:46 pm 
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Hey dude check this out
http://pforums.company-hosting.com/
according to this your intake gasses should flow at 290-300 ft/sec, so if you go and fit bigger valves your flow rate is going to be lower due to the larger valves, maybe this could be your prob??

 

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Posted: Sat Nov 06, 2004 11:18 pm 
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Spider have a talk to Mark from ITS. I was talking to him about this the other day and he said that if you fit oversized intake and exhaust valves you'll lose low down power or something. I cant remember the exact details, but talk to him about it.

 

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Posted: Sat Nov 06, 2004 11:39 pm 
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Thats it! Torque is all about gas velocity, so when you open up those runners or fit bigger valves you sacrifice your bottom end cause now the gas has got a larger area to flow through, and it slows down a bit. This upsets your fuel atomisation and can lead to droplets forming on your runner walls and piston crowns ect. unless your forcing gasses in there, you reach a point in NA motors where bigger isnt better. Cams vary gas velocity at different points so that is why the I6 sometimes has idling probs due to low manifold vacuume and MAP upset. Really do your research people on this topic before you spend heaps of your hard earned bucks on something that might not suit your needs. What good is a 6000rpm peak power producing track queen when you spend most of your time buzzing around town at around 2000-3000rpm. You dont need to learn the nuts and bolts of it all just speak to some one who does like the boys at Wade, Crow, JMM, ITS, Sure and they will probably point you in the right direction.[/u][/b]

 

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Posted: Sun Nov 07, 2004 6:41 pm 
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Top explanation! damn good short read to

 

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Posted: Sun Nov 07, 2004 8:27 pm 
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What size vallves are you actaully running?

The long stroke small bore I6 doesn't lend itself to bigger valves as there isn't enough room in the head. Look at a stock head and the valves and drop on a head gasket and you see why. Without changing the guide position and angle how much bigger can you go?
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Posted: Sun Nov 07, 2004 8:54 pm 
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Sorry Guys
All I Can Remember Is That There Bigger Then The AU XR6 Ones In There. I an Find Out Details Soon But They Are Bigger Vut A Bit Out To Get THem In From Memory
Cheers
Spider
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