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The mkiv Supra Owners Club

Oversize valves??


JamieP

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Oversize valves will give you greater curtain area (the circumference of the valve x the lift) and hence more flow capability.

 

When you've reached the limit of valve lift (limited by the piston stand proud height, or valve pocket depths; head gasket thickness; valve seat depth and most importantly valve timing) the increase in valve diameter will give the required increase in flow capability.

 

Being turbocharged it isn't such an important issue, but when looking for all out maximum power it will reduce the loading on the turbo(s) and allow more mass airflow for a given boost pressure.

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..... is this worth doing? ...

I wouldn't bother on anything else than a hardcore race engine.

You'd need to get many things right (new seats cut at the absolutely correct angles, weights, adjust for new cc shape/volume, blah blah) and even then you'd be creating more work for yourself with future valve clearance adjustments. Different metals and expansions might want to settle down to different gaps.

 

...and it's not like you're gonna see an extra 100bhp all of a sudden, either...

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