Oversized Valves?

[JayzVr 106]

What gains can I get from oversized valves, do I need to change any thing else and what size do i go for, I don't have a clue when it comes to head work and cams, just want to know how it all works and what's the point in bigger valves etc.

[Bealieboy 1,625]

If you think about it like this jay, the bigger valves, the more air in and the more gases out therefore increasing flow. Porting and polishing your head will also give small gains in flow. I believe that you need to be careful with the porting though as you can actually decrease flow if you're not careful.

Cams wise, it's best not to go too big, 263's will make good gains without moving the torque curve too much. 268's or 270's will remove torque from the mid range making the car less driveable for every day use. Nice if you like giving it the 'who's your daddy' all over the place or forcing your induction!

Edited April 7, 2015 by Bealieboy

[JayzVr 106]

If you think about it like this jay, the bigger valves, the more air in and the more gases out therefore increasing flow. Porting and polishing your head will also give small gains in flow. I believe that you need to be careful with the porting though as you can actually decrease flow if you're not careful.

Cams wise, it's best not to go too big, 263's will make good gains without moving the torque curve too much. 268's or 270's will remove torque from the mid range making the car less driveable for every day use. Nice if you like giving it the 'who's your daddy' all over the place or forcing your induction!

So 268s or 270s will be ok with a turbo conversion?

[FishWick 21]

They will....providing the overlap forced induction friendly.   Schrick 268s are OK.  263s better.

 

As for valves, I fitted a Schimmel head with +1mm oversize Inconel valves, a set of 263s and running exactly the same boost pressure (11psi, GT35R) I found an extra 50hp, so breathing mods can and do work.