Nitrous And exhuast valve size

[dub-disaster]

Im currently getting my cylinder head dine and eventualy I will put a 25 bhp shot of nitrous on my car just for a laugh , I'm trying to choose between a otter head wth standard valves r a big valve head wich is twice the price and I was wondering if when using nitrous in an engine a 29mm exhuast valve may become a problem ? or would this only be a problem if I was using over 25 shot of gas (wich I dnt intend on doing) should I pay the double the prve and use bigger valves or shall I spend my cash else where, like on a nice nitrous system

[breadman]

Personally I think a properly ported head would do fine as the valves are of reasonable size.
I know that fitting larger exhaust valves is popular, but I agree it gets very expensive. Until someone does back to back testing with specifically mapped and otherwise identical engines to prove an increase in power by fitting big exhaust valves I think we all just summise that its the way to go.
I reckon gains would be minimal, certainly against the relatively high costs involved.

[dub-disaster]

Yea that's a fair shout realy I'd rather spend the cash on somthing else realy plenty of other buts need doing thanks breadman

[Tommo]

Personally I would  look at nitrous as a cheaper and more effective alternative to a BVH.

[Andy]

Nitrous loves a bit more exhaust. But it comes down to cost as always... With a BV head my car was quicker than a stock head, but nothing more scientific than that. Just stick the gas on and see how it goes.

[hayesey]

my car vs robins car on john sleaths rollers, both turbo conversions to the same spec, both mapped by andy.  The difference was mine has a BVH with standard bottom end, Robin's has a 1341cc bottom end with standard head.  They both made the same peak power (within 1 bhp of each other) on the same rollers on the same day.  Robins made more power throughout most of the rev-range than mine except when it gets higher up the rev range where robins just runs out of puff and mine carries on rising, both ending up at the same peak.

although what would still be interesting to see would be a ported head vs ported head with 31mm exhaust valves. 

[polo classic]

Karlos made very good numbers on his G40 with BVH and stock cam

For me, BVH every time, as long as there's space in the camber, and the valves don't come too close to the cylinder walls

Reminds me, I have a 38/33mm BVH to put on the car I haven't driven for 2,5 years lol

[dub-disaster]

I'd like to go with the larger exhuast valves but we will see depends on budget if not I'll just go for ported and polished and get my inlet manifold matched, so time will tell ...