Oversize valves whats the verdict

[Faheemo]

Hey guys,

My head is currently off and i have the oppertunity to do some work on it.
I havent really seen any users, using oversize valves on the forum.

I'm doing a head port and cutting the valve seats, would like to know if its worth using oversize valves on the exhaust. and what size ?
I'm using both 7a cams , GT30 turbo and high rate valve springs.
the bottom end is getting a stroker crank and pistons are 82.5mm.
displacement will be 2.5L. chasing 600hp on this setup.

any info on bigger valves will be helpful.

[Audi_CQ]

Not much room for bigger valves. I've got +0.5mm valves in my 2.5.
This : http://www.034motorsport.com/product...roducts_id=397

No problem on intake side, but exhaust valve seat is already to small for the org valve so new seats has to be mounted. How much gain it makes I don't know. Haven't tested before and after. Just wanted new and better valves

[DJones]

I would also like be intrested in the answers to this topic.

Out of intrest i took the head off of a "Lieman" built S1 engine many years ago and was shocked at how small the valves where.. from memory no different to standard.. if it would make a large differance im sure he would have done it.

[Jay]

Faheemo

I am using larger valves (034) and was going to fit larger seats as they shroud the valves so you don't get full benefit of the increased area but... and its a big BUT, swindon racing looked at this and said there isn't enough metal in the head to fit the large seats with out a high risk of cracking and or dropping seats at high rev's and temps (Think Prosty had this problems!)

The up shot is I will be run larger valves in new reprofiled standard size seats BUT... will use a better material than stock.

Hope that helps

Jay

[Faheemo]

thanks Guys
Ill have to get the engineers to have a look at it.

[EspenW]

One option is to stick to the stock size, but use valves with thinner stems, thus increasing flow. I've got the Supertech http://www.supertechperformance.com on the Golf. Stock thickness of the stems are 8mm, but these are 7mm (requiring new guides). Undercut to 6.5mm in the area that does not touch the valve guide. Much lighter than stock too. Saves a lot more weight than TI retainers. In combination with lightweight lifters, this setup is good for 8K on the 8v Golf, thus avoiding stiffer valve springs (stiffer springs sap power at all rpms).