Is there any prformance with 1mm bigger valve on stock heads?

[alqatan]

Hi there, actually my mechanic is waiting for an answer.

My Eclipse is stroked with Wiseco pistons .020 inch over+Eagle connecting rod+4g64 crank.

I used to have ported heads done by my mechanic with 1mm bigger valve but he did wrong timing the result was benting some valve, thanks god nothing happened to my pistons now I have two ways to go

Stock 1g heads with stock valve and stock 1g head with bigger valve which is 1mm valve.

Is there any performance gain with 1mm bigger valve if I don't port and polish the head, actually I have drag season soon and I don't want to wait till my mechanic port my heads again.

My mechanic says it's better if I used the stock valve with none ported 1g head.

I have these two types head, I also heared it would be harder to tune a car with 1mm valve is that right?

I have DSM link with 950 cc injectors and I'm looking to run 30 psi.

Please reply fast guys I'm waiting for an answer
Thanks

 

[TSIfreek]

It doesnt make sence to put OS valves in a un ported head. Save up for a head that has port work and OS valves so as well as camshafts. Yea OS valves will flow more air in a unported head over stock valves sure but to get a full benifit from them they need the rest of the engine to breath accordingly. Look into a stage 3 head work for your application.

 

[alqatan]

I forgot to say I have 272 cams both sides do I still have to use the stock valves, as i said we don't have time to port the heads at the moment and I might not do this mod forever because I don't like to open the head back again and retune the car just for porting

Thanks

 

[RoasT BeeF]

OS valves in an un-ported stock head with stock cams will pick up flow about 12 CFM.

 

[D@nno]

I think the major problem with the larger valves is the amount they are shrouded in the combustion chamber. Try to unshroud them as much as possible if possible. I'm building a 2.4 and with the bigger bore you can unshroud them quite a bit.

 

[TSIfreek]

I forgot to say I have 272 cams both sides do I still have to use the stock valves, as i said we don't have time to port the heads at the moment and I might not do this mod forever because I don't like to open the head back again and retune the car just for porting

Thanks

Yes you can use OS valves with the 272s. If you are going with no porting just use stock valves. I would really look for a built head for your turbo/cams though. Its real odd to see a 11 second car with a stock head.

 

[RPMengine]

There is some airflow gain with the OS valves without porting. We cut the intake seats with a 30-45-60 cutter and follow up with a 75 and 80 degree cutters to open the bowl. The exhaust receive a 35-45-60 cut followed by an 80 degree cut. A quick blend of the bottom cut with an emery roll in the bowl will help.

It will not flow like a fully ported head, but will beat the stock flow numbers.