could someone tell me if there is an actual big gain from getting the head done and putting +1mm valves in it? how exactly does this give u a gain and what kind of gain is it? is it a faster turbo spool up or what?

 

Until your making big boy power, stock sized valves will work out better for you.

 

imo, the exhaust valves are too big on our engines.....

so going bigger on the intake will be good, keep the oem ex valves.

fwiw, the evo x has larger intake valves & smaller exhaust valves than the evo 8/9.

 

Based on the port sizes, choke area, and valve area, my porting friend says stay w/the stock size valves. IIRC the #'s show the stock sizes good for 8200 rpm on a 2.0 and 7800 on a 2.3???? Only need larger if you are turning big RPM. More of a sales gimmick IMHO.

Paul

 

Bigger valves alone don't equate to bigger flow. In fact, larger diameter valves can reduce flow in an otherwise stock head by choking a small port.

A ported head that is demonstrated with a flowbench to benefit from oversized valve is a different situation.

 

Well I'm going with an 850r setup already have everything for it. I'm just geting the head done very soon and am going to be putting down about 700awhp at iveys. So with that kind of power wat do u think about the +1mm valves??

 

It doesn't matter if it's 400whp or 800whp. It's not about power, it's about the port.

Factory ports? Stock valve sizes.

 

i would say that if you need to be asking this, than you really have no business getting into the 700hp club aka big boy club...

 

It's actually a good question.

Yes, in some applications where more airflow is required than the stock valve size (and ports) can provide, larger valves are necessary. This is only after the ports have been developed to their potential, then a larger valve is the next step towards more flow.

Velocity is another important part of cylinder head performance that can often be sacrificed by unnecessarily large ports or valves.

Check out the issue of Import Tuner hitting the stands any day now. It has part 2 of my 4G64 MIVEC build and details the cylinder head. I explain why the stock valves were retained on my 2.4L 4G64. The current issue has the shortblock build.

 

i dont get import tuner over here in NZ.
could you please let me know what you're explanation is?
i'm going 2.3 with some head porting and i'm wanting to know if i should go +1mm oversize too.

Cheers, Mike

 

well the reason I'm asking this is because I see all these big name brand heads coming with +1mm valves. I wana get the head ported regardless. I was just wondering why there all going +1mm on there heads instead of just porting the stock size??

 

I run stock size valves in my ported head for my 4G64.... my tuner in England doesn't think oversize valves make sense under 700 hp, so I went with that. Been running it for 3 years now. I have no idea whether bigger valves would have made the motor better. Doubt it.

There has not been a conclusive test done so it's all guess work.

 

I agree with this. larger intakes can make it easier for air to get in if the chamber is deshrouded correctly. making the exhaust bigger is not a good idea. the piston pushes air directly at head trying to push it out. making the head bigger hinders exiting flow.

stock 4g63 sixe is 34mm/30.5mm
I believe evo X is 35mm/29mm

 

On a set up like your i would suggest a 1mm larger intake valve and either a stock or +.5mm exhaust valve. After some testing on our CNC head it was determined the 1mm oversized exhaust valve was a little on the large side and really did not help out flow much on the exhaust side.

 

Great info! 2.0 here with 640whp but I want to get the head ported and enlarge the valves. Looks like I'll just do the intake side unless someone here has proven data to stick with stock size. I'd like to see 750 at the wheels with an HTA3586 turbo.