Increase valve diameter or 4 valve heads

[Galon]

I'm looking for input on increasing valve diameter on a 4 valve heads. The head I'm working on is a 2004 Mazda 1.8 turbo. In reading it has been suggested that over valving is problem on 4 valve heads. My business has been moving into the newer engines with turbos and I need to be a reliable source to make the proper repairs or improvements to my customers engines. Getting to the real question. Is it worth the effort and expense to increase a valve diameter 1mm in some applications? I have noticed when cutting the seats the top angle has a tendency to open the corners of the combustion chamber which exposes the head gasket fire ring. Not a good situation. This requires moving the seat angle back which the customer doesn't like seeing since they want the seat angle out on the edge of the valve. I have reduced the top angle on my cutter to allow the seat angle to be moved out. And this is all for a standard valve diameter. Adding an additional MM to the diameter doesn't make sense if the original valve diameter seems to be at a max for the combustion chamber. I haven't taken into the consideration the percentages for the valve to port. Any suggestions are greatly appreciated.

[Carnut1]

DV patented the 4 valve poly quad layout. he gets about 500 hp/ liter. Thanks, Charlie

[Brian P]

"in some applications" Sure, the ones that aren't overvalved!

Work out the flow cross sectional areas in the port just ahead of the valve guide, at the valve seat (taking into account the subtraction of the valve stem), and at the valve curtain area (taking into account that the flow is at roughly a 45 degree angle here). Work out the maximum piston demand, one cylinder displacement x (RPM/60/2) x (3.14159/2) ... the first term is obvious, the second relates to the amount of time for each stroke (nominal half revolution) of the engine, the third is the approximate (neglecting con rod swing) relationship between the peak piston speed and the average over one stroke. Then work out the nominal mach index at the three cross section areas identified. Other threads on this forum have identified what the approximate range of what those nominal mach numbers should be. The usual suggested range is mach 0.5 to 0.6 at the RPM at which you want peak power to be.

A common OEM approach these days is to use relatively big ports and valves combined with mild cam timing. That approach makes for an engine relatively insensitive to pressure waves and inertial ram filling (because it won't have strong pressure pulsations in the intake runner), which makes for decent cylinder filling at low revs (where most drivers spend most of the time) but unremarkable cylinder filling at high revs. Decent for a daily driver ... flat but unremarkable torque curve from idle to redline.

If you raise the redline (along with whatever other mods are needed so the engine doesn't blow apart) and put in cams with bigger bumps, maybe the flow velocities will start coming into a better range. If you stay with stock redline, it probably won't benefit from bigger valves and could possibly benefit from smaller ports.

[4vpc]

"in some applications" Sure, the ones that aren't overvalved!

Work out the flow cross sectional areas in the port just ahead of the valve guide, at the valve seat (taking into account the subtraction of the valve stem), and at the valve curtain area (taking into account that the flow is at roughly a 45 degree angle here). Work out the maximum piston demand, one cylinder displacement x (RPM/60/2) x (3.14159/2) ... the first term is obvious, the second relates to the amount of time for each stroke (nominal half revolution) of the engine, the third is the approximate (neglecting con rod swing) relationship between the peak piston speed and the average over one stroke. Then work out the nominal mach index at the three cross section areas identified. Other threads on this forum have identified what the approximate range of what those nominal mach numbers should be. The usual suggested range is mach 0.5 to 0.6 at the RPM at which you want peak power to be.

A common OEM approach these days is to use relatively big ports and valves combined with mild cam timing. That approach makes for an engine relatively insensitive to pressure waves and inertial ram filling (because it won't have strong pressure pulsations in the intake runner), which makes for decent cylinder filling at low revs (where most drivers spend most of the time) but unremarkable cylinder filling at high revs. Decent for a daily driver ... flat but unremarkable torque curve from idle to redline.

If you raise the redline (along with whatever other mods are needed so the engine doesn't blow apart) and put in cams with bigger bumps, maybe the flow velocities will start coming into a better range. If you stay with stock redline, it probably won't benefit from bigger valves and could possibly benefit from smaller ports.

Would you have the time and patience to run through a head with me? My maths is terrible, but I can measure.

[Brian P]

Bore
Stroke
Target RPM of peak power
Intake valve lift
Inside diameter of the intake valve seat
Valve stem diameter
Diameter of the intake port at the smallest point downstream of where it splits in two and upstream of the valve stem. If it's oval, give me height and width.
Diameter of the intake port at the face of the cylinder head. Same as above if it's oval.

[4vpc]

1.Bore
2.Stroke
3.Target RPM of peak power
4.Intake valve lift
5.Inside diameter of the intake valve seat
6.Valve stem diameter
7.Diameter of the intake port at the smallest point downstream of where it splits in two and upstream of the valve stem. If it's oval, give me height and width.
8.Diameter of the intake port at the face of the cylinder head. Same as above if it's oval.

Would CSA be more accurate for 7 & 8? I can get those. 7 is MinCSA right? It's a bit of an odd shape (not easily calculable by maths) as is the port entry which is a 'flattened oval'.

[Brian P]

Is this a BP4WT engine? (Mazdaspeed MX5 turbo) 1839cc
Bore 83mm
Stroke 85mm
still need all the other dimensions
Wikipedia says 180hp at 6000 rpm and 166 lb.ft at 4500 rpm. That's fairly unremarkable for a turbo engine; probably the boost pressure is pretty low. The normally aspirated version is indicated as 140hp at 6500 rpm and 119 lb.ft at 5500 rpm. That suggests unremarkable BMEP. The long stroke means it won't be a high revving engine.

And yes, if you can give me CSA directly, that's what I am after.

[4vpc]

No it isn't, i'll get some figures posted up later when i've measured.
Thanks.