MN47 vs. P90

[2eighTZ4me]

Opinions / empirical evidence encouraged to determine the better of the two heads for a particular application.

 

3.1L stroker with dished pistons from a KA24.

 

Given an identical cam and valvetrain setup, which would yield more power "out of the box" (meaning no port work)

 

Secondly, referring to the scenario above, but with a (for argument's sake) BRAAP port job on both heads, which would yield more power?

 

There are several thoughts plowing through my head from what I know and all the research I've done in the past.

 

* Fact - both the P90 and MN47 have 42mm intake valves and 35mm exhaust valves.

* MN47 has linered exhaust ports, while P90 has big open square(ish) ports.

* MN47 has a 39.5 cc chamber, P90 has a 53.6 cc chamber

 

** With using dished pistons... - would the smaller combustion chamber on the 47 outweigh the advantages larger exhaust ports on the 90?

** Would cylinder quench (power) diminished on the P90 be able to be regained by being able to advance ignition timing over the MN47?

 

I realize I'm green when it comes to these differences, but I am smart enough to know advantages and disadvantages of timing, flow and quench. Want to hear what the experts have to say about this. I know the exhaust liners are not "supposed" to rob flow, so does it really come down to port shaping and CC size between these two heads? (given all else is held constant)

 

This should be an informative discussion and am interested to hear what the experts have to say.

[ozconnection]

Opinions / empirical evidence encouraged to determine the better of the two heads for a particular application.

 

3.1L stroker with dished pistons from a KA24.

 

Given an identical cam and valvetrain setup, which would yield more power "out of the box" (meaning no port work)

 

Secondly, referring to the scenario above, but with a (for argument's sake) BRAAP port job on both heads, which would yield more power?

 

There are several thoughts plowing through my head from what I know and all the research I've done in the past.

 

* Fact - both the P90 and MN47 have 42mm intake valves and 35mm exhaust valves.

* MN47 has linered exhaust ports, while P90 has big open square(ish) ports.

* MN47 has a 39.5 cc chamber, P90 has a 53.6 cc chamber

 

** With using dished pistons... - would the smaller combustion chamber on the 47 outweigh the advantages larger exhaust ports on the 90?

** Would cylinder quench (power) diminished on the P90 be able to be regained by being able to advance ignition timing over the MN47?

 

I realize I'm green when it comes to these differences, but I am smart enough to know advantages and disadvantages of timing, flow and quench. Want to hear what the experts have to say about this. I know the exhaust liners are not "supposed" to rob flow, so does it really come down to port shaping and CC size between these two heads? (given all else is held constant)

 

This should be an informative discussion and am interested to hear what the experts have to say.

 

I don't consider myself as an expert, so can I reply?

 

P90 head has 44mm intake valves.

 

Compression ratio will be different with the two different heads. That will influence your power significantly. Both heads are fairly detonation resistant because of their quench, I think you can get away with the 47 head if

 

a)compression isn't too high for the fuel you're going to use

b)you don't have to overly retard the ignition timing to avoid pinging

c)you select the right thickness HG to get your compression to where you want it.

 

Your quench won't be as good with the dished pistons compared to flat tops with either head but it will work.