Guess my fren's HP figures

[ShaunSG]

Originally posted by f8.@Jul 21 2004, 01:46 AM
this is my own theory, so it is probably wrong. but i am a believer of small ports for higher flow velocities. i suspect the reason mitsubishi reduced the sizes of the port for evo commpared to vr4 is that it was too big to begin with.

we always think the bigger the better but i personally feel a smaller port with higher flow velocities encourage more momentum energy in the intake charge to enable you to cram more air in over a shorter period of time.

so with the evo3 head, just leave it as it is. port and polishing gives you the most gain on old american v8s where their castings are so poor and unfinished anyway. japanese heads are quite well finished and so the gain, if any is minimal. and besides, some roughness on the port walls, if it encourages a more homogenous mix of air and fuel by tumbling, would encourage a higher flame speed and more thorough combustion.

you see, when people do port polishing properly, they use a flow bench to verify the gains. to me, the problem with a flow bench is that it only gives you the results for steady flow. ie you just apply a constant pressure of air through the head for a given valve opening and measure the volume flow.

the air flow in a real engine is hardly steady. the valves are opening and closing all the time. instead of measuring how much air is flowing in by volume, i think a more useful metric is the velocity of the air that goes in. of course this doesn't mean the smaller the ports the better. there is a compromise between flow velocity and volume rate. and i think the manufacturers got it pretty spot on when they designed it. so don't mess with it unless you really know what you are doing.

but if you have already ported and polished it, then of course it is much better hehehe. ;)

just my 2p!

Really delighted to find such interesting discussions on a local forum. Thanks to a friend who pointed this way.

It is the combination of an efficient port that both flows large volumes at high velocities that makes power. Without both the port is nothing. If velocity comes at the expense of flow, power will be lost. If velocity is high enough to go turbulent over the short side of the port, it kills flow, killing power. If velocity causes fuel seperation (wet flow dynamics), it kills power.

Flow benches do not just measure volume flow. They measure velocity as well with pitot probes.

Port wall texture is still debated by the top people in the industry, and is dependent on many variables. Port wall texture does not affect tumble, only mixing. It is largely port approach, shape and positioning that does. Tumble and swirl do not come free either. To get either or both requires restricting all out airflow. Generally they help fuel economy and emissions, but more often than not, do not help with power unless the stock port does is extremely swirl-less. That is the difference with Chevy and Ford heads. The no swirl Ford guys make lots of power and are always messing around with it, the high swirl Chevy guys make ok power and are always messing with increasing flow, ignoring swirl. So they're kinda both trying to meet somewhere in the middle. So in the end it depends where you are and what you want.

Charge homogeneity is desirsable for power, but where homogenization takes place is important. Remember that the target is mass intake. If honogenization takes place before entry into cylinder, volume of the charge is larger, tougher to get past the intake valve. What is ideal is homogenization AFTER a very dense charge is delivered into the cylinder.

 

[ShaunSG]

Originally posted by coldfish@Jul 21 2004, 11:52 AM
end of the day, port n polish is more suited for NA applications that run higher compression than forced induction.

Efficient ports help FI just as much, if not more than, NA. Consider the higher velocities with the larger cross-intake-valve pressure differentials just before the intake stroke.

 

[ShaunSG]

Originally posted by coldfish@Jul 23 2004, 01:46 AM

volumetric efficiency is how much air u can flow thru, not the speed of air.
with respect to time, it becomes volumetric flowrate.
usually in CFM (cubic feet/meter), m³/sec, gallon/sec, etc.
imagine u have 2 barrels of water suspended in air (top vented) both containing same volume of water.
one with a 2cm hole at the bottom, the other with a 3cm hole. which one drain out faster? ;)

VE is not what you say it is. VE RELATES to what you say it is.

 

[ShaunSG]

The stacking up of air behind the intake valve is not really a benfit of smaller high velocity ports. In the realm of anything less than F1 and Champ car motors, the effect is not meaningful because of the time in between intake valve openings.

The main reason for wanting high velocity ports because high velocity air flow is the only thing that can keep intake flow going after the piston has gone beyond BDC and is on its way back up. A low velocity port cannot fight the rising cyl pressure as the piston is on its way up, so unless the valve is closed, you get intake reversion. A high velocity port will keep flowing though - at least for a while. This increases compression. It also extends total intake duration, allowing for gentler cam lobe profiles (more total time to open and close valve). Seconday effect is gentle seating of the valve, eliminating valve bounce which kills compression. The latter is a huge but often unconsidered benefit.

There have been people who get caught up in velocity though and end up building "torque-turds"....

1) High velocity heads but heads can't flow up top
2) so motor falls on its face by mid RPM
3) try to get top end by putting in big cams
4) huge cam is huge beyond high velocities.. killing low end. High end choke remains.
5) low sucks, high sucks... turd.

 

[trancebum]

:ph34r: :blink: :ph34r: :blink:

got flow bench testing, VE, fuyoooo....dam syiok. :lol: :lol: anyway, here's my 2 cents worth in this discussion. i'm not sure if mitsu's has this particular device but honda (integra GSR) and BMW (especially the M3) does. what they have is a butterfly valve (just like a throttle body) on the intake plenum. this valve opens partially (hence high velocities) at low engine speeds, giving sufficient charge of air. however during high rpm's, the valve opens up completely giving the engine enough breath for high rev's. this way....we dont need to port it, just polish. and this intake manifold is big enough to optimize high end as well as low end. ;)

justme2centsworth

 

[Jun9970]

Originally posted by ShaunSG@Jul 30 2004, 05:20 AM
The stacking up of air behind the intake valve is not really a benfit of smaller high velocity ports. In the realm of anything less than F1 and Champ car motors, the effect is not meaningful because of the time in between intake valve openings.

The main reason for wanting high velocity ports because high velocity air flow is the only thing that can keep intake flow going after the piston has gone beyond BDC and is on its way back up. A low velocity port cannot fight the rising cyl pressure as the piston is on its way up, so unless the valve is closed, you get intake reversion. A high velocity port will keep flowing though - at least for a while. This increases compression. It also extends total intake duration, allowing for gentler cam lobe profiles (more total time to open and close valve). Seconday effect is gentle seating of the valve, eliminating valve bounce which kills compression. The latter is a huge but often unconsidered benefit.

There have been people who get caught up in velocity though and end up building "torque-turds"....

1) High velocity heads but heads can't flow up top
2) so motor falls on its face by mid RPM
3) try to get top end by putting in big cams
4) huge cam is huge beyond high velocities.. killing low end. High end choke remains.
5) low sucks, high sucks... turd.

Shaun,

Is this equally applicable to forced induced engines as opposed to NA?

"The main reason for wanting high velocity ports because high velocity air flow is the only thing that can keep intake flow going after the piston has gone beyond BDC and is on its way back up. A low velocity port cannot fight the rising cyl pressure as the piston is on its way up, so unless the valve is closed, you get intake reversion."

Won't the turbocharger be pressuring the intake side of things, effectively negating the need for high velocity ports? Afterall, u got boost, even after BDC, the intake side of things is still being pressurised.

noobie :unsure:

 

[Torment]

Originally posted by Jun9970+Jul 29 2004, 06:52 PM-->

QUOTE (Jun9970 @ Jul 29 2004, 06:52 PM)

--QuoteBegin-Torment

@Jul 29 2004, 03:40 PM i think the purpose of having lighter wheels is not about gaining HPs but rather having better excelaration response and better stability in transient maneuvers. the advantages can't be felt or shown on a dyno right? the HP gain is an added bonus.

heavier wheels would result in greater transmission losses especially on a dyno. How much though is subject to debate. just imagine, opening a fridge from the handle as compared 2 opening it right at the hinge. opening it right at the hinge requires more effort. its about leverage. the bigger n heavier the rim, the harder the driveshaft has 2 spin the hub which inturn has to spin the wheels of the car. effectively, bigger rims would increase the radius from the end of the wheel to the centre of the wheel (ie hub/driveshaft). [/b][/quote] oh i din thought about that! thanks for info jun9970! :)

 

[ShaunSG]

Originally posted by Jun9970@Jul 30 2004, 10:49 AM
Shaun,

Is this equally applicable to forced induced engines as opposed to NA?

"The main reason for wanting high velocity ports because high velocity air flow is the only thing that can keep intake flow going after the piston has gone beyond BDC and is on its way back up. A low velocity port cannot fight the rising cyl pressure as the piston is on its way up, so unless the valve is closed, you get intake reversion."

Won't the turbocharger be pressuring the intake side of things, effectively negating the need for high velocity ports? Afterall, u got boost, even after BDC, the intake side of things is still being pressurised.

noobie :unsure:

Yes, FI ports require just as much attention paid to getting the balance right. A big lazy port is never ever wanted.

You are right in that a FI port is pressured and so velocity for a given port cross section will be higher. Still, you want as much velocity as possible for a given mass flow because you can extend intake duration on top of that which the boost pressure already allows for. Exact same benefits.

 

[Jun9970]

Originally posted by ShaunSG+Jul 30 2004, 01:48 PM-->

QUOTE (ShaunSG @ Jul 30 2004, 01:48 PM)

--QuoteBegin-Jun9970

@Jul 30 2004, 10:49 AM Shaun, Is this equally applicable to forced induced engines as opposed to NA? "The main reason for wanting high velocity ports because high velocity air flow is the only thing that can keep intake flow going after the piston has gone beyond BDC and is on its way back up. A low velocity port cannot fight the rising cyl pressure as the piston is on its way up, so unless the valve is closed, you get intake reversion." Won't the turbocharger be pressuring the intake side of things, effectively negating the need for high velocity ports? Afterall, u got boost, even after BDC, the intake side of things is still being pressurised. noobie :unsure:

Yes, FI ports require just as much attention paid to getting the balance right. A big lazy port is never ever wanted. You are right in that a FI port is pressured and so velocity for a given port cross section will be higher. Still, you want as much velocity as possible for a given mass flow because you can extend intake duration on top of that which the boost pressure already allows for. Exact same benefits. [/b][/quote] For discussion sake, lets take the EVO3 head as an example. Mitsu engineers probably took a couple of things into consideration in respect of their design of the valves, ports etc. If 1 were 2 upgrade 2 lets say a bigger turbine which in turn could boost higher, wouldn't the added boost be hindered by the port size of the stock EVO3 head which was designed for stock boost levels on a stock evo turbine? I'm sure there are a couple of design parameters that the mitsu engineers haf taken into consideration, but i a bigger turbine with higher boost wouldn't be hurt by a bigger port right?

 

[ShaunSG]

If 1 were 2 upgrade 2 lets say a bigger turbine which in turn could boost higher, wouldn't the added boost be hindered by the port size of the stock EVO3 head which was designed for stock boost levels on a stock evo turbine?

Not as much as you would think because the density of the intake charge is increased. If you are flowing an extra 20g of mass at a 15 psi pressure differential across the port and now you want to flow 40g of mass at the same 15 psi pressure differential, you are going to have to open up the port alot (about twice) OR somehow increase velocity also by about twice (which is just impossible). But if you want to go from 20g to 40g massflow but at a 30psi pressure differential (and assuming you get cool the charge to kepe density up), then you only need to increase cross section or port efficiency, just a little bit. The doubling of charge pressure makes for high velocity.

High velocity doesn't mean high MASS though - which is the actual target. If density cannot be kept high and you can't improve on intercooling, then you now have a problem getting required mass into the cylinder - even at high velocities. The port at this point is considered a restriction and so has to be opened up. The main thing is to work first on increasing turbo compression efficiency, intercooling efficiency, port efficiency... THEN and only then, if you still have problems.. increase port cross section. Even then, you can only open up a port so much before you grind into coolant passages.

I'm sure there are a couple of design parameters that the mitsu engineers haf taken into consideration, but i a bigger turbine with higher boost wouldn't be hurt by a bigger port right?

It can very well be by having velocity below optimal. As above, You want to keep velocity as high as possible as long as massflow requirements are met.

 

[kRiminaLz]

heh... really learn a lot frm all the profs. here.. hehehehehe...

i wouldnt expect this thingy could be very complicated!!.. juz abt to pnp my e3 head... hehehe...

so many issues here...

juz asking, whats the difference if i port the turbo manifold outlet n' turbo inlet? :ph34r:

 

[ShaunSG]

What is a turbo manifold? Do you mean exhaust manifold or turbo exhaust housing or compressor side outlet? When you say turbo inlet do you mean compressor side inlet?

 

[kRiminaLz]

Originally posted by ShaunSG@Aug 15 2004, 10:51 AM
What is a turbo manifold? Do you mean exhaust manifold or turbo exhaust housing or compressor side outlet? When you say turbo inlet do you mean compressor side inlet?

err.... sorry bro.. which one is which one?
my mech want to modify this thingy..
he juz said to port the turbo manifold outlet n turbo inlet.. n the fan look alike thingy at the exhaust outlet n the wastegate outlet also should be port for good air flow...
heh... dont really understand whats the function..
so anybody haf any ideas what this guy is talking abt? or u guys dont know what i'm talking abt... erkkk...




*dont really understand, but i'm really sure that he's talking abt this thingy.. :D

 

[loafer]

hi guys, very informative stuff we have here. sad to say after reading every single post on this thread, i'm still as confused as the day i was born. thank you :blink: