Port Volume Reduction.

[pandaah]

the dead space is really interested... would be good if you could get a flow testing machine which would emulate 1bar of boost..

[oldcorollas]

boost = more mass, not more volume/velocity

Casey.. 20V = smaller ports.... wonder why they flow better?

[lexsmaz]

I assume that you are after more low end torque ? ... How bad is your car now & what cam's & compression ratio etc are you running now ?

I dont know much about these 4AG engines, can you get a small port & a big port in NA Forms & if so are the torque characteristics much different ? in the 2 engines ( obviously other things come into play as well but it might give you an idea ? )

[mattysshop]

with the bigport NA versions... they had TVIS... the massive inlet port was literally halved through 8 runners... and a series of 4 butterflies closing them off at low engine speed (under 4500), to bring air speed up to actually give them torque..

my mates circut car (which has a stock bigport) has removed the butterflies and the shafts.. and filled the holes etc etc.. and it is pretty much like driving an 1.3L starlet life below 3000rpm... you really do need to control the throttle with street driving..

WOT without TVIS on a bigport is shocking untill about 4000rpm... then it comes on song...
WOT on a stock smallport is FAR more linier and robust in the bottom end..

if someone had a dyno plot for stock na or similarly modded in both forms would show that the smallport feels quite torquey for a 1.6 stock... and the bigport really does need that TVIS to close off half the port under 4k..

[amichie]

Where abouts did you fit these 'chokes'? More often than not, 'chokes' refer to venturi's in carbies. The 'choke point' mentioned in the mototune articles refers to the smallest point just before the inlet valve.

I put them about 8 inches from the intake valve. Just inside the intake manifold at the plenum end. This is about the same point they would be if you used a set side draft DCOE carbs.

[trdee]

Filling the ports isnt going to make you "more power everywhere" though. You can see it immediately just from t-vis. T-vis essentially cuts the bigport ports in half at low revs, but from 4300ish rpm the butterflies open. Why? Because if they remained closed you wouldnt make as much power in the high end.

So if you fill your ports and dont run tvis, its quite reasonable to assume that all you will be doing is reducing the power band of the motor, as you will now be getting the extra torque down low when the butterflies are closed, but you will be restricting flow when the butterflies should be open at the higher end of the rev range. If the bigport made more power in the top end with smaller ports, then why would the tvis butterflies open up in the higher rev range??

Also, there is a lot more to why a blacktop head flows well than just the size of the ports...

[mattysshop]

thats just the thing they don't... the smallports have a better short turn, and valve bowl shape, and they actually flow very nicley... samwith 20v's.. the ports are still smaller than the bigport head.. but the flow figures are much better..

[trdee]

i wasnt comparing to any other head. wait, what are you talking about? lol

[Billzilla]

Casey.. 20V = smaller ports.... wonder why they flow better?

The 20v's flow nice on the bench but in the real world they just won't make as good a power as the 16v's. There's problems with the flow between the little valves at high flows that you can't get on a flow bench and the combustion chamber is pretty ugly.

[amichie]

I think the japs have revised their massive intake port strategy since the early nineties. The europeans use much more conservatively sized intake ports on may of their designs. I think one motivation for the large ports is it promotes exhaust gas recirculation which improves emmisions.

[Duk]

Filling the ports isnt going to make you "more power everywhere" though. You can see it immediately just from t-vis. T-vis essentially cuts the bigport ports in half at low revs, but from 4300ish rpm the butterflies open. Why? Because if they remained closed you wouldnt make as much power in the high end.

So if you fill your ports and dont run tvis, its quite reasonable to assume that all you will be doing is reducing the power band of the motor, as you will now be getting the extra torque down low when the butterflies are closed, but you will be restricting flow when the butterflies should be open at the higher end of the rev range. If the bigport made more power in the top end with smaller ports, then why would the tvis butterflies open up in the higher rev range??

Why have a port CSA that bigger than the valve CSA. Unless the builder has some how incorperated a gradule and consistant taper from the runner inlet down to the back of the valve, the ports should be smaller than the valves.
The idea is to not have a port any bigger than it absolutely must be. The valves are the limiting factor.
Any excess volume is just dead space and causes the air to slow down and loose momentum. Probably more of an issue when running off boost.
Your example of TVIS equipped big port is a tad simplistic, but valid.
Obviously the 4AGZE engines don't have TVIS as there isn't much room for a decent designed manifold, let alone any sort of variable flow manifold.

The initial idea was to get port volume/CSA down to the point where I could make a new manifold that is basically like a set of 4 into 1extractors in reverse, while still providing a nice solid top mount for the SC12. Due to pipe bend radius, I was looking at 1 5/8 mandrel bends. They have an internal diameter of about 38mm, and as I previously posted, if propperly designed port that has a diameter of 38-39mm can flow enough air naturally to make 50hp per 500cc cylinder, then force fed with nearly 18psi, it should flow well enough too.

[Duk]

I think the japs have revised their massive intake port strategy since the early nineties. The europeans use much more conservatively sized intake ports on may of their designs. I think one motivation for the large ports is it promotes exhaust gas recirculation which improves emmisions.

I know the top and bottom halfs of an RB20 inlet manifold has holes that are 50mm in diameter. Pretty massive for an engine that has less than 330cc per cylinder.
The inlet ports look massive too. Unfortunately I'll be getting a closer look at that aswell .

[oldcorollas]

The 20v's flow nice on the bench but in the real world they just won't make as good a power as the 16v's. There's problems with the flow between the little valves at high flows that you can't get on a flow bench and the combustion chamber is pretty ugly.

as big ports? or small ports?

[gixer]

Couple of things I have found over the years,

Devcon works fine in intake ports, have used this in peripheral ported rotaries to piston engines, prepping the surface is important

Adding material can also be advantageous, for example RB30 heads have a very flat port floor with a shocking short turn, adding material in this area gives great gains on our flow bench.

[Casey-G]

Couple of things I have found over the years,

Devcon works fine in intake ports, have used this in peripheral ported rotaries to piston engines, prepping the surface is important

Adding material can also be advantageous, for example RB30 heads have a very flat port floor with a shocking short turn, adding material in this area gives great gains on our flow bench.

Thing is you would be better off to port a smallport head if you want smaller ports.


The devcon is okay but having an identical head more or less with already cast smaller ports should outweigh putting a putty or similar in your intake to modify the size/shape of the ports.


Again i want to mention a 1.6litre engine was never meant to be a low ender, the money would be better off spent on higher strength rods, longer duration cams and a lighter bottom end so you can rev without regret.