Port Volume Reduction.

[trdee]

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.

So what you are saying is that the ports on the bigport head are so big that you cannot take full advantage of them unless you run oversize valves to match the size of the port?

[oldeskewltoy]

Duk.... look for Kai Power. They made(or once made) a flow restricter that part of it slips inside the large port head to reduce the port size. Actually it "individual-izes" the ports



Also, I've actually been @ a Formula Atlantic engine shop, Loynings Engine Service, they did all the machine work on my smallport (but that's another story) - http://www.toymods.org.au/forums/sho...0&postcount=24

The ports on an F/A engine are HUGE

In fact they overbore the ports so much that frequently they'll get coolant leaks through the port walls...



I've also seen the intake valves are placed less then a mm apart (from edge to edge)

[Duk]

So what you are saying is that the ports on the bigport head are so big that you cannot take full advantage of them unless you run oversize valves to match the size of the port?

That's my interpretation.
It's the old "weekest link" scenario. The whole shooting match can only flow as well as the worst flowing component.
If the port can flow 20% more than the valves will let them, what's the point?
No one would doubt that a propperly designed small orifice can't flow as much as a properly designed larger orifice. But if that extra flow can't be utilised at the final stage, ie, filling the cylinder, where is all the bennefit?

[oldcorollas]

so why not start with a small port or a 20V?????

[Duk]

'cause I don't have 1 .
I do have a spare big port head tho

[jonathan yee]

so how much is it gonna cost you to fill and reshape the ports on your bigport head along with making a new inlet manifold to suit as oppossed to just sourcing a small port or 20v head?

i understand fully where your coming from, i'm building a 3sgte and i've ditched the tvis head and i'm using the gen2 NA head becuase they dont have tvis and smaller ports, tho i'm porting these out.

it'll be interesting to see how well it flows compared to the gen3 head but it's not gonna cost me as much as buying a gen3 head, either head i use i'll have to make an inlet manifold for (which is about %60 done) as unlike the 20v's they never came with awesome quad setups......

[Duk]

so how much is it gonna cost you to fill and reshape the ports on your bigport head along with making a new inlet manifold to suit as oppossed to just sourcing a small port or 20v head?

I dunno . I don't think I can apply my idea of a collector style manifold to the big port head. So I'm looking at simply adding material to the port floor and maybe some to the entry of the head ports and exit of the inlet manifold around the sides. I'll retain the standard GZE inlet manifold. But either way, 99.999% of work will be done by me so it's only material costs.

i understand fully where your coming from, i'm building a 3sgte and i've ditched the tvis head and i'm using the gen2 NA head becuase they dont have tvis and smaller ports, tho i'm porting these out.

Just make sure the ports actually flow better rather than just making them bigger .

[jonathan yee]

I dunno . I don't think I can apply my idea of a collector style manifold to the big port head. So I'm looking at simply adding material to the port floor and maybe some to the entry of the head ports and exit of the inlet manifold around the sides. I'll retain the standard GZE inlet manifold. But either way, 99.999% of work will be done by me so it's only material costs.


Just make sure the ports actually flow better rather than just making them bigger .

it's only marginally bigger, it's more to suit the port runner size and flutes i have, which are 46mmID. they'll still be smaller than the gen3.

more shaping and enlarging the area around the valve seats to get as much flow for awesome rpm potential. and so i'm not wasting my time installing larger valves.

so are you saying you are able to port fill yourself? what's so hard about making an inlet manifold/runners as well?

[Duk]

so are you saying you are able to port fill yourself? what's so hard about making an inlet manifold/runners as well?

Filling the ports isn't that hard. I plan to use JB Weld. Billzilla suggests Devcon.
Cleanlyness and surface preparation are the keys (from what I've read).
The hardest part about making the manifold would be the flange plate with it's oval ports. But we have milling machines at work .
I don't think I'll make new manifold now. Not for a big port anyway.

[jonathan yee]

i just drew up the manifold flange with accurate meaurements etc and had it cnc'd from 12mm plate ally. i had the ports milled at a 15deg angle to the plate as well to match the angle of the ports in the head.

only cost me $80, now i'm gonna use the flange as a template to port match/enlarge then weld the runners on etc.

it's been surprisingly easy so far........

[the_random_hero]

So are we talking about FI or NA here? My understanding was that for FI you need flow, but for NA you need velocity...

[Duk]

Turbo and supercharged.

[Casey-G]

Duk, i can sell you a small port head if you really want, its been acid bathed and everything so its ready for you to go nuts on it, i'd just hate to see a motor die from something coming loose from the intake side..

and you could drop your bigport cams in it if they are bluetop ones and get a gain from those as well.


Just food for thought, they are cheap and in good supply so yeah maybe its a better path than what your planning.

*Random hero, my beliefs are very similar to yours.

[the_random_hero]

Well it would make sense to me, NA you're reliant on pulse tuning/etc to make sure you have the airspeed up (whereas you don't need the max flow figures), but with FI something is actually pushing the air in (dictating the velocity).

[oldcorollas]

it doesn' tmake that much difference.

NA has 1 bar of force pushing air in,
FI has 1+boost bar of force pushing in.

it is wrong to think of them differently (just that with boost, it is easier to cover up mistakes with a bit more boost)