Twin cam head design

[cute wee gem]

[mikuni]

^ So when porting attempt to reduce the effects of any/all of the above and you should see positive results?

Regarding the velocity posts, and reducing port size. With reading I have done on XE's the tuners get good results from using taper throttle bodies that effectively reduce the intake runner diameter by a linear amount, from about 60mm at the outter most tip (bellmouth/trumpet) right down to the valve. The effect is supposed to reduce the expansion losses because once air is swirling and the volume of the object it is passing through is reducing at a steady rate, it will apprently continue to do this. I kind of relate it to the funnel of a tornado to try and make sense of it. Not sure if its related at all but picture the top of the tonado being the intake with the valve being at the bottom. Makes sense to my simple mind.

[peteretep]

i dont know a whole lot about flow characteristics, but i study stuff relating to it

but from what i understand, and what is obvious from the above picture, is that:

Changes in direction are bad, at my work an elbow/bend is considered in equivalent metres of pipe, and we generally use 6m of pipe when looking at lossess, to give you an idea

You want all changes in area to be smooth and no sharp changes in cross sectional area, ie going from small to big to small again will cause worse flow characteristics than staying small the whole way through

How the air enters and exits a pipe run makes a big difference, i would imagine especially with wanting to spread the air/fuel within the chamber

/probably worthless

[Hemi]

i dont know a whole lot about flow characteristics, but i study stuff relating to it

but from what i understand, and what is obvious from the above picture, is that:

Changes in direction are bad, at my work an elbow/bend is considered in equivalent metres of pipe, and we generally use 6m of pipe when looking at lossess, to give you an idea

You want all changes in area to be smooth and no sharp changes in cross sectional area, ie going from small to big to small again will cause worse flow characteristics than staying small the whole way through

How the air enters and exits a pipe run makes a big difference, i would imagine especially with wanting to spread the air/fuel within the chamber

/probably worthless

for the second point**

for some fucked up reason ive always thought that was true (due to turbulence losses) dunno its nice to know something that i thought , was true haha

[forced]

Looks like a load of shyte to me.

Flow through the port is dependant on valve lift....... that changes everything else.

As for port velocity, more BS. I think that's only relevent for dirty american V8s. It's not velocity that's important at all but inertia. Inertia is a function of both area and length. That's why big port 4 valve heads on EFI jappers have long runners (must be close to 1.5m long on my 3.5 quadcam Paj). Dirty old V8s can only make use of tunnel rams.

Steve

[Hemi]

Looks like a load of shyte to me.

Flow through the port is dependant on valve lift....... that changes everything else.

As for port velocity, more BS. I think that's only relevent for dirty american V8s. It's not velocity that's important at all but inertia. Inertia is a function of both area and length. That's why big port 4 valve heads on EFI jappers have long runners (must be close to 2m long on my 3.5 quadcam Paj). Dirty old V8s can only make use of tunnel rams.

Steve

no dissing but please show some data man , for once im interested in this shit

[forced]

Plenty of data. All you need to do is visit pick a part and take some imagination with you along with an open mind .

As for the % losses, if the valve is closed, there's no flow so losses at 1 through 8 are all nil. As the valve lift increases, the % loss across the valve decreses whilst the losses 1 through 8 in the diagram all increase. It doesn't show the loss caused by the intake port divider which in some cases is significant specially when you work out the peak airflow by other means, which is very close to supersonic at least in one of my motors.

Steve

[Spencer]

Looks like a load of shyte to me.

Flow through the port is dependant on valve lift....... that changes everything else.

As for port velocity, more BS. I think that's only relevent for dirty american V8s. It's not velocity that's important at all but inertia. Inertia is a function of both area and length. That's why big port 4 valve heads on EFI jappers have long runners (must be close to 2m long on my 3.5 quadcam Paj). Dirty old V8s can only make use of tunnel rams.

Steve

dude velocity is well relevant to port design its why all decent twin cam head manufacturers have stopped making the massive big port heads of the 80's. Toyota even realised this and placed a crude device called tvis to gain low end back from poor port velocity at low engine speeds. Any decent engine builer would laugh at you if you said it was a myth

As for the runner length and 'inertia' as you put it, the runners are there for intake resonance tuning plain and simple. Modern cars have chambers that give two or three different runner lengths as to tune the resonance for several rev ranges. The effect is from the pressure wave from the closing of the valve if you tune the runner to suit your desired rev range you get a standing wave and the pulse is reflected down the port. This gives a mild supercharging effect hence there are n/a engines that can achieve higher than 100% Volumetric efficiency. F1 cars had fully variable trumpets to maximise this effect but were consequently banned. This effect isn't really called inertia dude guess you could call it that.

And heaps of dirty old v8's owned by clever people i know have tuned length runners on them the principal still applies

[Spencer]

Also pressure wise the inlet port is a very unstable place it doesnt really get a chance to get 'inertia' going

[forced]

Also pressure wise the inlet port is a very unstable place it doesnt really get a chance to get 'inertia' going

You're obviously confused.

When the intake valve is closed, there's no flow through it.

When it opens, there is.

Velocity of something means nothing unless you take mass into consideration. That's where inertia comes in.

That said to confuse you further, a 4V Cleveland head is considered too big for street use due to insufficient velocity (at least according to all the experts out there). So why is it then that many Mitsi 4V ports are bigger per cylinder capacity and so velocity is less. The only reasonable answer is that all the experts are well and truely wrong.

You've confused yourself of course because air flows in 2 ways, there's a direct flow with a pressure wave superimposed over it, much like electricity where there's AC and DC but there's also pulsed DC which is far more interesting and important.

Steve

[Yowzer]

Isn't inertia a constant? Sounds more like you're talking about momentum..

[Yowzer]

Also pressure wise the inlet port is a very unstable place it doesnt really get a chance to get 'inertia' going

When the intake valve is closed, there's no flow through it.

When it opens, there is.

Not too sure why you're stating the obvious here..

When the valve closes, you have the momentum of the air still in it heading towards the valve. It then bounces, more or less, off the closed valve, creating the pressure wave that spencer was talking about.

Also, a misti engine tends to rev higher than a big fat 8, making its usable power up higher, and therefor has a higher intake velocity.

Big v8s are usually geared a lot lower, so their engine revs at the same vehicle speed is lower, meaning lower intake velocity.

On top of that you haven't taken into account the specific design of the ports, valves, or anything else at all.

[Testament]

Honda still made(make?) huge port heads for ages, hence high power/crappy torque on the B series performance motors. I don't know if the K20A/F20C are different though.

Brad have you got any good pics of the XEV head from various angles showing the ports and combustion chamber? How far are you going to go with this? Like ok I know that 300hp is possible out of an XE butat what cost, whats the realistic approximate hp target?

Also whats available for the XEV vs. the XE - cams, pistons, rods, race beaings, oil pumps (dry sumps?)

what about the rest of the drivetrain, can the gearbox handle whatever you throw at it?

both big and small ports can be made to work, and yes ultimately big ports can give more top end. It's alot more work to get a smaller port to really flow, and manufacturers often take the easy route, putting in a bigger port (not having to get as good a surface finish etc.) and tame cams along with intake manifold design to acheive their desired result. and hey it probably makes sense economically to do that for them.

As for the carbon fibre dinosaur LS motor, yeah it isn't an "ideal" design - the chev engineers must have been told to retain old style architecture for whatever reason. But within those constraints the heads work ok, the later ones more so as they have gone through a few different port shapes. But yeah crappy hp/litre 400hp/6L isn't that flash - but hp per kg they are quite good - they only weigh about 190kg.

[Truenotch]

Not going to comment too much cause I've already learnt more than I know but:

When the intake valve is closed, there's no flow through it.

When it opens, there is.

Why does it matter what the flow is when the valve is closed? No more air/fuel is going to make it into the engine.

Also in my experience smaller ports have been proven to work better, and I believe that velocity of air, as well as tumble and swirl are the most important characteristics of a good port.

I'm going to go browse Toyspeed for a while to find the million talks about helmholtz

[FLAWLES]

with out causing a massive shit fight here i am couriuos as to why you are saying port volicity doesnt work steve?

i cant find the article on the suzuki swift gti's but these things are pulling masive power out of there 1.3 n/a 4 pot doing this exact thing and that alone proves it works

lol im on a mission to try and find this dam article, maybe its in a mag that i have

EDIT

not the one i was looking for but this has to do with bike engines so weather or not you can apply this to cars i dont know

intake porting

http://mototuneusa.com/think_fast_intake_porting.htm

port velocity

http://mototuneusa.com/homework.htm

sorry brad for spaming only trying to help mate but may be sending you down the wrong path

[Roman]

Alright well I've been doing a bit of thinking about air intakes into motors. (rant in progress... contains thoughts from 2am, may not be fully coherent)

First of all, starting at the start. What is their function?

The function of an intake runner is to accellerate non moving air at the far end, to the highest speed just before getting to the head. (which is not to say that a higher speed is necessarily better... just that there's not much point in slowing it down, speeding it up again, along the length if you can help it)

Lets say that the ideal speed for air entering the head, to give the largest mass of air into the engine was was 300kph. And at the far end, the air speed is zero.

Fluids are lazy, and dont like moving if they dont have to. A linear rate of accelleration is the best way to move a fluid from one speed to another. In this instance, from 0kph to 300kph.

To do this with a tube, you need to have a proportionally smaller cross sectional area as it goes, to increase the velocity.

So lets say, that at the head, the cross sectional area where we want 300kph is 50mm square.

Lets also say that we've got 300mm long intake runners, with which we've got to accellerate air from 0kph to 300kph.

This means that for every mm of pipe, the air has to accellerate by 1kph.

So 0mm from the head, airspeed 300mm, cross sectional area 50mm squared.

10mm from the head, airspeed 290kph, cross sectional area is ((300/290)*100)*50 = rounded to 52 square mm.

Continuing this on at 10mm intervals for the length of 300mm tube, courtesy of excel doing the maths for me, and you end up with numbers like this:

Now, if we divide these numbers by pi, and then divide them by 2, we can know what the radius at each point is.

Getting excel to do the maths again, gives us these numbers:

If we know the radius at points from the head in 10mm intervals, we can draw a sketch to proper scale of what the 'ideal' intake would look like, assuming linear increase in velocity is ideal. How close this would match a 'real' intake would show whether or not this idea is barking up the wrong tree...

Which with a few minutes in autocad, gives this:

Then a spline line thrown over the points:

Then mirrored, to show what the intake runner cross section would look like, for one dimensional flow:

An obvious problem here, is that in an automotive application there's no possible way you could have a trumpet end that big in an engine bay. (or 4 or more!)

But the point is, bearing this in mind, assuming its correct, makes a few other things make sense.

1. Why having a taper makes sense over 'straight' intake runners... Flowing air at constant speed at one part of an intake runner is inefficient, as more 'work' has to be done accellerating the air from a slower speed over a shorter distance (?)

Also shows that a 'straight' taper, although better than constant cross section, is still not 10/10ths 'ideal'. (Even if in realistic terms, it is 98% as good)

2. That the most logical way to port a head and design an intake runner is to start at the valves, find cross sectional area at a relevant point. Apply the maths formula to figure out what the cross sectional area should be at mm intervals from this point outwards, based on what you want your total intake length to be. Fill in or expand ports/intake runner cross sectional area to suit this. Rather than just random grinding here and there to make it 'look' like it flows well.

3. That porting a head means nothing if it doesnt have the intake match it, they're parts of one functioning entity, different parts of the line on the diagram. cut a line vertically through any part of that picture above, one side is the shape of the port and other side is shape of the intake. It doesnt matter where the port stops and intake runner starts, the whole thing needs to follow that shape overall to work well. (theoretically?)

4. Decreasing the diameter of the ports at a particular point can be logical if it makes the air accellerate in a more linear fashion, even if this initially seems counter intuitive to making more air flow into the motor

5. Also explains why so much of the flow losses occur (in the previously posted diagram) around the valve seat sort of area, this is where the cross sectional area expands a hell of a lot. Imagine it being a big bump outwards in shape on the narrow end of the picture above.

6. Not entirely relevant, but something that sort of 'clicked' while I was thinking about this.

Why does water swirl, or tornado make that shape?

Water or air wants to accellerate at a linear rate. To do this when going down a sink hole, it takes the most direct route it can which allows a linear rate of accelleration. So the route which isnt necessarily the shortest A to B can be the most efficient getting the air or water to move there. In this instance, a swirl pattern is best. If you had a sink hole with the 'ideal' cross sectional area, then the swirl would not occur perhaps?

Disclaimer: I have no idea if the above is true or not, just some thoughts on the matter. possibly wildly wrong in some/all instances, will perhaps start some meaningful discussion however. Even if it's correcting me where I'm wrong. Keen to know!

[mikuni]

^ thats the idea of bellmouths intaking air from the perifery of the trumpet I guess, an attempt at increasing the outter intake diameter rather than having a straight tube.

Couldn't find the supporting pictures that I was looking for but I know you've seen them before.

This link has some pretty pictures.

http://www.bgideas.demon.co.uk/tmanual/tm02.htm

lol swirl

Honda still made(make?) huge port heads for ages, hence high power/crappy torque on the B series performance motors. I don't know if the K20A/F20C are different though.

BEAMS 3S ports are pretty huge. Its not so much just that huge ports are shit, just talking about the design of the heads and what works and what doesn't. Like spence said, lots of big port engines use some kind of system to allow them to work better at lower rpm, whether it be intake runner adjustment via TVIS, intake runner adjustment like most engines have now, a second cam profile like vtec or a variable in valve timing like VVL.

Brad have you got any good pics of the XEV head from various angles showing the ports and combustion chamber? How far are you going to go with this? Like ok I know that 300hp is possible out of an XE butat what cost, whats the realistic approximate hp target?

I think theres some in my project thread. I might try and fish them out tonight. They have a nice head design but tiny intake ports. The key is really how large they can go. Like someone said above, the XE is released in a production car so despite the large ports, it can produce a very good mid range punch.

And realistically the power output will be around 200hp in its first incarnation, going up to 230hp with the second and then hopefully I will end up chasing something around 250-260hp in years to come and when money allows. 300hp from an XE in unrealistic without having a huge budget and would be impractical in the car I will be putting it in, not to mention the tracks it will be run on.

Also whats available for the XEV vs. the XE - cams, pistons, rods, race beaings, oil pumps (dry sumps?)

what about the rest of the drivetrain, can the gearbox handle whatever you throw at it?

Bottom ends are different from the factory but all XE components can be used on XEV. Blocks are essentially the same. Dry sump setups can be bought for a reasonable price. The difference is with the top end, anything can be bought for the XE, where as XEV has very limited tuning parts available and everything will need to be custom.

Drivetrain can handle apparently. The XEV come with a wider ratio F25 which probably won't be suitable for track use, but F25 from the XE will bolt up. All gearboxes can have aftermarket kits fitted for dogbox arrangement, or adjustable final ratio only and can also have a quaife LSD fitted. The F20 has been put beside a C20LET which is the 2L turbo engine and the box has handled in excess of 300hp without too much complaining apparently.

Keep the yarns/info coming guys

[Roman]

Oh yeah, another thing.

It's interesting about port sizes.

With the 4AGE motors, started out with big ports, got smaller and made more power as they went on.

With the 3SGE motors, the NA one that makes the most power has the biggest ports.

I talked to Lynn Rogers about it ages ago, he reckons the Altezza M/T ports are too big. The single VVTI motors or the auto altezza motors are the pick of the bunch for port size, but I think they have smaller buckets or something which is less useful for big cams. Or something like that.

Here's a pic of one of the ports from mine, had some port work done that was particularly well done according to Lynn.(Came like that from Japan) Not that you can tell anything from a face on picture, but may be useful for comparison or something. Size of port at the face is approx 49across x 40mm high

[Unclejake]

At risk of sounding like a broken record : If I had my time again I would purchase a Honda S2000 motor and gearbox, smack it into my Cortina factory standard, change the oil and go racing.

It would be much cheaper, much faster and much more reliable than what I am currently doing (but not Pre65 legal of course).

[Honda Ass Dragger]

At risk of sounding like a broken record : If I had my time again I would purchase a Honda S2000 motor and gearbox, smack it into my Cortina factory standard, change the oil and go racing.

It would be much cheaper, much faster and much more reliable than what I am currently doing (but not Pre65 legal of course).

This man speaks the truth

There got to be a reason that the brown datsun that owns the ss2000 series runs a basically stock s2k motor, I belive they did put some TODA cams into the engine but couldn't get anymore form it

It's always best to follow the path well trodden, look at what other have done and improve on there work

Also remeber the manifacture always knows best, there will always be reason as to why a manifacture has done somthing in a particuler way

Remeber they spend $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ creating new motors