just a few pics to illustrate the difference from the 439cc 04-05 yfz heads ...to the 450cc 06 & up cylinder heads

the 04-05's had a slightly smaller volume\ more closed combustion chamber design...as well as a higher volume\ lower velocity intake port:


and the 06 & up models have a slightly more open combustion chamber of higher volume....with a velocity increasing , smaller tapered volume intake port:


if you look at the combustion chamber areas between the exhaust valves, you can see the shape\volume differences...

hope that clears up some of the questions about the differences.. :)

04-05 combustion chamber:






06 & up combustion chamber:

04-05 intake port:





and 06 & up intake port:

Evidentally, I don't possess that keen eye to notice the variances in the two different years.
To me, they look identical.

So, what cylinder head makes more power? The 06?

seriously?? you don't see any differences?? you don't need a keen eye to see these differences, you just need to know what you are looking for...

the diffs are as huge as any you will likely ever see in same model\differnt year changes....

the 06 style has sharper throttle response.... the 04 style comes into its own on big bore\stroker setups...that's where the displacement of the engine itself cranks up intake tract velocity...

I studied the picture for a while and, obviously, I really don't know what I am looking for...LOL.

I guess that's why I don't do head work and, you do.

I do have a question for you, on an 06' head how big do you usually open up the intake tract? Where the carb boot attaches.

That depends on what size mm carb you plan to run...

The 06 head has material removed from valve to valve to un shroud them, where as the 04/05 has sharper/ closed off more areas between the intake valves.

Granted his ported intake pics don't show the big difference with scale of the intake ports..... Like on a 04 head I can stick my skinny azz fingers in and touch the valve stems, where on a 06 head I can't get my fingers in that far before the roof and floor close in and block my fingers.

Question for Mix here or any one else...... are the intake runners longer on the 04 stock like that or is that how you ported it? I never noticed that before. Mostly because I have a 06 model.

I'm going to have Sredrum open my carb to a 41.5 taper. He told me to measure the opening of the intake tract. He explained to me that the carbs outside opening needs to be smaller than any other opening inside the head.

I had a local shop port my 06' head and, I took a crude measurement with a tape measure (Very crude....will have to get a dial caliper), and my intact tract is about 42.25-42.50mm. Like I said, this is a crude measurement. I was simply curious what a respected head porter opens it up to.

i open it up to a perfect\ seamless match for the size of the carb and matched carb boot assembly.....

if you had to have a mismatch one way or the other, it would be best to have the port slightly larger than the carb.... that way the airflow wouldn't have to run smack into a reduction step on its way into the port

they aren't really longer.... they look longer because they have a straight taper from the outside to the valve stem on the 04-05's


the 06's have a port reduction shortly after the carb boot mating surface.... sort a rolled edge to the smaller \ faster runners... that "roll in" area makes the port look shorter in the pictures

Thanks for the clarification. I've seen some heads with a steep "roll in" before and figured it was that way to create lots more velocity even though the opening of the port carb side is probably the least important pat of the intake port. Maybe they just did it that way because they thought that the customer had a 50mm carb to hang off it. Because bigger is better.

how about the extra material VS less material between the exhaust valves .... can you see that in 2D ??

Nope. Not at all. But I did find a 3D picture of a port showing what you are referring too :)

So do you mean like this...



How the port walls flare out around the valve stem to help flow around the valve as it flows/ over the short turn? I assume it also helps flow into the combustion chamber around more of the valv that would normally be partially shrouded.

OK... i can't let this go...LOL...

the flat squish are of the 04-05 head bows inward between the exhaust valves....and there is also more height to the remainder of the material between the valves....

the 06 & up head doesn't have the flat deck bow inward between the outer portion of the exhaust valves..and it is flatter in the combustion chamber between the valves too....

its like one of those trick pictures of "can you see an old lady and a young lady in the same picture?"...where at first you can only see one or the other....but when you finally see it, you can't see how it wasn't always visible.... :)

nice 3D model of a port!

it helps to think of airflow in visual terms... and that is usually easier to to with water being the flowing medium instead of air

the widening at the point of turning.... works just like it would for a flowing river.... if you have a wider space\ larger volume of confinement.... the river would flow slower at that point...and when it flows slower, it is better able to negotiate a turn without over-shooting the short side of the turn....

I found some other 3D modeling of water in a port too.... I'll see if I can't find them again. It shows in color the slower speed with a gradient of speed to the higher speed areas and also how it enters the combustion camber and swirls.

Engine Intake Port
Computational Fluid Dynamics (CFD) of an Intake Port Simulation

Knowing the level and stratification of the Air and Fuel is essential in predicting combustion, fuel economy, and emissions, leading to an optimized engine design. Cycle simulation (0-dimensional) simulations are fast and can explore operational parameter space once a the system is calibration. Calibration techniques involve experimental data. CFD (Computational Fluid Dynamics) simulations can reduce the amount of experimentation, decreasing cost and design time. Using a modified internal flow boundary layer model, the CFD simulation was able to accurately determine Swirl, Tumble, Swumble values of the flow at BDC (Bottom-Dead-Center) which were then incorporated into a cycle simulation for Model-Base-Mapping and cycle simulations. An automated system Digital Flowbench was developed which would take an STL of the intake port, create the surface and volume mesh, perform the simulation, and determine the flow characteristic of the design. This technique was patented, agreed within 5-10% of experimental values and was deployed as a design tool.

Three Dimensional (3D) Visualization of Internal Flow of Design A of an Intake Port



3D Intake Flow Velocity Contours from Simulation (Red-high, Blue-low in magnitude)

awesome pics...!

I like these pictures because even some one who doesn't understand much if anything about flow and porting can at least get an idea visually of what is going on, and then they may start to understand better about valve shrouding and high and low pressure waves.

they illustrate that perfectly

Just wanted to say Thanks for some really good information you guys. I never thought about some of the stuff you guys talked about, but it makes complete sense.
Now I'm going to try to find and old lady and young lady face in those pics of the head. Thats what were looking for right ;)

LOL... you got it...

if a moderator would be so kind... could this be pinned in the Venom section?

I see how you are... make work for me!