So Im stuck with the crappy Y7 intake manifold.
Everybody says upgrade to the Y8. Or buy something ready made.
Which is easy when your siting in the US but not when your half way across the globe.

the thought of designing a custom intake manifold and TB then entered my mind. We have been designing various Billet parts for race and bling for a decade. Shouldnt be too hard to fab up a unit. Though my first choice still remains to just buy a Y8 mani if I can get a good deal.

There are two issues Id like feedback on.
1. Runner Length
2. Material to use.
3. Size of Phlem.

1. The general rule is to start with 6000 RPM as your target RPM, and say 13 inches is the perfect length for that target RPM. For every 1000 RPM higher, subtract 1.3 inches and for every 1000 RPM lower, add 1.3 inches. So for my engine we get 11.3"

Now looking at the various options on Ebay I see that the runners are absurdly short. It sure makes the job of fabing up a unit easy but I dont get
How such short runners can work.
Most guys who fab their stuff here. Get a hold of something from the US and copy it. Im not too keen on taking that route.

2. Material to use.
The stock Y7 mani has very little metal on it. You have your mounting plate then the runners and the TB there is no Phlem. I like this idea because what ever metal you use. It gets heat soked and adds a lot of heat to the engine.
If you where to meaure the intake temp at the Vale. Your going to get cooler air with the Y7 than with the Y8. The Y7 uses your plasic air box as a Phlem.
The Y8 uses a metal box as your Phlem. Hence the air is hotter.
So what is it with the Y8 mani that makes it work better. Is it the Phlem ?
Or the length of the runners or the shape of the runners ?
What If we where to add a large Phlem to the Y7 mani ? And use plastic instead of Ali.

3. I see various Phlem boxes some are low volume like the sknunk ones and some are high volume. How do you calculate the optimum Phlem size.
Guess I need to dig out my copy of Blair. I can see an advantage with a smaller volume. Your air has less time to get hot.

Any help would be appreciated either with the design of a new intake or sourcing a Y8 mani.

When you look at modern Super Bikes how come they are not effected so much by intake runner length. ?

 

plenum.

phle[g]m=mucus.

i don't think heat soak from the air in the engine bay is your main concern. keep in mind that aluminum works well as a heat sink as well and the manifold has hot engine coolant circulating through it. more mass/material can dissipate that heat more quickly. however since you brought up material selection, plastic would work well. the problem with plastic is you need access to a large injection molding machine and tens of thousands of dollars invested in tooling/molds do build a reasonably durable manifold.

i think you've misinterpreted the design of the Y7 manifold. it does not have a plastic plenum. that is simply the air filter box. the plenum comes after the throttle body, which is under that plastic box. on the Y7 it is very small.

for plenum size, a smaller TB needs a bigger plenum volume and vice verse. the Y8 has a good size... laminar flow and resonance tuning are what you're shooting for. you're runner length would work fine, be sure the diameters are no larger than the ports. too small would be better than too large as far as flow is concerned.

i've seen some nice sheet metal aluminum manifolds that guys have made. if you're able to machine the flanges needed for the TB and the ports and the injectors... then weld it all together, this would be a good route.

all that to say, i wouldn't spend more than the price of a junkyard Y8 manifold to build a custom one for a Y7 unless it was a high investment race motor with a big cam and high end internals and tuning.

surely someone would send you a Y8 manifold from across the world..