Das Beast: My E30 track / street build

[dvallis]

Here you go, 20 psi inlet pressure. You can see there is pressure in all the runners, just bugger all for flow in #1. It's pretty clear from the S54 intake above that you have to design with flow in mind. The S54 has a throttle body angle and housing that directs flow evenly across the runners, which is captured smoothly by the velocity stacks. Makes a lot of sense when you see it like that.

[digger]

the reality is all runners arent flowing at the same time. the stock stuff is garbage when you do that as OE does not use pressure revovery except the S54 CSL. the boundary conditions are incorrect with all runners flowing. obviosuly if it does have pretty close to equal flow in case of all runners case then its going to work ok. but its a pretty meanginless analysis IMO as manifolds that fail can actually work pretty well.

here is stock a quick and dirty model. air wont turn the corner to 3 and 4. when you look at the firing order 3 and 6 are drawing at same time so there is potnetial for 6 to rob from 3 but its much less pronounced than the all runners analysis. the stock one isnt great even with the two runner analysis

[digger]

here are all runners drawing



firing orders



runners 3 and 6 drawing



runners 1 and 4



the difference in mass flow between them is very small. it would run ok atleast a from a distribution perspective

obviously a transient analysis simulating the pulses is better way to do but this is a cheap and nasty way to get an idea

[dvallis]

#Facepalm! Of frigging course. You need to open the runners in order of firing sequence. That makes total sense. Thanks Digger.

Like you said, flow looks a bit uneven in some runners. I think we'll still stick with OEM as it's a known quantity.

[Digitalwave]

I love science.

[dvallis]

Obligatory meme

[dvallis]

Finally got a transient analysis of the eBay intake manifold working. Video is here. Enjoy.

Cylinder 1 5 3 6 2 4 intake stroke shown below. It works, as in all runners suck air, but I'm not crazy about the flow. Going stock.

[digger]

What was the flow in each runner? I think stock will be worse.

[dvallis]

750 fps. You can see it in the video, has a legend. What is stock flow?

[dvallis]

I cranked the resolution up to stupid and let it run all night. Click here for new high resolution video.

The runners are hitting ~800 fps flow rate, which is good. With the higher resolution, you can really see the crazy flow turbulence as it switches between runners, which is not so good. Looking at the S54 manifold above, you can definitely see why it's shaped to keep the flow laminar against the housing and uses velocity stacks to smooth flow into the runner.

Say it with me ... "I am NOT going to design a custom E30 intake manifold" (Yeah, right) You know I eventually have to do it. But not until we get Das Beast running

[digger]

750 fps. You can see it in the video, has a legend. What is stock flow?

I mean the mass flow or cfm in each runner to see the distribution

[dvallis]

I'm showing 350 CFM per runner.



Cam profile is for the Schrick 284/272. Using 20 psi on the inlet and a 5 psi pressure drop on the runner outlet lids for valve full open. Not sure if that's correct.

[digger]

So it looks pretty balanced. It's always going to be pretty chaotic when you see what's really happening. From a balance point of view I don't think the manifold is bad at all there are some other design issues along lines of really short runners and large plenum.

[dvallis]

Yep. Weirdly well balanced for all its eBayness. Can definitely see why the runners should be longer and plenum smaller though. Obvious when you get down to serious simulation. I'll design and build my own intake manifold eventually. For now I think we'll use the stock manifold as a baseline, get dyno'd and go from there.

[dvallis]

I found this writeup on intake manifolds. A couple of interesting quoues lead me to think a large volume short runner intake manifold is the better choice for a turbo racing setup.

1. "Generally, a plenum volume of approximately 80% of engine capacity for naturally aspirated engines to 150% of engine capacity for turbocharged engines works best"

2. "In terms of intake manifold runner length, a longer intake runner produces better torque at low RPM, while a shorter intake runner produces better power at high PRM. Generally, an intake manifold runner that is in the region of 200-300 mm long will sustain power at high RPM but little power at low RPM while an intake manifold runner that is in the region of 300-400 mm long will start building power from low RPM but will run out of power soon after peak power is reached."

Anyone with an informed opinion care to comment?