Custom Plenum

[carbz]

Looking at making up my own plenum and im just after abit of advise.

currently its in the designing stage and was wondering what would be the best volume for the plenum.

now the hard part to try and explain.

Yellow - is there any reason why they have these single ports and not 1 big port cut out along the yellow lines. looking at the runner flange face it is recessed on 1 side and could cut down on turbulence created between the to faces (Red Squiggle) if it was 1 big slot.

was also wondering if someone could tell me what size hose fittings I would need in the green circled section.

I will post some pics up of the design once it is complete

Cheers

[Paulie2256]

Don't know much about plenums but I'd say that this is why the other manufacturers have spend hundreds of hours in Rnd for these things.

The best way would be to build a couple of designs and dyno them all. Who knows, instead of using an existing disign you may stumble upon one that flows a lot better.

[austcro]

It has been a long time since I completed my degree in Mech Eng, I forget what the exact reason is but I'll attempt to answer this. As the engine operates you get pulses moving back and forth along the inlet tract. The pulses need to be isolated so that the engine works most efficiently in its target rev range. Helmholtz resonance comes to mind now that I think of it Helmholtz

For force fed applications the runner length is not as important as it is in a NA application so I figure Fraud decided that the manifold setup was good enough to be used in both XR6 Turbo and NA as they already had the molds etc. The only real way to determine how good a manifold is for an engine is trial several designs.

Also, have a look at this: Intake manifold design

In short, intake manifold design is a complex topic. The scope of this topic is larger than can really be explained in this thread. I'd really have to go back and look all this stuff up again.

[GR8XR6]

Yellow - is there any reason why they have these single ports and not 1 big port cut out along the yellow lines. looking at the runner flange face it is recessed on 1 side and could cut down on turbulence created between the to faces (Red Squiggle) if it was 1 big slot.

I have seen some designs only having 6 holes and not 12. Like turn your yellow lines around 90 degrees. Not sure if that helps. Good luck with the design and keep us posted on your results. There are a few different types out there now. It would be nice if someone knew more in this area and could develop something better again.

[carbz]

Thanks for the replies.

That Helmholtz it abit over my head. I will show them links to my mate who is designing it with me.

GR8XR I know what you mean about slotting the holes the other way. I have seen it done somewhere on the net. I think the dude machined his runners out to suit the plenum aswell so would probs be abit pointless unless the runners were modified?

I was just thinking about slotting it along the yellow line to cut down on the turbulence in the recess between the 2 faces.

I got 1 design idea done so I have put a pic up to show you guys and see what you reckon. any feedback would be greatly appreciated.

the volume of the unit is 3.9L but it can be changed quiete easily if the volume should be more.

we can quite easily change the slotted holes back 2 single round holes if there is a reason to do so.

if any1 knows roughly the volume of the other plenums on the market that would be a good guidance for me.

I think if I keep the top the same height over the length of the plenum it works out to be 5.something liters

Edited 18/05/10 12:46 PM by carbz

[austcro]

Thanks for the replies.

That Helmholtz it abit over my head. I will show them links to my mate who is designing it with me.

I was just thinking about slotting it along the yellow line to cut down on the turbulence in the recess between the 2 faces.

IMO I wouldn't be slotting that. You most definitely will not be cutting down turbulence. What I would be doing is chamfering or bevelling the leading edge into the runners. This means you would be chamfering on the plenum side. A bevel would be almost as good and perhaps easier to do depending on the method you choose to fabricate this with.

Another idea would be to remove the bridge on each runner to make one large entry (east-west instead of north-south), and then mirroring that on your plenum with a chamfer or bevel machined into the slot to provide the smoothed entry into the runner.

By the way, which CAD product are you using? There are some packages out there that can provide fluids analysis capabilities that might make this a bit easier to quantify.

[GR8XR6]

RAJAB have a plenum also

7 litres in THIS PLENUM

Hope this helps a bit. I'll keep doing some sniffing around.

[carbz]

my mate drew it up in autodesk inventor. that's what I was thinking of doing first was going with single holes and chamfer them on the inside of the plenum. it will be quiet simple to make them single holes again.

I have read through the topic from 'f6 ute' that is pin in this section and his as around 3.9 liters so I was just basing mine around that. in that same thread people were saying that the greenslade one was abit on the big side.

isnt the volume of the plenum supposed to be about 1.5 times the capacity of the engine? so if there is 4 liters in the plenum and 2 liters(guessing) in the runners that would make up the volume? or would I get away with and extra 500mm-1 liter as it would cut back on the taper of the plenum.

[austcro]

Yeh, 1.5 x engine capacity(l) is a good rule of thumb. Some prefer a factor of 2. For a street car I don't think it will make much difference, using a factor anywhere between 1.3 and 1.6 is fine. However, the larger the plenum the better the distribution with consideration to decreasing your response. Runner volume is not a variable in a plenum calculation. The figure you calculate is pure plenum volume. I would keep the taper as well.

I also notice that you are possibly going to bolt through to the factory manifold from inside the plenum. I would be careful with this approach as the bolts can back out slowly over time until they eventually fall into the runner. A circlip will prevent this, as will bolting from underneath. The problem with the circlip approach is that you will have to machine a groove for the clip to sit in which will make this exercise more expensive.

I like that rajab plenum, very good presentation. Paint it black or silver and it will be pure stealth. But for $1400 I would prefer a Plazmaman plenum. The Greenslade plenum looks very agricultural, but it is cheap. Keep going with the custom job carbz, there is way more satisfaction to be had doing it your own way.

[icer]

fark...plenums for 650$... those where the days. Sif they jump up to 1500$+.