Thoughts on NA Quads Plenum Setups

[takai]

Alright, i got off my butt today (really i took a break from study) and built the first prototype plenum for the quads setup on the race car. It is a fairly simple affair, and i think it would be quite effective, and although there is that weird kink at the end to get around the brake booster i think it will flow reasonably.



While i havnt attached the trumpets yet, i will be using my old trumpets and getting the plate TIGd to the back of the bellmouth, so it will sit quite about 8mm from the end of the trumpet.
What i am really thinking about at the moment is that i have designed it to have around a 25-30mm gap at the top of the box to increase the volume and hopefully reduce starvation at sudden throttle changes, and also to mount temp sensors etc.

What do people think of such a setup, should i look at lowering the "ceiling" of the box down closer to the trumpets, or should i leave the extra capacity?
I probably have 25mm at least to play with there, and i easily have enough alloy to make a second box.

Opinions, thoughts?

[bbaacchhyy]

Are you talking about 8mm between the end of the bellmouths and the vertical wall of the airbox ?

If so, that's not much at all. If not, then the vertical height above and below the trumpets is probably not that important, but there seems to be a variety of numbers that help govern the size of a plenum, and for high revving engines, it typically appears to be about 2.0 to 3.0 times the engine capacity.

Make sure that none of the air comes from under the bonnet. It amazes me the number of cars (and a lot of workshop high powered ones at that) that take air from directly behind/near the radiator.

I think you know that already though !!

[Ben Wilson]

How much length have you got from the end of the trumpets to the end of the box? If it's 8mm, you will have issues..

I'd also try to make the end of the box not at 90 degrees to the airflow to avoid wierd standing waves forming between the trumpets and the flat surface.

Remember your motor is only using one throttle body at a time, so if you've got a decent air inlet, you shouldn't be able to empty the box in a hurry.

[takai]

Its 8mm between the lip of the trumpets and the bottom and back walls of the air box. The vertical wall is between 130mm and 90mm away until you get back to the 4th cylinder where it drops to 30mm because of the brake booster getting in the way. However that is only for about half of the trumpet.

Would be nice to have a pedal box so i can reclaim that space. Ohwell, not yet i guess.

EDIT: Ben, i see what you mean with the ends of the box, they are currently at 90* to the trumpets, i might see if i can increase the angle of the intake, but not much can be done regarding the "back" of the box around cyl 4. Thats brake booster territory, and even when i had the filter socks on it was getting pretty squishy back there.

[Ben Wilson]

That could also be a problem. I've read that you need at least half the diamater clearence at the ends, but, most of the airflow is from around the side of the trumpets.

I'd want as much clearence as I can around the trumpets.

[TurboRA28]

I think this is a good read - http://www.gt40s.com/ubbthreads/show...ge=9&fpart=all

Its one of the reasons i moved away from having the bellmouths protruding into the plenum.

The flush configuration beats the protruding configuration for all radii tested. Why does everybody have thier stacks just sticking up into the air? Even if you just used a piece of sheetmetal with holes cut in it and laid it over the stacks, you would get more airflow!

Also, what I managed to gather was...

At least 3" of air space above the bellmouth.
At least 1/2 the diameter of the bellmouth from any wall.

Cheers
Joel

[takai]

Heh, the 1/2 diameter from the bellmouth makes it damn hard with both the Alternator being too high up, and the clutch master being too far forward.
Cylinder 4 will, by necessity, be heavily compromised due to the clutch master and the brake booster.

I wonder if there is any way to mount the alternator lower down. That way i could get at least some more room below the bellmouths.

EDIT: Joel, sure the "flat" bellmouth design is reasonably superior, however, i would be interested to see if that were still the case if it was not at max flow. For NA engines i have heard that having it flat at the base can actually hamper the velocity due to the extra turbulence within the pipe, especially as the flow rate doesnt dampen out via length (short intake tracts).

[TurboRA28]

I think thats the biggest thing i've learnt building the 3S up.. Nearly everything is a compromise. You come up with these plans in your head or on paper, set down the design requirements.. Then when you go to fit it go, oh wait a minute the clutch master is in the way, or the sump hits etc.

I wanted around 50mm around the edge of each bellmouth, but this just could not happen, that would have made the plenum 500mm long, and 170mm wide, just not do-able.

I actually moved the engine forward slightly, to give more room for no.4 bellmouth. Which is a weight distribution compromise.

[Ben Wilson]

Can you lean the engine over a bit for extra room?

[takai]

Got buckleys room to lean the engine over, but that will also screw with the oiling of the engine.

I am however led to believe that a bigport 4AGE alternator bracket is mounted lower down than the smallport bracket, and so could provide the solution to that problem.

[Starfire]

Use a GZE alternator and mount it on the exhaust side.

I have also seen alternators run off of drive shafts with the obvious disadvantage that they arent very useful when the car isnt moving.

Apparently the best thing for a bell mouth's airflow is to have the bell raised slightly above the backplane and blended in to it, so that a half circle ring protudes above the sheet.

[takai]

Yeah, the GZE alternator im actually looking at, since i have a GZE here too.
The other option im going out to take photos of this afternoon, some mismash of a AE92 4AF and KE30 bits

[takai]

Ok, as promised i took some photos of the clearances i have to deal with

Here is the overall shot of how the plenum sits in the engine bay:


And a close up on the brake booster end:


And again on the alternator end:


And finally the clearance of the alternator in a bit better light:


On the alternator front i really have three options. Firstly i can run a 4AF alternator bracket and a KE30 adjustment bracket, which mounts it all over on the exhaust side, but it then lines up with the front half of the pulley, which doesnt exist.
Second option is a custom setup, which sits the alternator lower on the exhaust side.
Third option is the RWD 4AGE brackets which sit the alternator almost three inches lower than where it is in the pictures above. The problem with this is that it is likely to foul on my wingled sump in that location, would have to check on that one.

Not entirely sure what to do, im goign to check with Toyota for pricing on the RWD 4A alternator mount, but from what i hear they charge through the nose for it. My other thought is to make up a simple bracket out of plate steel which simply mounts the alternator an inch or so lower off the current bracket. This will probably end up the cheapest, and most durable out of all the options. Plus it keeps the alternator away from all the oil lines and heat which are on the exhaust side.

[Ben Wilson]

Just for drool factor, have a look at these airboxes....

Have you thought about some sort of angles stubs between the TBs and the trumpets - If the trumpets were at 45 degrees, you'd have a lot more room....

[takai]

45degrees to which plane? Vertically i come into the same issue, just higher up, and 45degrees forward it becomes even worse imho.