Z Intake Plenum Constructoin

[Ron Earp]

I am wanting to make a intake plenum for my 260Z. What I wish to do is make a "log" style plenum that will tie both carbs together. I can then take that log and connect it to a cone style filter out at the front of the engine bay to maybe help pull a bit of cool air in the engine.

Maybe the attached picture will help a bit with what I wish to do.


The space is tight in the engine compartment. I think it is even tighter than a 240Z on the intake side as the carbs seem to be a bit wider than what is on 240Zs.

Anyhow, I can envision a round tube that has two flat areas on it to mount to the carbs. I could drill holes through the tube to mount the bolts into the carbs and the outside holes can be patched with duct tape or whatever. The end of the tube near the firewall will be sealed. The end pointing toward the front of the car will be connected to a cone filter.

My problem is what to make it out of. I don't want to use muffler pipe as it is too heavy. PVC pipe won't bend or crush and is also heavy. Ideally I could see some thin walled aluminum tube, maybe 0.040", 0.060", or something in that range that I could manipulate with common hand tools.

Any ideas or suggestions?

[Ron Earp]

TWM makes this, it'd be perfect. It unfortunately costs $375. Back plate is blank to mount to your own induction setup.



Oh well, spoke too soon. I only have about 4.5" from the carb face to the shock tower. This wouldn't fit in that area. Dang.

[kthomas]

Well you can make one, and it'd look cool, but it may cause you serious induction problems. Some folks have made an enclosed airbox like this with no problems, and others like me have tried them and found there's a big flat spot in some part of the rpm band caused by reversion or some other wave phenomenon. I prefer an air cleaner backing plate that seals off the headers with a horizontal plate to the inner fender and a vertical plate to the hood, incorporating the entire stock backing plate of course so you can legally use the velocity stacks. I'll PM you a picture you can post for the group of what I'm talking about.

[seckerich]

Katman is right on with his suggestion. If you want to see why your design will not work, just blow over the top of a coke bottle. Air rushing past first carb to get to rear carb creates a vacuum and disrupts flow at certain RMP. Some very elaborate airboxes have a splitter design inside that you do not have room for. Go simple.

[Ron Earp]

I was thinking of putting a divider in the box so each carb "sees" it's own air supply. Sort of like a horizontal divider so each carb can pull air from one half othe diameter of the box.

[Mike Mackaman]

Use fiberglass, it is light, airtight and fairly cheap to work with. You might have to make a mold to start with, but then when something happens you can make a second. Aluminum, pop rivets, bondo and duct tape make good molds to start with!

Mike

[x-ring]

Well you can make one, and it'd look cool, but it may cause you serious induction problems. Some folks have made an enclosed airbox like this with no problems, and others like me have tried them and found there's a big flat spot in some part of the rpm band caused by reversion or some other wave phenomenon.

You could model a proposed design, using some CFD tool, to avoid that problem. FlowWorks would be a good choice because then the model can go right to rapid prototype.

If only I had more (some?) free time...

[240zdave]

I built a heat shield / air box for my 240, similar to what Katman describes. I used sheet aluminum, 1" wide aluminum strapping from Lowe's, 1/8" thick neoprene around the edges to seal up to the radiator, inner fender, firewall and hood, heat screen radiant matting by DEI on the header side for heat reflectivity, Seals-It grommet seals to let the coil wire and the block vent hose pass through, and a lot of pop rivets. I am using K&N air filters with air horns right now, which seem to work fine. I've got an inch clearance from the end of the air horns and the air cleaner top plate. I also calculated that the total area of the K&N filter material exceeds that of the stock Datsun air filters by several square inches, so the SU's are not starving for air.

I'm not a professional fabricator, but I think it turned out pretty well. I've attached some photos below to give you an idea of what I'm talking about:

[kthomas]

You could model a proposed design, using some CFD tool, to avoid that problem. FlowWorks would be a good choice because then the model can go right to rapid prototype.

If only I had more (some?) free time...

Well except for the fact that flow problems on the intake sode of the engine are often caused by sonic wave problems on the exhaust side of the engine. Wave energy is usually higher than flow energy, which is how reversion occurs. FlowWorks wouldn't give you the whole story, but the pictures would be cool.

And Dave Plott, your plastic thingy that goes in that hole in the radiator support that feeds cabin air thru the hood ledge (or, as the parts fiche calls it "food ledge") is missing.

[240zdave]

And Dave Plott, your plastic thingy that goes in that hole in the radiator support that feeds cabin air thru the hood ledge (or, as the parts fiche calls it "food ledge") is missing.

Point taken. That's a photo of Old Yeller, the car that got wrecked beyond repair at the Saturday rain race last July at Barber. It did not have the plastic thingy on it when I bought the car back in 2001. I'm working on the replacement car now, and it will have the plastic thingy in place. It will cut down a little on the air coming through the radiator support, but as it turns out, the carbs are not sucking up all of the air they are getting now. I know this because the neoprene that seals the trailing edge of the heat shield to the fire wall gets blown over toward the header (back) side of the shield by the end of a race / track session. I intentionally cut the neoprene a smidge long, and before I go out on track, the edge is curled toward the master cylinder (driver's side) of the car where it touches the firewall. After coming off the track at the end of a session, the back edge has been blown over and is now pointing toward the battery side, indicating to me that surplus air has been escaping in that direction.

[ITZ34]

I've used the TWM unit with a cone filter. Dynoed vs a foam style and gained 4hp. Will sell the TWM setup if you're interested

[ITZ34]

I used one of the TWM units with a cone filter . Dynoed it vs a foam style filter right on the carbs and picked up almost 4 hp with foam filter. I don't know how TWM unit would work with 260. It's available for sale.

[Ron Earp]

You mean you gained 4 rwhp with the foam type on the carbs versus a TWM style?

[kthomas]

Sounds like he gained 4hp with a cone filter intead of a foam filter. Wonder if that TWM unit had velocity stacks inside. Wait, is he talking about a ZX?

Need pics!!

[Ron Earp]

I ended up making something of a heat shield to catch air from the fron of the engine bay and used two individual round K&N filters. That plenium piece from TWM was far too large to fit in the available opening without just hacking it all to pieces. What I have not can use some improvement for sure, but I think it is a damn far sight better than the foam pieces I had that you couldn't even blow through with compressed air - no kidding!!!

[Parrish57]

[quote=Ron Earp;260608]I ended up making something of a heat shield to catch air from the fron of the engine bay and used two individual round K&N filters.quote]

It sounds like you are headed in the right direction but you might have to make some modifications. Not to the car, it's your terminology that needs tweaking. You see, a "heat shield" is not allowed but a "modified stock air cleaner assembly" is allowed by ITCS D.1.c. :

c. Air cleaner assemblies may be modified, removed or replaced. Velocity stacks, ram air or cowl induction are not permitted unless fitted as original equipment.

You also have to be careful that your "modified air cleaner assembly" doesn't "perform a prohibited function". Since our normally aspirated Zs came with velocity stacks that were an integral part of the air cleaner, they may modified, removed, or replaced. But what you can NOT do is create Ram Air Induction. As Katman pointed out, removing the "plastic thingy" is the first part of going down that path. If you then create an airtight box that utilizes the ram air from this new hole in the radiator support you might be crossing the line. That was my concern with the TWM peice.

So just to be on the safe side, make sure your modified air cleaner only attaches where the stock unit attached, leave the thingy in, and don't create a forward facing airtight ram air box.

Of course, this is just my interpretation of the rules. I've heard many other opinions over the years.

[Mike Mackaman]

Two thoughts on this:
1. Doesn't the fact that the 240 and 260 come factory with a velocity stack pretty much allow us to do whatever we want from the velocity stack standpoint as it is a replacement?
2. Playing around with a piece of string on the flow bench, what is more than 1-2 diameters in front of the openning doesn't even come into play. Several diameters to the side does however, even with a velocity stack. This may give you some direction to make sure you are ok.


Steve, I will call you , I have been out of town and then covered up at work and home. We'll work something out to get you the torque plate.

Mike

[JeffYoung]

Car was missing thingy when purchased -- are they available from Nissan?

Ron, he's right about what is legal on the "heatshield." It needs to be attached to something legal, meaning it needs to be an "air cleaner" or a "radiator". Some yours is good to go, some....you might have to hack on some.

[Ron Earp]

[quote=Parrish57;260660]

So just to be on the safe side, make sure your modified air cleaner only attaches where the stock unit attached, leave the thingy in, and don't create a forward facing airtight ram air box.

Of course, this is just my interpretation of the rules. I've heard many other opinions over the years.

I think mine is okay, but what is the thingy?

Bear in mind I have never seen a stock 260Z setup. I have two K&N filters on the carbs bolted on using three bolt holes in the body of the carbs, a "not a heat shield but a piece of aluminum that sort of keep radiator air away from the carbs and is attached to the header". Mine is far from "air tight" though, it is mainly wide open. Definitely not a forward facing air tight ram air box. I get semi-fresh air from two factory holes that are right beside the radiator.

[JeffYoung]

The foot ledge, that directs air from the open hole right to the side of the radiator back into the body and into the cabin. Your car is missing this, came that way from the "factory" down in Hot Lanta.