Z Intake Plenum Constructoin

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.
http://www.gt40s.com/images/Z/zintake.jpg

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?

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

http://www.twminduction.com/images/6-cyl_airbox.jpg

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.

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.

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.

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.

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

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Originally Posted by 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.

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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...

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:

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Originally Posted by x-ring

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...

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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.:018:

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Originally Posted by kthomas

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.:018:

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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.

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

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.

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

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!!

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!!!

[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.

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

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.

[quote=Parrish57;260660]

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Originally Posted by Ron Earp

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.

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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.

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.

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Originally Posted by 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.
Mike

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1. Not according to National Tech last time I asked ('course that was years ago). If you want to use stacks on a Z you need to use the entire stick backing plate according to them. Can't even cut out the stacks and use them, whole backing plate only.

2. True. You'd really want a big radius bell shape, not the tight radius sharp edge of the stock stacks.

FWIW, the K & N round filters will allow the stock velocity stacks to remain in place but they are a pain in the $%^ to fit and bolt on. :)

Factory backing plates/stacks are common on Ebay and on the z car sites. Expect to pay form $40-$75 on average with some going much higher.

The Pipercross filter with factory stacks and backing plate with a "modified air cleaner backing plate that has been extended and insulated" seems to be the ticket according to Katman. He even posted his up on here not too long ago IIRC.

I have all of the parts to make mine just haven't found the time. Hopefully by CMP it will be done.

Found the picture

What is that orange piece that all the stuff is attached to and has two pipes on it?

Paul... Very cool. Nicely done.

When I first started I was told the same thing that Katman said, except I was told that you could only use velocity stacks if you used the stock part. I was not told that you have to have the entire unmodified stock air box backing plate. That seems to contradict the rule allowing you to modify the air cleaner box. If that is the case, mine is "non-compliant". I have a call in to Topeka. I'll let everyone know what I hear.

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Originally Posted by Ron Earp

What is that orange piece that all the stuff is attached to and has two pipes on it?

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That is the factory backing plate and stock stacks! :D

Steve, That is the picture Keith sent me. Mine will be similar but my fab skills aren't as good as what is in the photo's.

BTW, that is one of Katman's motor's Notice the cool oil pan!

If anyone needs the stock backplates we have several layign around the shop you could have cheaper than from ebay (was going to ebay all but 1). I don't know if there were differences between the 240 and 260 backing plates though. Where can the pipercross filter be found???

Got mine here http://www.truechoice.com/prodinfo.a...er=PIP%20C603D
But I sure don't remember paying that much.

The easiest way to tell the 240 and 260 apart is that the 240 air horns are round, the 260 are rectangular. Other than that they are both orange. not sure about size. The 260 also bolts on with three fasteners per carb.

Mike

OK... I got a response from Topeka yesterday. I sent an email to John Bauer, a tech assistant. The email had a photo of a stock air cleaner box backing plate, a modified backing plate that retains the stock air horns, some modified stock air horns, and some aftermarket replacement air horns. I gave a written review of the rule and arguments for/against each prep level based on the GCR.

After reviewing my submission he called me to discuss it. To put it in a nutshell, he said that his interpretation would be that the stock air cleaner may be modified, but if you want to run velocity stacks you have to use the stock ones. He didn't fell like the second sentence gave any wiggle room on that. He did say that he thought that it would be OK to cut the velocity stacks from the backing plate and use them with any air filter you choose.

Note that this is not a formal "rules clarification". So without that $250 piece of paper it would be up to the stewards interpretation if someone had heartburn with your setup and protested you. It's good enough for me. I'm comfortable with my modified air box and OEM velocity stacks.

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Originally Posted by Parrish57

It's good enough for me. I'm comfortable with my modified air box and OEM velocity stacks.

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I am too, that is, I completely agree. You are using a stock piece and you are allowed to modify things in front of the carbs. You can certainly drill holes in the backing plate, right? You could snip off a piece of the backing plate to allow a hose to route around it, correct? Well then you've just snipped off the rest of the plate and left the stacks, seems like a good idea.

I need to find a plate for a 260Z so I can get to making my car all legal and make a new air box.

Anyone have a line on a stock piece for a 260Z?

Ron

"I need to find a plate for a 260Z so I can get to making my car all legal and make a new air box.

Anyone have a line on a stock piece for a 260Z?"



I'll check and see if we have one around. Inherited a warehouse with a ton of old datsun parts. Will get back to you this pm.

Ron,

I'm told we have a couple of 260z backplates though I haven't seen them with my own eyes. Email me at [email protected] if you would like one, and I'll be able to verify for sure by tonight that we actually have it.

chris

Here's my setup. Stock with K&N filter. Velocity stacks still in place.

i gained the 4 hp with the foam type vs the twm with cone on the dyno. the cone was ducted to the openings in front by the radiator with a heat shield blocking heat from the radiator and directing air to the filter
not sure what the effects of air flow with the car moving are.Obviously the car was stationary on the dyno. I had the stacks on in both cases. The engine builder had said that the TWM unit created too much turbulence inside it.I had run it like that for anumber of years but decided to check it out while the car was on the dyno

here's picture of twm with cone filter

May not be what you're looking for but good discussion none the less.

http://forums.hybridz.org/showthread.php?t=111342

Interesting picture........of course for a turbo car but I do see carbs and a plenum in this thread.

http://forums.hybridz.org/showthread.php?t=127595