Question About Surge Tank and Vapor Line Plumbing On 240z

[Cannonball89]

Here is what I have, I have a 140 GPH low pressure carburetor style fuel pump in the rear of the car that will pump fuel through the stock 5/16" hard line to the engine bay, which will then feed into a surge tank. The surge tank has a 3/8" outlet on the bottom to gravity feed a 70 GPH high pressure FI pump that will supply fuel to the my fuel rail, through the FPR, then back into the surge tank.

 

My question is mainly regarding the return to the tank. I know from reading that the stock 1/4" return line is inadequate, and one option some have suggested is to use the 5/16" hard line that is a vapor line in stock configuration and use it as the return. If I do so, what do I need to do for my vapor system? In stock configuration the vapors went through a valve that either let them go into the crankcase or into the aircleaner box. I'm sure I will have problems if I simply use this vapor line as a return and do nothing in exchange for the vapor system. Could I use the stock 1/4" fuel return and route it to the vapor valve so it functions as what the 5/16" vapor line was doing? I know some of you have used that vapor line for a return on your surge tank set-ups, I just haven't been able to find what you have done to modify the vapor system in exchange.

 

I suppose another option would be not to have a return to the tank, and allow the 140 GPH pump pump into the surge tank without a return... maybe... Please advise. Thanks.

[JMortensen]

Just as a matter of principle I would put the surge tank in the back next to the regular tank. Seems less likely to catch on fire in that position. Aside from that, the surge tank is just there to hold a small amount of gas so I would use a smaller pump (especially if you haven't bought one yet, since a smaller pump will be cheaper) and a large feed and return so that you don't generate pressure in the surge tank. Your lines will be much shorter.

 

The 5/16" line that goes to the vapor tank to the engine compartment leads to the very top of the vapor tank if I recall, and it is the one that bleeds off excess pressure in the vapor tank to the crankcase in the stock configuration. If you don't have that vent in place then I think you have an issue with the tank being sealed, so as the level goes down in the tank you might actually start to collapse the tank with the vacuum from the fuel pump. If it gets hot, a lot of pressure could cause a leak. Fix here is a vented gas cap.

 

There are other threads that deal with the tank and getting rid of it. I would get rid of the vapor tank, run the expansion tank right next to the stock tank, and then run your FI pump from there and run a new line and return up to the front. There are differing opinions on how and whether it should be done, but that's what I would do.

[Cannonball89]

Just as a matter of principle I would put the surge tank in the back next to the regular tank. Seems less likely to catch on fire in that position. Aside from that, the surge tank is just there to hold a small amount of gas so I would use a smaller pump (especially if you haven't bought one yet, since a smaller pump will be cheaper) and a large feed and return so that you don't generate pressure in the surge tank. Your lines will be much shorter.

 

 

The 5/16" line that goes to the vapor tank to the engine compartment leads to the very top of the vapor tank if I recall, and it is the one that bleeds off excess pressure in the vapor tank to the crankcase in the stock configuration. If you don't have that vent in place then I think you have an issue with the tank being sealed, so as the level goes down in the tank you might actually start to collapse the tank with the vacuum from the fuel pump. If it gets hot, a lot of pressure could cause a leak. Fix here is a vented gas cap.

 

There are other threads that deal with the tank and getting rid of it. I would get rid of the vapor tank, run the expansion tank right next to the stock tank, and then run your FI pump from there and run a new line and return up to the front. There are differing opinions on how and whether it should be done, but that's what I would do.

 

 

I understand your concerns about location, but the surge tank is made from fairly thick aluminum, so I don't think the odds of it puncturing during an accident are very high. The risk of fire from having fuel sitting in the surge tank is in my eyes at least, no more so than the risk of fire from having fuel sitting in the float bowls of the carburetors. But the location of the surge tank is really just personal preference. As far as having a smaller pump, just because the surge tank is only holding a small amount of fuel doesn't mean it only needs a tiny pump, the point is to make sure the surge tank never gets air in it, so the larger the pump feeding it the better. There also shouldn't be any pressure in the surge tank from using a 5/16" feed and 5/16" return, there would only be pressure in the surge tank if the return were smaller than the inlet.

 

Thanks for pointing out that the line to the engine compartment goes to the vapor tank in the rear of the car, not directly to the gas tank. For some reason I thought that it came from the top of the gas tank. Looking at my FSM I see that now. I wanted to keep the stock vapor tank system in place, because I have never smelled raw fuel from my car and would like to keep it that way, but I see that many people have removed it and run a ventilated gas cap. I suppose that would be an option. I just hate messing with factory the factory evap system. My racecar has a simple vent on the fuel cell that goes directly to the atmosphere, and it makes my trailer smell like raw gas on hot days.

 

Another problem with using the stock ventilation system is that I don't know how the system will respond to boost, IE positive pressure instead of vacuum or atmospheric pressure on the flow guide valve.

 

I'm still brainstorming how I want to run my return line. I guess I should either remove the vapor tank and have a simpler tank ventilation system, then use the 5/16" line as a return, routing it to the tank, or I could run a new line to the gas tank and drill and tap it with a fitting, and keep the stock ventilation system in place, provided that boost will not affect it's operation. I have to do some more research on how boost will effect the system. Any other suggestion are welcome.

[JMortensen]

The risk of fire is bigger with the surge tank simply because the float bowls don't hold very much gas. If you're going to put it in the engine compartment I'd put it against the firewall and as inboard as possible (actually I'd put it as far forward and close to the middle in a rear mounted surge tank too).

 

I don't think boost will be a big problem because the vent that goes to the crankcase is Teed into the PCV, so while the engine is running you should still have vacuum there, so long as you don't have a whole lot of blowby.

Edited March 28, 2011 by JMortensen

[Cannonball89]

Well I've got an interesting development in my 240z... it turns out I have a NON-EMISSIONS GAS TANK! WTF!!!

 

My car was built in 3/71, so it obviously was an emission compliant model, and all of the stock emissions components were in place, such as the vapor tank, flow guide valve, all of the balance tube mounted gizmos, but some one at some point had swapped the tank for what must be a VERY early U.S. Z tank or perhaps a Canadian, Euro, or JDM tank. The thing is that now looking at all of the lines running to the vapor tank, I'm pretty sure they were hodge-podged together by one of the idiot PO's. Basically the only vent line I have on the tank is the one on the very top, toward the rear. The one on the very top towards the front and the one of the drivers side under the spare tire well is not there. So someone took the two lines coming down through the floor boards from the vapor tank and basically ran them together, making a loop. The fact that I never noticed any raw fuel smell was a miracle, and come to think of it this would probably explain why I would intermittently have the car sputter cruising down the highway, and also intermittently have hissing coming from the gas cap area until I opened the cap for a moment.

 

What gets me is that I should have known about this over a year ago when I had the tank out of the car and had it proffesionaly cleaned by a radiator shop to remove a mouse nest (no lie) that was preventing me from getting more than a block away from my house before the fuel filter got clogged with mouse nest material, or whatever you would call that fluffy stuff. I was such a total noob that I never even bothered to look at how the lines from the vapor tank were routed. I just hooked it back up the way it was and never thought about it again lol.

 

So anyway my plan for now is to remove the vapor tank, and run it as if it were a pre-emission model, and I guess I will have to have the tank tapped for a larger return line. I hate to do that because this tank might be valuable to someone restoring a very early Z or some other non emissions Z. I hope to someday find a regular 240z tank or even better a 75-76 280z tank and swap it in place of mine so I can run the vapor tank and stock evap system, then sell this tank to someone who might appreciate it more, but for now ventilated gas cap appears to be my only option.

 

Here are some pictures to prove this insanity

 

 

This is where one of the vents should be, above the sending unit. You can see that the stock hose is there, but is the vent there... nope

 

 

This is on the drivers side below the spare tire well, again you can see the stock hose is there but is there a vent... nope. The hose you see shoddily stuck inside of it is what was connected to the hose in the above picture.

 

 

And here is the only vent I have on the tank, the one that's in the rear and is almost impossible to see, let alone reach without dropping the tank.

 

[Tony D]

What are the sizes of the fuel pickup and return lines?

 

That looks like a later model tank.

 

FYI: the JDM tank has all the same fittings as any US or Canadian model. They all had crankcase vapor accumulation.

 

The only tank that was different was the 100L unit, and you don't have one of those.

[Cannonball89]

The feed and return lines are 5/16" and 3/16", respectively, just like any other 240z. I mistakenly called the return 1/4" in an earlier post but it is 3/16".

 

I am going to drop the tank later tonight and take some pictures of the whole thing. I ran across this thread from another site where someone found a tank that sounds just like mine: http://www.classiczcars.com/forums/showthread.php?t=39219

 

My plan right now is to route the solitary vent hose on the tank to the filler neck, and run a ventilated gas cap like the 1969 240z's allegedly had. Anybody know where to buy a ventilated cap for a 240z? I hate to just drill a hole in my gas cap, it just seems wrong. For the return to the tank, I'm thinking now about putting a fitting on the filler neck itself for the return line instead of putting it on the tank. I would put the return line fitting on the portion of the filler neck in the rear tire well, not the portion that runs inside the car. I think that would serve the same function without messing up a potentially rare gas tank.

[Cannonball89]

Ok I dropped the tank and took some pictures. I've read about tanks like these but never seen pictures... Perhaps a HybridZ first? I doubt it but I couldn't find anything with searching. I did find some spirited debate between Mr. Jmortenson and Mr. Tony D debating the merits of eliminating the vapor tank. Coincedently these are the only two individuals who have replied to this post lol.

 

I'd also like to change the title of this post, since it has veered substantially off of it's original title, but it doesn't seem to let me edit the original post.

 

So here is what a non-emissions tank looks like

 

 

 

 

 

 

 

Markings on the top read 17201-E4100, and I can't make out the circular marking.

 

[Tony D]

That 15mm hose is a vapor vent. Why are you referring to this as a 'non emissions' tank? It has the provision for the EVAP lines and vapor phase separation tank in the 1/4 panel and must be run to that location, you CAN NOT 'run it to the filler neck'.

 

I have a non-emissions 100L tank, which ALSO have these vents, they ALL go to the vapor tank in the 1/4 panel.

 

The "Non Emissions" comes in the FILLER NECK. The breathing of the tank is still accomplished through the crankcase and air filter on your car.

 

On the car I removed the tank from, there was NO 1/4" vapor line running to the front of the car. The VENTING of the tank was accomplished in the filler neck with an overboard dump.

 

If you run the single 15mm hose to your fuel filler, and do not have the proper gas tank cap, you will suck the filler neck down FLAT and run out of fuel. These systems need an external vent. They either accomplish this from the vapor tank through that 1/4" line to the air cleaner/crankcase, or by a 1/4" line that dumps to the ground from the first plastic portion of the filler neck that bolts to the 1/4 panel.

 

I'll go check out the classic Z thread now...

[Tony D]

In my 100L tank, the 15mm line (on recalling better) went to the filler neck, and one to the vapor tank. But nothing to the front of the car. Venting was as previously described. While CZC page is loading, I'll banter further...

 

You could run the 15mm line to the filler neck--that will allow fast-venting of the high point of the tank (what it is there for) so you get a full fuel fill. The vapor expansion/fuel depletion compensation is done through a 1/4" line which must vent to atmosphere. In the 240, that was where the diverter valve came from--positive pressure went to the crankcase, and makeup air for fuel usage came from the air filter.

 

The 'round stamp' you see is the production date code. If you can get it cleaner, you can tell when the tank was made and determine if it was current production for your vehicle, or if someone swapped it in later from another car.

[Tony D]

Oh, i see where the term comes from now..

 

YEah, you will need a vented cap if you plan on doing a closed system.

[Cannonball89]

Ok I just drilled a small hole in the top of the tank and soldered in a peice of 5/16 brake line tubing for my return fitting. I'm running a peice of 5/16 rubber hose back to the tank from the surge tank for now, but will probably bend a peice of brake line tubing to serve as a more durable fuel hard line in the future for the run from the surge tank to the fuel tank.

 

For vapor expansion/depletion compensation I have the one big fitting on the top of the tank going to the filler neck, and drilled a small hole in the top of the receiver for the gas cap, and also have an overflow tube going down to the ground just in case.

 

Whenever I can find a regular tank locally I will probably redo the setup using the vapor recovery tank, and possibly put a sump on the bottom, but this will work for now. Thanks guys.

Edited April 13, 2011 by Cannonball89