Cutting gas tank, doing side exhaust, adding rear diffuser.
 

Well it's finally time. I'm tired of fuel starve so the gas tanks going to get cut in half. I'm going to have a local shop do it for about $150. It's not only the fuel starve issue though. The main reason I want it cut is to 1. Install a side exit exhaust out the side skirt in front of the rear tires so 2. I now can do a flat bottom and proper rear diffuser.

1. I'm going to have to figure out if I can reinstall the fuel gauge sensor.

2. How loud is it going to be because I wanted to do a fuel cell but the cost just sucks. So I won't be doing dual side exhausts at 2.5" but doing a single drivers side exit at 3" because the drivers side tanks getting the chop and not the passenger.

I guess wish me luck and comment with any concerns or ideas we might miss.

Sounds like a huge undertaking. Good luck bro! Keep us updated.

Single 3" side exit exhaust will be mega loud - maybe 105Db or higher on standard 30m drive-by test, even if you have room for mufflers.

Would be too loud for most race circuits down-under, let alone street.

If you are going to chop up tanks, and baulking at fuel cell prices, then I respectfully suggest you rethink your strategy.

If you are modifying your supply system to a return system, you can do a foam-filled tank (fabbed in ali) and 2-litre external fuel pot .. plumb a low-pressure lift pump from the foam filled tank to the pot and high pressure pump from pot to engine with return line to the main tank - that will solve the fuel starve issue.

If you are retaining the OEM fuel delivery system, your options would appear to be more limited (I assume you;ve already considered and baulked to the CJM fuel system)

There is benefit in keeping the fuel load inside the wheelbase, but even the Nismo RC race cars put the fuel cell in the spare wheel well which is the other option.

I'm interested in your fuel system design in any event - let us know your thinking ...

RB

Ok in less than 45min I unbolted the CBE from the X pipe, removed the W and Y braces, removed the crazy light carbon drive shaft, heat shields and disconnected the E brake. Moving nicely.

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I tested before as is and driving on the highway under normal 70mph db was almost 100. I think it was 95db. 80mph was like 98db. WOT windows up or down i was at 113db in the cab. I agree it might be louder. Behind the car i maxed the meter out at 130 with a 5k rev :). Normal driving though when its hot its not bad now! It could be a little louder :)

Why do all that if i dont need to? Cut the tank in half seems a lot cheaper at $150 no? My fabricator suggested fuel cell, external surge tank, return fuel system etc etc. keeping the fuel around the oem in-tank surge and everything OEM besides half a tank seems much easier too no? My fabricator is very worried about not doing an external surge though! He suggested it still no matter what i do but do 370's need it??? I meant id have to do the surge, pump, lines, new fuel rails etc etc $$$

We've look at everything placement wise and still need to corner balance and i did show him the RC rear fuel cell. He thinks low and forward is better even though ive told him im 58/42 weight ratio right now with 1/4 tank of fuel. Also my rear diff cooler and pump are in the way of that setup. We'd have to move it all. For corner balance my way isnt bad since im removing half the fuel from the side i sit on but it wont help front to rear weight. I just need to keep cost down.

I was thinking about noise outside the car ... which is what we need to manage to avoid citation by local EPA - my MY03 STi was pinged remotely by noise-police and I was required to revert to OEM zorst pending A$22K fine (I already had 2-strikes, re-installed OEM zorst - noise tested OK and re-installed 4" dump and 3" system twice an EPA knew it).

Not sure what regulations you need to comply with on the road or the track, but here, we are required to comply wit 75Dba @ 30 metres drive by under WOT for track day and 95Dba @ 30m on a race day.

Road regulations are 85Dba with noise meter microphone 1m fro exhaust outlet at 45 degrees and engine free rev'd to 65% of OEM redline at which time the test official side-steps off the throttle ... HFC are NFG as they cause a crackle which spikes the noise over the limit.

Anyway - good luck with your project .... I'll be fitting a 95-litre bladder tank to my car when the cage goes in.

Please take photographs of the tank inner structure if possible. I've been wondering about it since I got my car.

We don't really have noise police here. Just some get mad if it's to loud and will write a $100 ticket but nothing else. I used to live in a EPA county but not anymore. Hell Harley Davidson guys are louder than anything I can manage on the road! As for the track most are around 100db but I've never been told to stop. My zx6r was the loudest out there with a custom full exhaust I made and I never got yelled at and I know I was pushing 130+. Fingers crossed it all works out!

Thanks!

I will but there's lots out there already.

Ok the tank took about an hour alone. Pretty easy as its only held in by two straps and 3 hoses but the two 17mm strap bolts have zero room to remove from below which are above the subframe. I had to take two nuts and from inside the car, lock them together around the threads sticking up from underneath and then loosen them. Then below I could remove with my fingers holding the tank up with my other arm.

So much room! My heads spinning with all the activities we can do! So many activities!!!!

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Whole body can fit!

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Onto the cbe. Here's where it will go. After I finish cutting the hole we'll weld a box around there of mild steel to re-enforce what came out. As you can see through the egg shape hole there's about a 4x3" hole already in the middle of the frame the exhaust will pass through nicely. Then we just have to cut a hole in the side skirt and one more behind the side skirt in the quarter panel. Now to figure out if I'm going to buy a Y pipe or make one...

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Interesting and I hope it all turns out well. I am just thinking with half a tank you'll be filling up very often. I'd think a surge tank setup would be effective in handling fuel starve with the stock tank. I didn't go for one just because there's no real place to hide it and wanted to stick with a clean interior, I don't think you have that issue. Also with 95-113db inside I'd be less worried about tickets and more worried about ear protection.

Start on page 8 of this document...

http://host.cj-motorsports.com/pdf/3...uel%20Pump.pdf

Tracy Ramsey

The surge tank was 100% on my mind but after buying a tank, lines, fittings, fuel rails, CJ's return setup, external or internal pump etc etc I'd of been over the price of CJ's in tank fuel starve fix. Who knows, maybe this still won't work, however Chris Forsburg runs a cut tank, not sure about a surge though. All I know at this point is that this is easy and gives me my other 2 wants! (The new cbe and flat bottom with diffuser). As for filling up you're correct. But I've owned dodge trucks and jeep wranglers, I've been used to 200 miles on a tank. My car gets about 24mpg street driving so I'm guessing I'll keep about 10 gallons, so 240 miles will be fine. On the track i guess maybe 8mpg or 38 laps at Mid Ohio which is more than enough for a 20 min session.

Your way is definitely much more cost effective. Going easy on the track got me 8.4, harder was getting something around 6-7. Depends alot on the track/driver =P and I know I'm not that good.

I think we have a cut 370 tank sitting in the shop here somewhere if anyone is looking for one. Has worked for us in the past as a temp thing until a customer goes to a fuel cell. They have seen many track days. 350Z guys have been doing it for years.

Chris Forsburg did it so I hope it works. Now just checking to see if we can tap into the passengers fuel level float since we are removing the drivers float so my fuel gauge still works! I pray the ohms are the same.

Now that the tanks out I'm taking the time to delete all the evap. Once again more damn rear weight removed!! :mad:!

This was easy. My TB coolant lines have been deleted for years! So all I had to do was pull the sensor and cap the manifold nipples. In the rear I just cut all the metal lines and pulled everything out. The electrical plugs got taped up and I removed the fiber glass side bottom and pulled the 1/2" line running down the side up to engine.

I've also picked a Y pipe. Instead of modding my X pipe I'll just sell my full CBE.

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How was the pump modded? We were thinking about plugging the nipple where the black accordion hose attaches to that runs over to the passenger side. That way the only fuel pick up will be on the bottom of the white oem surge tank. It's a little black plastic corner with tinny holes drilled in it to feed the pump.

In for the result.

Me too. :)

Y pipe will definitely be much easier to deal with then the X. Keep us updated, sure looks interesting.

Something tells me I'll be doing resonator after resonator instead of exhaust pipe haha.

Im pretty sure we did the same, but I will see if I can find it and double check. Been a little bit since I looked at it.

Cool, thanks

OK so here's a couple of dumb question, because I'm dumb...

The fuel starve is caused by the saddle-style tank, so what you're doing here is actually cutting the other half of the tank off, reducing the capacity by half?

So I imagine that the passenger side bit of the tank is still in place, is there just empty space where the rest of the tank used to be?

I find this interesting because the gas tank in the 370Z is huge anyway and I actually only use half of it (because I can fuel starve the car even on the street when below half a tank just taking long off-ramps at a reasonably fun speed) so I kind of wonder why Nissan didn't just put a small tank in like this in the first place.

In summary, I'm not really seeing a down side to a 10 gallon tank and no fuel starve, especially if this were a relatively inexpensive (and still fully streetable) mod. Although it looks like you are removing a lot of evap/emissions stuff but that's understandable in your case.

Thats correct. Heres a pic of chris forsberg 370z and what mine will look like. Only difference is my CBE will turn out the drivers side skirt in this empty area. This will be 100% DD as nothings changing hook up wise. Evap is here nor there. Just turn the CELs off. Only thing i gotta figure out is how to remount the driver fuels float so my fuel gauge will work. Apparently i cant tap into the passengers float so my gauge wont work. Im thinking about cutting a hole in the new tank and mounting it somehow.

Cutting the tank in half will absolutely work great at reducing and nearly eliminating fuel starvation, and you should end up with a 10-11 gallon tank in the end because you will want to cut it closer to the driver side.

All the EVAP stuff, fill breather, and rollover valve etc is in the dead center top of the tank, and you will want to keep that stuff. So strategically cut the tank in the correct location and save yourself a lot of trouble.

Notice the photo I took from my RRP installation page and editted. The yellow areas are calling attention to parts of the tank you want to keep. When I cut that opening in the fuel tank, it was put there intentionally because lots of gizmos are attached to the top of the tank right there, and are still mounted to the panel I removed. This tank was never going into a car, it was purchased new for RRP development and now just hangs out at the shop, so it was fine for me to remove those devices.

You should cut around the red line area.

Like I mention in a PM, you need not even consider the in-tank siphon transfer hose, no need to plug anything or any considerations, just dont hook it up to the fuel sending unit anymore.

The largest struggle with this procedure to the fuel tank you are undertaking is that you will be missing one of the fuel level floats that are essentially variable resisters in a series type circuit.

The driver and passenger side level sensors have a slightly different OHM sweep range... why, I cannot tell you. But this means that fuel level has more value to the gauge on one side of the tank than it does on the other side of the tank.

If you simply bridge the 2 wires together for the missing driver side float sensor, you will basically be telling the gauge that the driver side is full. If you measure the OHMs across the sensor in the bottom position and wire inline a resister that matches, you will be telling the gauge the opposite, that this side of the tank is always empty. This would be ideal because the gauge would always be accurate, it just wouldnt ever reach the pegged full position. The only way you are going to get the gauge to operate entirely OEM like is to add that driver side sensor back in to the passenger side of the tank, which will be a hassle.

It is possible to swap the potentiometer chip inside the level sensor with chips from otherwise identical float sensors. So perhaps if you look in some Nissan service manuals for FWD vehicles that would only need a single sensor, such as maybe a maxima, its possible that the potentiometer chip from one of those vehicles is calibrated to produce the sum of 2 sensors in the Z, either that or their instrument cluster is just calibrated for a single chip of half values like the Z.

PS external surge tanks dont work out well in the 350z or 370z, which is why nobody usually tries them! However, with the tank cut in half and no more need for the jet pump off the regulator bypass.... if you still experience mild starvation with your cut tank, let me know, and I can set you up with everything you need to add an external surge tank for very low cost... you do not need rails or anything crazy. Just a little canister, a cheap walbro pump, and some hoses and fittings. Under $500 easy.

Or let me slightly adjust my recommendation... Cut the tank at the red line to begin and gain visual line-of-sight with the things you want to keep. Then alter the vertical cut into a downward slope cut where at the top still matches the red line, but the slice angles towards the center of the tank and meets up with the peak of driveshaft mountain. This should be able to keep all the objects in the tank, and also make sure to not leave a pocket for fuel to get trapped, all while maintaining maximum capacity without sacrificing much surge protection. Obviously the overall smaller you make it, the better it will reduce starvation, but there is a balance to juggle there as you probably dont want terrible range/capacity.

We ended up cutting it in between the rear 1/2" nipple and 1/8" nipple. So pretty much dead center so im guessing 9.5 gallons.

Anything in the tank is now gone. I dont understand your roll over valve comment. The 1/8" line has no valve from what i can see. Its a direct hole right out of the tank below the gas cap unless theres a valve in that small line somewhere. I do find it odd that gas and fumes can just come out of there. To me everything in the tank had to do with the 1/2" nipple that went directly to the evap can.

As for the transfer hose to getting plugged, id feel safer to plug it. Since its about 3" higher than the bottom of the tank it just seems at less than 3" of gas i could get air in there. I dont think it'll hurt to do a plug right?

What im thinking for the float is cutting the white head off the float that gets pinched between the metal ring and gasket wen installed about half way down the white plastic. This will leave about a 1/2" x 2" rectangle. On the tank ill cut a hole or a slit in a flat section near the fuel pumps white head with connector and fill nipple. Ill bolt a thin piece of metal to the plastic and from the inside bring that metal up through the slit and weld it to the tank. Then just need to run the wires oit somehow and seal it up real good.

Ok sweet! Ill let you know how it goes and if i need that stuff.

Thanks for the help.

The smaller line is just an air vent so that when you are filling the tank, trapped air doesnt make the pump stop short of full.

It sounds like you are saying you entirely eliminated the EVAP and breather system from the tank. This will create some side effects you need to address where the fuel tank can generate pressure when the fuel heats up or create vacuum when the engine has been running and the fuel level is going down. You need to have a way for the fuel tank to breath... OEM cars vent to the intake manifold so the car doesnt always smell like fuel vapor and of course evaporative emissions. Consider how much area a couple gallons of liquid displaces: then imagine how much vacuum will be inside a sealed tank to remove that volume of liquid without allowing air to replace it.


If you want to do something with that connection that would be really clever, clamp on a few inches of 5/16" gates submersible hose, thus creating a new (and stubby) jet pump inlet hose. Adjust its length to reach about 1/4" from the floor of the tank. This will put that jet pump to use as a canister filler, helping to fill that little bucket with fresh fuel from outside. The little black piece on the bottom of the canister is the exact same thing already doing that, this addition will double up on canister filling.

Better yet, forget the gates submersible hose, since you have the actual in-tank hose with its QD fitting already cut out of the tank, just cut that Nylon hose real short so it lays on the floor... or actually, cut it to a length where you can route it to somewhere else in the tank to act as a remote transfer pickup. I dont know, maybe all the way in the back of the tank to promote pickup when accelerating out of a turn at full throttle. Fuel consumption is obviously the highest at full throttle so somewhere towards the back would make the most sense.

This is a jet pump, so its not a real fuel pump pickup, its just a solid state transfer device that is delivering whatever it picks up to the inside of your fuel canister where your actual fuel pump pickup can get it.

I pressure tested that small line with the gas cap on, i was wrong. At a few psi the gas cap has a release valve open so its not a direct atmos vent like i thought. The hole i saw under the gas cap just drains onto the tire. So when the tank does build pressure the air can escape. As for a vaccum im gonna guess thats a one way only valve. Not sure how i can test that or if it'll be a problem. I always thought the main issue was pressure and all tanks need a release which i tested and it has. My guy did say we could weld on a new nipple and run another line up by the filler neck for even more pressure release. He said that'd make him feel more comfortable. Again as for the vaccum i dont know. Maybe on the new line run we can install a 2 way valve with a low pressure open/close.

I see what youre saying about the 5/16th hose. I could even Tee it and make like a sideways E for 3 pickups and more volume.

Sounds like you found a high pressure blow-off in the cap, probably some sort of safety feature, I am not sure I would rely on it as a constant duty device.

The hole that drains by the tire is not a part of the fuel system and can be ignored... this is just to drip out water or fuel that has pooled up outside the gas cap. There is another hole connecting the small port on the rear center of the gas tank to the filler neck tube just inward of the cap. This is a vent that only applies when filling the tank to allow air to escape while fuel pours in. Any time the gas cap is installed, this vent tube is irrelevant.

Sometimes high HP cars will starve fuel when the engine consumes fuel faster than the tank ventilation can alleviate the vacuum. This burdens the fuel pump and will reduce its output. Tank vacuum can create significant problems, so its something you want to make sure to address with priority.

If you add additional legs to the jet pump pick-up, you will defeat the functionality of it any time all the legs are not submerged.

To be entirely honest, If I were in your shoes, I would just weld back in the panel with the stock fuel ventilation system... it is quite effective and Plug-and-Play with your car! Rather then invest a ton of time into reinventing something that is less than OEM quality, you can just put it back in.

Gotcha, i can do that. Even zip tie it to the rear baffle pointed down at the floor like a 1/4" up on more of the inside tank for though fast right handers.

So what would i do about the 1/2" nipple that was going to the evap can? If all that oem stuff is left in the tank whats going on the other side of the tank? Run a hose somewhere with a filter installed?

Make sure to use 100% Nylon zip ties!

Well you would have to put the evap canister back in there and hook it all back up as it was! Your other option is to make your own fuel tank vent and route it upward somewhere maybe by the filler neck and put a rollover valve on it so it doesnt dump fuel if the car finds itself upside down.

Be warned though - cars with open ventilation fuel tanks stink like fuel vapor! I have a very sensitive nose and it would annoy me personally, but im sure plenty of people dont mind.

Over the years I have seen plenty of people just drill a big hole in the gas cap for ventilation after removing all the OEM stuff. The downside here is there is no rollover protection. You may want to check rule books to make sure this wouldnt disqualify the car should it receive a detailed tech exam.

Rummaging the service manual I see that the gas cap does indeed also have a vacuum relief function.

Go ahead and suck on your gas cap to see if it flows well enough that you can just ignore everything I have been talking about! Or if its just a like a final relief intended to open before the gas tank collapses.