quote Originally posted by 30+mpg: Any updates. I think you are the first person on this forum to figure out how to actually get more gas into the tank by modification. And this forum has been around for years. MY CONGRATULATIONS to you. A lot of members are too Raphly (as in Nader) to mod the gas tank.

Thanks. Nothing new to report. No explosions or anything

quote Meanwhile, I hope you are obtaining good results with your job search.

Interview set for Wed.

[This message has been edited by 84Bill (edited 05-14-2007).]

I got a question: Doesn't that air gap serve a purpose? Like for expanding vapors, or increased pressure as the temperature rises?
I'm a bit worried about that.

Side question: How are 87+ tanks different from 84-86? I've heard many places that the capacity is about 2+gallons more, but what's the difference?

-M

the 87 and up have an extra "tank" in the fender well in front of the passenger rear tire. That acts as the air reserve for expansion of the fuel. I would guess it is about a 1 gallon capacity tank. the vent form the main tank goes to the bottom of that tank, then the top line goes to the charcoal canister. This gets around the required expansion volume required for the tank and allows the ain tank to be filled more completely.
The later tanks are also slightly differrent shape which gets a little more capacity also.
This mod removes the expansion volume from the main tank, but I don;t think it is an issue as these cars will quickly suck the gas down anyway.

There is plenty of room for expansion of the fuel when full. There is still room in the fuel tank itself (one klicky), the expansion tank and the filler neck.


I know the previous capacity was 10 gal every 250 to 270 miles, which was the old max capacity.
So I would only go beyond that IF I knew I could burn off the extra in a short time frame.. say like long distance driving.

This mod will work very well if you do distance travel. BUT if you dont plan on long distance travel in your 87 / 88 with this mod then just put 10 gallons in it. You will still get more miles per tank IF you lower the FP as I did.

If you choose to lower the pump only and not alter the filler vent you will still get an extra gallon out which translates to slightly more range.. Instead of 250 miles on a tank you will get + (miles per gallon) out of the tank when full....

That's a lot of effort for an extra 20 to maybe 40 miles. :shrugs: But every bit counts. I would love to see the capacity increase to like 16 gals. :dreaming:

-M

I believe this came from LamboLounge.com . The center section holds about 15 gallons. A lot of work, but worth it if you want the capacity. I have the plans in a zip file, but I don't know how to upload them. If you're interested, email me at sspeedstreet@earthlink.net

84Bill, any news to report ?

quote Originally posted by PaulJK: 84Bill, any news to report ?

12.4 gallons since last fill.. still had fuel sloshing in the tank before I filled it, probably another 25 to 40 miles or so.
340 miles on the tank.

[This message has been edited by 84Bill (edited 09-08-2007).]

you do know that fuel expands when it heats up right? i really hope you took that in to account when you did this. also at it heats up gasoline vaporizes, the space at the top of the tank is designed to allow for this, and the recovery system taqkes up the slack. if liqiud fuel gets in to the charcol canister it will ruin it, that and it will always smell like gas.

------------------

Currently a student at Wyotech in Sacramento.
1987 Pontiac Fiero GT, 151,000 miles! decklid window, silver guages. rear ended someone, and now the rebuilding starts! More pics of my 87 GT can be found here
1985 Pontiac Fiero 2m4 auto, 222K miles and counting <-my first car, and i still cant get rid of her!
2005 Jeep Grand Cherokee 3.7L 4x4, 62K <-Daily driver
A 4 year olds knowledge of science: No matter how much jello you put into a swimming pool you still can't walk on water.

quote Originally posted by tednelson83: you do know that fuel expands when it heats up right? i really hope you took that in to account when you did this

Yes... I did.

quote also at it heats up gasoline vaporizes, the space at the top of the tank is designed to allow for this, and the recovery system taqkes up the slack. if liqiud fuel gets in to the charcol canister it will ruin it, that and it will always smell like gas.

I already addressed this issue.. the 87 & 88 have a vapor tank on the right side of the car to prevent fuel from getting up into the canister. In addition this mod isnt for your average daily run to the store to get the maxim mag. It's a mod for people who USE alot of fuel and dont want to stop every 250 miles. When I top off the pump clicks and thats it! No clickey clickey to top off.

[QUOTE]Originally posted by 84Bill:
The real problem is fuel in the cannister on the left. Fuel in the cannister will destroy the charcoal and that is the purpose of that tank on the right side, it acts as an accumulator. Getting fuel up high enough to fill it is highly unlikely.

One more comment on the (highly controversial) tank flushing.

While doing a tank "restoration" a while back, I washed the tank with a gallon of alcohol. I don't recall how long the denatured stuff was in the tank but it definitely did a number on the plastic baffle. Turned it to putty and cracked it in a couple of places.

In light of this my advice would be to use soapy water and air to dry things afterwards.

A good means of proving if there is residual bomb liquids left the tank is to put a hair dryer on the filler. Then using a long drop cord, plug the dryer in from a remote location. The static discharge, if not an outright spark coming off the dryer, should provide your litmus test.

Soap will leave residue behind... But to each his own.

This might not be a very good idea and I will explain why. I have had my racecar in my garage for awhile. It only has a bit of gas in it. But everytime I bring it out of the garage and into the sun so that it heats up, fuel will run out of the fuel lines. They are unhooked as there is no engine in the car. YEa I know not the safest thing in the world. But my point is if it is expanding that much then taking up that extra space may not be good. I know the engineers at GM didn't always get things right, but they may have had a reason for this.

quote Originally posted by The_Stickman2: This might not be a very good idea and I will explain why. I have had my racecar in my garage for awhile. It only has a bit of gas in it. But everytime I bring it out of the garage and into the sun so that it heats up, fuel will run out of the fuel lines. They are unhooked as there is no engine in the car. YEa I know not the safest thing in the world. But my point is if it is expanding that much then taking up that extra space may not be good. I know the engineers at GM didn't always get things right, but they may have had a reason for this.

that is the vapor expanding - not the fuel. all automotive fuel systems have compensated for this. the fuel system runs at 40 psi. vapor expansion wont reach that.

quote Originally posted by Pyrthian: that is the vapor expanding - not the fuel. all automotive fuel systems have compensated for this. the fuel system runs at 40 psi. vapor expansion wont reach that.

It came out as raw fuel. I don't see how vapor would leave a puddle on the floor.

quote Originally posted by The_Stickman2: It came out as raw fuel. I don't see how vapor would leave a puddle on the floor.

the fuel pickup is still in the liquid. the vapors expand, and create pressure. the only release for the pressure is to push the liquid out the fuel pickup.
much like an aerosol can.

Two main things heat the fuel. One is ambient temperatures while driving and sitting in the sun or on hot surfaces, the other is the heat added to the fuel by the pump (cool the pump, heat the fuel!) and picked up in the engine compartment as unused fuel is returned to the tank. Aside from the savings of eliminating the return plumbing this heat buildup is one reason why everyone's gone to returnless fuel pump systems now.

Liquid expands with heat, like everything else. If the air above the liquid has nowhere to go then the air pressure increase from thermal expansion will push the liquid down, and out via fuel lines. When the liquid expands due to heat it pushes air out if there's a place for it to go, in the case of our Fieros that place is the charcoal canister where the fuel is grabbed from the air as it goes through. If there is no air space and no place for liquid to go the hydraulic force from expanding liquid will quite easily tear apart a gas tank, hence the airspace above the fuel on pre-87 Fieros and the separate air expansion tank in the right rear fenderwell of 87-88 Fieros.

FWIW...

JazzMan

quote Originally posted by Tha Driver: Just to clarify for others; water does NOT wash out any gas that may remain in the tank. It could have blown if you introduced an open flame or too much heat.

No. it would not. I used to put out cigarettes in gasoline all the time. Yes if you havea bucket of gasoline you can throw a lit butt in it and it will go out. liquid gasoline will not "blow", gasoline vapors mixed with air and oxygen can and will burn or "blow". you need air+gas fumes or atomized gasoline to get ignition. a tank filled with water will NOT "blow". even if it had a gallon of gas floating on top of it. and yes filling it with water and letting it overflow will easily get all the gasoline out. Gas floats on water. it will was out easy you just need lots of flow. adding alcahol speeds this.

Side note: old timers used to braze gas tanks filled 100% with gasoline. Now it's hard to find a mechanic that can braze let alone work on a gas tank.

[This message has been edited by timgray (edited 10-11-2007).]

Welp.. it's been several months. The fiero hasnt gone thermal, gas hasnt cascaded out of the tank in any way shape or form and I havent seen any black helicopters or EPA marked vans.

"If" I fill the tank to it's capacity of about 13.5 I'm usually driving further than 27 miles which will bring the level down one gallon.. which is just slightly less than the original "full" capacity.

The fiero fuel tank CAN carry more than the spec but due to the design of the fill it effectivly prevents the fuel from filling it to FULL. For some reason everyone is under the mistaken belief that the tank is solid full.. It's not, there is at least an inch of airspace in the tank. I even went as far as to reseal the supply, return and vent lines on the tank cap to ensure a complete air tight system. There is no way I can fill this tank to the very top.. it's un possible.

Remember the FP is about a half + off the tank bottom. Mine is on it. so I can scoop up about an extra gallon from that alone.

Last fill was 13.0 on 370 miles Works for me.. I like going 2 weeks between fills.

This is definately a mod I'll try if I ever have to take the take out to change the fuel pump or something like that.

On the subject of welding on a gas tank, I've heard some welders will fill the tank with argon or another nonflammable gas to displace the gasoline vapors.

------------------
I believe in the sun,
even when it's not shining;
I believe in love,
even when I don't feel it;
I believe in God,
even when He is silent.

quote Originally posted by 600racer: This is definately a mod I'll try if I ever have to take the take out to change the fuel pump or something like that. On the subject of welding on a gas tank, I've heard some welders will fill the tank with argon or another nonflammable gas to displace the gasoline vapors.

It's definatly worth the effort. My next idea is to fab up a sump and baffle system. I was thinking of cutting a hole in the bottom of the tank to put in a 1/2 inch deep well right where the pump sits and replacing the current plastic baffle with something just a bit better designed. I also want to add a low fuel warning light.

Mihhh... when I get time.

You guys doing a mod that kills expansion in the tank really need to install the overflow tank in the fender like the 87-88 cars have. GM didn't go thru the cost of adding that thing for the fun of it. It's a major safety and pollution item.

W/o enough expansion room it is Very easy to poison the EVAP canister and even have fuel run thru it when the tank is full. Any liquid in the canister ruins it permanently. Fuel grows quite a bit when it heats up. And remember that besides weather, it gets heat as it loops thru the engine.

In fact in order to cut loop heating, Delphi and others moved to not only having the pump but the regulator in the tank as well. That way they can go back to one line to the engine. Cutting the heat from that loop has a direct effect on Evap emissions, which USEPA and most states want reduced.

In the summer, fuel can move thru a huge expansion right after a fill up. You'll be pulling rather cool fuel from an underground storage tank and putting it into a surface tank where it could easily increase in temperature by 50-80F in pretty short order.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top of every forum page...)

sspeedstreet I sent you an email but it bounced back, been happening to me alot lately. I even tried twice, so I sent you a PM instead about the gas tank plans

84bill do you have any more photos of your mod? theres a 88 in the junk yard near me im thinking about grabin the tank and what ever comes with it. i wouldint mind takeing the fiero on a road trip sometime and could use the extra gas. awsome mod!

quote Originally posted by slinger: 84bill do you have any more photos of your mod? theres a 88 in the junk yard near me im thinking about grabin the tank and what ever comes with it. i wouldint mind takeing the fiero on a road trip sometime and could use the extra gas. awsome mod!

I dont have any pics of the mod in progress but I can help you with whatever you need.

I'm currently thinking about altering the baffle and adding a shallow sump with a low fuel warning light. I seem to have been granted free time by my boss so I'll be getting on it soon... Oh and road trips arent very likely at the moment. My boss is a prik.

Feel free to PM me.

[This message has been edited by 84Bill (edited 01-17-2008).]

84Bill - are you still in one piece ?

Although your ID is 84, it seems that this mod was done on an 87 or 88 with the extra expansion tank on the passenger's side. Have you done a complete fill-up and had any problems with fuel back-up ?

Any problems or news to report ?

Anybody else done this mod ?

Bill won't be replying any time soon. At least not with that screen name.

Hopefully a name change due to an engine upgrade and nothing bad ....

quote Originally posted by PaulJK: Hopefully a name change due to an engine upgrade and nothing bad ....

Well, concidering he was banned....

shows how much i pay attention to the ratings bar .... thanks

i guess no one else has tried this ...

[This message has been edited by PaulJK (edited 01-04-2009).]

Great. crash it and get investigated, claim... DENIED!
Modified gas tank?
Are you crazy?
Do you actively seek problems out?
Just stop for gas more often.
<shesh!>
'Ever hear of the the adage; "Penny wise / pound foolish"?
Buy a truck...

no, but i've heard of "newbie foolish'

maybe if you stick around and read posts longer than a month (dec 2008 ?!) or unless you get banned too, you'll find out that the small gas tank and limited range has been a common complaint here ....

Wait a minute ..... 84Bill ....izat you ?!

quote Originally posted by 85GT3.4Track4spdCar: Great. crash it and get investigated, claim... DENIED! Modified gas tank? Are you crazy? Do you actively seek problems out? Just stop for gas more often. <shesh!> 'Ever hear of the the adage; "Penny wise / pound foolish"? Buy a truck...

Suuure, I see modified gas tanks cause crashes all the time.

Kevin

Kevin,

Where did I ever say that a modified gas tank "Caused a crash" ????
(Don't quote me and then misconstrue my comment, please).

Crashes, most often, are caused by, well, people like you...

and I.

The real problem, with a modofied gas tank; "The integrity of the cell may be compromised".
Do YOU want a customized tank rupturing next to you, while you are still belted in (and possibly in motion)
Immediately after a significant impact ?

I don't.

[This message has been edited by 85GT3.4Track4spdCar (edited 01-07-2009).]

Here was my attempt to do something similar w/o modifying the tanks itself (part of my 4.3 swap thread. I also did the math for the fuel expansion.

Unfortunately, my first attempt did not work. The very first fillup was in the 10 gallon range and I routinely fill up 10 to 10.2 gallons. I am pretty sure the snorkle fell off due to vibration in the chassis and lack of a positive means of holding it in place. Eventually, I will pull the tank again and try it again.

quote Originally posted by fieroguru: Here is my version of the 84bill fuel tank capacity increase... I call it the snorkle version... USE AT YOUR OWN RISK. Fuel expands/contracts with changes in temperature and it is important to ensure there is enough room in the tank for it to expand or it could push fuel into the evap canister. Gasoline expands at a rate of 0.00069 per degree F. So a 100 degree change in temperature with a 12 gallon tank will require .828 gallons of additional space. Expecting a 100 degree change is probably extreme, but it provides a since of scale. Since my car is an 88, it has an external expansion tank on the upper passenger frame rail (I never measured it, but it might be .5 gallon). The top of the fuel fill vent tube is about 3" from the top of the tank. This creates an air pocket about 3" x 7" x 20" which is room for about 1.8 gallons of fuel (1 gallon more than needed for a 100 degree change - and assuming there was no secondary expansion tank). The goal is to lessen the size of this air pocket and allow more fuel in the tank. Step 1: Drop the tank and remove fuel pump. Step 2: Find someone with hands small enough to fit inside the fuel tank (my hands are now scraped and gouged, but I got the job done). Step 3: Use a round tapered punch and insert it into the vent tube. You want to work it around the inside of the vent to smooth out the entrance. Step 4: get some 1/2" aluminum tube from Home Depot (about $5 for a 3 foot piece) and bend it to this general shape. Step 5: File/sand the end that will go into the vent tube. It needs to be tapered so it will slide into the vent tube and be held in place tight (the pic above has one end tapered already). Step 6: Drill the smallest hole that you can in the bottom of the bend. Step 7: Apply a thin coating of RTV to the tapered end (make sure to stay away from the hole) and insert into place. Apply pressure while rotating and slide it in as far as possible and make sure the tube is held snugly into place. With this mod, the top of the vent is now 1" from the top of the tank. This should allow me to fill the tank with 1.2 additional gallons of gas which is more than a 10% increase for $5 and a little time. This will leave about .6 gallons of air space in the tank + the approximate .5 gallons in the expansion tank for expansion of the fuel. A potential problem with the snorkle concept is that once the fuel goes over the top, the fuel will go down the new vent tube and be trapped there. This may (or may not) hinder the next fill up. A quick application of the brakes once the tank was 3/4 tank or less would most likely clear the snorkle. However, the very small hole will allow the fuel to seep out of the vent tube once the fuel level in the tank drops below the vent. The hole will also allow the fuel to enter once the fuel level is above the vent tube, but I think the last 1.0 to 1.5 gallons of fuel will enter the tank before the small hole will allow enough fuel to fill the vent tube... just have to wait and see. I also took the time to see how close the fuel pump was to the bottom of the tank. With a nail wire tied to the bottom of the pump and sticking out about 1.5" from the bottom, the assy was put back into the tank. The nail hits the bottom first and then is pushed up the side of the pump. Make sure the pump assy is properly seated in the tank and then remove being careful not to bump the nail. On my tank the pump is within about 1/4" of the bottom and that is close enough for me. The next step is to get the fuel sender reading correctly... reading E when the tank is within a gallon of being empty, not with 2-3 gallons of fuel left.

There are some good ideas here.

I have an 86' and would love to at least upgrade to an 87-88' tank with expansion tank. Does the tank fit earlier Fieros?

quote 85GT3.4Track4spdCar:... crash it and get investigated, ...

I'll let you do the crashing, not me.

The gas tank will be the one of the last items to be damaged due to it's location.

How many insurance investigators open an undamaged gas tank?

?? Why does your post make me think of Ralph Nader ??

quote Originally posted by fieroguru: I am pretty sure the snorkle fell off due to vibration in the chassis and lack of a positive means of holding it in place. Eventually, I will pull the tank again and try it again.

Did you think about trying JB Weld for gas tanks ? it might hold better than the RTV.

quote Originally posted by fieroguru: The very first fillup was in the 10 gallon range and I routinely fill up 10 to 10.2 gallons.

Since you must be using the 11.2 gallon 87/88 tank, that only lets about 1 gallon of gas spread across the bottom of the tank. How deep would that be ? If your pump is 1/4 " from the bottom, i'd say no one is gonna get much better than that (how many gallons is 1/4 "depth ? )

quote Originally posted by 30+mpg: ?? Why does your post make me think of Ralph Nader ??

Judging from his posts AND the PM he sent me AND the new (-) in my rating bar, he's not able to add much and is just trying to make trouble... probably some RTF escapee ..

[This message has been edited by PaulJK (edited 01-08-2009).]