Surge tanks and overall fuel capacity
 

So I'm not used to having such a small gas tank. I've had my BRZ for almost a year now so I've gotten used to it, but it's still an inconvenience. I know our tanks are split and shaped weird so simply swapping a larger tank in is not so simple. I was looking into various surge tanks and was wondering if adding a surge tank would basically allow my car to carry more fuel? For example, I was looking at a 3.5 liter (0.93 gallons) modular surge tank; would that basically add another gallon to my overall fuel capacity? I understand the real purpose for a surge tank but I'm just wondering if this could be an added benefit :thumbsup:

What problem are you trying to solve? 300+ mile range not adequate between fills? After that many miles, I figure the driver would want to stop to take a leak, if nothing else.

oh man I WISH I got 300+ miles between fills haha. I get like 250 at best. But I just want to fill up less often honestly. Mo' fill ups = mo' money lol. But this is far from a make or break situation I was just bouncing an idea I was thinking about onto the forum.

You could throw a pretty good sized fuel cell into the trunk, I guess. Maybe another 20 gallons?

I understand not wanting to go to the gas station as often, but how does this make any sense?

But really in a 4cyl car that gets like 25mpg, how much bigger would you really need? Are you taking road trips every day or something?

Er...

Get a gas can to put in the trunk?
Rotopax spare fuel tanks are pretty rugged and have a good record
in the Adventure motorcycling field. Can get a pack mount to fix them solidly.

What cars have you had before that went farther than 250 to a tank?
Ford F150 might get that with the camper special reserve tank I suppose.
Might want to consider Oregon or New Jersey if it's beneath you to pump gas...

You'll be carrying around 6.3 pounds extra weight per gallon wherever you go.

It doesn't.

I wouldn't think an extra 0.93 gallons would make enough difference to be worth making the modifications to your fuel system. Besides, you'd be adding weight which could at least partially offset the extra fuel in terms of the benefit to range - maybe not by much, but if you're only getting an extra 0.93 gallons to begin with that's a pretty slim margin to chip away at.

Technically it is just the opposite, The heavyer you car is the worse you gas mileage will be.

How much gas do you put in your tank each fillup? If you are only going 250 mile per tank, and you are refueling when the light comes on, you would only be averaging like 20-21 mpg...

Are you in serious stop and go traffic? Or do you just romp on it too much?

You would easily get the equivalent of .93 gallons by changing your driving habits just a smidgen. Getting your average to 23 mpg would more than cover you.

How exactly does that work?


10 fill ups of 10 gallons at $1 a gallon = $100
1 fill up of 100 gallons at $1 a gallon = $100


Frequency of fill ups does not impact cost in any way, shape, or form.

I travel back and forth from CT to VT often. I definitely romp on it too much haha. But I've had a few cars (Saab 900s, 9000CSE, 9-3) that got more miles per tank, except my modified Audi A4B7 and my Saab 9-3 Aero. Yes, 0.93 gallons is a small amount, but even at 25mpg thats almost another 25 miles. And driving conservatively could increase that. I was looking at surge tanks for other reasons though not just to increase fuel capacity.

That equation (10x10=1x100) doesn't correctly represent the issue. If you have to fill up twice a month versus four times a month, that definitely impacts cost.

Still not sure how that works. If you had to fill the same size tank more times ya sure but filling up larger tanks less often doesn't save you squat.

You're forgetting the reserve. Your ~13 gallon tank has approximately 12.5 gallons of usable fuel in it when full (the last half gallon is not accessible). The light comes on when you have approximately 2.4 gallons reserve left, or when it has used about 10.1 gallons. That would put you in the vicinity of 25 miles per gallon (24.75 if you want to get picky).

At that rate of burn you could go another 60 miles or so after the light comes on before you actually run the fuel pump dry. If you run Torque as an engine monitor, you can actually monitor the remaining fuel in gallons (or liters) so that you know when you're really getting desperate.

New math I guess?

Not sure if trolling but I'll give it a try...

If you were to get 10 mpg for example, and you drove 1100 miles per month, you would need 110 gallons per month (1100/10=110) Depending on the size of the gas tank, here are the ways you could do it:

11 fill-ups at 10 gallons each = 110 gallons.
10 fill-ups 11 gallons each = 110 gallons.
Now you try:
??? fill-ups at 55 gallons each = 110 gallons.

Unless price varies drastically during the month in a predictable way, and you can alter your gas tank size to need to fill up ONLY when prices are low (this doesn't happen), then you will pay the same amount per month regardless of how many times you fill up.

The only real way to reduce your fueling cost is to use less fuel by either reducing milage, or increasing mpg. Not going to get into how that may affect global economics but you get the picture.

Also, an extra gallon is not going to cut the amount of times you fill your tank in half...

This math that OP is using hurts my head. Assuming gas prices stay on par, you arent saving any money at all. Less trips to the gas station, but thats it. Why did you even get a BRZ if you wanted a fuel efficient car.

That's because it's not math.

Honestly, I'd like a bit bigger tank myself. My fuel mileage sucks in the winter.

Also, when I do roadtrips home, it's about 660km. I get about 630km to a tank when making that trip.

And stopping for gas is a major inconvenience? A bigger tank just means you would go even further before filling but it would still need to be filled.

You guys would have shit with some of my old cars that had to be filled up two or three times a week.

Nah, more like just a little OCD on my part. On the original Primacies I could *just* make that trip.

I still struggle with the fuel mileage drop with a cold engine on the BRZ. I've never heard of any other car being this affected. I easily take a 20% fuel mileage hit when temperatures drop. Only affects short run city driving. If I do a long highway trip it's still reasonable.

I go from my normal average of 6.9L/100K in summer to 7.1 in the winter. That is 99.5% highway though.

Normally I'm 6.6 highway, winter or summer.

Short run city driving in the summer is about 9L/100km for me. In winter that jumps to 11L/100km, not counting extra idling for shoveling out/defrosting.

Moved to a new apartment last year with indoor heated parking, saw a 1L/100km improvement by having a warm engine in the morning.

Its possible the drop may have something to do with the winter blend of fuel offered in your area? Ive never heard of major drop in fuel mileage in most cars for different seasons.

Winter mileage difference may be related to:

1. My ltft goes from -3 in the summer to +4 in the winter. While that by itself would not necessarily cause this effect, it shows that the there is some calibration in the ECU that may be off. I am running oft stage1, but I dont think they messed with the ambient temperature calibration.

2. Oil temperatures are about 30 degrees lower in the winter, making it slightly thicker.

3. Colder air is more dense, meaning you have to push greater mass out of the way at speed.

4. Tires don't have a chance to get as much heat in the winter as summer, so the air inside doesn't expand as much, causing running tire pressures to be lower.

5. Freezemiester hates us.

I've read a lot of really stupid things on this forum, but this may win.

6. Fuel mixtures in the winter are slightly different (not sure if better or worse for mileage but probably worse)

7. Denser air means you can burn more fuel which means more hp / less mileage if press the gas as hard as you normally do.

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Also my '74 Lincoln Mark IV which is 6k lbs with PAX and fuel gets 10mpg and has a 26 gallon fuel tank. It goes about 250 miles before a fill up. Hows that for some math? I find it amuzing your BRZ has the same range but maybe you modded the shit out of it? I drive for at least 40 more miles after the light comes on though because I always have waze on wherever I go even if I know how to get there. (for traffic, distance, police trap info.. plus it reroutes automatically if you detour into unknown territory)

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We definitely use a different fuel blend in the winter. It's needed so that the gasoline actually vaporizes in the cold and can be ignited.

I believe my poor winter mileage is simply down to an agressive engine/cat warning cycle, and a cold automatic transmission. The auto takes a long time to warmup and will not lock the torque converter when cold.

If I'm doing a lot of driving in a day, and getting the engine/trans to steady-state temperature my fuel consumption is basically normal.

1. What?! This makes no sense.

2. Aren’t surge tanks thousands of dollars?

I suppose personal labor and expensive shoe leather could factor in to the equation
if you're a powerfully built company director.

But then you'd get your personal assistant to fill up for you.

I go 360 miles/tank on 100% real gasoline and 340 or so on shell premium. fill-ups are 12.2 to 12.5 gallons going 40 miles past the low fuel light.

I actually wish I had a bigger tank. Where as I've never owned American, I have had many German, Italian and Japanese cars. All except my BRZ were rated from the factory to get around 400 miles to a tank. It has nothing to do with long trips but everything to do with having to go in the wrong direction to get my gas and wanting to do it less times per month. Once I'm at the station it doesn't matter to me if I'm there 5 minutes or 10 minutes. Another 2.5 Gal would be nice

It doesn't have to be modded to shit. I put wide, sticky tires on my car and lost a full 6 mpg. I was averaging 31 mpg in my first year and couldn't understand what the hell all these people on the board were doing to only get 25 mpg. Then mine instantly dropped to 25 mpg with the wide rims and tires and no other performance mods at all.

This car is finely balanced from the factory. You mess with the balance on this car, it's going to mess with you.

🤔 MT > AT

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I feel like you've said everything I've wanted to.

Never in my ownership of my FRS have I ever wished for a bigger tank. I feel like I rarely fill it up anyways.

Recently I made a trip from Scarborough, to Arthur, to Sauble Beach, to Guelph, to Scarborough on one tank. Pretty great, IMO

I got my BRZ 3 months ago. I am a conservative driver. Half highway half city. I always get to 380 miles till the light comes on. I then drive about 30 miles more and fill up with Shell 93 octane. The gas pump clicks off at about 11.3 gallons. My BRZ is an automatic.

If you fill up twice a month with a tank twice as big as the frs tank you will be spending the exact same amount as if you fill up the frs tank 4 times a month

36.25 mpg is impressive