Ya know, I've wondered about the same thing. My thought is that the small inset area in the trunk floor might make a nice place to put an additional small fuel tank. Make it the size of the area and put in new carpet and presto! You'd never know it was there. I'm sure it could be done safely too.

Of course, it would be higher than the other tanks which is both a good and bad thing - good in that gravity would feed it into the other tanks with appropriate piping, bad in that it might be hard to fill.

Thoughts, anyone?

An 8 gallon fuel cell does not weigh much and filled would be under 80 lbs. Since I hardly ever have passengers that weight is not a big deal. Obviously on a planed track / hard driving day one would not fill the extra tank. The 19MPG doesn’t bother me much, the two trips a week to the gas station does. I would like to have a 375 range for day-to-day driving.

run new piping from the fuel door to the tank in the trunk then tap from the tank in the trunk to the original inlet of the tank under the seats........the fuel gauge would stay full till the tank in the trunk emptied out and the one under the seats would start to deplete.

how much could the weight of a plastic tank weigh in addition to 3-5 gallons oif fuel?? how can it throw off the cars balance?? what?, you guys dont put passengers in the car?? or a suitcase?? are you saying the weight of 3-5 gallons would would be so drastic as to negate the additional 45-75 miles from the fuel itself??.......I dont think so.

But I do believe by making the car lighter you would inturn get way better gas mileage.......so dropping 20-30lbs on rims and a couple pounds on lighter seats and some carbon fiber and titanium replacement parts might actually help out alot, hmmm, has cortc reported any increases in gas mileage since his various attemps at lightening his ride??

I completely agree... this is one of my big pet peeves- I hear so many people bitch and moan about how the RX8 needs 300hp... no, it doesn't. Pure sports cars are about high power to weight ratio- not necessarily high power. Mazda did a good job at bringing the '8 in under 3k lbs, but after owning a Miata for 5 years I really appreciate it's nimble, lightweight nature. I don't like where Mazda took the Miata- keep adding power to keep up with the added weight isn't the best path. I hope they don't do that with the 8.

I would like to find ways to "add lightness" to the 8, and I think our overweight 18" rims are a good start... I don't know if it was the fast and the furious crowd they were aiming at with 18's, but I'd much rather had some lightweight 17's- removing unsprung weight has a huge impact on agility and handling.

the thing is also how much weight would you have to drop to actually increase gas mileage by lets say 3 miles per gallon?? thats an extra 45 miles, carbon fiber hood/fenders/trunk lid and front bumper, lighter wheels I bet 175-200lbs less weight might come close to that but its just a guess

how much money would you have to spend to save a few dollars a week on fuel??plus after getting the CF parts I would have them painted........dont want my car looking like something from NFSU2 so thats more money but you do get the extra performance from lightweight parts, I dont know :confused:

I guess I'm not really worried about gas mileage... if I were, I'd be driving a Toyota Echo, not a rotary. I just want the weight savings for better agility and handling... I could definitely see myself in a Lotus Elise someday-- 190hp in a 2000lb package is a lot more fun than 300hp in a 3000lb package. Better yet, put the Renesis in a Miata and I'll write a check tomorrow.

good points but the thread starter is trying to come up with a solution to having such a short distance between tanks...........the miata doesnt even come close to having the looks of the 8 and thats a pretty big point in the purchase.......I really dont care what type of engine is in the 8........if they had a nice small V6 that had the same weight proportions, power and 9000 redline of the renesis I would take that instead along with the 24 city/32 highway, dont get me wrong the rotary is awsome but people want a little more gas mileage in their 8's than viper owners who get 12mpg city and 21mpg highway :p :D

I understand- I'm just clarifying my reasons for not wanting to see any weight added to the 8. I'm pretty much the opposite- I do think the 8 looks great, but the rotary was the primary reason for the purchase for me. If the RX8 was just another V6, I'd probably would have bought a 350Z or dropped a turbo in my Miata.

ditto on the weight........the rotary is very special and awsome engine but in the end even though I dont want to, I question the low fuel economy.

But you can't. The entire design of the RX-8 is predicated on the rotary's engine size and placement. Replace the engine with a V6 and you will lose something; most likely beginning with the rear seats, and probably higher cowl line and other unfortunate compromises, not to mention handling issues and weight distribution. They didn't design a car and then say "hey let's put a rotary in it". They asked themselves how they could take maximum advantage of a the attributes of a rotary engine to build a car that had a truly unique combination of desirable features.

As far as additional tank -- sure it's possible. With enough money all you need to do is say where you want it and someone can fabricate it. But it's doubtful that they will be doing the same type of analysis as the original designers especially in the area of crashworthiness and survivability.

Not to mention, you couldn't call it an RX (Rotary eXperement, if I remember correctly) if it has a piston engine. ;)

Off topic...I'm not complaing about the rotary or the fuel economy, just the range of the 8.

Also, I know some people would like a 20 gallon tank but I just want another 1.1-2.1 gallons. Adding weight (I HATE THAT TRUST ME) should not be a problem for another 1.1 or 2.1 gallons while giving us an additional...

I use up 13-13.3 gallons per fill up (FYI) on a 15.9 gallon fuel tank so if I went up another 2 gallons (thats all 2 gallons...not 5-10, 2 gallons) then that would give me another...

36 miles in the city or 48 miles in the highway

Range is what I'm talking about not fuel economy, range.

Heck...if you Kramerize it....

Currently our MAX range is: (286.2 miles city and 381.6 miles highway) per the evil EPA...lol

With another 2 gallons:

324 City
432 Highway

So, the formula needs to be (to get the most bang for the buck).

Find a company that makes fuel cells (that are crash worthy and SAFE) that are lighter than our OEM one and has a 18 gallon capacity.

Again, I would settle for 17...I just want another day or two worth of driving before I come in to feed my baby. That's all...

Reviving a really old thread, but...

I'm wondering if anyone actually went down this route. I've been one of the more vocal "Quit complaining about mileage" crusaders. At the same time, I could use the extra range for a couple projects I'm prepping for. A run across the state last year with a pack of Corvettes demonstrated the issue rather accutely. Same speed, they made the 300 mi journey no problem. I had stop for fuel 2/3 of the way through (no, we weren't behaving, yes we were completely safe).

One of my projects will require cruising speeds that activate all the digits on the speedo. Another is just going to suck gas down more quickly.

is everyone filling up the tank and the pipe from the tank to the cap?
is the tank the 15 gallons, or tank plus pipe?

cause if you fill up the pipe and it looks quite long, would it give you much out of a gallon?

just a thought as i always fill my other mazda til the petrol is near the cap to get a few extra miles.

i have also seen a product in the states on the internet caled MPG CAPS, if you google it, its a pellet that's supposed to dissolve in the petrol and help the petrol combust in a cylinder. i did email them and ask about the rotary, no reply as yet.
but they are saying you burn petrol better and get an extra 3-4 miles per gallon, so would it be the answer?

1) there are no miracle products

2) just fill it the same everytime, that loss 10 mile is not gonna kill u =p

Filling up the tank all the way to the top of the neck will cause problems. Gasoline will run down the line thats meant to suck out the tank fumes and pollute the charcoal canister that is a part of the emissions system.

Oh, i didn't know that.
How far up the neck does the petrol go before this can happen?
I take it petrol pumps switch off when the fuel rises up the nozzle and activates a cut off? then you know you are full etc.

At the end of the day, going out for petrol(gas) is a good excuse for a blast in your 8 lol.
But as its a sports car and a rotary i think the consumption is not bad, whats really peeving everyone off is the price of filling up. Here in the UK, its £1:06 a litre for unleaded and £1:12 for super unleaded. I put £30 super unleaded in this morning which was a mark shy of the 3/4 level. I did 63 miles roughly and the needle was a mark above the 1/2 level, so roughly the same use as unleaded.

My engine light is on, I am seeing the dealership on Thursday to get the code pulled and see why. I thought I was using more petrol than normal, but it worked out the same, and a bit better as i was doing 70mph to work and back on the motorway.

The super unleaded does give you a little bit more mpg, but is so much more expensive. Pity they could not invent a fuel cell type rotary that replaces the petrol all together, the hydrogen rotary is only just coming out in Japan.

Has anyone ever used any fuel saving technology and it has worked?

no no no no...

i tried 89 for 2 tanks, noticeable lack of acceleration.

plus the car acts a bit funny, not knocking but funny. just pay up if u wanna play.

fuel saving technique is not to carry stuff around, spare tire no, passenger no, and perhaps a lightweight 19-20 incher wheel.. but u will end up paying more for the wheel.

yeah, i noticed a bit of a pick up driving up the road out of the shell garage.
but with my light on i dunno if the plugs are foul'd or cat a bit stuffed up, like car a bit stuffed up.

would a blocked cat cause your cat back exhaust system to not growl as much?
the car isn't dying, it idles ok, and is quick enough, i will be bringing it in to see what it is, i have been using unleaded and oil level ok etc. was doing the red line a day or close to it to keep the engine clean. just bugging me what it might be.

after the shell, i wanna try the bp ultimate to see what its like as its supposed to last longer and give your engine more pep and clean it etc.

adding more gallons would actually DECREASE MPG.
its like driving around with junk in your trunk... just with more fuel to carry you that extra distance.

imagine a 2 gallon bike that gets 100MPG. thats easy, its 100MPG. but if it had a 10 gal tank... it would get less MPG. maybe down to 90 MPG.

lightening your car with some REAL lightweight parts will definitely be cheaper than paying for a custom fabbed tank. and i'm not talking about CF hood/trunk that shaves literally only a few pounds off our already lightened oem parts... try looking elsewhere like those heavy seats in your GT pkg., those 18" wheels, or those premium bose audio system.
granted, if you can lose 150lbs while keeping your car near stock trim you'll maybe get 1~2extra MPG even with the same 15.9 gal tank.

are you getting 18MPG?
when you have a 18 callon tank, you can kiss your 18MPG down to maybe 17.8~ MPG., given just extra capacity to go further.

you just paid for the fabbed tank, and your reward is just a visit to the pump a day later...

worried about getting stranded on a 280+ mile trip with a gas station few and in between? keep a 2 gallon gas jug in the trunk bro. be safe.

not disagreeing with you about what we get for this car... but i just don't see any gains that yield only the positives without any compromise.
so best bet is to just drop unwanted dead weight.

Not worried about getting stranded. I do have a couple 2.5 gallon cans, and 1 gallon can for the trunk if it really becomes necessary. But the time to stop, pour the gas in, and get going again is something I want/need to minimize. So, how big is the stock muffler (width/height/length)? If no one has that info handy I'll get out the tape measure this weekend while I'm doing other maintenance. I'm thinking of re-routing the exhuast out in front of the rear wheels and hanging a fuel-cell, with internal bladder and safety foam, where the muffler is now. Hust brain storming at the moment. I really want to use my 8 for this project, we means adding fuel capacity. But if I can't I'll have to find something else that can handle the job.