Does it make sense that if with a full tank of gas you will get better performance? I used to always fill to half a tank, believing that less gas = less weight = better fuel economy/performance. But could it be that more gas helps fuel pump push more gas with its weight?

 

Haha I used to do that too. But in the end I got tired of going to the gas station so many times. People tell me it's bad for you to have less than half a tank but whenever I ask why, they have no answer.

 

less gas is better for weight, but more gas makes the oil pump run cooler, and i guess the momentum of the car makes it feel faster

 

more gas also gives you better fuel pressure...


I like to think so atleast but i could be wrong

 

i heard if you get in an accident with a half tank, your car has a much higher chance of turning into a ball of flames.

 

As far as seat of the pants, full tank feels better than close to fill-up for sure.

 

Yours, and also anybody else who says they think a heavier vehicle is more responsive **** dyno are in serious need of recalibration

You guys must get to grips with one basic truth in life :

NOTHING IS FOR FREE - it takes power to get weight to move - the more weight you have on a vehicle the more power you need to make it move - better power to weight ratio = better performance (in general)

 

I like the way you think ...

 

when you are low on gas, the sediment from the bottom of your tank will be sucked into the fuel system, better to keep above 1/4 or even 1/2 a tank.

 

 

This is an argument of whether the increase in fuel pressure from full tank of gas umm outweighs the increase in weight. Two questions need to be answered - Is there a fuel pressure increase with a full tank of gas? How much does half a tank of gas weigh?

 

More weight = slower car, period. They say that you want a 1/4 tank whenever you run at the track. I know that is what I aim for. If you live closer to the track you could probably get away with less.

There are filters to get rid of any sediments both at the pump and in the fuel line (Z32 if you are special).

Your fuel pressure will not drop unless you are running on empty (in the tank not by the gauge). However be more careful if you boost because I have seen maximas that loose fuel pressure when low on gas. I think it is either incorrect install or just that all of the gas is moving to the back of the tank. I think install is more likely but the rushing to the back of the tank probably doesn't help it. If you are not boosting, spraying, or just have a walbro for no reason don't worry unless your car is acting up when low on gas.

 

BTW each gallon of gas weighs 6 pounds. Our tank holds 18.7 gallons. 9.35 gallons of gas should weigh 65.1lbs. It is pretty significant.

 

ive always been confused about this general idea. why would it be bad for you to get below a 1/4 tank and let the fuel pump pick up sediment. doesnt the full pump take fuel from the bottom of the tank regardless? so whether you have a full tank, 1/2, or 1/4, its always taking the fuel from the bottom...

 

hhm never thought about it like that, but what kind of sediments would get in there?

 

rust, dust, pubic hair

 

The last one is just too funny.

 

This is not an argument at all - it a damn shame!

All of the gas in the world will not increase your fuel pressure if you would have been able to fit it into the Maxima's tank for one simple reason - you have a fuel pressure regulator that dictates only about 40psi reaches the injectors ....................... now excatly how did you see more fuel in the tank increasing fuel pressure and therefore performance - AT ALL?


Where the hell did you people get the basics of a engine and efficiency from?

 

You assume that you always get 40psi. I am sure that even a new car will not get the full 40psi, moreover a used one. So, why is it not possible that weight of the gasoline helps the gas pump send in more fuel (by more I mean more than with less than half the tank)? I just remembed that I read somewhere that the reason it is bad to drive with near empty tank because it makes the gas pump work harder and may lead to its premature failure. So I guess it makes sense that its easier for the pump to work with a full tank.

 

Because we are not using a gravity fed pipe but a extremely tightly controlled injection system.No I don't - I said "you have a fuel pressure regulator that dictates only about 40psi reaches the injectors" and the fuel pressure is modulated by engine load and speed between about 36 and 43 psi actually by means of the fuel pressure regulator................

Now ISO asking me to justify facts that we can continue to do ads-nausea, why don't you explain the mechanism you see involved by the increased fuel volume in the tank increasing performance and prove the whole of the Formula 1 circus don't know what they are doing when they say every 10Kgs of fuel they carry it costs them about 0.3 seconds per lap

 

The only way more gas might help performance is giving the rear tires more grip. But I don't see how more weight helps performance.

 

When the tank is really empty (below the pickup of the fuel pump) then yes you will loose fuel pressure. At this point performance is not your biggest concern; it is getting to the closest gas station. This situation is avoided most of the time anyway for fear of being stranded so this is by no means a leading cause of fuel pump failure unless the pump is failing anyway.

In a fuel return system, your fuel pressure is mainly dependent on two things, fuel pump and fuel pressure regulator (without an FMU). The fuel pump will try to send a constant stream of fuel to the rail. The FPR will restrict the return after the rail causing there to be a pressure build up on the fuel sending lines. With more pressure the fuel pump will actually flow less fuel. The injectors will push more fuel out with the increased pressure, but if the fuel pump can't flow enough fuel then all the pressure in the world won't do any good.

Gravity fed systems work fine for lawn mower and other 2 cycle engines but to maintain the pressure we have to have a complex fuel delivery system. The weight of the fuel in the tank has little if any effect on the fuel pressure. Nothing nearly close enough to give you power magically to overcome the additional weight.

Most Engines make the most power when they run slightly lean. This is part of how an ECU gives you power. However when boosted or running really high CR, etc. you want to be a little more conservative with the tuning since it can lead to engine damage at such high loads.

The Higher fuel pressure would actually make you run richer. This would actually make you have less power if the weight of the fuel increased fuel pressure to any extent.

If you are really that worried, get a fuel pressure gauge and watch it while you drive. It is your money and your car, not mine. Don't take my word for it; investigate this further. Prove all of us wrong.

If you feel that you are faster with a new tank of gas then you are just feeling it. There is absolutely nothing to support it. I used to have this feeling too but it is just your imagination tricking you.

 

but we have fwd cars, and I'm pretty sure they're talking about straight line performance

 

with more gas it takes longer for you to run out of gas....

 

I still swear that under 1/4 tank our cars lose power (or make less power on purpose) I got wasted by a first gen 5 spd altima one night, with almost no gas. I think mrgone has also experienced this lack of power. It could be in my head tho.....

 

is 5th gen alti the 3.5?
cause if so those would eat you no matter how much gas you have.

 

It only helps to have more gas in the winter because of a greater potential for increased moisture in the gas tank. That's why special winter additives are added for gas line anti-freeze, as well as some people dump methyl hydrate in their gas tanks to absorb water and avoid gas line problems in the winter.

 

he said 1st gen...................5 speed ALT.

not 5th gen.

 

WTF? makes the oil cooler run cooler? When does your fuel meet your oil pump?

Fuel is used to cool the the FUEL PUMP. When running it near E it decreases the life of the fuel pump.

 

my friend has a 1G altima 5 speed, those aren't that slow, it can stay with a stock auto max, the 1g altimas can run a 15.8-15.9 in the 1/4. they have a huge 2.4L 4 banger with loads of torque, i underestimated it at first until i drove it, it picks up very well.

 

Close but not quite, and before this leads to yet more crappy ideas, let me put this right:

The FP actually has quite a constant flow as long as the engine is running (electronics sensing the need to have the pump running continuously) and the FP pickup sits below the fuel level of the tank's contents - this happens because the FPR simply returns whatever fuel the FP tries to supply via the return if its in excess of whats required to maintain about 40psi on the fuel rails (or to prevent an argument - the actual load/speed modulated fuel pressure between 36 and 43 psi - VG in my case pre '01 ).

The FP is able to supply the required flow at way more than 40psi, and in normal operation also does supply fuel at way more than 40 psi to the FPR - its the FPR that does its job and keeps the fuel presure constant on the injector rails by bleeding of, via the return line, any un-needed fuel.

 

This information is only up to 01. With the VQ35, maximas convert to a returnless system which works a little different. On a return setup the FPR is on the return side, after the rail and injectors.

http://forums.maxima.org/showthread....fmu+fpr+filter
Just take out the FMU part unless you have one.

According to my understanding which could be wrong, the fuel pump if creates no pressure on its own. What the FPR does is restrict the return line somewhat and create pressure. If boost or some change in vacuum is sensed then the FPR will bleed off less and creates more pressure.

 

Ok - cheers for the info - have not played around with those nice toys myself. The "more fuel in the tank increase performance" doesnt hold for those setups either.

I have updated my last post to reflect your info.

PS: The FP is a strange "chicken and egg" situation - you cannot create flow whithout a pressure differential (aka FP) but you can have a pressure differential whithout a flow

 

the only way a full tank could supply more pressure is if it was above the fuel rail, which it is not, therefore a moot point.

 

WTF?
overheating fuel pump?
sediments in your tank?
higher pressure when the tank is full?


and let me guess.. you guys still think a CAI works by sucking cooler because its closer to the ground instead of 2ft in the air where the factory intake is...


How many of you guys have opened up your fuel tank and looked inside?
I've replaced probably a dozen in-tank pumps in the last few years and NONE of them had anything but fuel in them. the sock filter on the pump was kinda grey, but that's all I've seen on cars with 200,000+ miles on them. Sediment in gas tanks was an issue back in the 60s and 70s when they had horrible filtration systems on the in-ground pumps at the gas station. now the fuel you get is MUCH MUCH cleaner..

overheating fuel pump? Bah. not unless you run the tank so low that you're sucking fumes in through it. and you'll definitely know when you're doing that.
put a gauge on your fuel line and drive around until your tank is almost completely empty, and watch the fuel pressure. that thing is rock-steady at around 40psi until the pump starts sucking vapor, then the pressure will fluctuate and finally drop when there's no more liquid fuel in the tank. that said, the pump doesn't create that much heat, and the only way it could overheat is from running with no fuel in it at high load for a long time.. i.e. run the tank almost empty while you have your pressure at 80psi.

just another FYI... your fuel pump runs about 1gpm.. (180 lph = 3lpm = 3/4 gallon per minute)... your engine uses MAYBE 1/4 of that. think about how long it takes you to use a gallon of gas, even under the harshest conditions... at the road course, my car gets about 7mpg.. at average of 85mph on the track (2:04 lap times on a 2.9 mile track= 84.Xmph average. top speed of about 135, low of about 45), that comes out to 5.25 minutes per gallon of fuel, or 0.19gallons per minute. Keep in mind, the pedal is floored the entire time except for the few seconds at the end of each straight when I'm braking.
little things aside, I'm running a walbro 255lph pump, which is almost exactly 1 gal per minute of flow to the engine. that means that 80% of the fuel flowing up to the engine doesn't even get used and is pumped back into the tank.

unless you're sucking vapors, then your fuel pressure is going to be rock steady and the pump will not overheat.

 

This is one of the dumbest threads I have ever read

 

With the fuel pump in the tank the fuel then acts as a cooling agent for the pump. As long as the pump stays submerged it won't run the risk of burning itself out.

 

Clean your Throttle Body.....

 

I made 135 runs at the track last year.

How much gas do I run in my tank? 1/8-1/4

Does it make a difference in fuel pressure? No

Is Ben correct? Yes

I do take a 5 gal can with me though just in case, nothing like making the finals and seeing the gauge on empty.

 

Was it the same engine that was in the 240sx?