So I'm still confused about one thing though; HOW DOES IT WORK? I mean I know what it does; it ensures that the fuel pump has constant fuel supply under high g loads to prevent starvation, this I understand. But HOW does it work? I have never used one of these and as a result I don't know much about them. Any info would be appreciated, thanks.

 

Two points: Cannot expect to get something for nothing. And since this system envolves fuel distribution, I want to be assured that it is safe under all driving conditions; do not like things that go "boom" in the dark!

Later, Ken

 

Here's how the VIII/IX systems work:
they keep a small "tank" of fuel with a fuel pump. If there's no fuel coming from the tank pump, then send the fuel from their tank until it runs dry or the fuel comes back from the tank pump.

In M3's the common mod is to add another fuel pump to the other side and "T" the inputs and outputs. Not sure if this is something that could be done on the X.

 

There are two kinds of surge or swirl fuel pots: internal and external. The latter consists of a bucket sitting on the floor of the OEM tank. The feed for the fuel pump is taken from the base of small bucket aka swirl pot with the smaller dimensions of the bucket preventing the fuel from sloshing away from the pickup. The fuel return from the injector rail is delivered to the bucket/swirl pot while its open top and holes in the base of the pot allow fuel to enter from the tank at large. External swirl pots consist of a closed small reservoir tank exterior to the main tank. A low pressure fuel pump delivers fuel to the reservoir tank from the OEM tank. The high pressure EFI pump draws from this reservoir to supply fuel to the engine. Even if the low pressure pump momentarily starves, the secondary reservoir pump will keep on supplying fuel to the engine w/o any fuel delivery problems even in hard cornering.

Later, Ken

 

I'm not an expert or anything. But I was at 2 pretty intense long track days in which i took the car down from full to 1/4 tank or less. I never ever had any problems resembling this.

Car is still bone stock though, and as mentioned I'm not a pro by any means. But if your like me, which I'm gonna guess alot of you are, then I really don't think that you will need this.

 

our system works as such

The factory pump feeds a small secondary tank that typically holds about a gallon of fuel. From there a secondary pump (walbro) feeds it into the fuel stream and to the rail.

The point of the tank is to minimize sloshing and thus starving the pump of fuel. With a tall narrow tank fuel really has nowhere to slosh to. So even if the stock in tank pump has moments where it is not supplying fuel the surge tank will have enough in the tank to make it through regardless. We have run our car on the track with the gas light on and not had a problem with our surge tank system.

Eric

 

Very well put. Ours is the latter or an external system

 

Ah, makes sense, thanks. So the in tank pump is just T'd to the surge tank for supply, and then another is used to pump from the reserve to the fuel rail. Do both the in tank pump and the surge pump constantly flow to the injectors at all times, or does the surge tank pump only kick in when the in tank pump is starved? If so, how would it know? Also, since the reserve tank holds about a gallon of fuel, I guess now the X can go a bit further on long trips without running out of fuel? Although, would running on "E" force the secondary pump to run full time while the in tank pump is starved? Couldn't this cause it to burn out? Not that it really matters anyway; there'd be no reason to run the car past the "E" point. I just like knowing how exactly stuff works. Thanks.

 

Murphy and his law are a live and well in my universe

 

The address your last question first, don't run the fuel down to a point where starvation is an issue.
Now to your first question: There are two basic design options for the fuel returning from the fuel rail-Go directly to the swirl/surge tank OR Go back to the OEM tank.
For the former you do not have to worry about the flow capacity of the low pressure fuel pump feeding the swirl tank. However, there is one major problem with this design. Depending upon the speed of the EFI pump and fuel usage you are recirculating fuel over and over again back into the swirl pot. So what, you ask? By so doing, especially at low fuel usage (cruizing), the recirculated fuel is getting hot (because it has just returned from engine locals that are hot, very hot)especially in the surge fuel tank. This is not good for as we all know the hotter the fuel, the greater potential for detonation. So the other surge pot design (latter) reduces this heating potential by sending the fuel back to the larger OEM tank where it is mixed in with a larger reservoir of cooler (and being cooled) fuel. If one does go with the first design i.e., fuel return directly to swirl tank then I have read that this tank must be at least 2 litres in volume with temperature monitoring during dyno and/or track events. If significant temperature elevation occurs, then a heat exchanger should be installed in the fuel line to cool the fuel. Since this will be on the outside of the vehicle, protective measures need to also be installed to ensure road debris will not be a factor compromising fuel delivery or more importantly your a$$ under aggressive driving conditions vis., the track or off road.
Sorry this went on for soo long but you asked.

Later, Ken
AMS Intake & Exhaust
Iveytune (322 all around)
Robispec K&W

 

Well, I am glad you did not have any intermittant loss of fuel. However, this could have occurred with others, as above, because of either the track having more turns, sharper turns or differences in driver's aggressiveness into each turn or combinations of each of these. Bottom line: Most if not all track cars use fuel surge tanks to prevent fuel interruption especially in those cars with forced induction engines which can result, if not accounted for, catastrophic engine failure. Not trying to hype this out of proportion but there is a big difference in fuel distribution in drag racing and street driving relative to track driving and appropriate adjusts need to be made.

Later, Ken

AMS Intake and Exhaust
Iveytune (322 alla round)
Robispec K&W

 

delete

 

There are no high speed left turns at SOWS. The highest speed one would be the gentle one right before the bowl but even that isn't tight enough. The problem is notable in high speed left turns only and not right turns.

 

Well... I'm now gonna eat my words.
I ran the SOW CCW yesterday, and coming down the hill into the kink (T1 in the other direction) with slightly less than a half tank, BOOM! The fuggin thing started cutting out. What's weird is, while I'm tapped in 4th gear at that point, the car's not leaning a whole lot (thanx to being Muellerized), and it's certainly not the spot on the track with the highest G loads. Filled the tank, and no more problems.
I came back into this thread, as I ran a search on a fix for it. I just hope it's not (as speculated) $700. For that, I'll need to just deal with the problem, and keep the tank more than 1/2 full if I'm on a track that causes it.

 

Well, this surge tank looks to be a good upgrade for those of us who want to track the X. Hopefully mitsu will fix this on later models, but likely not. AMS, any updates?