Fuel system with Swirlpot

It was not long ago I uprated my fuel pump and since then I only used my car once. But I never felt satisfied with the new system. I feared the fuel surge while cornering problem would be even worse than before, so I decided to do it properly with a swirl pot and a low pressure pump.

Pumps

The fuel demands for a 280 hp NA engine is according to the book Four-stroke performance tuning: power * k = 280 * 6 = 1680 cc/min = 100.8 liters/hr including 30% oversupply.

The pumps and filter is located under the trunk.
A pity to hide those expensive AN-fittings?

According to Cosworth their 280 hp crate engine should have fuel in excess of 1.4 l/min = 84 liters/hr.

I want to be able to run E85 in the future if I decide. That is another 30% = 131.0 l/hr. And as before, I don't want the pistons to melt if the alternator fails and the supply voltage drops a volt or two.

The low pressure pump doesn't need quite as much flow as the high pressure pump as it always have the swirl pot as a buffer. The Facet Posi-flow pump can deliver 32 gal/hr = 121 l/hr which will be enough. It turned out that the Facet fuel pump is extremely noisy! I don't think I can stand it and I probably need to find a more quiet one.

Generally it is not a good idea to just fit the biggest pump you can find because all that fuel flowing back and forth will increase the fuel temperature. High temperature could mean detonation problems or less power. As the stock CSR fuel system is a non-return type with the regulator in the back, that might not be a big problem as the fuel never goes that far. Also, the fuel tank is cooled by the wind. But anyway.

A one litre swirl pot in the trunk compartment. 

The classic Bosch 044 pump is too much with >250 l/hr @4 bar and 13.8V. It also uses a lot of power and is very expensive, at least the originals.

Biltema 52-203 pump flows a bit less with about 156-174 l/hr @4 bar and 13.2V (source). It is also very cheap and quiet!

Hoses and fittings

Rubber hoses tend to leak a few fuel molecules now and then. Teflon hoses doesn't. Instead they have the problem with build up of static electricity and small sparks can jump through the hose to the mantel and cause small holes in the hose and even cause a fire. To solve that problem some manufacturers have added a bit of carbon to the hose, allowing the electricity to flow and avoid this problem. The cheaper hoses (including Torques' hoses) doesn't have any carbon in them. Some say that the fuel flow in a car's fuel line is too small to cause any problems. I don't have enough knowledge to trust that statement, so I went the safe path and bought more ordinary nylon braided rubber hoses. If someone would like to calculate on this, I found a good source of information including formulas and samples.

I bought all AN6 hoses and fittings from Torques.

One challenge was to connect the system to the already mounted hard fuel line that goes through the car all the way to the engine. The fuel line's thread is 16x1.5mm. I couldn't find an AN-6 adapter that fit, so I used the existing fuel filter adapter and a Saginaw AN-6 adapter from Earls part number 9894DBJ.

The end result.

Doing the plumbing was much harder than I thought it would be. It was like a puzzle to get the pieces to fit in a small space without occupying the whole trunk. The braided hoses are very rigid and did not make it easier. I also realized I should have ordered more 90-deg fittings and less straight ones, but too late for that now. Also, holding things in place with zip ties is probably not considered the best engineering but will do for now.


Allright, I haven't tested this properly yet, but at least there is fuel flowing to the engine :-)

Fuel filter

MANN WK612/2 or MAHLE KL158. Available in your local car parts store.

Must be one of the parts on this car that is hardest to remove, and even harder to get back due to the tight location.

Take care not to get fuel in your eyes when releasing the pressure. (Don't ask..)

Uprated fuel pump

In my search for a more robust fuel system the time has come to the fuel pump.

According to Cosworth a 280hk Duratec engine need 1.4L/min regulated to 4.3 bar. That equals 84 L/Hr.

Inside the white container there was a Walbro ERJ 197 fuel pump. The spec sheet says @3 Bar: 108 L/Hr, @5 Bar: 54 L/Hr and is obviously very marginal.

I bought a Walbro 255 LPH from eBay. At 12V and 4.3 bar it can deliver about 180 L/Hr. That is plenty of fuel. In fact, I could run two engines with that pump. If I in the future would decide to run my engine on E85 I could do that too without problems. At least not with the pump.

On the existing pump mount, the big plastic container works as a small swirl pot. The fuel from the return hose goes back into the container and fills it up as a buffer. On the bottom is a one way valve. Instead of sucking air while cornering the pump still can get fuel from the buffer. Since I've always had problems with fuel surge in long corners it apparently doesn't work that well.

First I tried to make the new pump fit inside the existing plastic container, but as the pump ends are different I couldn't make it fit very well. It worked, but when in a low fuel scenario it would pump air and the pressure would be lost. I verified it by pumping water in a bucket.

Then I modified the existing holder. I straightened one of the tubes. Used an old saw blade and stainless hose clips to hold it together. The old fuel level sensor was wired in place using steel wire. The saw blade acts as a spring and hopefully will keep the pump from moving around too much. The car's tank is v-shaped so it won't move much anyway.

Fuel surge might still be a problem. Maybe even more now without the plastic "swirl pot". I intend to try to put some "Easy Pour Fuel Tank Baffle" in the bottom of the tank to avoid the fuel move around too much. A problem will be the balls obstructing the fuel level sensor, so I can't put in too much of it.

Maybe I should have done it properly with a swirl pot instead.

Now I probably need to remap the engine without the old pump's pressure drop.

Finally some driving!!

A "test drive a Radical SR3" event at Mantorp. I was also invited but drove my own car.

The engine runs great! The car handles great! Even the weather was great! My driving - not so great, but who cares? Well not that bad, today's best was 1:22.3. Compared with my all time best 1:21.8 it is all right considering I had no "rabbit" in front of me and I was feeling a bit rusty. The Radicals didn't stand a chance with those inexperienced drivers.

But of course...

Fuel surge and alternator problems!!

This spring when my engine broke, it was because of the small wire from the alternator went loose and it stopped charging the battery. The fuel pump couldn't keep up with the lower voltage and the engine run lean. Things got hot inside the cylinders and the engine got damaged.

Today the alternator broke completely.

The same symptoms - no power on the long straight. But this time I knew, and backed off the throttle immediately. Also the no-charge light on the dash was lit this time.

I also experienced fuel surge in the long right hander "Parisern" when the fuel level was below half. I always had that problem, even with the stock CSR200 engine. Today it annoyed me more than ever before.

I need a more robust fuel system! I can't risk loosing my engine because the alternator fails, or if a connector jumps loose.

Anyway I got five or so laps on film. Here are a couple of them. I'm not very satisfied with my driving here, as soon as I try to push hard I get sloppy and miss the apexes.

Fuel injector voltage compensation

I've noticed that the engine sound changes when the cooling fan kicks in. Not a big deal, I thought, but now I understand it is something worth a bit of attention.

Injector "dead time" is the time between pulse and fuel is delivered. What makes it a little bit complicated is that the dead time is not only voltage dependent but also fuel pressure dependent.

When the fan kicks in, or the headlights are lit, the battery voltage is dropped. The ECU have a voltage compensation map that add some time to the fuel map. If that map isn't correct the engine rpm may drop, causing the alternator to generate less current, even less fuel, and the engine could eventually stall. If we use closed loop lambda control the ECU would stable the engine within a second, but what would be written to the long term fuel map?

In my case the compensation map set up was not correct for my injectors.

The easiest way to measure injector dead time is to have the engine running and measure the lambda. Then remove the alternator control cable to drop the voltage about 2v, and see if the lambda changes. Adjust the map until the lambda reading is as before the alternator was disabled.

A more accurate way is to start the engine, remove the battery and connect a variable voltage source, and then disable the alternator and measure lambda at different voltage levels and adjust the map accordingly.

Or, you could do as I did and Google the injector's specs.

Bosch "Green giant" injectors at 4 bar, MBE 9A4:

It worked.

Inertial switch

Who said highway driving isn't exciting?

Fortunately it was only the inertial switch that cut off the fuel pump. Never happened before and took a while to figure out standing roadside with oncoming darkness and decreasing battery power.

A press on the top and I was back on the road.

Inertial switch