Fuel Pressure issue - the story so far

General General Lotus Talk
1

As regular viewers may recall I had a fuel pressure issue. Basically Dave Walker raised my fuel pressure to 4 bar as he was having to run the injectors flat out at high RPM with the standard fuel pressure.

The problem wasn’t picked up until later when I fitted a fuel pressure gauge. As the revs rose over 6,500 rpm the fuel pressure started to drop off in a linear way reaching a low of 3.3 bar at 8,000 rpm

The map was correct as the extra .3 bar at 8k was enough to make the injectors safe.

But I don’t like stuff only just working, so I thought I would uprate the pump. A call to Demon Tweeks had an Elise Motorsport pump from Walbro on its way (�100). However that is where the fun and games started.

The standard fuel pump in our cars sits inside a swirl pot inside the tank. The pump has two inputs, one sucks from inside the swirl pot, the other from outside the swirl pot. The fuel return from the engine returns the fuel to the swirl pot.

The Mortsport Elise pump that I received only had one input and it was a different shape and size and everything. So when fitting a lot of modification to the standard swirl pot / fuel level sender assembly had to be made and I knew that what I was doing wasn’t going to be the final solution . The main reason for this being that as I only had one input to the pump I had to take fuel from outside the swirl pot (as under full load the swirl pot would empty) the problem with this is fuel surge, as when I took left hand bends at speed all the fuel moves away from the pump and cough and splutter city ensues.

The pump however is awesome, the pressure is now 4 Bar all the way to the rev limiter and it is also quieter than the standard pump.

My next plan is to install an external swirl pot. The in tank pump, will feed the swirl pot and then another pump will feed the engine from the swirl pot. The return from the engine will return to the swirl pot and the return to the tank will run from the top of the swirl pot.

I have drawn up an aprox 1 litre design as I reckon that will be more than enough to keep the fuel flowing even through the longest left handers!!

I’ll take a few pics and stuff when it is all installed.

Fingers crossed it will all be done for Croft. Otherwise it wil just be a case of keeping the tank full. I had to do this at Bruntingthorpe at the weekend and it wasn’t that much of a pain in the neck.

Sean…

2

Sean,

I know you’re not shy when it come to abusing the funds… But would an inline pump been just as effective?

3

Sean,

I know you’re not shy when it come to abusing the funds… But would an inline pump been just as effective?

The easiest way is to do what I do on the Audi’s. Use the existing in tank pump to fill a swirl pot so it’s pumping against a very low pressure. Then use an auxiliary pump to supply pressure to the injectors. Works great.

I might do a kit if there is enough interest.

Bernard

4

Bernard I thought you were just using an inline pump and not bothering with a swirl pot?

Here’s my setup

[image]http://i2.photobucket.com/albums/y28/iwilson/Yettobesorted004smallLabelled.jpg[/image]

5

Bernard, i’m interested if u plan to provide a kit.

6

Yes that is what I am going to do. The in tank pump will simply supply the swirl pot. I will then have an inline pump to get the fuel from the swirl pit to the engine.

Sean…

7

Bernard I thought you were just using an inline pump and not bothering with a swirl pot?

You are partly right Ian. I used to have an inline pump that just boosted the pressure from the intank pump. This is the method that Turbo Technics use on the supercharged cars. What I should really have said is “The easiest way is to do what I do now on the Audi’s”.

On the latest car I’ve added a swirl pot, not because of fuel delivery problems with the previous set up, but because when the fuel tank gets low the inline pump sometimes makes an annoying whirring noise at tickover. Never could find out why.

Bernard

8

OK, for those that are interested I have finished installing my new fuel pump and swirl pot and stuff.

The guys at Pro Alloy made the swirl pot to my design. It has a capacity of about 1 litre

[image]http://img.photobucket.com/albums/0903/SeanBicknell/Swirlpot.jpg[/image]

Here it is all installed. I used some fittings I had knocking around and the pump is an uprated RS500 cosworth pump I had in the workshop.

[image]http://img.photobucket.com/albums/0903/SeanBicknell/Fuelsystem4.jpg[/image]

[image]http://img.photobucket.com/albums/0903/SeanBicknell/Fuelsystem3.jpg[/image]

The pump and swirl pot are mounted on rubber bobbins to cut down on vibration and noise transfer and stuff

I didn’t have a relay, so I just have to do the wiring tomorrow night. Did wire it up temporary though to check it all worked with no leaks.

A few pics with the airbox in place, nothing gets in the way of anything else, and Iam pretty chuffed with how it turned out.

[image]http://img.photobucket.com/albums/0903/SeanBicknell/Fuelsystemwithairbox3.jpg[/image]

[image]http://img.photobucket.com/albums/0903/SeanBicknell/Fuelsyetemwithairbox.jpg[/image]

Sean…

9

Looks good - you really had all those fittings knocking around?

10

Pretty big airbox for such small trumpets.
What kind of throttle bodies have you got?

11

Yeah they were all of the fuel system I had in my Escort Cosworth. That had four fuel pumps and a whole host of giggery pokery bits and bobs.

Uldis, the trumpet length is actually quite long as there are sapcer blocks on the end of the Jenvey’s before the backing plate for the airbox. I do have some longer staggered length ones on order to have a mess about with. You have to admit though, the air box looks BLING!!!

Sean…

12

Looks good Sean, the only thing I would change on mine if I did it again would be to use a pot with only 3 inlet/outlets. This would get rid of the fuel returning from the regulator which would be warmer than the fuel in the tank. I would just tee the regulator return into the return from the swirl pot. A little bit anal I suppose but every bit counts.

13

The return from the fuel rail to the swirl pot is vital in my opinion to keep the swirl pot full at all times. If you had the return from the fuel rail simply going back to the tank, you are relying on the lift pump in the tank to be able to pump more fuel into the swirl pot than the second pump can pump out. I agree that in most cases the lift pump as it is under no pressure will be up to the job, but if you have a half juicy second (pressure) pump, I reckon you could end up with a dry swirl pot in certain scenarios.

I have looked into fuel temperatures though and I agree the cooler the fuel the better. I was present when a V8 race engine was being dyno’d and to keep the EGT’s the same the fueling had to be increased progressivly on each cylinder to a point where cylinder 8 needed 10% more injector open time than cylinder 1 to keep the fueling right and this was due to the fuel heating up along the rail.

Our Cosworth installs feed the fuel to the centre of the rail and then drain it from each end in order to try and combat this problem.

I have stuck a heat strip on the swirl pot to see what temps I see in the fuel, so I will let you know how I get on.

And as a Post track day report, the fueling is now spot on, it holds 4 bar right to the rev limiter even when under hard cornering / braking etc, so another problem solved.

14

Sean

How do you get 4 bar in the first place ? did you replace the regulator ?

15

Yeah I changed the fuel pressure reg, for an adjustable one.

Sean…