The Vortech Fuel Management Unit

There's a bunch of ways of adding more fuel when you've fitted a turbo or supercharger to a previously naturally aspirated engine. You can go for bigger injectors or extra injectors. You can run higher fuel pressure all the time and or you can run higher fuel pressure just when on boost. Some ways are technically better than others, but some could also cost you a helluva lot more cash.

For this story we talked to Matthew Spry of ChipTorque about using a Vortech Fuel Management Unit, a rising-rate fuel pressure regulator. It's used in conjunction with the standard fuel pressure regulator which continues to regulate fuel pressure when off-boost. But come onto boost and the new reg effectively takes over, upping the fuel pressure considerably and so squeezing more through the same size injectors. It's a relatively cheap approach and as he makes clear, works well when you want to retain factory off-boost driveability and emissions.

"Any normal automotive fuel pressure regulator rises one pound of fuel pressure when one pound of boost pressure is applied on top of the regulator," he said.

"But when your injectors aren't big enough to flow enough fuel for the horsepower that you want - usually in supercharged applications - the use of a rising rate regulator is a valid upgrade without having to totally upgrade the whole engine fuel system.

"They're mostly used on V8s that have a bolt-on supercharger - a Vortech or a Powerdyne.

"The nice thing is that they keep the standard fuelling on the standard regulator until you actually come into boost pressure. They're available in 4:1, 6:1, 8:1, 10:1 or 12:1. What those numbers relate to is the amount of boost pressure that you put on top of the regulator to the amount of fuel pressure that you get."

So the 4:1 ratio regulator will increase fuel pressure by 4 psi for each 1 psi of boost. However it's important to realise that they only do this when they see boost - at lower manifold pressures, the factory reg keeps right on doing its normal job.

"I can't really see the 4:1 rising rate regulator making a difference unless it's on a centrepoint injection system which runs low pressures like a 15 psi base," Matthew said.

"Mostly we put 8:1 and 10:1 regulators on. At 12:1 you're getting too much fuel pressure and you're going to get to the point where your injectors simply won't open.

"You also need to keep in mind fuel pump performance because as you rise in fuel pressure, you get lower pump flow - it's a juggle."

Matthew said that once one of these regulators has been fitted, the fuel pump will need to be upgraded.

"Usually you need a Bosch Motorsport 600hp or 700hp pump. If you do the sums, at 10 or 12:1 rising rate on 10 pounds of boost pressure you've got 100-120 pounds of [additional] fuel pressure. Your pump has got to be good - and you want to make sure that your hoses are right, too.

"The hardest part of the whole job is picking the 8, the 10 or the 12. For that you've got to know the boost pressure, know the pump that you've got there, to know where your customer's going in the future."

With this particular design there's no way of mechanically adjusting the shape of the on-boost fuel curve that you get. Vortech do make an adjustable rising rate reg (the "Super Fuel Management Unit") however Matthew Spry is not in favour of this approach. He believes that such a design would be more prone to in-service problems and also suggests that having it so easily user-adjustable is not always a good idea.

"A customer's mate could get under there and say 'Oh, I'll have a play with this'," he says of the adjustable design.

ChipTorque fine-tune the on-boost air/fuel mixtures by modifying the factory ECU software - in their opinion, the rising rate fuel pressure regulator should not be regarded as a standalone device. Matthew said while some people did see the device as an overall fix, he didn't think it should be used without further engine management modifications.

"There's no way of retarding timing - apart from globally retarding timing - and so you should be doing something with the management anyway," he said of engines that have been adapted to forced aspiration.

Rather than anything else, Matthew said he thought the rising fuel pressure regulator was a way of getting around the need for larger injectors.

"You're probably saving yourself AUD$700 over the injectors," he said. "But you're also saving yourself a lot of time in remapping the whole aspirated side of the ECU to suit the larger injectors. If it's a standard engine that you're putting a supercharger or turbocharger on, as you go into boost you need more fuel - but the rest of the fuel demands stay the same."

Matthew said that some other rising rate regulators were used as standalone regulators, rather than being used as a secondary reg. Additionally, their rate was as low as 2:1.

"With those regulators you have to usually raise the base fuel pressure to 60 psi, which means that the fuel system is under strain all of the time. An advantage of the Vortech regulator is that the main pump doesn't have to work its butt off the whole time - most of the time when you're driving, it's under normal pressures."

However Matthew said that he wouldn't recommend the Vortech rising rate fuel pressure reg approach on a circuit racing car which would be under high loads (and so high fuel pressure) a lot of the time.

"In that case I'd put big enough injectors in it," he said.

And what about cost? From ChipTorque the Vortech Fuel Management Unit costs AUD$329, while fitting is another $85. Tuning of the management on the dyno - which includes ignition timing changes as well as fuel trimming - typically costs about $1250.

http://www.vortechsuperchargers.com/tech/fmu_sfmu.html

www.chiptorque.com.au

How Much Extra Fuel? So for a given increase in fuel pressure how much extra fuel will flow? We've done an article on just this topic, measuring the variation in fuel flow at different pressures for three different injectors. Go to "Boosting Injector Flow" to see the complete article.

But Bigger Already? Another common use of the Vortech reg is when people are chasing more power out of a kit that they have fitted. Many supercharger kits come with large injectors, meaning that sufficient fuel supply is available without the need for the rising rate regulator. However if the kit is tweaked to make a bit more power than normal - eg by changing the size of the blower pulley - then rather than buy (another!) lot of new injectors, the rising rate fuel pressure reg can be fitted.

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