Project Professional Awesome Time Attack Evo: Part 3 - Fuel System

by Daniel O'Donnell

At Professional Awesome Racing, we take pride in thinking through problems and coming up with solutions that are as efficient and reliable as possible, all while fitting into a modest budget. We try not to do things that other people do just because “it’s always been done that way.” As you can read in our previous articles, this has lead to unique designs with our chassis/roll cage and powerplant. We like to think this same mentality translates into our fuel and computer systems and that’s the topic we’ll dive into today. So enjoy reading while sitting on your favorite throne or perhaps fire up MotoIQ at work with a finger quick to pop up a spreadsheet if the boss walks by.

So time attackers usually choose one of two routes for the first stop in our fuel system talk, the fuel tank. One is to keep it stock. The advantages here are simplicity; no need to run new lines and build mounts, better polar moment of inertia; generally stock tanks are mounted within the wheelbase, and cost; free is always nice when building a racecar. Disadvantages are generally heavier weight, potential limitations on fuel pump installs and limited fuel line sizing. The other option is to go with a fuel cell, generally mounted in the trunk, but this costs money and while it can help with weight distribution, it does it in a way that we don’t like. We like centralizing mass, not increasing torque levers.


So taking a current picture of our half gas tank that's now hidden by a flat bottom was next to impossible. Luckily for you I found this photo following one of our first Buttonwillow Super Lap Battle events. Unluckily for you, it's covered in Southern California's finest desert dirt and isn't pleasent to look at, but you get the picture. You'll notice we cut the tank a little past the halfway point, towards the driver's side and then took a flat plate of steel, cut it out to match the open area of the tank and welded into place.

What did we do then? We cut the stock fuel tank in half. This solves a few problems. It cuts the weight down of the stock fuel tank and we don’t need to carry around the extra 5 gallons of gas required to keep the fuel from starving under left hand turns. It also freed up a healthy amount of room for a Radium surge tank, which solved the fuel cut issues we previously had with a full sized tank.


Here's our Radium Multi-Pump Fuel Surge Tank. We have it installed where the rear seat was on the passenger side. We placed the tank in the existing opening used for access to the OEM fuel tank as a way to sink the surge tank further down to lower CG. Our goal was to keep everything as close to the center point of the car and as low as possible. The main fuel tank on the driver's side fills the surge tank and any overflow is directed back to the main tank.

Now our Radium surge tank is their “Multi-Pump Fuel Surge Tank.” This particular tank is shorter, but larger than their more familiar, standard fuel surge tanks. The baller feature of this design is the ability to squeeze 3 fuel pumps internally into one tank, simplifying installation for multi pump systems. Machined from 6061 aluminum, fully sealed and with the ability to be pressurized, it met our needs perfectly.


Zeitronix's Ethanol Content Analyzer is mounted in our center console so the driver, me, can make sure the content is in a safe range. Ethanol content and fuel temperature is relayed to the AEM Infinity ECU which will vary injector pulse width, boost pressures, timing maps and more depending on content percentage.

I should inform the readers that are not in the know, that we are from Indiana. Because of this we use E85 straight from the gas station that’s about 1 mile down the road from the shop. Being in a state that is covered in corn means that in our modest town, I can think of 5 stations off the top of my head that sell E85 and they all seem to know how to blend precisely. God bless America! We do keep close tabs on our ethanol content and fuel temperature with Zeitronix’s E85 Analyzer. This little tool integrates perfectly with our AEM Infinity ECU, which has a flex fuel feature, and has proven to be an engine saver when traveling to places with unknown blending abilities.

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Thursday, June 18, 2015 7:21 AM
This FPR has a rising rate 1:1 ratio, meaning it will add or remove 1psi of fuel pressure for 1psi of air pressure.

What could be used here is a rising rate FPR with a different ratio. This would still allow for a low fuel pressure at idle / low load, with an increased fuel pressure at higher load. a 4:1 rising rate FPR would actually add 4psi fuel pressure for every psi of air pressure.

The ECU would need a fuel remap, but this would allow for more pressure on boost without problems off boost.
Thursday, June 18, 2015 7:34 AM
Seems like a can of worms to me. That was the way to go when the general populace believed a proper tune was the devil. I get why you bring it up, but it'd require massive fudging on the VE and spark tables, and if those tables are used to calculate anything else you'd end up chasing your tail on a lot of stuff. How much headroom do the current injectors have? It seems like a lot of people like to go too big on injectors so they have headroom for future mods, but never take into account what's been brought up here right now.
Thursday, June 18, 2015 7:38 AM
How does a rising rate FPR work under vacuum? Since the AEM Infinity constantly monitors fuel pressure, it may compensate accordingly with very little change to the volumetric efficiency table as long as the injector flow vs pressure accurately matches the table in the ECU.
Thursday, June 18, 2015 8:09 PM
"Well my special little friend,..."

I'm sincerely touched you thought of me and the fact I'd have exactly this question. Now off to enjoy my bologna sandwich!
Friday, June 19, 2015 6:13 AM
I please to aim!
Tuesday, June 23, 2015 4:42 PM
The AEM Infinity ECU should be able to compensate for a FPR that is non-linear in the way it increases pressures. Reason being the ECU has a table for flow rate vs. pressure, and with that information it will know how much pulse width is required so long as it can reference running Fuel Pressure.
Wednesday, June 24, 2015 8:02 AM
Does the AEM use a decent amount of signal filtering when using the fuel pressure for IPW compensation?

Love the half fuel cell approach and have considered doing the same on my own VIII.
Wednesday, June 24, 2015 10:11 AM
Not sure what you mean by signal filtering, but if you're referring to the fact that there are miniscule fluctuations in fuel pressure and thus reference voltage, then my answer would be no. I looked through the AEM Infinity software and could not find anything for that. My guess is you probably don't need any filtering on it being that fuel pressure will fluctuate in conjunction with manifold pressure, making everything balance out, so to speak.
Thursday, June 25, 2015 7:51 AM
Signal filtering -> or signal averaging if you prefer

The fuel pressure can actually change very significantly (for a very short period of time) in the rail with each injector opening/closing event, that's why OEMs use fuel pulse dampers. Depending on when the ECU samples the pressure sensor relative to the injector events, the ECU can see fairly high variability in the signal level. If you directly use that level without any averaging to compensate fuel pulse width it will cause variability in your actual AFR. A quick fix would be a software filter (FIR for example).

In practice though, with how you have the sensor out on the regulator and likely a flexible line between the regulator and rail that is smaller diameter than the flow area of the rail, you probably have some damping built into the mechanical side of the system which should greatly reduce the pulses.
Thursday, June 25, 2015 8:06 AM
Radium makes a fuel pulse damper https://www.radiumauto.com/Fuel-Pulse-Damper-In-line-Kits-P751.aspx

Would this alleviate some concerns on your end?
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