Fuel Delivery for 600hp using an FMU
Fuel Delivery Introduction Fuel Delivery for 780 hp Fuel Delivery for 1000hp
I don't claim that my original fuel system design is the best or cheapest way to keep 600 or more horsepower fed and happy. One of the rules I was playing by, namely that you can't cheaply reprogram the GM PCM (the engine control computer) to control large injectors, no longer applies. Reasonably priced software is now available that enables twiddling injector parameters in the PCM, which will in turn enable the use of high flow injectors (50 lb/hr, or bigger) in a daily driver that can still chug happily in rush hour traffic.
My original design was intended to support very high fuel pressures generated by a Vortech FMU (Fuel Management Unit) in response to supercharger boost. I chose the high fuel pressure route so I could support 600 hp with easy-to-live-with 30lb/hr injectors. This requirement drove my original selection of the SX 18201 fuel pump. Rob Scharfenberg at Essex told me that their pump was optimized for high pressure (up to 90 psi), while competing pumps sacrificed high pressure performance for maximum flow at more typical pressures (40-50 psi). The flow vs. pressure graph they provide certainly bears that claim out.
The charts below compare the Vortech T-Rex, which is made for Vortech by Walbro (left), the Granatelli #8001688 and Kamekazi (center), and SX 18201 (right). If you blow up each of these curves by clicking on them, then note the flow at 80 psi, you'll see that the SX provides the highest flow at that pressure.
With the pump selected, the next hurdle was to put together a delivery system that would not cause excessive pressure drop from the pump to the fuel rail at high flow volume. Rob at Essex cautioned me that the 18201 needs to have a large ID gravity feed to prevent cavitation at the pump inlet. So I had Craig Hill at Top of the Hill Race Cars in Pleasanton, CA, weld in a bung and 5/8" thin wall steel pickup tube into the tank The tube locates the pickup point in the bottom center of the plastic baffle GM puts in the tank.
The bung is connected to an SX filter by -10 teflon-lined AN hose. The filter contains a 60 micron stainless steel element, recommended by SX to keep the big chunks of crud out of the pump without causing too much cavitation-inducing restriction. The filter and pump are connected by another hunk of -10 hose, though I plan to replace it with 5/8 aluminum "someday". Both filter and pump are located below the bottom of the tank. The filter is bolted to the t-top well, and the pump to the spare tire well, which needed a bit of reshaping.
The pump outlet is connected with a short piece of -8 teflon-lined AN hose to a long, convoluted piece of 1/2" aluminum tubing. Getting this tube to fit well was one of my happier mod moments. The pix below were shot with the fuel tank removed. From left to right, they trace the routing from the pump up and forward, then across the back of the rear seat. The black dots you may be able to see on the tube are Sharpie marks I used to place the bends.
The shots below are obviously from a completely different perspective. The first one picks up the 1/2" aluminum supply tube as it bends under the floorpan behind the left rear seat cushion and connects to the second SX filter. This filter has a 10 micron replaceable paper element to trap stuff that might plug an injector. The left hand pic also shows the new 3/8" aluminum return line running behind the filter, and the 3/8" aluminum EVAP canister tube in the lower part of the pic. Another twiddle in that pic is the re-bent brake line. That small diameter steel is tough to bend without total removal, which I didn't want to do.
The middle pic doesn't add a ton, but maybe the slightly shifted perspective is helpful. It shows more of the EVAP tube routing, as well as the modified brake line routing. Both of these changes were done to get the tubes away from the driver side cat in the long tube header y-pipe (related story). The right hand pic shows the adel clamps used to support the tubes in the tunnel, and more detail of the new EVAP line (the 3/8 aluminum tube routed away from the tranny tunnel) and the revised brake line routing.
The next pic show the larger aluminum supply tube joining up with the -8 AN teflon-lined hose that runs up the firewall to the fuel rail. The smaller return line stays in aluminum tubing up to under the lip of the cowl. The reason for the difference is accessibility of the fittings. It's easy to "paint yourself into a corner" when the engine and tranny are removed and access is not an issue. I work on this car a lot, so easy maintenance and access to stuff is extremely important to me. Easily worth a bunch of extra effort at the beginning.
The pic on the right shows a bunch of AN fittings welded to the fuel rail. The outlet has the -6 AN teflon-lined AN hose that goes to the FMU. The -8 AN on the end of the other rail is the inlet, which connects to the droopy hose in the middle pic. The other two fittings are for the Autometer electronic fuel pressure gauge, and a drain port I use at the track to pump out the street gas so the 104 octane unleaded race gas doesn't get diluted. (There is a connector in the wire bundle located on the passenger side fender well, under the hood, that runs the fuel pump when hooked to 12V.) The injectors are 30lb/hr Bosch.
Click here to go to the next page with my solution to the 700 hp fuel problem