I ran almost 30 PSI on 93 octane with stock fuel rails (3/8") and an aftermarket regulator placed before them (dead-head system) in my Nova. Zero issues ever.
The C4 never had a parallel system on it either. I ran the stock OEM fuel rails on that one too, but with the OEM regulator, and made just as much power on E85.



Selection. A single AEM 400 pump flows more than a Walbro 450 at high pressure, is cheap, and 1 of about 1000+ options. I ran 9s on E85 with a single AEM 380 (the previous model) with a check valve on the outlet that supposedly reduces flow by 10%.

Also, I've tuned 210 lb/hr Bosch injectors on a stock 0411 Gen 3 ECU and they idled fine. Don't stress over 80s too much.

 

Put the 80s into my supercharged 1993 (with stock $da2 batchfire type fuel injection)

Using tunercat, I set the injector lb/hr flow constant to 27% higher.

Started right up. It idled great, absolutely no issues.

Wives tails on this forum (that batchfire wont idle with bigger than 60 lb/hr injectors).

Though its possible injector technology is better than it was at one time

Datacat showed fuel trims showed lean. However wideband afr trims (coming in off the driver side and logging via the ac pressure sensor ) indicated it was able to adjust and achieve 14.7:1.

 

I made an Excel sheet that calculates pressure drop for whatever application and walks through reading a pump curve to use that number. Lots of assumptions, but it should be a good ballpark. Hope this helps someone else!

I'm returning to this to nail down my plans. Right now I'm thinking I'll do a beefy in tank pump and add an external pump when the time comes. If I recall, the big disadvantages to external pumps are noise and cooling, but those should both be alleviated by having the external only come on when needed (at WOT). It's a little complicated to do the math for non-identical pumps, but I think I figured it out.

• In parallel: same as usual (put the pressure into the pump curve and get a flow rate), but do it twice and sum the flow rates. If this is at least what you need, great.
• In series: put the flow rate you need into the pump curves and sum their corresponding pressures. If this is greater than the pressure drop calculated, great.

I'll have to do some research first to figure out if parallel or series is my best bet. I'm thinking series due to the relatively high fuel pressure I'll be seeing of 70psi @ 132 gal/hr. Also, series would be easier to plumb, and it seems weird running different pumps in parallel. I guess there's nothing wrong with it though?

I think I want to size my always-on pump to just barely handle my short-term power goals. I'd prefer to size it even smaller (no reason to be circulating 100gph at idle), but that would mean I'd need to do the external pump right now too.
I calculate that 600hp of fuel (79 gph on E85) only needs 62psi at the pump. A Walbro 450 high pressure would flow about 98 gph there, which is overkill. A Walbro 400 high pressure would do 90 gph, which I think is a pretty good place to be.

Now to figure out what external pump would push it to 1000hp (132 gal/hr @ 70psi). The Walbro 400 can't do 132 gal/hr at 0psi, so it would need to be a parallel setup. At 70psi, the 400 does 85 gal/hr. This means the auxilliary pump just needs to do 132-85 = 37 gal/hr at 70psi. A Walbro 255 would do the trick, putting out 46 gal/hr at 70psi.

This just seems like a kind of backward way to do it. Maybe I'll just do dual pumps from the start and pair a small, quiet, in-tank pump with a large external one. Heck, I wonder what the stock pump is good for. For some reason I hadn't considered using it. Edit: A replacement pump at Autozone is shown as 22 gal/hr free flowing? There's no way that's right? Also, larger external pumps are inexplicably expensive. Walbro doesn't even make one over 255 lph, and I can't find anything larger for less than $200. So I guess this idea sucks too? That would take me back to the Walbro 400.

Edit: I realized I overestimated my fuel requirements. The injectors are sized to make 1000hp at 90% duty cycle, so I don't need enough fuel pump for eight times their flow. Instead, I just need ~123 gal/hr. I'm wondering if I could get a large in-tank pump and PWM it to reduce fuel heating at lower load. As a warning to others, PWMing a gerotor pump like a Walbro 255 can be hard on the pump. A turbine style pump, like the 450, should be fine.

 

It turns out this isn't quite as simple as I thought. Solid state relays are quite expensive, so I thought I would just combine a heavy-duty MOSFET with an optocoupler to isolate the gate from the load. After quite a bit of searching, I found a reasonably-priced and very heavy-duty MOSFET from IR that would do the trick (AUIRFSA8409-7TRL). Its rating of 523A continuous is overkill upon overkill, but I was attracted to the low R_ds of just 690µΩ. This means that a 20A load would only generate 1/4W of resistive heating, which should be manageable without a heat sink. I'm thinking the bare device should be able to dissipate 5W or more without issue, but I believe switching causes some additional heating, and I wanted to make sure this was very robust. It's also good to 175°C. Oh, and its switching time of ~90ns is plenty low for the PWM frequency I planned. Again, likely overkill, but it's $5.

After selecting the MOSFET, I realized that the inductive load of the pump (brushed DC motor) would cause issues. Each time the MOSFET switches off, the magnetic field in the motor's windings collapse and can cause pretty significant voltages. You ever notice how the brushes on a power drill can spark when you rapidly let off the trigger? Same deal. That MOSFET has a drain-source breakdown voltage of 40V, which is the max voltage it can resist. If the inductive effects caused a voltage spike greater than this, it could feed back through the MOSFET into the car's electrical system. Not good. My initial thought was to put a giant diode in series, but it turns out the right way to do this is a "snubber" circuit. From what I briefly read, this is a beefy diode with a relatively low breakdown voltage (say, 16V) in parallel with the motor. Any voltage spikes greater than this breakdown voltage (which must be lower than the MOSFET's breakdown voltage) short-circuit through the diode and are dissipated by a load resistor you'd have in series with it.

In the middle of figuring this out, I realized that 500hz (max PWM of the ECU I'll be using) is pretty low frequency. And sure enough, you really need frequencies in the kHz range for an application like this. Less, and it can cause the motor to growl or just not work. This gives me two options. I can add an RLC circuit to damp the 500Hz PWM into a constant(ish) DC voltage - e.g. 14v at 50% duty cycle would be 7v - but I'm not sure how well the pump would run at lower voltages. Walbro only gives data at 13.5v and 12v. Maybe someone who knows more about electric motors can chime in. My other option is to increase my PWM frequency. It's possible to get/make a circuit that multiplies a PWM frequency. In this case, I think I'd need a factor of 20-30. The downsides there are cost and added complexity to a critical system.

At this point, I'm thinking I'll plan for the pump to run 100%, and if it bothers me I can figure this out down the road.

 

Another upgrade I realized will be necessary is a fuel filter. Aeromotive stuff is nice, but in the name of budget I think the Summit 230123R (10µm) will do the trick for $65. Cellulose filters aren't the best for E85, but I can live with replacing the filter a bit more often. I'll have a fuel pressure sensor to tell me if it's getting clogged, and the standalone will correct injector PW if fuel pressure drops before I notice it.

I'll need to crawl under the car to see where/how I can mount the filter. It's a bit bigger than stock, so I'm not sure the factory location will work. I'd love to hear from anyone who's upgraded their filter.