Pump research

[attworth]

I'm looking for a fuel pump that will serve me now and in the future.

 

Current car is a stock 81 NA. It'll eventually be a turbo car, my goal is roughly 300 horse. I'll be running an aftermarket fuel rail with an aftermarket regulator with both applications, different injectors for each.

 

I'm a little confused as to what I'm actually looking for. I'll list these to make it easier to understand my questions.

 

1. Can I buy a pump that will work well with both applications?

 

2. Is it okay to run a pump that has a higher pressure and higher volume than what I need?

 

3. Would I be able to just turn the pressure down, or will it still push too much fuel into the motor?

 

4. Would I be able to turn a high volume pump low enough to get the appropriate volume and still keep pressure high enough?

 

5. Is the appropriate volume based upon HP numbers supported by the rest of the build, or on the flow rate of the fuel injectors?

 

6. Where can I find something detailing where to get those appropriate volumes based upon injector size/HP as per question 5?

 

Sorry for all of these questions. I couldn't really find specific answers for this, more so recommendations for specific apps. using specific components. I want to make sure I don't have to buy parts more than once if I don't have to. I plan to run my car on the stock motor until I can afford a full turbo build like I want. I can't afford to do it all really quickly, and I have no idea when I'll have everything together, could be 6 months, could be a couple years. I may be better off sticking with the stock FI for now, but I am going to be redoing my hard lines as well as using stainless braided lines in the next month or so.

 

It ain't broke, but I might as well fix it.

[X64v]

Your questions answer themselves with a bit of a tutorial on how fuel flow and fuel systems actually work.

 

Fuel pumps don't 'make' a certain pressure. The fuel pressure regulator (FPR) is what opposes fuel flow (working against the fuel pump) to pressurize the fuel. The more the FPR resists the flow of fuel through it, the higher the pressure. If a fuel pump is 'rated' for, say, 125psi, it means the maximum pressure at which the FPR can be set is 125psi, else the pump will be damaged, or its internal bypass will let off pressure.

 

You don't choose a pump based on a flow rate to 'match' your engine or injectors, you want the pump to out-flow the engine's greatest needs. As long as the return line is large enough to return all the unused fuel without a pressure increase (on your ZX, it definitely is), then tons of unused flow doesn't hurt anything (besides maybe heating up the fuel in your tank faster, as Tony D has written about thoroughly).

 

The brake specific fuel consumption for a turbo motor can be as high as .7lb/(hp*hr). This means that your engine may use up to .7 pounds of fuel per hour per every horsepower it makes. I'm assuming you mean 300 wheel hp, which is 350 crank hp at 15% driveline loss. So, 350hp times .7lb/(hp*hr) is 245lb/hr, or about 41 gallons per hour. This means you're looking for a pump that can flow at least 41 gph to suit your horsepower goal. More than that is fine, though it may come at the cost of a noisier pump (not always), or a more expensive pump (again, not always). As a suggestion, the Walbro 255lph pump will flow 64 lb/hr, more than enough. Plus they can be had for cheap and are decently quiet and reliable; they seem to be the pump of choice around here (I love mine).

[attworth]

Thanks for that. I got to thinking about all of that last night and basically was under the same assumptions that you just confirmed for me.

 

Thank you!