Walbro Gss315 vs Gss341hp: useable fuel pressure
 

OK so I just bought the Gss315 fuel pump from the Rx7 Store. Like all good new parts, it's sitting on my coffee table.

The GSS 315 is very nearly identical to the GSS341hp in flow rates up to about 70 psi.

http://www.autoperformanceengineering.com/

Does the extra flow rate above 70 psi matter? seems like the Gss315 actually flows a little less than the STOCK pump at 90 psi and above!!!!

http://www.vfaq.com/RX7-Miata-pumps.html

Again, why does this matter? I guess at low RPM and injector flow rates, the fuel pressure will be higher so that's when it matters.

I really don't KNOW. Should I get the Gss342hp instead? I have a stock motor, turbos and injectors. I run about 13 psi (when i can get it ;) ).

Thanks in advance.

You'll never be anywhere near 90psi with the setup you're running. At 13psi of boost, you'll be about 40-45psi fuel pressure, depending on what your base pressure is.

Hummm
 

Ok I guess I'm confused. I thought my fuel pressure would be the lowest at max RPM and WOT and highest at idle. Though the 7 uses some resistor to drop fuel flow at lower rpm (Boost pressure? Inj Duty Cycle?)

So i'm thinking at WOT, the GSS315 should be a nice upgrade and equal to the GSS342hp. I figured at lower RPM (or at least something less than WOT would be the max fuel pressure point. In reading manual, they expect the stock pump to output a max pressure of 71-100 psi.

Does anyone know how the fuel pressure will vary with RPM (like a graph)? Is it correct that fule pressure will be the lowest at Max RPM. Accounting for the fuel pump voltage resistor, would expect max fuel pressure to be at just after the fuel pump gets max voltage. I just don't want to find out that point is like 2500 RPM. If it's like 500 ROM then should be no problem. Hope this makes sense. If not please help clear up my confusion.

One reply?!?

The answer is......
 

From the department of "who cares", this just in. Though the stock pump is rated to a minimum of 70 psi, a reliable source is quotes as saying that less than 70 psi has been observed. Furthermore, this does not matter because the fuel pressure typcially is 32 psi give or take.

All the speculation in my previous post was simply wrong.

NEEVOSH WAS RIGHT.

On this basis I the GSS315 pump is more than adaquate. I see no reason to get the GSS342 unless your going to run higher fuel pressure.