FMU vs AFPR

[95'RS-T]

ok found a good price on a 255lph hp pump from extreme psi all i need now is the 12:1 fmu I was wondering what the difference is between the Fmu and AFPR but at the same time i believe I'm answering my own question by saying the AFPR is constant pressure even at idle, thus creating too much fuel correct? I know the fmu uses vac/boost so it then raises and lowers the pressure when off and on the throttle right?

 

[LD25Delta9]

You are correct. Unless you have a way to tune some injectors, the FMU is the way to go. I would reccomend a Walbro 255HP instead of the 255LPH if you plan on going crazy with boost. They have minor differences, but the HP has a higher pressure threshold.

 

[Locke]

An AFPR is an adjustable 1:1 FPR. The 1:1 is only to keep an adequate pressure differential between the fuel and atmosphere in the intake, so the injector will spray will spray with an acceptable pattern.

A FMU allots full flow under boost, which is why it must supplement a real FPR, but with a high gain ratio such as 12:1 or 10:1. In this case, the added fuel pressure is used to increase flow through the injector in a proportion to boost in an effort to adequately fuel the motor.

A SFMU is a FMU who's static fuel pressure is adjustable, along with interchangeable springs and disks to alter the gain and rate of gain.

 

[LD25Delta9]

An AFPR is an adjustable 1:1 FPR. The 1:1 is only to keep an adequate pressure differential between the fuel and atmosphere in the intake, so the injector will spray will spray with an acceptable pattern.

A FMU allots full flow under boost, which is why it must supplement a real FPR, but with a high gain ratio such as 12:1 or 10:1. In this case, the added fuel pressure is used to increase flow through the injector in a proportion to boost in an effort to adequately fuel the motor.

A SFMU is a FMU who's static fuel pressure is adjustable, along with interchangeable springs and disks to alter the gain and rate of gain.

I wish there was a smiley for getting a bitchslap....cause I'd post one on myself for that!

 

[95'RS-T]

ok i got the FMU AFPR situation i was just wondering if i could use a AFPR instead of a FMU but i think i'll just stay with the 12:1 FMU and 255HP pump

 

[Locke]

Use an AFPR when an ECU will be controlling fuel in boost, such as with MegaSquirt.

 

[rstare]

You are correct. Unless you have a way to tune some injectors, the FMU is the way to go. I would reccomend a Walbro 255HP instead of the 255LPH if you plan on going crazy with boost. They have minor differences, but the HP has a higher pressure threshold.

If your planning on using a 12:1 fmu at all, with the basic "Star" setup and 8psi, you need a Walbro 255lph hp pump.
You can do the calculations

Edit: Be aware that the chart is in GPH, not LPH.

 

[david-b]

Use an AFPR when an ECU will be controlling fuel in boost, such as with MegaSquirt.

Going a little off topic but still close... what about a SFMU with MS instead of a AFPR? With a 1:1 disc?

 

[Locke]

A 1:1 SFMU would function like an AFPR.

 

[david-b]

A 1:1 SFMU would function like an AFPR.

Excellent. That's what I wanted to hear.