420A 12:1 FMU + FPR worth it

[midfb6]

I'm turboing my 99' GS.

I've been collecting parts and I'm down to my final stages and my fuel system I'll be running a 255 fuel pump stock injector and a FPR. I've been reading about the 12:1 FMU and was wondering if its worth doing since most threads I see about this are years ago I can find and can not find a defined answer that tells me if I should or shouldn't run one on my set up.

I plan on dailying around 8-12 psi.

 

[jesse12345]

If your engine is stock i would definitely stay below 12 psi. If your engine is untouched, factory stock and you boost past that your ringlands will crack. I went down that road once. My advice if your going to run your setup is to get a wideband, boost and fuel pressure gauge. There are a few 420a veterans on here that have messed with them way more than I have. This is just what I'd do and my experience.

 

[midfb6]

Motor going to have je pistons eagle rods cometic top end gasket arp head studs bc valve springs and retainers and crower regrind , i do have afr guage for when the car is read to be put together my fpr comes with a fuel pressure gauge built into it also

 

[jesse12345]

To be honest if I were to do it id run a MegaSquirt.

An FMU is not bad at lower boost levels. A while back I built my 420a and only had an FMU but if I were to get a do over I'd run MegaSquirt. I just feel if your putting all that money into the engine to handle boost you might as well get something to tune it with. I get an FMU is simple and cheap but it only limits you. There are many discussions out there on this, it all comes down to what you want. I'm not bashing as I am currently running an FMU which I feel I fight with often. But my car is stock.

 

[midfb6]

To be honest if I were to do it id run a MegaSquirt.

An FMU is not bad at lower boost levels. A while back I built my 420a and only had an FMU but if I were to get a do over I'd run MegaSquirt. I just feel if your putting all that money into the engine to handle boost you might as well get something to tune it with. I get an FMU is simple and cheap but it only limits you. There are many discussions out there on this, it all comes down to what you want. I'm not bashing as I am currently running an FMU which I feel I fight with often. But my car is stock.

i definitely wanna do a mega squirt in the future but i jus wanna get it driveable so i can make sure everything is broken in and tighty up b4 i start to think abt even getting the car fully tuned

 

[BLACK'98DSM]

12psi on the stock injectors is not a good idea. Even people running 7psi are shoving more fuel through them than they're meant to flow, normally by ramping up the pressure significantly. I've personally maxed out stock injectors on a naturally aspirated engine at 50psi fuel pressure and a 215LPH pump. I could have forced more pressure to them but not reliably or accurately for a naturally aspirated engine.

If you want a rough idea of what size you need for that amount of boost pressure, use the calculator I post below. There are far too many factors to get an exact prediction, but I've found these numbers to be quite close most of the time.

Horsepower Calculator

Fuel Injector Clinic's Horsepower Calculator helps you know what horsepower each injector size will support. Enter a injector size and we can give the max horsepower supported for the entered injector size.

fuelinjectorclinic.com

 

[midfb6]

12psi on the stock injectors is not a good idea. Even people running 7psi are shoving more fuel through them than they're meant to flow, normally by ramping up the pressure significantly. I've personally maxed out stock injectors on a naturally aspirated engine at 50psi fuel pressure and a 215LPH pump. I could have forced more pressure to them but not reliably or accurately for a naturally aspirated engine.

If you want a rough idea of what size you need for that amount of boost pressure, use the calculator I post below. There are far too many factors to get an exact prediction, but I've found these numbers to be quite close most of the time.

Horsepower Calculator

Fuel Injector Clinic's Horsepower Calculator helps you know what horsepower each injector size will support. Enter a injector size and we can give the max horsepower supported for the entered injector size.

fuelinjectorclinic.com

i’ll definitely look into that i didn’t plan on doing injector till i went on mega squirt i’ve heard some people not getting it run to good on stock ecu

 

[BLACK'98DSM]

If you install larger injectors it's going to idle rich with the stock ECU. Plain and simple. On the contrary, if you overshoot the boost on stock injectors it's going to run lean under heavy load and cause engine damage. It's a lose-lose situation without MegaSquirt.

Plenty of people have run 7psi on stock ECU and injectors which is considered "safe" (objectively). But by totally ramping up the fuel pressure. It isn't the right way to do it but holds up for a little while on backyard builds.

If you're going to invest a good chunk of money and expect reliable results, just do it right the first time. The second time can get even more expensive. Get a tuning solution and the proper fuel system first. That way you only build the engine once.

 

[midfb6]

If you install larger injectors it's going to idle rich with the stock ECU. Plain and simple. On the contrary, if you overshoot the boost on stock injectors it's going to run lean under heavy load and cause engine damage. It's a lose-lose situation without MegaSquirt.

Plenty of people have run 7psi on stock ECU and injectors which is considered "safe" (objectively). But by totally ramping up the fuel pressure. It isn't the right way to do it but holds up for a little while on backyard builds.

If you're going to invest a good chunk of money and expect reliable results, just do it right the first time. The second time can get even more expensive. Get a tuning solution and the proper fuel system first. That way you only build the engine once.

Might as well be safe then sorry , would i just buy the diy kit , and i saw the ms3 mini kit with the harness it gives options to add sensors would you recommend getting any of them, i do have afr guage and i don’t think ill need the wideband also looking at a fic 650cc injector

 

[midfb6]

would the ms3pro mini work the same as the ms3 ems . not sure on which one i should buy. MS3ems, MS3 with ms3xexpansion or the ms3pro mini

 

[import solutions]

you're buying piston but not want to put a correct device to control engine

 

[midfb6]

you're buying piston but not want to put a correct device to control engine

You might of missed the most recent post i replied about asking which mega squirt to go with and if the mini works the same as the others. Also going with 775cc injectors

 

[VelocitàPaola]

would the ms3pro mini work the same as the ms3 ems . not sure on which one i should buy. MS3ems, MS3 with ms3xexpansion or the ms3pro mini

That'll be fine--the only thing it's missing is the ability to control the 420A's idle air controller. You can install a PMW IAC instead, though. It's not as modifiable as the standard MS3, but it's small and I believe you could install it in the engine bay.

 

[midfb6]

That'll be fine--the only thing it's missing is the ability to control the 420A's idle air controller. You can install a PMW IAC instead, though. It's not as modifiable as the standard MS3, but it's small and I believe you could install it in the engine bay.

i did end up getting the ms3 pro mini and quad spark, will be getting 775cc injector , only thing im waiting on is my cams to be finished