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420A Best boost setup for stock ecu?

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Brad Bell

Proven Member
192
5
Aug 15, 2014
Levant, Maine
I'm currently running a stage 2 hahn turbo kit on my 420a. I'll give the rundown of my setup.

Super 16g turbo
Stock injectors
Walbro 255
BEGI AFPR rising rate fuel pressure regulator (adjustable static fuel pressure and rate of increase)
Wiseco low compression pistons (don't know the exact numbers)
Forged eagle rods
stock ecu
Greedy Type RS bov
MSD coil and wires
EGR and EVAP delete
Autometer mechanical boost gauge
Autometer electric fuel pressure gauge
Autometer narrowband A/F gauge (doesn't tell me much need wideband)

I'm currently running 8psi which runs decent but sometimes sputters when coming on to boost slowly, maybe need missing link of FCD? I want to know how much boost I can run safely on the stock ecu. I know megasquirt is the best option but it's out of budget as for now. I know I need larger injectors but what are the largest I can run on a stock ecu? I have heard of 550cc working great but wanted to double check. I also need a wideband of course before any of this, which I am working on. Thank you guys!
 
Your tapped out on fuel as it is. You really need a WB even with the setup your running. Megasquirt is the best option at this point. There are other options but they aren't any cheaper. You can upgrade the injectors, but you will just be tricking the ecu into trying to run them. You would need some type of fuel controller and your rise rate regulator will now be too large. At the end of the day you will have spent almost as much as a megasquirt system. Now along with megasquirt comes a whole lot of tuning. So be prepared for that.

Or just buy a portfueler system.

You are wasting money trying to do anything else.

Edit* I just saw that your regulator is adjustable. In the past I have ran larger injectors (500cc) and turned the base pressure down, along with the rise rate. And had a decent running car. I think my base pressure ended up around 25 or 30psi.
 
I had 36 lb injectors (378cc) in my 2.4L turbo Neon with a Hahn S16G kit and an FMU (22 psi base, 82 peak at 8-9 psi). On a 2.0L, you'd probably run into running problems with the same injectors, since you would probably need sub-20 psi base pressure, and injectors don't atomize well below 20 psi. Stock is 220cc, so you're probably coming close to maxing them out at 8 psi, but they'll work at idle. I'm not sure how DSMs are, but the Neon ECU for the 420A(ish) motor would flip out if you didn't have a MAP clamp.

Your problem of stumbling while coming onto boost slowly is exactly why you don't want an FMU. Above a certain throttle threshold, the ECU runs off of a pre-set fuel map, and doesn't read the o2 sensor. The FMU is only "accurate" in open loop, since it's tuned based on that map. Below the TPS threshold, the ECU will read off of the o2 sensor according to the stock tables, and pull the extra fuel that the FMU is injecting by reducing the injector duty cycle to meet its AFR target. You might be seeing 14.7:1 or higher AFRs while in boost, and your ECU doesn't know the difference. If you're in boost with the FMU, you NEED to floor it to get into open loop, otherwise you'll run lean, and it could cost you that forged motor.

Short version: this is a disaster, FMUs are so 90s. Go MS.
 
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I agree that MegaSquirt is the way to go, but I just wanted to offer some more thoughts:

1. I'm not sure Hahn even makes the PortFueler for the 420A anymore.
2. Old school wisdom taught us to switch to an S-FMU as an intermediate step between the FMU and MS. But they're pretty expensive brand new and they're hard to come by on eBay these days.
3. There's so much more than pressure that goes into this, but back when everyone was running 16G's or T3's, they'd say you can go up to 8psi on an FMU and the stock ignition system, then up to 15psi on an S-FMU and CDI.
4. You definitely need an FCD or MAP clamp--there's no question about it.
5. Get a wideband.
 
I agree that MegaSquirt is the way to go, but I just wanted to offer some more thoughts:

1. I'm not sure Hahn even makes the PortFueler for the 420A anymore.
2. Old school wisdom taught us to switch to an S-FMU as an intermediate step between the FMU and MS. But they're pretty expensive brand new and they're hard to come by on eBay these days.
3. There's so much more than pressure that goes into this, but back when everyone was running 16G's or T3's, they'd say you can go up to 8psi on an FMU and the stock ignition system, then up to 15psi on an S-FMU and CDI.
4. You definitely need an FCD or MAP clamp--there's no question about it.
5. Get a wideband.
What exactly is a SFMU and how I'd that different than my AFMU that I can set fuel static fuel pressure, and the rate of increase (12:1, 10:1, all the way down to 1:1). It's a BEGI fully adjustable fuel orepress regulator. No stock regulator installed. What is CDI? And what is the best place to get a missing link or FCD? Thank you for your response I really appreciate it!
 
What exactly is a SFMU and how I'd that different than my AFMU that I can set fuel static fuel pressure, and the rate of increase (12:1, 10:1, all the way down to 1:1). It's a BEGI fully adjustable fuel orepress regulator. No stock regulator installed.
The relationship between the amount of air and fuel your car's engine needs isn't exactly linear, but FMU's and AFPR's are linear devices. The beauty of aftermarket EMS's is that you can program them to supply the exact amount of fuel your engine needs under various conditions. The S-FMU was supposed to be kind of a compromise between the FMU and an aftermarket EMS. You can somewhat tune it by adjusting a couple of bleeder valves, which changes its pressure curve into something that looks less like a straight line (linear) more of an S-curve (sigmoidal).

What is CDI? And what is the best place to get a missing link or FCD? Thank you for your response I really appreciate it!
Capacitive discharge ignition. At a point, the stock inductive discharge ignition system can't keep up. Crane used to make the go-to option, but IIRC, they stopped making the module everyone used to buy. There are other options these days, though: MSD has been around forever and still makes ignition systems; Dynatek is another.

And what is the best place to get a missing link or FCD?
I'm not sure, you'll have to look around.
 
The relationship between the amount of air and fuel your car's engine needs isn't exactly linear, but FMU's and AFPR's are linear devices. The beauty of aftermarket EMS's is that you can program them to supply the exact amount of fuel your engine needs under various conditions. The S-FMU was supposed to be kind of a compromise between the FMU and an aftermarket EMS. You can somewhat tune it by adjusting a couple of bleeder valves, which changes its pressure curve into something that looks less like a straight line (linear) more of an S-curve (sigmoidal).

Capacitive discharge ignition. At a point, the stock inductive discharge ignition system can't keep up. Crane used to make the go-to option, but IIRC, they stopped making the module everyone used to buy. There are other options these days, though: MSD has been around forever and still makes ignition systems; Dynatek is another.

I'm not sure, you'll have to look around.

Alright so i got a wideband installed finally, and by the looks of it. Im running quite rich on 8psi of boost. WOT at 8psi reads around 11 to 12 AFR. Which i understand is a good place to be. Would it be safe to up the boost a little bit with a boost controller? I know probably my next step is to get my hands on larger injectors but i'm still not quite sure what size exactly.
 
AFR's appear to be reasonable. On pump gas I like to target closer to 11:1 especially with increasing boost. Controlling ignition is the main key factor to avoid preignition. What is your timing advance showing at peak torque & how much are you advancing it as you approach redline?
 
11.5:1 is a good target on boost. You're pretty much out of injector though, be very careful. And from here, you start running into difficulties due to fuel pressure window. Just get the MS man, this is painful to read. On a stock motor, sure, but there's no reason to cripple a forged motor with the FMU.
 
11.5:1 is a good target on boost. You're pretty much out of injector though, be very careful. And from here, you start running into difficulties due to fuel pressure window. Just get the MS man, this is painful to read. On a stock motor, sure, but there's no reason to cripple a forged motor with the FMU.
Yeah I agree with you, at some point I will get a MS but for the meantime I'm trying to get the maximum amount of power out of this stock ecu. However, is there an injector size I could go with that would work with both stock ecu and MS? Just so I wouldn't have to buy two sets of injectors. Thanks!
 
Yeah I agree with you, at some point I will get a MS but for the meantime I'm trying to get the maximum amount of power out of this stock ecu. However, is there an injector size I could go with that would work with both stock ecu and MS? Just so I wouldn't have to buy two sets of injectors. Thanks!

Doubtful. You could maybe run something in the 360cc range max for the FMU, while you would probably want 650-750cc for MS. Not even close.
 
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