Largest injectors on std ECU Mk2 1.8L

[Lloyd_D]

Hi,

I have a supercharged 1.8L 1999 Miata using a Powercard. I am wondering what the largest injectors I can run on the std ECU ?

I will need the car to idle properly.

I think the std injectors are 260cc/min @ 3bar.

Help much appreciated.

Lloyd

[FormerDatsun510Man]

Stock size :). That is 250cc. You can get away with as large as 280cc... above that you will have problems with idle/cruise driveability. 310cc is just enough over the edge that it will work one day and not very well the other.

You have a few choices to get the fuel you need for the power you are after:

1) extra injector(s) - this is the FFS approach and works quite well if done correctly. Correctly means on a Hotside that you use a minimum amount of extra injector (placed in the dummy TB) so as to not upset the fuel distribution since the stock intake manifold is not a very ideal setup for injecting fuel upstream into. On a Coldside, we already did the work for you and after many months of testing utilizing a 4 EGT setup and dyno, we determined the absolute best method of injecting fuel into the manifold and having very good fuel distribution and power (both essentially equal to a four larger injector only setup).

2) My MAF box - this you can read about here:

http://www.fastforwardsuperchargers.com/forum/showpost.php?p=23936&postcount=2

3) piggyback or standalone that can handle larger injectors. You can talk to the guys running Megasquirts, Hydra, Xede, Emanage, etc. to find out if this is for you.

Bill

[d-A-w]

Lloyd_D

I have installed Supra Injectors (Green top #23250-70080) on my '99 (powered by FFS Powercard), and they idle pretty good. (idles is perfect since dual TB on my hotside)

It's a bit rich on coldstart (10:1), but it idles allright and it doesn't take long to reach happiness.

If I start driving right away on cold days, it looks like it's going to die on the first take offs because there's too much fuel, but 30 seconds later it's ok.

I have a problem, it looks like I don't have enough fuel over 5000rpm (11 intercooled psi). I changed the fuel pump for a Walbro 190, and I still have the same problem. I wonder if the fuel rail is the culprit?

[Lloyd_D]

Ok thanks for the advice. I use mine as a daily runner so idle and cold start is very important.

Maybe you need bigger injectors still, 410cc RX8's :biggrin:

I am only looking for about 10-11psi eventually after the intercooler. I am in the process of assembling a JRSC mounted M62 hotside. This is from a Mercedes SLK 1999. I have got the rotor case ali welded to copy the JRSC M45 flanges. This will be a project for next winter.

Lloyd

[FormerDatsun510Man]

With the stock ECU and no extra injectors, the name of the game is the smallest injector size that can get you to the hp level without going static. By my calculations, if you are going for 10-11psi on an intercooled Hotside that would be a setup of 330cc injectors (310cc just a tad too small). 10-11psi on a Hotside equates to a 120/65 pulley ratio and approximately 200-220rwhp (depending on tune). This would put the 330cc at 90% max duty (perfect). If you run the PC Pro this will be just a little large unless you pull down the MAF voltage about 10%.

One question though, does your Miata have a return or returnless fuel system. If it is a return type, this is another way you can run larger injectors. You can install a fuel pressure gauge and an adjustable fuel pressure regulator.

[rins]

If its european '99 model it has return type fuel system (stock pressure ~55psi)

[d-A-w]

Bill,

I've got the 126/65 combo, which should be good to give 12psi, but I can't get there on the upper band yet.

The supra injectors were tested at 320cc@43.5, so they should flow more at the NB Pressure (360?)

I have tried different setting, and the result would always be the same above 5000rpm. I now run it as Green/Blue-4, Yellow/Blue-5, Red/Blue-5.5.

Could the injectors be at 100% duty cycle or the fuel pressure drops in the stock fuel rails, even though I installed a Walbro 190?

[Lloyd_D]

Yes, Datsunman its a European model MX5 1.8L

This MAF box sounds interesting. So your saying with the box and the larger injectors it will idle and start ok and not stumble etc ?

With the fuel pressur reg, would the Powercard need to be removed ? thinking the two would interfere with one another...

Lloyd

[FormerDatsun510Man]

With an adjustable fuel pressure regulator, I think that would be the way to go. The reason is that adjusting the fuel pressure gives the ECU no different feedback. Same ignition timing, same pulse width, etc. You are adjusting adjusting the flow of the fuel mechanically so as to get the ECU in the region where the fuel trims will be good again. The PC Pro will not interfere with this as it only adds to the pulsewidth... also not to the knowledge of the ECU. I would suggest trying this method first with larger injectors. Only if it is not enough or satisfactory, then you could try my adjustable MAF signal box if you are interested. The MAF box adjusts the MAF signal to the ECU to read lower and yes it will stop the richness and give great driveability if a reasonable amount of adjustment is made (preferably less than 20%).

The nice thing with an adjustable fuel pressure regulator is that you can fine tune the flow of your injectors. You can turn 330cc/min into 345cc/min or to 315cc/min with a twist of a knob. I think between that and the PC Pro you will be able to get a good idle with larger injectors. The MAF adjuster would be the last step... which only would likely be necessary if you were making a pretty big jump in injector size over stock. Also I might add to get the most of whatever size injectors you are using, make sure you have the FPR signal going to the boost line... not just vacuum only.

[Lloyd_D]

I understand FPR's adjust pressure of fuel relative to the manifold pressure. It is a linear relationship. The powercard pro is also doing the same. It is basically an electronic FPR, it has no feedback from the O2 sensor. It is a simple device.

I am concerned that with a FPR and the powercard under boost the fuelling will become hard to control since the increase in flow with respect to manifold pressure on the FPR and the non linear increase in pulse width from Powercard Pro will cause headaches.

It is a cheap non standalone option however and I will defo consider it.

When you say connect the signal line into the boost pipe not vacuum only where do you mean ? Not into the intake manifold ?

Also with an adjustable FPR what additional flow would I be able to reap from my std injectors ? Or is this not a good idea ?

Lloyd

[Lloyd_D]

Ok so I have decided to fit an adjustable fuel reg with a gauge to my Mk2 1.8L.

Is it definitely possible to fit one to this model car and whereabouts is the std fuel regulator located ?

Lloyd

[d-A-w]

On a '99 here, the regulator is in the tank.

:tank:

[FormerDatsun510Man]

If you have a returnless type system, then the pressure regulator is in the tank and you cannot adjust it or put in an adjustable one very easily. You are stuck with the fuel pressure the system has. In this case, I would recommend pulling down the MAF output slightly to run larger injectors.

If you have a return type system, then the pressure regulator should be on the fuel rail at the engine. The pressure regulator will be a small round metal vacuum actuated device with a vacuum hose hooked up to it. Not to be confused with the fuel dampers used on the fuel rail on the returnless systems (which are similar in appearance except they do not have a vacuum hose connected to them). Also a return type system has two fuel lines coming from the rear of the car that both come up on the side at the same place in the engine compartment. In contrast, the returnless systems only have one.

It is my understanding that in Europe they used the return type fuel systems a few more years later than in the U.S. For example, in the U.S. the last year they used the return type fuel system in the Miata was 1997. In Europe I believe it was 2000 or 2001???

[Lloyd_D]

Hello,

Right I have fitted an adjustable fuel pressure regulator and converted my fuel rail to a dual feed type.

This UK model 99 Mk2 has a 43.5psi regulator as std on the end of the fuel rail FYI.

I have calculated that the std ECU can pull enough fuel at idle to handle 60psi maximum. I am not going to run this high. I am going to set idle fuel pressure to be about 55psi. This will give about 83psi at 11psi boost pressure.

My question is, based on these percentage of fuel flow increases, what would be the recommended reduction of the Powercard Pro settings ?

I am guessing I will need to fine tune with a wideband, which I have.

Lloyd