13.8 a/f ratio, why?
 

As breifly discussed in another post, I had my car dyno'd yesterday on a Dyno jet. Current setup is

Begi t25/28
Begi fmic
1.8 inj
Stock pump
Begi AFPR

We only did 2 pulls cause at 4500 rpm my car leaned out to 13.8 and nobody wanted to blow any engines. I have the Begi AFPR set at full pressure. My boost guage shows a max 7-8 psi and the fuel guage barely passes the 70 psi mark. I will scan my graph when I get back to Fort lauderdale from Orlando. I suspect that its time for a 190hp pump. Should this bandaid my problem?
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I would bet that your stock fuel pump is a little weak. I'd upgrade and then turn up the boost if you have too much fuel with the 190 <G>.

I have a pierburg inline pump that I used for like 1k miles before I switched to megasquirt, Ill sell it to you for a fair price (which I do not know atm). Pm if interested, otherwise ... well dont.

Stock pump needs to put out ~80 psi to handle that setup.

i got a 190 is interested. i just bought MS too.

ok, silly question,
did you try to adjust the BEGi FMU at all?

also, which 1.8 injectors are you running? my experience is that NA injectors suck and NB injectors fuckin rock.

Yeah the AFPR was already at full pressure (adjusting screw all the way clockwise). My injectors are NA 1.8 injectors.


So ok, im gonna just pick up the 190hp pump and i might as well look for some 305 0r 330 injectors to be safe since im probably close to maxing out mine already. Yes or no?

Thanx for your help everyone:bigtu:
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just get a fuel pump

^I agree, the Walbro 190hp is your answer. That, along with 305/310/330 will give you all the fuel you need to run 12psi. I think with an adequate margin of safety, you should be able to run the 1.8's at around 110-120psi of fuel pressure and around 10-11psi of boost. Get the 3xx injectors and you can run more boost at less fuel pressure.

If you're going to turn up the fuel pressure that much, you'll need good quality hose clamps on your fuel lines... not the little alligator pinch types that come stock. I use bolt-clamps... didn't feel safe with the standard metal worm-types: https://www.miataturbo.net/forums/sh...1&postcount=24

Have you done the dual feed mod to your fuel rail?
How high does your fuel pressure gauge go?

Also, when you install the Walbro, YOU MUST USE THE SMALL PLASTIC RESTRICTOR THAT GOES IN THE BOOST LINE TO THE AFPR. BEGI SUPPLIES ONE WHEN YOU BUY IT NEW, BUT IF YOU GOT IT USED, OFTEN THE OO DOESN'T SEND IT.

Call Steph at Begi and she'll send you one. If you don't use it, you won't have the resolution of adjustment you need and probably won't be able to dial down the fuel pressure below around 100psi.

After that, pretty much your only remaining bandaid is an O2 clamp.

Thanks Sam for the info. Yes I did the dual feed fuel rail mod when i first did the install. I'll go ahead and get some of those bolt clamps, I've seen them in my local parts store. The pack actually says fuel line clamps. Thanks for the tip on the restrictor for the AFPR, but where does it actually go? Fuel line or vacuum line? I think I have seen some people use those plastic straws from brake cleaner or WD-40. Oh my fuel guage only goes to 100psi, so im gonna have to pick up another.
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:gtfo:
you don't need a fuel pressure gauge. your fuel pressure is not important. you are not tuning to achieve a desired fuel pressure. you're tuning to acheive desired a/f ratio, so you need a a/f gauge. the fuel pressure it takes to achieve a correct ratio is completely unimportant.

i don't see any reason to run anything larger than 1.8 miata injectors.

the restrictor goes in the vac signal. a wd-straw will work just the same. you also need 2 check valves. do a search to see pics of mine.

B

Geesh, conflicting info im gettin here. Here is a scan of my dyno sheet
Attachment 215891
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Ben I found your post about the 2 check valves, I will do that tomorrow. As far as not needing a fuel guage, well at this time I cant afford to buy a wideband, so I do have to tune my fuel as much as possible without the wideband. I know that im playin guessing games without the wideband but thats my only option at this point.
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Ben, you know I've been around here while, and you're the first person I've ever heard say that. I agree that in the end, you're tuning for A/F, but there are a lot of things I wouldn't have known about my tune if I hadn't been able to see my fuel pressure. It's an easy thing to plumb in and it's always good to check the numbers. It's important to know, if for anything just increasing your own knowledge of what's going on with your system. My fuel pressure gauge cost me about $15 to install, so there's absolutely no reason not to get one. And you know as well as I do that widebands and dyno time are expensive. A fuel pessure gauge, plus doing the math is an easy way to get yourself relatively safe until a real tune can be managed.

For example, in my orignial build, I wasn't using the restrictor in the boost line and was getting over 130psi of fuel pressure that I didn't know about... and good A/F's with my 1.8's at around 13psi. Corky says that much pressure is fine with these injectors, but I didn't trust (and still don't really) the stock fuel lines and the stupid stock clamps. I thought everything was good until I watched the gauge go skyrocketing past 100psi and knew it wasn't good to run that way for long. It was then after posting about such high fuel pressures I learned about the boost-line restrictor that the OO had failed to sent me. And it was then I decided to upgrade to 305's to get my fuel pressure down.

And now I've figured out through tuning on a dyno, that my car needs about another 5-8psi of fuel pressure for every extra psi of boost to keep the A/F's in check. Believe me, it's nice to know that.

Every piece of data you can add to your tuning equation is important. You've gotta have one to set your ~0 pressure, so you DO need one at the beginnng. Doesn't make any sense to take it out after.

IMHO, a fuel pressure gauge absolutely has it's place in a bandaid setup.

So if im doing MS with 310 injectors I dont need a pierburg? In fact i should probably go with a 190?

pierburg is a good pump but i don't see the reason to use anything other than a walbro 190 on a miata. It's cheap, installs easy, and it's in the tank with no extra wires or anything like that.

for the fuel pressure gauge, whether or not you think you need permanently installed on the car, you should still have one in your tool box, it's not all that hard to hook one up with a meter of hose and duct tape it to your windsheild for testing. You are tuning for air/fuel ratios but looking at the gauge and having a fuel pressure in mind for a starting point helps.

Loki: the pierburg can only add pressure. it doesn't add flow. in a stock pressure based system, there is no reason to have a pierburg or any external pump. in fact, odds are it will only add restriction and waste electrical energy. you're going to be limited by your injector size. you've alluded to wanting to run big power (in the 6 spd tranny thread) but those 310's aren't gonna get you too far over 200 wheel.

Sam: i have a fuel pressure gauge, a nice MAC one that goes to 200 psi; I really didn't learn anything useful from it. again, i don't care what the fuel pressure is; I only care what the a/f ratio is. i tuned everything with a wideband, including the 0 vac pressure. i think a fuel pressure gauge is useful as a diagnostic instrument, but frown upon using it as a tuning instrument.

phil: that graph is useless w/o any telemetry. next time you go to the dyno, pay the extra $10-15 to capture a/f, intake temp, and mani pressure. that way you get the whole picture. search for the JAW wideband. it's dirt cheap and will help you tune properly.

i just through that out as a idea, i havent decided on injectors yet.

Thanx for the info Ben, next time at the dyno I will deff ask for that. I never heard of the Jaw wideband but im searching now.

Thanx again guys.
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Ben the injectors are rated at a particular flow per psi of fuel pressure. If he is lossing pressure in the line becouse the pump will not keep up with his flow then his AF is gonna go up duh. Even if he sticks in 400cc injectors and keeps the pressure closer to stock wich he isn't with his FPR system his pump would be working itself pretty hard since it is old and tired. And it might have already been failing. Swaping a in a 190 hp would solve this and he could use it when and if he ever upgrades to a electronic solution. The fuel pressure gauge will tell alot about what kinda supply he is getting and is a very important tunning tool. Not using one is akin to not using a timming gun to set your baseline timming. It can be done, but the chances of being off are pretty high.