fuel pressure settings.

[i218127]

Was reading the ignition timing after full header back exhaust installation post and noticed his fuel pressure set to 42 psi. Not sure one can do this is a 1992 1.3. Anyone know how to get that much pressure in a '92? My regulator comes at 38 psi. I seem to start running out of gas above 5500 rpm. Can make it to 6000 and 6200, but can only make it to absolute limit of 6450 on a down hill grade. Suggestions?

New WIX filter, New 38 psi regulator, Replacement injectors cleaned by machine off the car (equal, smooth flow)
Strong mid range, using MSD and Hi Performance coil.


i218127

[i218127]

I see that Turbo systems are using the SARD (?) adjustable pressure regulator or something like it. Anyone have any information on it ?? How does it adjust? With the Hex nut on the top ? My '92 doesn't have an outlet to attach a pressure meter to. I understand that the Aspire rail has one. Can the Aspire rail be used on the older 1.3's? (I live in California and want to keep my 1.3, but get everything I can get LEGALLY out of it) Suggestions, besides junking it.

1218127

[rmoltis]

Hey chief in response to your post.
If your vehicle is in stock shape I would say you won't need to really make adjustments.

I personally needed one to compensate for the additional air flowing through the engine at higher rpms by adding more fuel.

So in order to get your vehicle to really wrap out at higher rpms you would need a freer flowing exhaust.
I have noted and noticed that a cone filter on a stock vehicle even with the exhaust has lost me air flowing in and power.
Which led to fuel pressure being turned down to get my wot afr back to normal.

I would suggest finding a way to see your air fuel ratios at wot and then if needed use an adjustable fuel pressure regulator to compensate by adding or subtracting fuel.

If possible your narrow and o2 sensor voltage output can get you close to the correct afr
By adjusting it to between .83v-.85v @ wot.
I would suggest having a brand new sensor when doing this though, for increased accuracy
(Or at least what little accuracy you can get from a narrowband)

Also keep in mind that as your change your air fuel ratios away from stock.
The flame front burn speed of the combustion process will change,
And will also require an ignition timing change/adjustment as well to get things to their optimum.
I personally got my adjustable fpr from mattickmeyer with the fuel rail adapter.

The main reason your car runs out of steam around 5500 is because the exhaust primaries on a stock festiva.
Are designed to create the highest exhaust velocity speed at peak torque around 3k.
Now past 3k the hp keeps rising to around 5k even though the torque keeps dropping past 3k rpms.
What this means is that as the rpms rise past peak torque the volumetric efficiency starts to drop more and more.
This is due to less air being able to get pulled in and out of the system.

Airflow into the engine stabilizes at its peak of 3k and remains constant until red line (stock 1.3)
But as the engine turns faster it wants more air when in reality it gets a % less as rpms keep rising compared to what it needs for peak volumetric efficiency at those points.

So once past 3k and you want more power.
You will need to use the increase the flame burn rate by making the afr around 12.5-13 @ wot.
Then compensate with altered ignition timing towards optimum.

There will come a point between adjusting the fp and ignition timing where you can't get any more gains.
You personally will know where this is.

I would personally wait for more modifications before chasing the extra fuel.
Because after all you need more air before adding more fuel to create new power.

So when it transitions from 14.7 afr to 12.5 you will feel a power gain even though the airflow into the engine remains the same.

[i218127]

Not sure of all that's written, but get some of it. Will talk to my mechanic friend and go from there. I do have a big "Cat Back" exhaust and had some head work done. ( I'm truly very old school) Oh ! Saw your video and can tell where you were driving. Saw the Shadyside Hospital sign. My air box is drilled and I've set the hood rear up 1/8 inches. (Old hot rod trick). It goes like blazes below 5k, but starves above 5.5k

i218127

[Advancedynamix]

There are 2 members that are active in Palm Springs area now. You shouldn't be having fueling issues with a stock b3. Even if you've got a high flow exhaust.

[rmoltis]

I agree with advance for his words. Unless you add a header you wont need it.
The header primaries determine exhaust velocity and airflow demands.
If you haven't changed it out your stock engine can probably compensate or get close.

Only way to know for sure is to get a wideband.
The best way i know to get the most out of your mods is verifying and getting your wot air fuel ratio into the correct range after every modification..

[i218127]

Not sure what a WIDEBAND is. But did have my heads Ported and Polished by a real pro and have a newer roller bearing head. The engine is somewhat new and may not have loosened up enough yet. My Smog numbers are: 1 at idle and 2 at 2500 (HC), and .00 for both idle and 2500 for % CO. My % CO2 is 14.20 Idle and 14.64 at 2500. Really happy with those numbers. After the mods, was kind of concerned about SMOG. California is tough on this subject. I can't have headers here, but have done the next best thing. This thing breaths !!!

i218127

[gergorian]

A "wideband" is a wideband O2 sensor. It is called so because its output voltage range is 0-5v. Where as the single wire O2 sensor on a festiva has a voltage range of 0-1v. The wider the range the more data and the more accurate the reading will be. You can get a wideband so you can see what your air/ fuel ratio is and to see what effect changing the fuel rail pressure does to the air fuel ratio.

Also, I have a B3 that was heavily worked over by Matt Dickmeyer. Possibly the best and only person who did performance mods to the stock festiva engine. My head was ported/ polished. Bigger valves, valve springs, custom cam, longtube header and I also got an adjustable fuel pressure regulator from him that comes with an adapter to work with the factory fuel rail. I do have an issue with fueling but that is my own fault for having too big a radiator because I wanted to make sure I wouldn't over heat it. Now all I'm doing is over cooling it and the computer almost never goes into open loop unless its hot outside or I let the engine warm all the way up at idle before driving.

[Advancedynamix]

I've driven a Festiva with a b6d swapped into it that was running stock B3 fuel injection. That's a larger engine, with a head that flows twice as much air as the B3, a much higher flowing exhaust manifold and a completely different combustion chamber design. The car didn't have noticeable fueling issues. That's 30 more hp without fueling issues! I highly doubt even a header and straight pipe on a b3 will change the tuning enough to cause an overly lean condition.

[gergorian]

I agree Charlie. My issue is that the engine is running too cool to go into open loop so when I go wot it only richens slightly. I just need to get a smaller radiator.

[Advancedynamix]

Your problem may be your thermostat. In theory, the radiator doesn't control the temp, the thermostat does. I use 192 degree dual element thermostats. They are easier to find for the miata. I've found them on eBay for as little as 12 bucks shipped, but the retail price can be quite high if you search locally (it's a 50 dollar thermostat).
The dual element thermostat regulates the engine temperature much more consistently, and the engine will come up to temp faster. When the thermostat is closed, your coolant bypasses the radiator, so the size of the radiator is irrelevant.

[rmoltis]

I've driven a Festiva with a b6d swapped into it that was running stock B3 fuel injection. That's a larger engine, with a head that flows twice as much air as the B3, a much higher flowing exhaust manifold and a completely different combustion chamber design. The car didn't have noticeable fueling issues. That's 30 more hp without fueling issues! I highly doubt even a header and straight pipe on a b3 will change the tuning enough to cause an overly lean condition.

When I installed my header back exhaust my aspire was running very lean lol.
It had hesitations upon acceleration and was generally down on power until higher rpms.
There were even a couple wot pulls where I noticed smoke coming out the exhaust lol.
This was of course after a heated 02 sensor to get it out of open loop since the narrowband was further away and wouldn't heat up.

The ignition settings were at factory specs for the longest time before I started toying with it.
The air box is factory with drop in k&n filter.
And it wasn't untiI found a code for my scan Guage to read my 02 sensor voltage I learned just how lean it was.
It would sit around .63 volts at wot which by looking AFR narrowband graphs looks close to between 14.7 and 14afr.
Which apparantly is super bad for wot.

Now on a side note the factory computer can compensate in closed loop.
But at wot it would always show its true colors.
Way too lean.
But once I dialed in the narrowband voltage up to .83-.85 which is in the ballpark of 12-12.5afr at wot on the wideband.
The smoking stopped, the power was restored at wot and closed loop performance was slightly improved
As well as the car generally ran cooler.
Then once wot afr was dialed in the ignition timing was adjusted its at about 9 degrees btdc.
It had to be retarded due to the extra air being crammed into the cylinders at higher revolutions at higher pressure.
Because it would give me pinging above 10 but at 9 it seemed like the piston wasn't fighting the added pressure of igniting the flame too early causing parasitic losses.
It was as if the dynamic compression ratio had gone up when at peak torque 4k rpms or peak airflow through the primaries.
The negative pressure wave from the tuned header really helps draw in more air through the system.

I have been looking for a local dyno to see where I sit real time to verify some numbers before moving on to other mods.
But I must say the added fuel pressure to restore the lean condition to the correct afr was possibly the best thing I have done after the exhaust. To bring it back into its zone.

41-42psi give me a reading of 12.5afr with peaks of 12afr on the wideband
due to the nature of the heated narrowband the computer reads from.

The stock fpr with the header combo was just a restriction to proper fuel delivery.
which the computer is capable of controlling if supplied with the correct volume of available fuel to be delivered.

If it makes you feel better dickmeyer was also running stock injectors on his festiva.
But he had the fuel pressure up in the 80+psi range to compensate for the fuel flow requirements.
Enabling his injectors to spray for less time while delivering more fuel.
Thus lowering the duty Cycle.

Another variable to consider is that I am 1000ft above sea lvl I think here in pittsburgh.
And my 41-42psi may read much differently at sea level.

All this talk makes me wanna go for a drive.
My aspire has been sitting for a while lol.

[Advancedynamix]

I can't speak for the aspire management, only the Festiva. I typically like to see 13.5-13.8 afr on an N/A engine under full throttle in the peak tq range. 12.8 is a better target for either boosted engines, or high comp. N/A builds. Smoke would indicate lean misfires, but the engine should not lean misfire at stoich. Many modern direct injected engines will run great at 15:1 and leaner under load.

[Dragonhealer]

The Aspire management is slightly different as it uses a hot wire MAF.
Lean A/FR on 90-93 Festiva (or Miata) at WOT is most often a bad/mal-adjusted AFM followed by an aging fuel pump followed by partly clogged (gummy) injectors or one injector not firing or squirting at all, (the system is batch fire, the original L-jet patent, with timing control),
Be aware that the fuel pressure is modified by manifold depression, which is generally different when you hot-rod the engine.

Way too much personal experience on all of the above , we just lost the developmental engine for Carolyn's racing Festiva at Pueblo Motorsports Park this last weekend. testing showed fuel pressure falling off at 7k rpm. A new pump fixed it, but the engine was already done.

[rmoltis]

Gotchya.
I am by no means trying to challenge your professional opinions.
Rather just discussing my thoughts as to pick your brains on these ideas.

My main idea for the 12.5 afr was to use the increased flame burn rate to decrease the total combustion time since my PowerBand had shifted upwards in rpms 4200 seems to be the resonant point.
Its other purpose was to find that peak burn rate so I could retard the ignition timing thus also increasing efficiency due to less parasitic loss of the upwards traveling piston fighting the expanding combustion mixture earlier than its peak point for proper combustion timing.

Thus gaining me a small amount up top between 4200 and 5500
While making cruising situations feel as if the engine is working easier with less throttle input.
Only relative to my aspire (every vehicle has its own wants and needs)
It seems to respond best around 12.5 during my test drives and experiments
(But this is all by feel as to what I perceive as best) which isn't always necessarily accurate.
Even though I can see the data it is just numbers which are useless for determining efficiency
Unless i can visually pair what it likes via dyno graph or tailpipe sniffers to the data itself.

You have any ideas as to things I should toy with as far as tuning variables?