L28 stock AFR change

[gira]

Hi Folks,

 

I finished a stout little engine build for a customer of mine here in South Florida. It's a 10:1, 40 over L28 with a decent cam. I assume I'll have to throw some more fuel at this engine but it's going into a stock 1976 280Z with the original fuel injection that was working fine. I have done many engines like this but never into a stock FI system. What is the preferred method of adding fuel? The less complicated the better!

 

Thanks,

 

Greg Ira

RevTec

[Chickenman]

I have a similar setup on my 1976 L28 with Stock FI. OEM Analog ECU and  AFM ( Vane style ) does a surprisingly decent job at fuel management on a mildly modified ( 10 to 1 CR, headers, 270-280 degree cam ) L28 engine when everything is running correctly.... up to where the AFM maxes out, which is around 4,000 to 4,500 RPM depending on the VE of the engine.

 

 Generally, you will hit a lean spot between 4,000 to 5,000 ( Peak Torque )  as the AFM maxes out due to airflow and then ECU relies solely on an RPM and WOT TPS controlled Fuel Mapping Table. After 5,000 rpm the factory WOT Fuel Map tends to go on the rich side as a safety feature ( Common Japanese ECU strategy in the day ) and this can sometimes put you in a safe AFR reading with a mildly modified engine. Laen at Paek Torque is the worst thing for an engine... so keep the mechanical advance on the conservative side.

 

However, you really need top throw it on a chassis Dyno with a WB Air Fuel Meter to see what it's doing. These old ECU's are Analog ( not Digital ) and they can drift all over the place. Sometimes you can get lucky and they drift into a sweet spot. Sometimes thye go the wrong way. It's all dependant on the condition of the 40 year old capacitors and resistors in the ECU.

 

Once you have your Dyno figures, you have a baseline on what you can do.

 

Best way... Complete standalone ECU and $$$$ or switch to Triple carbs $$$.

 

Poor mans way.

 

Aeromotive adjustable EFI  fuel pressure regulator. The 13129 can be found for around $129 at Summit and Jegs. It's a compact unit so easy to fit.

 

On the Dyno, raise the Fuel pressure till your WOT AFR's are in a safe range. This will compromise partial throttle AFR's somewhat ( they will go rich ) but it's an Analog ECU and you'll just have to live with it. If you have to go over 45 to 50 PSI ( 37.5 is stock pressure )  consider slightly larger injectors. Don't go too big as you have limited fuel compensation with the Analog ECU . Stock injectors are rated at 188cc at 3 Bar ( 43 psi ) . ZX Turbo injectors ( 295cc ) at 3 Bar  " may " work with the NA ECU... but I'm not sure if that will throw the stock NA ECU calibration out too far. Perhaps others can chime in with more info.

 

After getting the WOT AFR's corrected. You should be able to trim the part throttle AFR values by tightening the AFM Vane " clock spring " a few clicks. Go easy and make sure you mark the original setting. Read up on the old " flappy doodle "  Vane style AFM's if you're not familiar with them, and remember you are dealing with Dinosaur Technology. There is limited adaptability.. but some mild tweaks can be done. Bear in mind that everything is going to be a compromise.

 

Biggest challenge will be avoiding Detonation in the critical 4,000 to 5,500 RPM range. What cylinder heads and pistons are you running? Some combo's are better/worse than others. The N47 and N42 heads ( what do you have ) are more detonation prone than the P90 heads.

 

With 10 to 1 CR, be conservative with mechanical ignition timing and use the best fuel available. 94 or 94+ Octane preferred. If you can only get 91 Octane in your state, be REALLY conservative on ignition timing. I'd say no more than 30 to 32 degrees total until you get the AFR's corrected. The last thing you want is too much ignition timing and a lean out at Peak Torque or High RPM.

Edited June 7, 2016 by Chickenman

[Chickenman]

Back in the early days of Analog non feedback ( O2 soreness ) ECU's the really good tuners would modify the ECU;s with different resistor values or adjustable Pots. Pots were the easiest. Lot's and lots of Dyno time and soldering skills in those days. Todays Digital, Wide Band ECU';s with self tuning features make EFI tuning a " piece of cake " compared to what we did in the late 70's and through the mid 80's.

Edited June 7, 2016 by Chickenman

[gira]

Chickenman,

 

Great info. It's an ITM kit on and N42 block. I'll be conservative with the ignition timing for sure. We have good gas down here. I'll make sure the customers only uses 93. 

 

Thanks!

 

greg