I've got an 88 EEC-IV speed-density EFI system on an older 302 truck. I'm thinking of adding a 50 shot of nitrous to aid my 4000 lb vehicle in passing on the highway. I've never used nitrous but it seems to be a practical performance add-on for my use.

My question is, will a speed density system adjust to the say 10 seconds of 50 shot without any issues? I'm intrested in using a "wet" kit. If you guys think this is OK, where is the proper place to mount the spray nozzle? In front or behind the throttle plate?

 

i have a wet kit that has a plate between the carb and manifold but not sure about fuel injection, i dont think SD will comensate with extra fuel for the nitrous but i'm not sure. hopefully someone else will post thats done the SD nitrous combo

 

There are two ways of doing this, MAF or SD.

The EEC can correct the A/F ratio to a point based on what the o2 sensor(s) see. So some correction of fuel can occur. However there are limits so it's common have the nitrious system add fuel as well as gas to the mixture in the intake.

The easiest way to do this on EFI systems of any kind, is to install a vaccum adjustable fuel pressure regulator in place of the stock unit. Then with a small electric valve, when the nitrious button is hit, the nitrious solenoids open as well as the valve for the fuel pressure regulator, so the fuel pressure goes up with the nitrious.

Then you have fuel, and air. For a 50HP shot that's a very easy, reasonable solution.

If you're going to use staged, or 200HP shots, then you'd want the nitrious trigger mechanism to also tell the EFI computer that nitrious is being shot, so the pulsewidths on the injectors significantly increase to add the fuel. It's more reliable and easier to tune this way, but then you need "stuff" to tune the EEC and know what you are doing to a much greater degree. i.e. less of a bolt on solution.

 

Thanks Frederic. I don't quite understand how the regulator/valve works? How does it know how much fuel pressure to spike to compensate for the extra nitrous shot?

I was thinking that the wet kits have calibrated nozzles one each for the gas and fuel. If they are suppose to be matched, shouldn't the nitrous/gas mix along with the engines stock incoming fuel mix be enough for the O2 to correct any minor imbalance?

Also one last question. Since nitrous is triggered only at WOT, doesn't the ECM overlook the O2 at WOT?... thanks

Mike

 

At WOT, the O2 sensors are ignored, and that's where the nitrous systems are designed to operate.

An adjustable fuel pressure regulator will help to increase/maintain the fuel pressure at the fuel rails. It'll increase the fuel pressure under heavy throttle conditions (less vacuum), and it will push more fuel through the injectors because of this. I'd recommend getting some initial air/fuel ratio reading, on a dyno or using a wideband O2. You'll be able to see what the mixture is like and make any neccessary changes. One thing to note with speed density is that it doesn't adapt to climate changes so testing in warmer and cooler temps is a good idea.

 

I used a wet kit for years. The kit adds the extra fuel needed, so the ECM doesn't have too. You will need to drop the timing back a few degrees to avoid detonation. This will make your "off the bottle" performance a bit weaker.

 

Maybe on your truck

And excellent explaination of the variable fuel pressure regulator. Cool.

 

Yes, my 94 Lightning does go into open loop at a certain throttle position. My brothers 94 F-150 also goes into open loop at a certain throttle position.
Ford did program some truck ECU's to stay in closed loop at all times. However, at WOT, this is not a good situation with aftermarket parts and/or power adders without some type of aftermarket tuning.

 

Thank you gents for each of your replies, but I'm still lost on two things yet.

So would most of you agree that a 50 shot will work with a "Speed-density" system providing that I compensate for altitude?

In comparing an adjustable fuel regulator to a stock, doesn't the stock regulator already increase pressure as manifold vacuum decreases? How does the adjustable f/reg adjust pressure only when the nitrous is activated? does it tap into the micro s/w at WOT? If so then will it still increase pressure at WOT even without activating the nitrous?

sorry for the stupid questions

 

An adjustable fuel pressure regulator (or FPR) increases the fuel pressure, at the rails, when there's less vacuum or heavy throttle conditions. The adjustment determines how much more pressure the fpr will make. Now the stock unit is fixed in the amount of fuel pressure it is able to make. An adjustable FPR can be adjusted to make more pressure at the rails given the need, and yes, it will increase the pressure with or without the nitrous being that it is vacuum operated. Again, fuel pressure increases will be noticed under heavy throttle. You can make adjustments to an FPR, but it'll work best with a guage. I prefer ones mounted in the cab, but a diagnostic type gauge (mounts on the rail) will work fine.

With speed density, the air/fuel charge will vary with outside air temps (more so in open loop/WOT), and yes, with altitude. A safe way to tune it would be to monitor it with a wideband O2 to get accurate A/F ratios. These can also be mounted in the cab as well.

Also, as LxMan1 mentioned, turn your initial timing back a few degrees if you don't plan on any aftermarket tuning. You may also want to get a different set of spark plugs that are one heat range colder than stock to keep the combustion temps down. Someone else might chime in about the heat range though.