Last month, we showed you how we turned The Big Block From Hell from a pump-gas thumper into a nitrous-swilling beast of an engine. This time around, we'll dive deeper into the tune-up of our engine, because it represents one of the most difficult examples of tuning an engine to run safely on N2O. The tips here apply to most any engine you'd like to tune, and although there is a multitude of ways to arrive at the same result, these are just the steps that worked for us. Entire books have been devoted to the subject of nitrous tuning and we won't pretend to be experts on the subject, this is simply what worked for us.
As you recall, we rebuilt the bottom end of the engine using a piston design and ring package that will withstand up to a 400 shot of nitrous. We then added a Nitrous Supply direct port fogger nitrous system to the intake manifold and an Aeromotive fuel pressure regulator for the system. We also wired up an MSD Digital 7 ignition system and HVCII coil, which gave us a ton of tuning options and the firepower needed to light the mixture of air and fuel.
The nitrous system was flow-tested and blueprinted by Steve Johnson of Induction Solutions. Steve provided the baseline tune-up for our system, which gave us a safe starting point for the nitrous and fuel jetting and ignition timing. We then took that info and the engine to Westech Performance Group, where we utilized the shop's Innovate ST-12 wideband O2 air/fuel ratio data-logging system to aid in tuning the engine.
When all was said and done, the engine cranked out 1,284 horsepower at 7,100 rpm without grenading on the dyno. Along the way, we learned the effects of jetting and timing changes and how we could fix a bad fuel distribution problem with some creative nitrous tuning. Here are the results of our latest engine experiment.
Part One: Firestarter
We last tested this motor using an MSD 6AL box and a blue HVC coil. The 6AL is capable of firing the engine even with the nitrous oxide, but we'd have to add a separate retard box to pull timing advance from the engine when the nitrous system is activated. We have to pull out some timing to avoid detonation when the nitrous is activated so we looked for a box that had that feature built-in. The Digital 7 box (part number 7531) not only contains several different programmable retard functions, but it also offers a start retard, programmable rev limiter, individual cylinder timing, and data-logging capabilities. The new box requires switching to the red HVCII coil though. The blue coil will work on a naturally aspirated engine, but it's not optimized for the Digital 7 box.
1. This screen shot from our...
1. This screen shot from our laptop will give you some idea of the level of power of the Digital 7. It’s got all the bells and whistles, so making quick changes is as simple as pushing a few buttons.
2. For our test, we utilized...
2. For our test, we utilized the pink output wire of the Digital 7, which is a trigger wire for the Step 1 retard. By tapping the pink wire into the 12-volt input wire of the nitrous solenoids, we were able to tell the Digital 7 to retard the ignition timing any time the nitrous system was activated. The amount of retard is programmed via the laptop from this menu.
3. If you want to get really...
3. If you want to get really tricky, you can ramp in and ramp out the amount of ignition retard over a specific amount of time, as well as trigger the nitrous for specific amount of time, or program a launch rev limit curve on a graph on your laptop. The options for tuning are mind-boggling with this system.