Ignition Timing And Nitrous - Edelbrock 70005 Installation Manual

5.0

Ignition Timing and Nitrous

Because we are oxidizing the air/fuel mix going into the engine when nitrous oxide is used, we must pay close attention to
the ignition timing profile. Remember, "nitrous" oxygen is more dense than "atmospheric" oxygen and resulting in an
accelerated burn rate of your fuel.
In anticipation of the quicker burn time, you must retard the timing of the ignition system when using nitrous oxide. The
more power we try to make, the more timing in degrees we must remove from the timing profile. This is not in total advance
but the time in which we bring timing in (the advance curve).
This is why all nitrous users are so concerned with evidence of detonation. The accelerated burn rate of the air/fuel charge
can cause severe detonation without a "nitrous" ignition strategy. A timing profile that is accelerated and a total timing
number retarded will keep you from experiencing catastrophic engine damage.
The general rule of nitrous use ignition timing should be to retard the "total" advance number approximately 2 degrees for
every 50 HP increase when using nitrous oxide. It is always best to start with your engines best total timing (without nitrous)
and reduce total timing from there. Use an initial timing retard setting that is at least 2-4 degrees more retarded than you
expect to be the best setting for your application. All stated timing adjustments listed in jet maps is where the motor being
tested worked best.
Every aspect of the vehicle and engine affects your nitrous systems performance-- vehicle weight, converter, gearing, engine
displacement, cylinder head type, camshaft, compression, manifold and induction type ect.. The exact amount of timing to
pull out varies for every combination. Start conservatively, and put timing back in gradually. On a Nitrous system, even 1
degree change in advance can make a big difference.
When using aftermarket ignition components and/or systems, it would be advisable to contact the manufacturer for
information on using their components with a nitrous system. It is always better to be very conservative in your timing
approach and tune towards an optimum timing setting.
Example:
Ignition timing without Nitrous Oxide
100 HP increase from Nitrous Oxide
Initial safety margin
Total timing with Nitrous Oxide
The following test plan, for determining ignition timing, will give you a guide to determine the best timing profile for your
vehicle, hopefully avoiding engine damage during the tuning phase:
1. Install the nitrous jetting for a selected horsepower increase. Use the 100 horsepower setting to learn the finer points
of working with nitrous oxide. This will keep your margin for error as large as possible.
2. Estimate the reduced ignition timing that you think will produce best power, based upon the 2° retard per 50 HP increase
rule.
3. Set ignition timing 2°-3° retarded from your best power estimate setting. This is your cushion for error.
4. Stabilize nitrous bottle pressure at 900 to 950 psi. It is best to select a pressure and keep the pressure to ±¼ psi.
5. Run your vehicle in a controlled manner (like a ¼ mile drag strip) without the use of nitrous. This is called "on motor".
Note vehicle mph as a baseline to measure nitrous assisted increases.
6. Adjust your ignition timing to a nitrous timing setting.
7. Run your vehicle in the same controlled manner (like a ¼ mile drag strip) with the use of nitrous. Note vehicle mph
increase and compare it to your baseline.
Note: Listen for any knocking sounds when running the vehicle. Watch your temperature gauges. Continued nitrous use
will elevate coolant temperatures. See Testing Checklist for more testing methodology helpful hints.
Catalog #70005
Rev. 07/08 - AJ/mc
38 degrees "total"
2 degrees "retard"
2 degrees "retard"
34 degrees "total"
Page 15 of 20
©2008 Edelbrock Corporation
Brochure No. 63-70005