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high boost pressure

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i have tuned lot of cars with 30-40 psi of boost with good success

i always tackled the ignition issue the same way of removing ignition with the increased boost.

the most i went is 40psi with about 16-17 of advance at that boost.

now the question is this.if you have a motor that you want to put 70 psi in, would you remove the same amount of ignition per psi?

how do you approach it?

or there is a point were you dont have to remove all that ignition?what ignition are the big guys running with 70 and 80 psi?


Hey hiper,

The correct ignition advance for an engine is always a moving target that will depend on load and rpm (as well as obviously the basic mechanical design of the engine). As a general guide, as rpm increases we need to advance the timing since there is less time available for the burn to occur. Conversely as we increase boost pressure we need to retard the timing as the combustion event happens faster with more fuel and air packed into the cylinder.

So yes, as boost increases we need to retard the ignition timing. The approach I use is the same regardless if I'm tuning on pump gas at 15 psi or methanol at 50+ psi. I always start with conservative or very retarded timing and then advance it to find MBT (or the knock threshold). If you're aiming for 50-70 psi you may decide to add a little caution and stop advancing the timing when you see the torque begin to plateau though as any hint of knock at the sort of specific power levels you are likely to be seeing at this boost level could be damaging.

It's not uncommon to see ignition advance on methanol drag engines at 60+ psi boost in the high teens, but obviously you can't expect to apply the same ignition advance to every engine - There are simply too many variables.

The key is to start at low boost and work your way up. This will let you build up an idea of how much timing you need to retard per pound of boost for example. Before you increase the boost, you can then remove the correct amount of timing from the next load row (actually for safety you would want to remove a little more timing than you expect and then slowly advance it again and watch the torque change).

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