What is the different of Higher Timing Lower Boost with Lower Timing High Boost?
Why are you changing timing at all loads? You have a map that you can change the AFR and timing at a given load and RPM point.
A motor will have a given AFR and timing correlation that can produce stable combustion at a given load and RPM level on a given fuel. You might be able to run 40psi on 91 octane, but you have to run negative timing to get it stable. If it's not making more power at 40psi then 25psi, what the point though is the only question you need to ask.
Tune a given boost level. Play with fuel and timing combination to find the best power at that load leve. Now move to the next load level and tune it. Does the car make more power at the higher load? Yes...go higher. No, you've reached the limit where adding more boost won't do anything for you and you should go back to the lower boost level.
IMO, if you have to go richer then 11:1 AFR on even 91 octane, you are getting close to the limits. I usually try to stop raising boost around that level as the gains are going to be small from there on out and it's just a lot more stress on everything for minimal power.
A motor will have a given AFR and timing correlation that can produce stable combustion at a given load and RPM level on a given fuel. You might be able to run 40psi on 91 octane, but you have to run negative timing to get it stable. If it's not making more power at 40psi then 25psi, what the point though is the only question you need to ask.
Tune a given boost level. Play with fuel and timing combination to find the best power at that load leve. Now move to the next load level and tune it. Does the car make more power at the higher load? Yes...go higher. No, you've reached the limit where adding more boost won't do anything for you and you should go back to the lower boost level.
IMO, if you have to go richer then 11:1 AFR on even 91 octane, you are getting close to the limits. I usually try to stop raising boost around that level as the gains are going to be small from there on out and it's just a lot more stress on everything for minimal power.
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Evolved Member
Joined: Aug 2010
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From: The Universe
Why are you changing timing at all loads? You have a map that you can change the AFR and timing at a given load and RPM point.
A motor will have a given AFR and timing correlation that can produce stable combustion at a given load and RPM level on a given fuel. You might be able to run 40psi on 91 octane, but you have to run negative timing to get it stable. If it's not making more power at 40psi then 25psi, what the point though is the only question you need to ask.
Tune a given boost level. Play with fuel and timing combination to find the best power at that load leve. Now move to the next load level and tune it. Does the car make more power at the higher load? Yes...go higher. No, you've reached the limit where adding more boost won't do anything for you and you should go back to the lower boost level.
IMO, if you have to go richer then 11:1 AFR on even 91 octane, you are getting close to the limits. I usually try to stop raising boost around that level as the gains are going to be small from there on out and it's just a lot more stress on everything for minimal power.
A motor will have a given AFR and timing correlation that can produce stable combustion at a given load and RPM level on a given fuel. You might be able to run 40psi on 91 octane, but you have to run negative timing to get it stable. If it's not making more power at 40psi then 25psi, what the point though is the only question you need to ask.
Tune a given boost level. Play with fuel and timing combination to find the best power at that load leve. Now move to the next load level and tune it. Does the car make more power at the higher load? Yes...go higher. No, you've reached the limit where adding more boost won't do anything for you and you should go back to the lower boost level.
IMO, if you have to go richer then 11:1 AFR on even 91 octane, you are getting close to the limits. I usually try to stop raising boost around that level as the gains are going to be small from there on out and it's just a lot more stress on everything for minimal power.
Thread Starter
Evolved Member
Joined: Aug 2010
Posts: 1,426
Likes: 2
From: The Universe
You forgot to talk about air density. The more boost you run, the denser the air charge is. The denser the air charge is, the less timing is need, because the flame front moves faster though denser air.
Also, when on knock limited fuel (like 91oct), they usually take boost better then they take timing, making a high boost, low timing tune a better option.
Also, when on knock limited fuel (like 91oct), they usually take boost better then they take timing, making a high boost, low timing tune a better option.
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