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Soft Rev Limit & Boost

Old 04-30-2012, 01:43 PM
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Default Soft Rev Limit & Boost

According to the 2.6 Hydra users manual, the soft rev limit "begins to cut fuel events to reduce torque output and produce a “soft” limiting effect on engine speed."

Since it is a rev limiter it is typically going to be doing this at high rpm and high load (max boost).

I would think pulling fuel under those conditions, especially on a boosted car, would be a very bad idea. Am I missing something here? Should I set my hard rev limit lower than the soft and let it just cut ignition to begin with?
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Old 04-30-2012, 08:27 PM
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Originally Posted by disney7 View Post
According to the 2.6 Hydra users manual, the soft rev limit "begins to cut fuel events to reduce torque output and produce a “soft” limiting effect on engine speed."

Since it is a rev limiter it is typically going to be doing this at high rpm and high load (max boost).

I would think pulling fuel under those conditions, especially on a boosted car, would be a very bad idea. Am I missing something here? Should I set my hard rev limit lower than the soft and let it just cut ignition to begin with?
I wondered this also but never got around to asking. Also wondered the same for the fuel cut on overboost protection.
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Old 04-30-2012, 10:41 PM
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It will cut fuel sprayed per combustion stroke

Now auck me
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Old 08-15-2012, 12:16 AM
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My understanding is, as you thought, that cutting fuel on a boosted engine is a bad thing. So using the ignition cut out is much safer.
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Old 08-16-2012, 02:31 PM
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It probably cuts it completely... many stock turbo cars have a fuel cut overboost protection on them. It was fine.
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Old 08-17-2012, 10:39 PM
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Originally Posted by concealer404 View Post
It probably cuts it completely... many stock turbo cars have a fuel cut overboost protection on them. It was fine.
Yes, and fine for the safe boost that OEM's use. Pushing 15+ psi on an engine not originally built for a turbo is a different scenario. If you have the capability of choosing fuel cut or ignition cut, why not choose the latter and eliminate the lean mixture risk?
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Old 08-18-2012, 01:34 AM
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Originally Posted by dynodragon View Post
Yes, and fine for the safe boost that OEM's use. Pushing 15+ psi on an engine not originally built for a turbo is a different scenario. If you have the capability of choosing fuel cut or ignition cut, why not choose the latter and eliminate the lean mixture risk?
Not how fuel cut works. Typically revlimit cuts a percentage of ingnution or fuel events. If there is no fuel in cylinder, you are not lean. There is just air. Nothing to burn.
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Old 08-18-2012, 10:49 AM
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Originally Posted by dynodragon View Post
Yes, and fine for the safe boost that OEM's use. Pushing 15+ psi on an engine not originally built for a turbo is a different scenario. If you have the capability of choosing fuel cut or ignition cut, why not choose the latter and eliminate the lean mixture risk?
Not how it works.

Originally Posted by Faeflora View Post
Not how fuel cut works. Typically revlimit cuts a percentage of ingnution or fuel events. If there is no fuel in cylinder, you are not lean. There is just air. Nothing to burn.
How it works.


That said, if i had the choice, i'd go with ignition as well. Mostly because i'm a ricer and think it sounds cool.
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Old 08-18-2012, 02:30 PM
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Originally Posted by disney7 View Post
According to the 2.6 Hydra users manual, the soft rev limit "begins to cut fuel events to reduce torque output and produce a “soft” limiting effect on engine speed."

Since it is a rev limiter it is typically going to be doing this at high rpm and high load (max boost).

I would think pulling fuel under those conditions, especially on a boosted car, would be a very bad idea. Am I missing something here? Should I set my hard rev limit lower than the soft and let it just cut ignition to begin with?

The purpose of soft and hard limit is for driveability.


Originally Posted by concealer404 View Post
Not how it works.



How it works.


That said, if i had the choice, i'd go with ignition as well. Mostly because i'm a ricer and think it sounds cool.

Yah. It is cool. Actually it is frikken awesome. One of te joys of turbo car
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Old 08-18-2012, 02:52 PM
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Originally Posted by concealer404 View Post
That said, if i had the choice, i'd go with ignition as well. Mostly because i'm a ricer and think it sounds cool.
x2
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Old 08-19-2012, 06:10 PM
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It washes down the cylinders, increases the chances of fouling the plugs, sends your turbine housing temps through the roof, and will add quite a bit of spool to your turbo when you might be trying to limit boost (if you are using it for boost cut and not rev-limiter).
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Old 09-03-2012, 10:16 PM
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Originally Posted by Faeflora View Post
Not how fuel cut works. Typically revlimit cuts a percentage of ingnution or fuel events. If there is no fuel in cylinder, you are not lean. There is just air. Nothing to burn.
Right. Thanks. I looked up my Hydra manual and it describes cutting 40% of the injector cycles...
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