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Tie One On
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Discussion Starter #1
I am looking at a SEPST file that is loaded from an update I did online and it is showing a cc displacement of 1250 and this map is for a 2006/07 vrscr model which only has an 1130 cc engine size.
Is there a benefit to upping the cc size of the engine in the SEPST that someone can point out to me ?
I am at a loss as to why you would tell the ECM that you have a larger displacement than you actually are running unless it is a way of tricking the ECM or something like that .

Any info would help me to learn more about the SEPST since I am looking to become well versed in its management of the V ROD tuning.
 

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I am looking at a SEPST file that is loaded from an update I did online and it is showing a cc displacement of 1250 and this map is for a 2006/07 vrscr model which only has an 1130 cc engine size.
Is there a benefit to upping the cc size of the engine in the SEPST that someone can point out to me ?
I am at a loss as to why you would tell the ECM that you have a larger displacement than you actually are running unless it is a way of tricking the ECM or something like that .

Any info would help me to learn more about the SEPST since I am looking to become well versed in its management of the V ROD tuning.
The displacement value is used in determining how much air is available for combustion. If this "constant" is set to a value that's larger than what the engine displacement actually is then the calculated fuel will tend to produce a rich mixture.

Some tuners adjust this value up if the VE values are maxed out in some cells and the engine is still running lean there. Another way to do this would be to change the injector size to a smaller number.
 

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Tie One On
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Discussion Starter #3
Thanx, Now I want to ask a Q as to when you may use this.

So, for a change in a slightly modified air cover ( only a couple additional small holes) it would not be benefit to up the cc size any
But, if a moded air cover (like topless) would be a benefit to up the cc size ?

I am asking this to put it into perspective on when you may want to up the cc size over the actual size of the engine.
 

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...So, for a change in a slightly modified air cover ( only a couple additional small holes) it would not be benefit to up the cc size any
But, if a moded air cover (like topless) would be a benefit to up the cc size ? ...
Someone like Leon Brown (lbrown) would have more experience with this but, from what I know, this would only be needed with radical changes involving pumping efficiency like different cams or length of velocity stack changes. It also becomes necessary sometimes in race applications when very low AFR targets are required to avoid knock or excessive combustion temperatures. A stock motor with exhaust and air filter changes should only require minor corrections of VE values in order to hit the target AFRs. Most tuning changes will be done on the AFR and spark advance tables to get the most out of the fuel you're using.
 
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