FI guys
12-28-2013, 11:38 PM
#1
Burning Brakes
Thread Starter
FI guys
Any of you FI guys added a Vararam without a retune? I am wondering just what would be the reason for a retune? I am new too all this, I am sure that is obvious by the question, but I don't understand what there is to retune for. I am running 10# of boost now, is that going to change with a vararam? How would you tune for a vararam on a dyno? I realize there is more to this than I am seeing, but a little explanition of why I would need a retune would be GREATLY APPRECIATED. Thanks 
12-29-2013, 01:56 PM
#2
Le Mans Master
Member Since: Aug 2005
Location: CA.
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St. Jude Donor '13-'14-'15
Varrarams are known to throw codes even un boosted----Reason being ANY cold air intake that is very efficient adds so much more air that the fuel mixture become lean during P/T---(closed loop) and then rich at WOT ( open loop P/E)
During P/T operation the ECM is always correcting the AFR to 14.68 using the front 02's to collect data---Then takes that data to either add or subtract fuel to get 14.68 using the fuel trims---- Simply more incoming air would require more fuel .You would be having a + fuel trim
However when you FLOOR it the ECM goes into Open loop. The 02's are not being used --the fueling will be commanded by whatever is programmed into your PE table
in your tune
Where it gets complicated---- IF you have a + fuel trim "just before going to WOT" the ECM will ADD the % to your WOT AFR----
If you have a negative fuel trim "JBGTWOT" the trims will lock on "0" The ECM will never subtract fuel as a safety at WOT to prevent damage
In your case say the Varraram is adding 15% more air-- to compensate the ECM is then adding 15% more fuel to get back to 14.68 at P/T AFR--this can make the eng
run rough or surge or try to die--
But worst of all the ECM is now adding 15% more fuel at WOT as a safety---A typical blown AFR at WOT is about 10.20 AFR---so you are getting 10.20 plus 15% more--which equals 8.67 !!!! AFR at WOT
Your P/T fuel is lean and creating surging dying--rough running
Your WOT fuel is PIG RICH making your engine really lazy and getting horrible mileage
A lean or rich code will not appear until the trims get around +/- 20 %
which would tell you you need a tune -BUT if the trims are under 20% NO code will appear and it will just run like crap
During P/T operation the ECM is always correcting the AFR to 14.68 using the front 02's to collect data---Then takes that data to either add or subtract fuel to get 14.68 using the fuel trims---- Simply more incoming air would require more fuel .You would be having a + fuel trim
However when you FLOOR it the ECM goes into Open loop. The 02's are not being used --the fueling will be commanded by whatever is programmed into your PE table
in your tune
Where it gets complicated---- IF you have a + fuel trim "just before going to WOT" the ECM will ADD the % to your WOT AFR----
If you have a negative fuel trim "JBGTWOT" the trims will lock on "0" The ECM will never subtract fuel as a safety at WOT to prevent damage
In your case say the Varraram is adding 15% more air-- to compensate the ECM is then adding 15% more fuel to get back to 14.68 at P/T AFR--this can make the eng
run rough or surge or try to die--
But worst of all the ECM is now adding 15% more fuel at WOT as a safety---A typical blown AFR at WOT is about 10.20 AFR---so you are getting 10.20 plus 15% more--which equals 8.67 !!!! AFR at WOT
Your P/T fuel is lean and creating surging dying--rough running
Your WOT fuel is PIG RICH making your engine really lazy and getting horrible mileage
A lean or rich code will not appear until the trims get around +/- 20 %
which would tell you you need a tune -BUT if the trims are under 20% NO code will appear and it will just run like crap
12-29-2013, 06:37 PM
#3
Burning Brakes
Thread Starter
Varrarams are known to throw codes even un boosted----Reason being ANY cold air intake that is very efficient adds so much more air that the fuel mixture become lean during P/T---(closed loop) and then rich at WOT ( open loop P/E)
During P/T operation the ECM is always correcting the AFR to 14.68 using the front 02's to collect data---Then takes that data to either add or subtract fuel to get 14.68 using the fuel trims---- Simply more incoming air would require more fuel .You would be having a + fuel trim
However when you FLOOR it the ECM goes into Open loop. The 02's are not being used --the fueling will be commanded by whatever is programmed into your PE table
in your tune
Where it gets complicated---- IF you have a + fuel trim "just before going to WOT" the ECM will ADD the % to your WOT AFR----
If you have a negative fuel trim "JBGTWOT" the trims will lock on "0" The ECM will never subtract fuel as a safety at WOT to prevent damage
In your case say the Varraram is adding 15% more air-- to compensate the ECM is then adding 15% more fuel to get back to 14.68 at P/T AFR--this can make the eng
run rough or surge or try to die--
But worst of all the ECM is now adding 15% more fuel at WOT as a safety---A typical blown AFR at WOT is about 10.20 AFR---so you are getting 10.20 plus 15% more--which equals 8.67 !!!! AFR at WOT
Your P/T fuel is lean and creating surging dying--rough running
Your WOT fuel is PIG RICH making your engine really lazy and getting horrible mileage
A lean or rich code will not appear until the trims get around +/- 20 %
which would tell you you need a tune -BUT if the trims are under 20% NO code will appear and it will just run like crap
During P/T operation the ECM is always correcting the AFR to 14.68 using the front 02's to collect data---Then takes that data to either add or subtract fuel to get 14.68 using the fuel trims---- Simply more incoming air would require more fuel .You would be having a + fuel trim
However when you FLOOR it the ECM goes into Open loop. The 02's are not being used --the fueling will be commanded by whatever is programmed into your PE table
in your tune
Where it gets complicated---- IF you have a + fuel trim "just before going to WOT" the ECM will ADD the % to your WOT AFR----
If you have a negative fuel trim "JBGTWOT" the trims will lock on "0" The ECM will never subtract fuel as a safety at WOT to prevent damage
In your case say the Varraram is adding 15% more air-- to compensate the ECM is then adding 15% more fuel to get back to 14.68 at P/T AFR--this can make the eng
run rough or surge or try to die--
But worst of all the ECM is now adding 15% more fuel at WOT as a safety---A typical blown AFR at WOT is about 10.20 AFR---so you are getting 10.20 plus 15% more--which equals 8.67 !!!! AFR at WOT
Your P/T fuel is lean and creating surging dying--rough running
Your WOT fuel is PIG RICH making your engine really lazy and getting horrible mileage
A lean or rich code will not appear until the trims get around +/- 20 %
which would tell you you need a tune -BUT if the trims are under 20% NO code will appear and it will just run like crap
02-28-2014, 03:06 PM
#4
Any of you FI guys added a Vararam without a retune? I am wondering just what would be the reason for a retune? I am new too all this, I am sure that is obvious by the question, but I don't understand what there is to retune for. I am running 10# of boost now, is that going to change with a vararam? How would you tune for a vararam on a dyno? I realize there is more to this than I am seeing, but a little explanition of why I would need a retune would be GREATLY APPRECIATED. Thanks
Varrarams are known to throw codes even un boosted----Reason being ANY cold air intake that is very efficient adds so much more air that the fuel mixture become lean during P/T---(closed loop) and then rich at WOT ( open loop P/E)
During P/T operation the ECM is always correcting the AFR to 14.68 using the front 02's to collect data---Then takes that data to either add or subtract fuel to get 14.68 using the fuel trims---- Simply more incoming air would require more fuel .You would be having a + fuel trim
However when you FLOOR it the ECM goes into Open loop. The 02's are not being used --the fueling will be commanded by whatever is programmed into your PE table
in your tune
Where it gets complicated---- IF you have a + fuel trim "just before going to WOT" the ECM will ADD the % to your WOT AFR----
If you have a negative fuel trim "JBGTWOT" the trims will lock on "0" The ECM will never subtract fuel as a safety at WOT to prevent damage
In your case say the Varraram is adding 15% more air-- to compensate the ECM is then adding 15% more fuel to get back to 14.68 at P/T AFR--this can make the eng
run rough or surge or try to die--
But worst of all the ECM is now adding 15% more fuel at WOT as a safety---A typical blown AFR at WOT is about 10.20 AFR---so you are getting 10.20 plus 15% more--which equals 8.67 !!!! AFR at WOT
Your P/T fuel is lean and creating surging dying--rough running
Your WOT fuel is PIG RICH making your engine really lazy and getting horrible mileage
A lean or rich code will not appear until the trims get around +/- 20 %
which would tell you you need a tune -BUT if the trims are under 20% NO code will appear and it will just run like crap
During P/T operation the ECM is always correcting the AFR to 14.68 using the front 02's to collect data---Then takes that data to either add or subtract fuel to get 14.68 using the fuel trims---- Simply more incoming air would require more fuel .You would be having a + fuel trim
However when you FLOOR it the ECM goes into Open loop. The 02's are not being used --the fueling will be commanded by whatever is programmed into your PE table
in your tune
Where it gets complicated---- IF you have a + fuel trim "just before going to WOT" the ECM will ADD the % to your WOT AFR----
If you have a negative fuel trim "JBGTWOT" the trims will lock on "0" The ECM will never subtract fuel as a safety at WOT to prevent damage
In your case say the Varraram is adding 15% more air-- to compensate the ECM is then adding 15% more fuel to get back to 14.68 at P/T AFR--this can make the eng
run rough or surge or try to die--
But worst of all the ECM is now adding 15% more fuel at WOT as a safety---A typical blown AFR at WOT is about 10.20 AFR---so you are getting 10.20 plus 15% more--which equals 8.67 !!!! AFR at WOT
Your P/T fuel is lean and creating surging dying--rough running
Your WOT fuel is PIG RICH making your engine really lazy and getting horrible mileage
A lean or rich code will not appear until the trims get around +/- 20 %
which would tell you you need a tune -BUT if the trims are under 20% NO code will appear and it will just run like crap
02-28-2014, 05:00 PM
#5
Racer
Member Since: Sep 2011
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ram air is not a kind of forced induction. driving on the highway relying on wind speed will never increase the atmospheric pressure inside the engine. all it does is gives you is the coldest air intake temp possible.