Big injectors,tune diff /w 98 vac fuel regulator?
05-27-2003, 02:57 AM
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Big injectors,tune diff /w 98 vac fuel regulator? Im reading through on how to use LS1Edit to tune for swapping in larger injectors on http://ls1edit.slowcar.net/tuning.html
It says "The only tricky parameter to set here will be injector constant. This is because the LS1 does not have a manifold vacuum regulated fuel pressure, so as manifold vacuum changes (and rail pressure stays constant) the pressure drop across the injector change, so the injector flow/constant itself changes. A spreadsheet to simplify the calculation is made available:
Excel spreadsheet to calculate injector constant
If you are using a vacuum referenced regulator (some supercharger setups, etc.) then you will simply fill in a constant value across the range"
Now i have a 98 fuel rail on my ls1 conversion with 30lb SVO fuel injectors. How do i tune for 30lb injectors (rated at 43.5-45 psi) for a car that came with 28.8 injectors @ 58 psi)???? Does the vacuum controlled fuel pressure regulators on 98 cars change the tuning (because the feed and return fuel system)???
It says "The only tricky parameter to set here will be injector constant. This is because the LS1 does not have a manifold vacuum regulated fuel pressure, so as manifold vacuum changes (and rail pressure stays constant) the pressure drop across the injector change, so the injector flow/constant itself changes. A spreadsheet to simplify the calculation is made available:
Excel spreadsheet to calculate injector constant
If you are using a vacuum referenced regulator (some supercharger setups, etc.) then you will simply fill in a constant value across the range"
Now i have a 98 fuel rail on my ls1 conversion with 30lb SVO fuel injectors. How do i tune for 30lb injectors (rated at 43.5-45 psi) for a car that came with 28.8 injectors @ 58 psi)???? Does the vacuum controlled fuel pressure regulators on 98 cars change the tuning (because the feed and return fuel system)???
05-27-2003, 08:41 AM
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Re: Big injectors,tune diff /w 98 vac fuel regulator? just multiply the Injector flow rate by 127% then go log your ltrims. If still positive, go a little less. If too negative, go a little more. 127% will get you very close.
Don't muck around with the injector offset table. There's no need.
Don't muck around with the injector offset table. There's no need.
05-27-2003, 12:25 PM
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Re: Big injectors,tune diff /w 98 vac fuel regulator? 98 f-body are not vacuum referenced either as far as I know. (97 vets were and possibly 98 vets) So basically you do the same trend as stock.
to find out the new injector rate use this
square root of (58 psig/43.5)*30 = new flow rate (lb)
new flow rate (lb) /(28.8) and multiply this value by the injector flowrate table in LS1-edit or whatever you are using. The tables in edit are g/s but this does not matter.
Gary
to find out the new injector rate use this
square root of (58 psig/43.5)*30 = new flow rate (lb)
new flow rate (lb) /(28.8) and multiply this value by the injector flowrate table in LS1-edit or whatever you are using. The tables in edit are g/s but this does not matter.
Gary
05-27-2003, 03:04 PM
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Re: Big injectors,tune diff /w 98 vac fuel regulator? Well I have the fuel rail off of a 98 corvette. I should have mentioned it. So does that mean it needs to be tuned funny??????
98 f-bodys were not return fuel lines were they?
98 f-bodys were not return fuel lines were they?
05-27-2003, 05:01 PM
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Re: Big injectors,tune diff /w 98 vac fuel regulator? Forget that stuff you read.
These cars are made to stay around 58 lbs fuel rail pressure if your at idle or at WOT.
I use 44 lb injectors and still the fuel rail pressure stays at 58 lbs even when I am at high engine load.
I would not use 127% either.
Look at what your LTFTs were with stock injectors.
Now as example if you were 10% too lean with them if you used the 127 value with the SVO 30s then you would be smack where you were before still too lean.
If you had 28 and go to SVO 30, using the 80% duty cycle rule the new injectors are 36 lbs. If you choose to use 100% DC then change 36 to 39.
28/36 = .7777 1 - .7777 = 22.23% more fuel flow by using the SVO 30.
Now to make it right, your 10% to lean ( in this example) so 22.23 - 10 = 12.23% too rich so to be safe go with a 112 in flow table,should be close enough in calibration to drive for about an hour, then do your LTFT average as it now tells you exactly what % your at and tweak part throttle from that with injector flow table.
These cars are made to stay around 58 lbs fuel rail pressure if your at idle or at WOT.
I use 44 lb injectors and still the fuel rail pressure stays at 58 lbs even when I am at high engine load.
I would not use 127% either.
Look at what your LTFTs were with stock injectors.
Now as example if you were 10% too lean with them if you used the 127 value with the SVO 30s then you would be smack where you were before still too lean.
If you had 28 and go to SVO 30, using the 80% duty cycle rule the new injectors are 36 lbs. If you choose to use 100% DC then change 36 to 39.
28/36 = .7777 1 - .7777 = 22.23% more fuel flow by using the SVO 30.
Now to make it right, your 10% to lean ( in this example) so 22.23 - 10 = 12.23% too rich so to be safe go with a 112 in flow table,should be close enough in calibration to drive for about an hour, then do your LTFT average as it now tells you exactly what % your at and tweak part throttle from that with injector flow table.
Im reading through on how to use LS1Edit to tune for swapping in larger injectors on http://ls1edit.slowcar.net/tuning.html
It says "The only tricky parameter to set here will be injector constant. This is because the LS1 does not have a manifold vacuum regulated fuel pressure, so as manifold vacuum changes (and rail pressure stays constant) the pressure drop across the injector change, so the injector flow/constant itself changes. A spreadsheet to simplify the calculation is made available:
Excel spreadsheet to calculate injector constant
If you are using a vacuum referenced regulator (some supercharger setups, etc.) then you will simply fill in a constant value across the range"
Now i have a 98 fuel rail on my ls1 conversion with 30lb SVO fuel injectors. How do i tune for 30lb injectors (rated at 43.5-45 psi) for a car that came with 28.8 injectors @ 58 psi)???? Does the vacuum controlled fuel pressure regulators on 98 cars change the tuning (because the feed and return fuel system)???
It says "The only tricky parameter to set here will be injector constant. This is because the LS1 does not have a manifold vacuum regulated fuel pressure, so as manifold vacuum changes (and rail pressure stays constant) the pressure drop across the injector change, so the injector flow/constant itself changes. A spreadsheet to simplify the calculation is made available:
Excel spreadsheet to calculate injector constant
If you are using a vacuum referenced regulator (some supercharger setups, etc.) then you will simply fill in a constant value across the range"
Now i have a 98 fuel rail on my ls1 conversion with 30lb SVO fuel injectors. How do i tune for 30lb injectors (rated at 43.5-45 psi) for a car that came with 28.8 injectors @ 58 psi)???? Does the vacuum controlled fuel pressure regulators on 98 cars change the tuning (because the feed and return fuel system)???
05-27-2003, 09:33 PM
#6
Re: Big injectors,tune diff /w 98 vac fuel regulator? heres the foggy part.. you have a vette fuel rail with a return line.. all is fine.. but the regulator that is on that return line on the rail is still the same one thats in our tanks..
it doesnt become vaccum referenced until you put a vaccum line onto it.. and to do that you have to convert it with a popular aftermarket regulator for 97-98 rails.. until you do that the IFR table will just be a multiple of the stock one depending on what injector you go to using the math above.
it doesnt become vaccum referenced until you put a vaccum line onto it.. and to do that you have to convert it with a popular aftermarket regulator for 97-98 rails.. until you do that the IFR table will just be a multiple of the stock one depending on what injector you go to using the math above.
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05-29-2003, 09:02 AM
#8
Re: Big injectors,tune diff /w 98 vac fuel regulator? 2001 guy.. the stock table has a slope that does the exact same thing as the referenced regulator does.. the programmig tries to simulate that..
now that you have the regulator you dont need the slope.. so it is flat.
mine is curretly 5.51 flat straight across but i have 42# injectors
just start with something save and move it until you have slightly negative ltrims... and thats it.
now that you have the regulator you dont need the slope.. so it is flat.
mine is curretly 5.51 flat straight across but i have 42# injectors
just start with something save and move it until you have slightly negative ltrims... and thats it.
05-29-2003, 05:50 PM
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Re: Big injectors,tune diff /w 98 vac fuel regulator? So does that mean with my 97/98 Vette fuel rail. I should have NO vacuum line ran to it and then do my ls1edit tuning??? Since I do have a vacuum line on it, is it hurting performance or just doing nothing
05-29-2003, 06:16 PM
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Re: Big injectors,tune diff /w 98 vac fuel regulator? hmmm that doesnt make sense still. with no vacuum line the car will like any other f-body fuel setup correct?? Because i have a stock f-body tune in the car with the vette fuel rail/regulator. So no vacuum line should run like a normal f-body correct?
05-29-2003, 06:45 PM
#12
Re: Big injectors,tune diff /w 98 vac fuel regulator? yes....if you leave the stock tune, then you do not want the vacuum reference on the regulator. The vacuum reference cuts fuel pressure and the stock tune has a formula for removing fuel (like droping pressure) as vacuum increases. With both the vacuum line AND the stock tune, you would be doubling the "pulled pressure."
The vacuum line setup is a better way to go but you would need to tune out that "formula" in the computer (custom program).
The vacuum line setup is a better way to go but you would need to tune out that "formula" in the computer (custom program).
