You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
How much torque will true dual flowmasters add to a 98 gmc sierra?
- Thread starter bar906
- Start date
Molson02536
New member
Stay to a single exhaust Muffler. Muffler will have duel inlet and single out let or duel outlet, MagnaFlow has a Exhaust system for your Sierra.
MagnaFlow Part#15602. V8 5.7L Extended Cab Pickup, GAS, 78.0 Bed Length 5 x 11 x 22 in. Dual Inlet Muffler, 2.5 in. Tubing, 3.5 in. Tip; SINGLE REAR SIDE EXIT.
MagnaFlow Part#15750 V8 5.7L Extended Cab Pickup, GAS, 78.0 Bed Length 5 x 11 x 22 in. Dual Inlet Muffler, 2.5 in. Tubing, 3.5 in. Tips; DUAL SPLIT REAR EXIT
This cat back system from MaganFlow clams to add 22HP and 22LB.-Ft. Gain.
Dropping to much back pressure will cause you to loose HP, Back pressure help the engine seal the valve seat at higher RPMs and promote higher compression when tuned properly. That is why a engine without a muffler that has fallen off has less HP then one that has.
Here are a few things you can do you your 5.7 Vortec if it has not been done already to wake it up. There are a few cheap or free performance tricks for the 4.3L and 5.7 Vortec specifically the 96 and up version. Since the intake gaskets on the newer vortec engines are notorious for leaking, I recomend replacing them with the alluminum gaskets available at your local GM parts department. There a little more expensive but they last forever. While you have the intake off go ahead and gasket match the intake ports on the heads and intake. Next take off the plastic upper intake and smooth the port inlets on the lower intake, just take the raised part out and make a smooth entrance into the port. Then take to throttle body off, remove the baffle that is on the throttle blade, just use some needle nose pliers and rip it off. Fill the rivet holes with JB Weld or Quick Steel, I my self just cut the deflector off and took the grinder to the blade to smoothen out the ruff edges smooth. Next remove the Screen on the MAF sensor, Remove the MAF and place it on a bench screen side down. With a flathead screw driver, snake it through the MAF not to touch the Filament and tap the screwdriver to knock out the screen. Once done, reattach all electrical connections to the MAF when reinstalled and go for a test drive.
To improve the 4L60E transmission, replace the Servo with Corvette Servo, replace the Boost Valve with 0.500" or 0.490" Boost valve and add a B&M ShiftPluse electronic improver for GM B&M Part#7038O. If you like you can start with the B&M Shiftpluse and it runs around $40.00 and takes 20min to install from start to finish. Servo can be done without dropping the transmission pan and the Boost valve can be done when you get the transmission serviced for the oil and filter and take an exrtra 5 min to replace when the pan is dropped. Servo runs around $25.00 and so does the Boost valve around $20.00.
Good luck and keep us posted on your project.
MagnaFlow Part#15602. V8 5.7L Extended Cab Pickup, GAS, 78.0 Bed Length 5 x 11 x 22 in. Dual Inlet Muffler, 2.5 in. Tubing, 3.5 in. Tip; SINGLE REAR SIDE EXIT.
MagnaFlow Part#15750 V8 5.7L Extended Cab Pickup, GAS, 78.0 Bed Length 5 x 11 x 22 in. Dual Inlet Muffler, 2.5 in. Tubing, 3.5 in. Tips; DUAL SPLIT REAR EXIT
This cat back system from MaganFlow clams to add 22HP and 22LB.-Ft. Gain.
Dropping to much back pressure will cause you to loose HP, Back pressure help the engine seal the valve seat at higher RPMs and promote higher compression when tuned properly. That is why a engine without a muffler that has fallen off has less HP then one that has.
Here are a few things you can do you your 5.7 Vortec if it has not been done already to wake it up. There are a few cheap or free performance tricks for the 4.3L and 5.7 Vortec specifically the 96 and up version. Since the intake gaskets on the newer vortec engines are notorious for leaking, I recomend replacing them with the alluminum gaskets available at your local GM parts department. There a little more expensive but they last forever. While you have the intake off go ahead and gasket match the intake ports on the heads and intake. Next take off the plastic upper intake and smooth the port inlets on the lower intake, just take the raised part out and make a smooth entrance into the port. Then take to throttle body off, remove the baffle that is on the throttle blade, just use some needle nose pliers and rip it off. Fill the rivet holes with JB Weld or Quick Steel, I my self just cut the deflector off and took the grinder to the blade to smoothen out the ruff edges smooth. Next remove the Screen on the MAF sensor, Remove the MAF and place it on a bench screen side down. With a flathead screw driver, snake it through the MAF not to touch the Filament and tap the screwdriver to knock out the screen. Once done, reattach all electrical connections to the MAF when reinstalled and go for a test drive.
To improve the 4L60E transmission, replace the Servo with Corvette Servo, replace the Boost Valve with 0.500" or 0.490" Boost valve and add a B&M ShiftPluse electronic improver for GM B&M Part#7038O. If you like you can start with the B&M Shiftpluse and it runs around $40.00 and takes 20min to install from start to finish. Servo can be done without dropping the transmission pan and the Boost valve can be done when you get the transmission serviced for the oil and filter and take an exrtra 5 min to replace when the pan is dropped. Servo runs around $25.00 and so does the Boost valve around $20.00.
Good luck and keep us posted on your project.
Last edited: