[Sharp Shifter]

On having low side fuel pump, Flex fuel sensor on, ported throttle exhaust....... But was going to do a pulley.

Suggestion on which one to do, best bang for the buck as far as power and money?

[1leftw]

lower pulley will give better belt wrap but be more expensive. The upper pulley will be cheaper but more prone to belt slippage in most normal supercharged applications. id go 18% lower if it was me.

[Sharp Shifter]

Which would be cheaper labor?

[Rlhay2]

All things being equal, doesn't the lower pulley usually show a greater increase in torque production?

[chicagosam]

Originally Posted by 1leftw

lower pulley will give better belt wrap but be more expensive. The upper pulley will be cheaper but more prone to belt slippage in most normal supercharged applications. id go 18% lower if it was me.

^This.

[drfeelgood]

Originally Posted by Sharp Shifter

On having low side fuel pump, Flex fuel sensor on, ported throttle exhaust....... But was going to do a pulley.

Suggestion on which one to do, best bang for the buck as far as power and money?

There is a number of threads on this topic. Regarding belt slippage (theoretical or real), various OD % on lower, need for accessory mods (like Headers) for various applications, etc. Lot's of good info, you just have to sift through a little bit

[WEAPON-X]

Originally Posted by Sharp Shifter

On having low side fuel pump, Flex fuel sensor on, ported throttle exhaust....... But was going to do a pulley.

Suggestion on which one to do, best bang for the buck as far as power and money?

Here is an LT4 pulley combo chart for you guys to peruse for some general info. We've done an insane amount of these across all platforms and our LSA chart helped a lot of people over the years, so I put this together a couple of weeks ago too:

https://weaponxmotorsports.com/blogs...ng-mods-needed

There are a few factors that come into play. The lower pulley being replaced reduces the rotating mass on the front of the crankshaft; however, when going to a larger diameter of rotation, this affects the MOI (moment of inertia) as you're essentially moving some mass (albeit less) further out from the vertex of the crankshaft.

The upper pulley we can go all the way to a 15% increase aka 2.175", but the snout needs machined with anything less than a 9% aka 2.3" upper. We offer the snout machining, porting, and pressing a pulley on and can ship back. Our Griptec pulleys eliminate the static slip that occurs when the crank taxes the upper pulley, so "the lower is always better" thought process is gone.

https://weaponxmotorsports.com/produ...-zl1-gen-6-lt4



Doing the lower, you can actually go up much further with over-driving the supercharger, but anything over a 15% really needs headers anyway to get rid of the restrictive cats which hold in heat. You can run up to a 25% lower with heads/cam/headers etc for that high 700whp range though.

IW lower kit goes up to 31% lower:
https://weaponxmotorsports.com/produ...-zl1-gen-6-lt4


ATI lower kit goes up to a 25% lower:
https://weaponxmotorsports.com/produ...ts-v-gen-3-lt4


Belt choices for various combos:
https://weaponxmotorsports.com/produ...ts-v-gen-3-lt4

[Can'tHave2MuchHP]

Thank you Ben for stepping in with the info. You're not too far, I may ship out my snout to you for an upper on my Z06.

OP, what Weapon-X said is all you need to know. :cheers:

[Sooner Cole]

Originally Posted by WEAPON-X

Here is an LT4 pulley combo chart for you guys to peruse for some general info. We've done an insane amount of these across all platforms and our LSA chart helped a lot of people over the years, so I put this together a couple of weeks ago too:

https://weaponxmotorsports.com/blogs...ng-mods-needed

There are a few factors that come into play. The lower pulley being replaced reduces the rotating mass on the front of the crankshaft; however, when going to a larger diameter of rotation, this affects the MOI (moment of inertia) as you're essentially moving some mass (albeit less) further out from the vertex of the crankshaft.

The upper pulley we can go all the way to a 15% increase aka 2.175", but the snout needs machined with anything less than a 9% aka 2.3" upper. We offer the snout machining, porting, and pressing a pulley on and can ship back. Our Griptec pulleys eliminate the static slip that occurs when the crank taxes the upper pulley, so "the lower is always better" thought process is gone.

https://weaponxmotorsports.com/produ...-zl1-gen-6-lt4



Doing the lower, you can actually go up much further with over-driving the supercharger, but anything over a 15% really needs headers anyway to get rid of the restrictive cats which hold in heat. You can run up to a 25% lower with heads/cam/headers etc for that high 700whp range though.

IW lower kit goes up to 31% lower:
https://weaponxmotorsports.com/produ...-zl1-gen-6-lt4


ATI lower kit goes up to a 25% lower:
https://weaponxmotorsports.com/produ...ts-v-gen-3-lt4


Belt choices for various combos:
https://weaponxmotorsports.com/produ...ts-v-gen-3-lt4

Weapon-X, I really appreciate your post. They are very informative, particularly for those of us that are new to this. Keep up the good work!

[Sharp Shifter]

That is awesome input, I don't have headers but I do have CA delete pipes so would 18% still be to much?

[drfeelgood]

Originally Posted by WEAPON-X

Here is an LT4 pulley combo chart for you guys to peruse for some general info. We've done an insane amount of these across all platforms and our LSA chart helped a lot of people over the years, so I put this together a couple of weeks ago too:

https://weaponxmotorsports.com/blogs...ng-mods-needed

There are a few factors that come into play. The lower pulley being replaced reduces the rotating mass on the front of the crankshaft; however, when going to a larger diameter of rotation, this affects the MOI (moment of inertia) as you're essentially moving some mass (albeit less) further out from the vertex of the crankshaft.

The upper pulley we can go all the way to a 15% increase aka 2.175", but the snout needs machined with anything less than a 9% aka 2.3" upper. We offer the snout machining, porting, and pressing a pulley on and can ship back. Our Griptec pulleys eliminate the static slip that occurs when the crank taxes the upper pulley, so "the lower is always better" thought process is gone.

https://weaponxmotorsports.com/produ...-zl1-gen-6-lt4



Doing the lower, you can actually go up much further with over-driving the supercharger, but anything over a 15% really needs headers anyway to get rid of the restrictive cats which hold in heat. You can run up to a 25% lower with heads/cam/headers etc for that high 700whp range though.

IW lower kit goes up to 31% lower:
https://weaponxmotorsports.com/produ...-zl1-gen-6-lt4


ATI lower kit goes up to a 25% lower:
https://weaponxmotorsports.com/produ...ts-v-gen-3-lt4


Belt choices for various combos:
https://weaponxmotorsports.com/produ...ts-v-gen-3-lt4

Ben, I will call you in the AM regarding pulley combos. Thank you for posting this

[WEAPON-X]

Originally Posted by Sharp Shifter

That is awesome input, I don't have headers but I do have CA delete pipes so would 18% still be to much?

You CAN do this, we have done it, but you'll be leaving some on the table; however, it's certainly better than running cats. You should still cut out or gut the rear resonators though too.

I deleted my cats when we did my ported blower, stage 2 intake, and 103mm tb and I made 660whp on E85 running the stock pulley combo; however, headers still would've really picked up more. This was just testing before we started the rear mount turbo.

Originally Posted by WEAPON-X

From here, we did our WEAPON-X 103 ported blower with our WEAPON-X Griptec pulley but still a 2.5" stock size and the NW103mm throttle body and upgraded the intake to the WEAPON-X Stage 2 carbon air intake and we were pretty amazed without any additional pulley, we picked up over 30whp and 40wtq in the mid range RPM band and increased peak power to 670whp and 639wtq. This is without a cam, headers, or even any pulley change!

Run 2 - intake stage 1, flex sensor, injectors, hpfp, tune
Run 3 - intake stage 2, flex sensor, injectors, hpfp, ported blower, 103mm tb, tune

Originally Posted by drfeelgood

Ben, I will call you in the AM regarding pulley combos. Thank you for posting this

[Sharp Shifter]

I have catback already and then these cat deletes will get rid of the last 2 other than having mufflers. have the stainless works system

[Can'tHave2MuchHP]

Originally Posted by Sharp Shifter

I have catback already and then these cat deletes will get rid of the last 2 other than having mufflers. have the stainless works system

Why piece it together and have doubts...Just order a pair of Headers and connection pipes. Once you're past the Headers + Primary cats, the rest doesn't matter nearly as much, hence why running a stock cat-back is standard procedure on these cars even when highly modified. Cat-backs do essentially nothing for your engine's needs. A secondary cat delete or even a primary cat delete does not replace the job of Headers/Catless or GESI cats.