TKT-MKR

Hey all,
I have a 99 Maggied LS1 (stock internals) that I am getting ready to have alot of work done on it (including going from a 3.1 pulley to a 2.9 pulley). Now I figure i have seen alot on here about under and over drive pullies, but I am not quite clear which would be the better solution. So I ask the experts (i hope)...... which is the better?

Why would I want to get an underdrive pulley versus and overdrive pulley? (or why an overdrive versus and underdrive).

I have seen people say that when they go over drive they get more torque and increase in boost pressure.

I have seen that underdrive pulley free up more engine power.

So what do you think? what will be the better benefit. I sure wouldnt mind a increase in torque, but will i really see it? i would not mind an increase in boost either but can my stock block take it with the 2.9 pulley and the overdrive? will the underive pulley decrease any boost or slow down the spool up?

TKT-MKR

bump?

BLOWNBLUEZ06

Underdrive is for people to gain a little power with N/A cars. Not a good way to go for supercharged cars. The smaller the pulley, the greater chance of belt slip. If you put a larger pulley on the crank, it will spin the blower faster without having to decrease the size of the already relatively small blower pulley. You are effectively increasing the contact area for both the drive and supercharger pulleys.

vettefamily

Blownbluez06 is correct, your boost will increase and your belt will be less likely to slip. Many people go with Overdrive balancers instead of going with a smaller S/C pulley, you get the same results without the belt slipping.

TKT-MKR

ok, so since i am looking to go 2.9 from my 3.1 and possibly do the 8 inch over drive pulley, do you think my stock internals can take it with a decent tune?

BLOWNBLUEZ06

With a 2.9" and 8" balancer, you're looking at 17,932RPM at 6500 engine RPM. 3.1" with the 8" balancer and you're at 16,772RPM. The 2.9" with the stock 7.5" balancer puts you at 16,881.

The volumetric efficiency of the Maggie 112 really starts to flatten out after 14krpm.


Furthermore, the temperatures increase exponentially with rotor RPM and pressure as you can see in the image below. Since you will be higher boost with those RPM's, you can start your line on that graph higher and then with the RPM, put an exponential curve in there and I expect you'll have a situation where most of your boost is created by the heat expansion of the air, but you won't be putting so much oxygen in the cylinders due to that fact.


That's not to say people haven't done it. We all know Funcool has spun his to the moon. I certainly wouldn't be doing it with a stock piston though.

M_T_0

i could give you all kinds of tech info on this but bottom line, this is what you want to see. overdrive installed on my 99 (see sig) no other changes except to correct AF. and yes this is on stock 120k mile bottom end. bottom line is that I would never install a maggie without an overdrive pulley.

TKT-MKR

Hey all,
Thanks for the input, I really appreciate it. It really sounds like MTO has a VERY similar setup as I do. So let me give you my details and any input you have would be great on what you think.

1999 Corvette with a stock LS1 with 48k on the clock
Magnuson 112 Supercharger with MagnaCooler Intercooler with 2.9 pulley
LS9 CAM
Centerforce 12" DF clutch with Tick master and slave cylinder
C6 Z06 Snap Shift
Morley Hardened Push Rods
Dual Chain
Raptor Shift Light
Z06 Springs
Z06 Stabilizer Bars
Z06 Shocks
Z06 Transmission (MN12)
FLP Long Tube Headers w/High Flow Cats
Corsa Indy (Pro Tips) Exhaust
BPP Vortex Cold Air Intake
and I havent decided to buy new springs for the heads or buy some 243 or some upgraded heads
and I guess I would also be looking at an Innovators West 8" Overdrive pulley

TKT-MKR

???
anyone
bueller?
bueller?
???

STEEL

will an 8 inch overdrive pulley work well with a flip drive?