dar02081961

I read this particular "how to". Does the steering rack actually need to be moved as suggested here?

Reason for the question is the Super Chevy article the OP provided I didn't see it mentioned.

I have done lower pulleys on C6's and it is not difficult technically but it is a PITA. The C7 looks less involved from what I can see.

If the rack needs to be moved, I agree with Joe@CPR the labor for either task looks to be about the same.

Bad Dad

Joe is the shaft difficult to get out of the LT4 blower to press your hub on?

0Terry@BMS

Lower is probably "better" but upper is easier from a DIY perspective. And while the blower is off maybe send it off to get ported too.

Cordes Performance Racing

the snout gets removed from the blower to do the pressing. it's easy a few bolts and hit it with a soft mallet to separate it from the blower.

not any better, both make the same power 18% vs our 2.3 is the same.

1rawTA

I had the hood popped today and was analyzing this. The electric motor on the rack looks like it is def going to be in the way.

1rawTA

Damn right, if my blower is getting removed you best belive its getting ported!!!

Z06NJ

So am I reading correctly, installation effort aside, that the lower pulley will generally generate less heat than an upper pulley? Or I have it backwards?

TRANS DAMM

Correct. That's the main advantage of the lower vs upper

Cordes Performance Racing

It's the exact same

TRANS DAMM

Really? I was alway under the impression the upper generated more heat. If that's not the case you may have sold another pulley to me.

ajrothm

Here is what I came up with, please correct me if my math is wrong:

LT4 Crank Pulley : 7.48"
LT4 blower pulley : 2.5"
Pulley ratio = 2.99
Blower speed = 19,435 rpm (6500)

LT4 Crank Pulley : 7.48"
CPR blower pulley : 2.31"
Pulley ratio = 3.24
Blower speed = 21,060 rpm (6500) [+1625 rpms]

IW 18% : 9.5"
LT4 blower pulley : 2.5"
Pulley ratio = 3.8
Blower speed = 24,700 rpm (6500) [+5265 rpms]

So with an extra 3,600 rpms of blower speed with the 18% lower, it's definitely gonna make more heat then an upper. In a situation with no cooling mods for the intercooling system or a bunch of meth, I could see the same or less power from the 18% lower due to more severe timing retard from high IAT...and on the flip side, if you can control the IATs, you'll likely make more power with the 18% lower... (in theory).

The people making 800 ish are using the 2.31" upper and the 18% lower....along with lots of porting...lots of cooling mods and lots of meth...as well as E85.

Seannyc

so whats a good combination pulley to use along wit the 18% we lower without over spinning or having issues


Since I'm goin to Take the car in for blower pulley install Might as well find a good upper to go wit the lower

1rawTA

If you are going to use both pulleys it seems meth is something that is almost mandatory to add. 5k+ RPM increase between the 2 pulleys is going to generate some more heat for sure

6Speeder

Running an 18% bigger lower pulley AND a smaller upper pulley seems like overkill to me. You're trying to make a small supercharger work like a big supercharger, and will make too much heat. Sounds like time for a bigger supercharger.

Now MAYBE you could run the 9% bigger lower with the smaller upper, giving a pulley ratio of 3.53.

ajrothm

The 18% lower will already be over spinning the blower on its own. We don't even know what the true max blower speed is but, a 5000+ rpm jump in blower speed is a LOT, especially for a roots style blower.

Something else you are going to have to look at is crank case ventilation. With the 18% lower alone, i'd seriously look at doing -10 breathers on both valve covers... If you were to go 2.31 upper and 10% lower, you are CERTAINLY going to need a killer breather system..otherwise, you are going to be blowing the front and rear seals out with ease..

Honestly, I would stick with one pulley or the other...you are getting into "no mans land" spinning the blower that hard, you'll be making so much heat you likely won't be able to control the IATs and probably make less power then no pulley at all.. The other problem you may run into is, with both the upper and lower pulley, running a stock cam, the engine will likely bottleneck up top and choke itself, it just can't move that much air through the cylinders with the tiny stock cam..(189*/220*).

Let it be known that I have not tried any of this as my Z06 is still stock, so I am just talking out of my *** with theory with this point, take it with a grain of salt please, all of my experience is with prochargers on LS engines but......same theory applies.

I think if you want to just "throw a pulley on it", not create any issues (mechanical or heat), and drive and enjoy without worry, the way to go is the 2.31 upper pulley only..

If you are trying to get considerably more power gains and will be using meth and E85, then do the 18% lower only. This is the route I'll be going, but I'll be doing a -10 breather system as well..

jbsblownc5

Here's some "real life" input from what I've actually done...

I bought Joe's Pulley, but did not have a press in my little personal shop, so decided to shift gears for now, and since I do have a full two post lift, we went ahead and put on Redline's 15% overdrive pulley.

I still may do something with Joe's 2.3 pulley down the road, maybe just for 1/2 and standing mile stuff...

I do have one of Joe's Custom pulleys on my supercharged C5, and the machined in "grit" he uses on the groves works pretty well!

As far as what else I did with my C7, I added the Halltech Intake, Ported TB, Meth and Billy Boat Exhaust, including X pipe.
To help with Cooling, I also added the Granitelli Expansion tank and an extra Radiator with spal fans for that extra fluid in the expansion tank.

I then went ahead and tuned the car on 91/Torco with Meth. We came out with 660/690.

Let me simply say that I'm SUPER happy with the outcome and power levels!! For what I do, it's a GREAT combo. I like to hit the canyons, road course once in while, and then go to the runway twice a year. I've already been to the runway, and done many canyon runs with this combo, and will be hitting willow Springs this Saturday. I've been on the road course twice, just not with the pulley yet, NO HEAT ISSUES. Since I added the Pulley, I will be running Meth as well of course, to aid in cooling...

For me, these power levels combined with the handling/braking the Z07 package offers, and Toyos I put on the car, make this Z a blast to drive. If you are looking to break records at the 1/4 o 1/2 mile, or are just concerned with BIG dyno #s, then add more boost, and have at it.

Again, my real world input, is that this 17 Z is an AWESOME looking and driving car, that just needed a few tasteful and light mods to get to where I needed it to be in order to have a ball with it!

Larry M

So this gets you to spinning the blower about +3,600 rpms? +5psi?

Seannyc

Thx for the info I wasn't sure if 18% would be the only pulley to add witout over spinning I was thinking for another. Upper pulley to add maybe 1-2 Psi

but I guess I'll stick wit the 18% lower

maybe down the road when I get bored I'll port the blower and TB Cam and maybe add see if it's over to add the pulley after

David4359

Hey guys sorry I was busy. Where I got my work done they have done a lower and upper pully and their was no gains over just doing the lower because the blower is pretty much maxed out. It's a very small blower. To answer your questions I went 10.7 at the track my car was cutting out when I was shifting I think it was because I didn't transfer the sensors from the stock tires to the replica 19" rims and nto5r tires. I'm putting a F1a-94 procharger with the install it's $10,100 and I'm doing a McLeod clutch and meth kith everything is $15000

Seannyc

what upper pulley did they do

i would assume there is power to be made by doing both