Pulley Change

[PKFIRE]

I'm planning on getting a retune hopefully this week and torn if I should leave the 2.8 pulley on it, goto a 2.7 or put a 2lb lower on it. Currently the car makes 501whp SAE and 469ft-lbs of torque. It picked up 59whp from just a port, x pype and Dragon TB from my old 2.8 pullied setup and made good difference at the track. I kind of want to change It since it's a decent amount of money to get it retuned and I wouldn't mind some gains if I have it done. Thoughts?

03 Cobra

[NXcoupe]

2 lb lower. That's my vote.

[IWRBB]

I'd leave the stock lower on there for the crank support. If you take it off and want to sell it tho, I'll buy it from ya. I'd like to pick up a stock one.. Mine was modded to a 4lb 10 rib version.

[smytty]

Check out svtper
alot of people have done testing with a port I believe 2.93 w a 4lb lower nets the best gains

[PKFIRE]

Have you had issues?

[PKFIRE]

A 2.8 and 2lb lower spins the blower about the same as a 2.93/4lb lower and I don't need an additional alternator pulley. I'm running 11.5@120.8 with just the 2.8 upper at full weight. I'm hearing that a lower can drop it quite a bit.

[IWRBB]

I used to run the Metco setup, but I was somewhat concerned by the lack of crank support. It's not a huge deal, crank failures are very rare on these cars, but it can happen and it's always the cars without the factory crank support that break. So when the opportunity arose, I bought one of the custom caged 4lb lowers made by modifying the stock parts that a guy was making a few years ago. It's the only 10 rib caged 4# 03 Cobra lower anywhere in the world.

How's about this- I'll trade you my Metco lower kit for your stock lower if you are interested. I like to have all the stock parts from my car, and I don't have a stock lower anymore since mine was modified. Only thing is with my Metco kit, it was the X10 kit with 10-rib crank rings and I would like to hold onto those. You can buy whatever size 8 rib ring you want separately though.

[08 Vette]

I have a pulley puller if you need to use one! It's sitting in the garage.

[smytty]

A 2.8 and 2lb lower spins the blower about the same as a 2.93/4lb lower and I don't need an additional alternator pulley. I'm running 11.5@120.8 with just the 2.8 upper at full weight. I'm hearing that a lower can drop it quite a bit.
I know they spin about the same but guys are getting different results.
Theres tons of threads about this and plenty of testing.

[IWRBB]

I don't buy it. Blower RPM is blower RPM. Whether is a smaller upper, or bigger lower- assuming belt slip is not as issue, there is no difference. There's no logical explanation of why there'd be any difference either, except belt slip. A bigger lower and bigger upper would help with belt slip.

If it were my car, I'd drop the money on the alt pulley and run the biggest lower and biggest upper possible to achieve the blower RPMs I was looking for. It's easy math, lower pulley diameter/upper pulley diameter*engine RPM. I used to run a 6 lb lower and a 3.7 upper to get between 15-16 psi on my Whipple. Now I run that 4 lb caged lower and a 3.5 upper to get the same blower RPM.

[smytty]

Nvr said belt slip wasnt a reason for results.
Of course with a bigger upper the belt slip chance decreases.
Over on svtper its stated in many threads with multiple test a 2.93/4 lower nets the best results with a ported blower.
Buy it or not.

[IWRBB]

I know you didn't say belt slip wasn't involved, but the "belief" out there is that a lower pulley gives you more torque- blower speeds and belt slip being equal. That notion has been floating around the forums since way back in 03/04 when Metco released their lower kit. Like I said, I don't buy it. It's a belt driven mechanical system, and the driven speed of the blower is the only thing that matters.

Right now PKFIRE is at 17642 RPMs (blower speed) at the 6500 RPM engine redline.
A 2 lb with a 2.8 is 18571 RPMs.
A 4 lb with a 2.93 is 19078 RPMs.
A 6 lb with a 3.2 is 18484 RPMs.
A 6 lb with a 3.0 is 19716 RPMs.

With a 2 lb lower, I'd just run the stock alt pulley. With a 4 lb, I'd go with 3.0 alt pulley. 6lb would be a 3.2 alt pulley.

[NXcoupe]

I don't buy it. Blower RPM is blower RPM. Whether is a smaller upper, or bigger lower- assuming belt slip is not as issue, there is no difference. There's no logical explanation of why there'd be any difference either, except belt slip. A bigger lower and bigger upper would help with belt slip.

If it were my car, I'd drop the money on the alt pulley and run the biggest lower and biggest upper possible to achieve the blower RPMs I was looking for. It's easy math, lower pulley diameter/upper pulley diameter*engine RPM. I used to run a 6 lb lower and a 3.7 upper to get between 15-16 psi on my Whipple. Now I run that 4 lb caged lower and a 3.5 upper to get the same blower RPM.
Agreed. Belt slip is the factor in any hp difference between the pulley combos with the same resultant rpm. That's why I suggested using the lower. I've sold and installed quite a few of the metco units back in the day. Had one for my 03 I bought new in 12/02.

[PKFIRE]

I just went ahead and got a 2.7 upper. I wasn't planning on increasing the power but since I needed a Dyno tune with the new MAF I thought why not. I'm not going to risk reliability for 8 more horsepower. I had a job at last work doing life cycle testing on bearings. I ended up having to place an additional support bearing on the motor shaft. After 1.5 years of accelerated testing the motor bearing would fail. So up front it worked fine but down the road It would fail. With the additional bearing I couldn't get it to fail even with a larger offset load. This was a ball park hotdog machine so not apples to Apple's. Probably with the small eaton and the stock tensioner there probably Isn't any issues. I bet if you loaded the belt enough failures could happen. Still they been selling the underdrive pulley for so long you would think if the issue was bad enough they would redesign.

[IWRBB]

Ford put that support on there for a good reason, something like Metco's hub would have been much cheaper to produce. I ran the Metco setup for about 10K miles, but I jumped on the change to get a 4lb caged lower when they were available.

Where you taking it to get tuned?