S/C Pulley Talk

[Flatliner]

I know a few of you are experts and yes I could go to other boards for more information, but let us see what we can get here.

I am in for the purchase, but would like more information.

Here are my options:

2.760", 2.930", 3.100", 3.400", 3.650
NEW Non-slip pulley:

Hub and 1 Pulley Ring (Non-Slip S/C Pulley) $169.95 + $10.00 for color

Hub and 2 Pulley Rings (Non-Slip S/C Pulley) $219.95 + $15.00 for color

Hub and 3 Pulley Rings (Non-Slip S/C Pulley) $269.95 + $20.00 for color

1 Non-Slip Individual Pulley Ring (2.76", 2.93" or 3.10") $99.95 + $10.00 for color

I know the difference in sizes is the amount of boost. If I remember correctly most of the people I have met have the 2.93. What is the main difference with the 2.76?

Also the price ranges include # Ring(s) What are these? Are these the idlers or do I have to purchase them separately?

Is it better to buy dirrectly from Billetflow or Distributors?

Other mods I will have are CAI, exhaust (Bassani/ Borla Stinger, still debating), and most likely SCTuner. All parts will be put on together.

Click to read more...

 

[Dana]

I would suggest the hub and the 2.93 ring.
The advantage is that later if you want more boost, you can slip on a new ring, say, the 2.76, or less for winter driving, say the 3.1 or 3.4. You only install the hub once but can change the pulley diameter/boost at will by switching rings that are mounted to the hub. The ring and the hub are two seperate pieces.
I don't know the exact difference in boost levels between the 2.76 and the 2.93, but it is probably a couple of pounds.

Even with the 2.93 you should be at 450 HP or so with the rest of the mods you list.

Idlers are purchased seperately and I would recommend at least the third (upper idler in the pic) to decrease the slippage on the blower pulley. You can get the rest of the pulleys to match, but the mechanical effect is minimal. Looks nice though!!

I would and have purchased directly from Doug at BilletFlow. A very good guy to deal with.

Tell him I sent you.

Dana

 

[hj16]

2.93 = Roll Racer Pulley
2.76 = 1/4 Racer Pulley

The rings are just that, rings. Different sized pulleys that slip over the hub. This way you can change pulley sizes without having to use a pulley puller.


Personally, Id get the non slip 2.76 with the 3 piece Idler set. Straight from Doug :biggthump

 

[Flatliner]

Ah thank you so much now it all makes sense. I was under the impression that one pulley is usually it, I didn't realize that I could get both the 2.93 and 2.76 rings and both would be interchangeable on the hub. Thanks again guys

 

[hj16]

So what did you decide on Victor??? Stop holding out on us

 

[Flyn]

Does Victor have to have 2 seperate belts for the 2.93 and 2.76? I assume that's enough of a size difference to necessatate [sp?] different belts?

 

[Dana]

2.93 = Roll Racer Pulley
2.76 = 1/4 Racer Pulley

The rings are just that, rings. Different sized pulleys that slip over the hub. This way you can change pulley sizes without having to use a pulley puller.


Personally, Id get the non slip 2.76 with the 3 piece Idler set. Straight from Doug :biggthump

I just installed a set for Mike last weekend. Looks nice, blue pulleys on a gray car. Oh,well...

Dan

 

[Wharf Rat]

2.93 = Roll Racer Pulley
2.76 = 1/4 Racer Pulley

Could you pleeze explain that (using boost and HP estimates and track times)?

I was going to hold off on the pulley and tune but I don't think I can handle it much longer.

Also, why do all the L guys run lowers and the Cobra crowd runs uppers???

 

[Flatliner]

This from Brian Hill's FAQ that is posted in the knowledge center

3.4. Is a chip needed with a pulley swap?
Usually, yes. For an upper pulley swap, with a pulley
smaller than 3.2” you should at the very least get a dyno pull with a wideband
A/F check. In general, you want the A/F ratio to be below 12.0 (12 parts air to 1 part fuel). Some people have run as small as a 2.93 pulley without any
noticeable detonation (including the author of this document), but it is
important to have the A/F checked just in case.

3.5. What is the difference between upper and lower blower pulleys?
The upper blower pulley attaches to the blower snout and is
pressed on and must be pulled off. To swap this pulley, a specialized “pulley
puller” tool is usually recommended. The stock upper pulley is 3.65”. For more
boost, you reduce the size of the pulley. Smaller pulleys, however, also have
less belt wrap, making belt slippage a strong possibility. Lower pulleys, on
the other hand, are bolted on. Lower pulleys are the opposite of upper pulleys, and bigger pulleys provide more boost. Lower pulleys typically do not suffer from belt slip as badly either. On the other hand, the lower pulley kit
consists of several pieces of supporting hardware, and can be more difficult to
install. The stock lower pulley is 7 5/8”.

3.6. How much boost will a Cobra make with “XYZ” pulley?
3.6.1. Upper Pulleys
Stock (3.65”): 8-10 Lbs.
3.4”: 10-12 Lbs.
3.2”: 11-14 Lbs.
2.93”: 13-15 Lbs. (Boost may Fluctuate)
2.8”: 15-17 Lbs. (Boost may Fluctuate)

3.6.2. Lower Pulleys
2 Lb.: 10-12 Lbs.
4 Lb.: 12-14 Lbs.
6 Lb.: 14-16 Lbs.

3.7. What size belt should I use with a pulley mod?
Stock (3.65”): Goodyear Gatorback Belt 4080750 - 75”
3.4”: Goodyear Gatorback Belt 4080750 - 75”
3.2”: Goodyear Gatorback Belt 4080745 - 74.5”
2.93”: Goodyear Gatorback Belt 4080740 - 74”
2.8”: Goodyear Gatorback Belt 4080735 - 73.5”
Lower 2#: 77”
Lower 4#: 78”
Lower 6#: 79”
NOTE: Some have reported less slippage with .5” smaller belts.

For custom lower and upper pulleys, consult your tuner for proper belt size.

 

[Dana]

Also, why do all the L guys run lowers and the Cobra crowd runs uppers???

I don't think they can get much smaller on the blower, so their only option is the lower swap.

Dana

 

[ChicagoMike]

I would have thought it to be the other way around since the 2.76 gives you more boost, therefore less traction, so you'd want the 2.93 to help with the launch?

Can you please explain your idea behind this theory? I mean, shouldn't a 2.76 be fine for both ... and with an Apten port job?

Also, with a 2.76 ... what belt sizes have you run with success?

2.93 = Roll Racer Pulley
2.76 = 1/4 Racer Pulley

The rings are just that, rings. Different sized pulleys that slip over the hub. This way you can change pulley sizes without having to use a pulley puller.


Personally, Id get the non slip 2.76 with the 3 piece Idler set. Straight from Doug :biggthump

 

[ILLINI-SVT]

I don't think they can get much smaller on the blower, so their only option is the lower swap.

Dana

Stock on the L is a 2.93 upper and a 7.4 lower for 8 lbs boost. I could swap out the upper, but then I'd have to pull it off and add tensioners (the L's tensioners are farther away from the pulley). Lowers are much easier to add since it's just 3 bolts instead of pulling it off. No cages needed, no tensioners, no pullers. People do swap the uppers but its sort of pointless since you can get up to 10 lb lower pulleys on it.

 

[Flatliner]

And that answers everyones question, thanks

 

[ChicagoMike]

HEY! My questions have gone unanswered!

And that answers everyones question, thanks

 

[ILLINI-SVT]

I would have thought it to be the other way around since the 2.76 gives you more boost, therefore less traction, so you'd want the 2.93 to help with the launch?

Can you please explain your idea behind this theory? I mean, shouldn't a 2.76 be fine for both ... and with an Apten port job?

He's talking about how overspinning the blower works to shift the power curve down the rpm range. Making the blower spin faster with a smaller pulley on top moves the blower's optimum efficiency to a lower engine rpm, since the blower's spinning faster now in relation to engine rpms compared to the bigger pulley. So, you're getting more power at a lower rpm.

Switching to a 2.93 adds boost, but keeps the power curve in the higher rpms, where you'd likely be if you downshifted and pulled someone from 50 mph. Putting on the 2.76 adds more boost, but causes the optimum power curve to hit at a lower rpm, which is more useful when you're using the entire rpm range of the engine, like starting off a tree.

The thing I believe though is that all of the talk about the "optimum power curve" is really overrated. The L people did a lot of testing on the Eaton M112 in 99-00 when the 2nd generation L's first came out. They thought it would be really bad to overspin them because of durability and efficiency issues (namely, could it hold up, and then does it have a huge power drop off when overspun?). They found neither to be problems, and now successfully run 8 and 10 lb lowers (the equivilent of roughly a 2.76 and a 2.5 or so upper on a Cobra). Sure, they lose a couple of lbs of boost as they approach the redline, but the drop off was found to be really insignificant compared to the total effect of the added boost.

Hope this helps.

 

[Wharf Rat]

If the 2.76 brings more power earlier then wouldn't it be more fun on the street?

How safe is a 2.76 with say a Preditor tune and what kind of ballpark tq/hp are we talking.

Also, are pullies and tensioners an easy swap? Don't you just need some pulley tool?

You guys are total bastards for making me want a pulley all ready.

R.I.P. warrantee :burnout:

 

[Flatliner]

Look at the dyno day numbers... Jack has a predator on his so you can compare what it was like, but I don't know which pulley he has. Compare this to Hanks, who has a 2.90 I think, but the higher TQ he claims from the full length headers.

 

[hj16]

I would have thought it to be the other way around since the 2.76 gives you more boost, therefore less traction, so you'd want the 2.93 to help with the launch?

Look at all of the fastest upper Eaton cars out there. They all run 2.80s or smaller. It is because they take advantage of all the extra TQ down low. They can hookup outta the hole, and benefit from more TQ once they shift into a higher gear. Whereas a 2.93 or larger will have less TQ at those points.

I dont know what it is about 2.93 upper cars, but they are monsters from a roll. 03CobraRed pulled 00SVTdubs on the highway last year when dubs didnt have the Apten. And last December I beat 00SVTdubs even with his Apten.

Id chalk it up to the blower being at peak efficiency, instead of overspinning.

 

[Flyn]

Sounds logical, Hank.

The June MMFF talks about this exact subject in an article on the new Metco 10 rib set up. Very interesting reading. They came to the same conclusion that you guys wrote about.

 

[SVTdubs]

Look at all of the fastest upper Eaton cars out there. They all run 2.80s or smaller. It is because they take advantage of all the extra TQ down low. They can hookup outta the hole, and benefit from more TQ once they shift into a higher gear. Whereas a 2.93 or larger will have less TQ at those points.

I dont know what it is about 2.93 upper cars, but they are monsters from a roll. 03CobraRed pulled 00SVTdubs on the highway last year when dubs didnt have the Apten. And last December I beat 00SVTdubs even with his Apten.

Id chalk it up to the blower being at peak efficiency, instead of overspinning.

yep.... h: 2.76 will have heat in it if beaten on a lot. The 2.93 will be a little better car from a roll if raced many times in one night. :idea:

 

[hj16]

yep.... h: 2.76 will have heat in it if beaten on a lot. The 2.93 will be a little better car from a roll if raced many times in one night. :idea:

How about this, when I get my ported blower and your car is fixed we'll do a roll race, then hit up the 1/4.

All you'll have over me is a 2.70 to my 2.90.

 

[SVTdubs]

ok :biggthump