What I've got now is 4# lower and a 2.80 upper and I know there is less belt surface area with a smaller upper... But does changing the upper out always mean more heat? If I got rid of the 4# lower and the upper, and went with a 5# lower even, during the same track temperatures can I see any improvements? Or is boost boost whether it comes from the upper pulley or the lower?
On a side note I am starting to get a little belt slippage from the upper now. So I was going to need idlers or see if I can swap to a bigger lower... Any info, I'd appreciate it. thanks, Shane

 

Boost is boost, and all that matters is the ratio of the diameter of the lower to the diameter of the upper. It's plain and simple physics.

All this crazy talk on the board about a smaller upper pulley providing "quicker spool up" is plain silly. You'll get more belt slip due to the smaller contact surface but that's it.

I see no point in going with a 4# lower and 2# upper, when a 6# lower works as good or better. You will get more reliable high rpm boost with a big lower pulley.

The only benefit of the upper is the ability to change pulleys in minutes for varying air temps, etc, versus a bit of a PITA to change the lower.

 

Has anyone thought about putting a bigger diameter pulley on the blower to combat the belt slip ?
For example, if your goal is 6psi over stock.... you could put a +8psi lower pulley on the crank and a custom made - 2psi pulley on the blower.
I was going to try it after I put on a 6 lower. But I didn't notice any slippage. No belt dust or anything... so I didn't bother with it.
Maybe I just don't hear it or don't drive it hard enough to make it slip. ?

 

I thought of that too, but it would probably be easier just to add an idler pulley instead.

 

Yeah, a metco idler pulley would be an easier route.
Now if I ALREADY had an aftermarket interchangeable pulley on the blower, then I would be tempted to whip up a bigger pulley for it.

 

True.

 

The ultimate setup would be a metco idler, 100mm idler and a Reichard Racing pulley.......

 

The reason I went with the upper was because I already bought a 4# upper. If at the time I had stock pulleys, then I'd of skipped the upper and just gotten a 5 or 6 pound lower. But I didnt want to have to sell the 4#er and get a 6. So I went with the upper and pressed it on and got an extra pound of boost...
So instead of getting a 6# lower (for better surface area) just get idlers and keep the upper on there?
my question was...
4# lower and a 2.80 upper is the same heat as just a 5 or 6# lower? if so, I will keep what I have, and get idlers to prevent the slippage. From there I will work on getting the motor cooler (ie supercooler, electric fans, intercooler fans...) Thanks for your help, Shane

 

Hmmm, I'm not sure what you mean by a 4# and 2.8" upper being "the same heat" as a 6#. Both should be real close to the same boost level, and hence the same heat level. The 4# and 2.8" (5-6# total boost) will SLIP more than the 6# lower and stock 2.93" upper.

Plenty of guys around here run just a 6# lower with the stock upper, so if you've still got the stock upper, that would be one option. You can get a 6# for about $225 vs. $200 for the idler pulley.

Option #2 would be the idler with your current setup, which would likely give you better results and more dependable boost at high rpms.

 

Yeah. I can either get a bigger lower, or an idler. I still have the stock upper but even easier than pressing that back on, I can get an interchangable upper for like $50 and just put that on in 5 minutes... and leave the upper hub on... (stock upper and 2.80 upper use my same 4# belt???)

 

How about I get a 5# lower and idlers and a stock (interchangeable) upper... and sell the 4# lower.

So I will always have a 5# lower and then at the track I can go from stock upper to 2.80 upper. (is that to much boost)
Or should I just run with 5# lower and the stock upper?
Thank you very much, Shane

 

The only reason I went 4# lower and 2.8 upper was cause I already had a 4# lower and wanted more boost... But I didnt want to go out and buy a 6# lower after I already got the 4 on there... So like you said the upper does have more slippage, but is easier to change out...
thanks, Shane

 

I have to agree!!

 

I'd just add the idler pulley, rather than screwing with the 5# lower at this point. You already have an interchangeable upper, so it makes sense to keep the smaller upper.

You will get better belt grip at high RPM with the smaller upper and a Metco idler, than you would with the stock upper and a 5# lower. I thought I saw the Metco idler adds about 20% more belt wrap to the upper pulley. That's more than you'd get by going back to the stocker.

$200 and your set, plus the Metco looks cool. Not sure what belt you will need though.

 

Thank you very much. who sells idlers? Most venders on here do right? And they should cost me about $200... thanks, Shane