Why both and not just one???

 

at one time, lower pullies only went up to a certain size. for a while it was 4lbs additional boost, then 5 and 6 and so on. so for a while, when for example you could only get a #4 lower, people would by the #1.5-2lb upper and get some extra boost that way.

IMHO now that you can get pretty much any lower pulley that you want, upper pullies are useless since they are much more difficult to install or remove.

just my .02

later,
chris

 

yea I figured you can achieve the same result with just one pulley.
Just depends on the size.

 

Yes AND NO

For guys like me, it works out quite well

I keep my 4lb lower on 24/7,
and then with the quick change upper I use,
I can switch from 4 to 6lbs, or 6 to 4lbs in @ 1 minute.
For instance I like to drive the streets on 6lbs,
but I like to race with only 4lbs.

I also like the option of being able to give or take away
a few HP at the track, to dial in on the conditions and my ET.

Plus this way I have them tune for 6 or 7lbs of extra pulley,
but only use 4-6 (much richer + much safer)
Slower yes, but more forgiven.

One thing is for sure
You'll never hear me Detonate

 

Heat, Blower RPM, Effeciency, and HP.
When you have tried it all, it becomers evident.
Dyno, Dyno, Dyno all changes for your truck. I don't care if you just change plug types and gap, dyno for true results, NO GUESSING.