Changing from a 3.7" to a 3.4" procharger pulley....belt size reduction?

**BMWDON** · 05-03-2012, 08:02 AM

So currently have a 111.5" gates on her, the circumference of the 3.7" is 11.62" and the circumference of the 3.4" should be 10.68". So if the belt rests on roughly 60% of the pulley circumference, I'd guess it's slightly .6" less overall path. But I'm not seeing a gates in 111", but see a 110.5". The dayco tensioner is sitting right at the midpoint of the gap for the alloted travel area for the tab. And I should have a little variability on the pulley on the procharger mounting plate too.

So to recap, is changing the belt from 111.5" to 110.5" the probable right size when changing from a s/c pulley 3.7" down to 3.4"?

Or is my thinking too small and I'm not considering enough variables in this?

**DarthCharger** · 05-03-2012, 08:31 AM

Subscribed. I would suggest contacting Procharger also but in my experience their customer service is not very good. You mentioed that the Dayco tensioner is sitting as recommended. If the smaller 110.5" belt is used, is this likely to reduce the travel of the tensioner to the point that it does not function as recommended? I am not sure how the 0.5" difference translates relative to the tensioner travel.

How much more boost do you expect with the smaller pulley?

**BMWDON** · 05-03-2012, 08:43 AM

I've been told it should gain 3ish psi. That's why I'm thinking with the adjustable pulley that's on the procharger bracket will come into play, it's not maxed out at the moment, I've got a little adjustability in that too. I'd actually like to see the dayco tensioner just a little on the "tighter" side than dead center, not quite at 75%, but more like 60-65% or 5/8's of the movement availability on that tab

**Knuckles** · 05-03-2012, 11:46 AM

Curious myself as I have a D1 with a 3.4" pulley as well..... Will check in the next few days to see what belt was included in the box.

Check out this website below as they have a bunch of cross reference part numbers for belts. Then you can look up the specs on one part number above or below on the the current belt that you are using to help you find a 111" belt.

http://crossbelts.com/serpentine/6ribkseries.html

**BMWDON** · 05-03-2012, 01:20 PM

Thanks for the link, lots of useful cross belt info. Are you using a ATI dampner/OD pulley too?

**HEMI~C~** · 05-03-2012, 01:53 PM

Why aren't we just buying the belt and trying it already?

Swap the pulley take a look at the tensioner and make a judgement call. There is no magic slide rule identifying exactly which belt for a given pulley combo.

**BMWDON** · 05-03-2012, 02:00 PM

pulley ain't here yet!! just ordered it yesterday

First I get the gauges in so I can see afr and fuel pressure in front of me, then I change pulley and belt. I have both belt and pulley ordered, I hope to see them next week, maybe install the weekend of the 19/20th...probably not, but hopeful.

**Knuckles** · 05-03-2012, 02:01 PM

Originally Posted by BMWDON

Thanks for the link, lots of useful cross belt info. Are you using a ATI dampner/OD pulley too?

Anytime man! I will be using a stock crank pulley on my stock 6.1 block and will be running aroun 9 psi... I am with Hemi C though I would buy the pulley that I think should fit and then try it. if its too big or too small then decide from there on another belt.... Let us know what you find...

**SCOTT57RT** · 05-04-2012, 02:10 AM

Sent this over to bozo4. He's done a ton of pulley changes.

**bozo4** · 05-04-2012, 06:08 AM

I used the stock belt all the way to 3.5 making just under 9 psi.. Still had adjustement left.. Went from 3.5 to now running a 3.1 pulley with a 6pk 2790 belt... This belt just fits on.. I havent even adjusted the tentioner up.. I do run an extra idler pulley and dayco tensioner with this though.. Making 11psi.. Sorry I couldnt be more help..

**BMWDON** · 05-04-2012, 06:14 AM

thanks for the inputs guys, I'll let you guys know how the 110.5" fits after I get the other stuff (gauges) installed first and then put on the smaller pulley and belt.

**Knuckles** · 05-04-2012, 03:41 PM

Originally Posted by BMWDON

thanks for the inputs guys, I'll let you guys know how the 110.5" fits after I get the other stuff (gauges) installed first and then put on the smaller pulley and belt.

Keep us posted man.....

**Knight** · 06-19-2012, 08:54 AM

Anyone ever come up with an answer? I am installing my 3.4 today lol

**BMWDON** · 06-19-2012, 09:18 AM

I swear I'm going to do this soon!!!!!

**Knight** · 06-19-2012, 12:48 PM

Im doing this tonight. Ill take it around the block and give her hell. I'll update it lol.

I DO however have an extra tensioner from DTP on my pro charger as well. So that may make a difference