ok here's what ive got. 3.0 and 3.49 rear pulleys and a 3.2 front pulley

from what im finding the rear pullies set up in the 86% underdrive configuration and a 3.2 front will net aprox. 6 lbs or so on a 6.0L. blower rpm at 5500 engine rpm is 11,090rpm

I can overdrive the rears at 16% and use a 4.0 front pulley to eliminate all chances of belt slip and spin the blower to 11,975rpm

this is going on my stock E85 fueled LQ4 on my '05 2500hd

im not looking for a lot of boost, anything from 6 to 10 lbs should be plenty safe and provide plenty of fun.

will overdriving the rear create problems im not thinking of?

 

Belt will fall off if too much, and a lot of heat.

 

That blower is hugely overkill for you with your goals... not only that but I think you are underestimating the amount of work it will take to make the jack shaft blower fit your truck. If I were you I would look for a bolt on TVS1900 unit instead. At the boost level you want to mak eit will be more responsive and feel much more snappy as well.

I make 13# with a 1900 on a cammed 6.0, so I think running out of blower is the last of your concerns.

If it were me I would sell the jack shaft, buy a 1900, and pocket the extra cash. It's a win win. Extra money, and a blower thats better suited to you.

 

With those boost levels you are going for over kill. I would suggest a bolton kit with an 8rib setup. 1900 will be plenty, but a 2300 would be cool too just not necessary.

 

I will trade you my 1900 for your 2300 .

 

That would be best for both of you... not joking.

 

I didn't ask if the 2300 was too big. this blower has been sitting on my shelf for 5 years. I guess I should have mentioned that once I get this dialed in I will be turning one of the 3 spare LQ4s into a 390 or 408, leaning torwards the 390 though. at that time I will either jump down to a 1900 or keep this 2300 on there. IF I end up with a 1900 the 2300 will go onto another project with plenty of tire and < 3000lbs

the belt lines up perfect with the truck accys. thanks to my Bridgeport. it was super easy to make work.

2.5 gal watertank and phenolic spacer have been made, currently working on the tensioner bracket.

so back to my original question. is there a disadvantage to overdriving the rear vs underdriving assuming the same final rotor RPM? bigger front pulley seems like a win win

I have no problem with more boost but im figuring with only 40K miles the ring endgaps are probably still pretty tight

 

I wasnt worried about the belt lining up... im worried about your accessories beign in the wrong places. Your water pump wont work I dont think... and most have to change their PS and Alt bracket to make more room for a jack shaft blower.

You should have given us more info... hard to give someone advice when then only paint half the picture. We have a lot of really naive new members on almost a daily basis, so sorry If what I recommended wasnt what you were looking for.

With more cubes planned I would stick with the 2300, and being underdriven I don't think will cause you any problems... other than a lack of power

 

Yes, I'd use the bigger pulley up front if you can. Keep the speed on that shaft down a bit. There have been a few of them come apart. I don't know if it was rpm related or otherwise...

Are you running a cog set on the rear? They sound wicked.

 

I didn't read all the thread, just the title

Overdrive the rear with a cog so you can run the largest pulley up front to reduce belt slip.