I'd like to verify with some of you KB guys the different boost levels you're getting. I have an 03 with a 3.25" upper and 4# lower (just under 9"). According to KB I should be getting a max of 15.5 psi of boost. I'm hitting 18#'s. Their testing was done with 100% stock truck exhaust. Mine is an 03 so I'd like to think it's okay, but my boost levels tell me there's a restriction somewhere. I initially had a 6# lower and was hitting almost 20#'s of boost.

Before I try to test the back pressure or start removing things, I thought I'd ask what boost numbers you are getting. I know long tubes and cats will drop it some, but I love the stock quiet exhaust for this truck. My other reason for suspecting an exhaust restriction is that on a recent dyno of my Apten blower I only gained 20 rwhp and lost 30 rwtq. That had me confused and may explain what was going on.

Jody

 

I was getting around 21/22 with a 6lb lower and a 3" upper or a 2lb lower and a 2.5" upper... Some of the other guys are claiming super low boost, either they have some great flowing heads or are mistaken...

 

Thanks Leonard. Do you have any idea what backpressure reading would be normal in a stock system? In other words, at what psi in the system is it considered to be too high?

From your boost readings I'm not too far off, but I have a friend who's getting 13.5-14 psi with a 4# lower and 3.5" upper. That's only supposed to be a 2# difference from my 3.25" upper but it's almost 5 psi more on mine.

Jody

 

I think I was getting around 16 with the 6lb lower and the 3.5" upper. I'm thinking the 2lb lower and 3.5" upper gave me around 11.

It would be more accurate if everyone measured the pulleys instead of going by 2lb and 4lb and 6lb lower because each manufacturer made them different sizes. Then we could just figure out the blower RPM and determine who had better flowing heads or exhaust or whatever. Then the only error problem/ excuse would be how much your belt was slipping.

 

I have Dynatech long tube headers, high flow cats, Bassani x pipe, and Dynomax Bullet race mufflers. With a JLP 8# lower (10"?) and KB 3.5 upper, I'm seeing 15 - 15.5 #'s. I also have a 3.25 & 3" upper, but haven't installed them yet.

 

I have the Dynatech longtubes, high flow cats and single X pipe Magnaflow.

3.20" (2lb) reichard upper and JLP 9" (6lb) lower, gator belt and metco idler set up - any temps above 65 degrees and I am pushing a consistent 16lbs of boost sometimes spiking at 17lbs, any temps below 60 degrees and my boost has been in the 18 - 19 lb range.

I can tell you this, when I dumped the original exhaust I dropped one lb of boost.

On initial WOT from zero my boost jumps immediately to 10-12 lbs and builds from there. The faster I go the more boost I get - yeah baby!!!

D-Day

 

I run a Metco 6lb lower = 9 inch lower pully

with my:
3.5 upper = 14 lbs and spikes to 16 lbs right before the shift
3.25 = 16 lbs and spikes to 18
3.00 = 18 lbs and will hit 20

stock heads and cams, stock exhaust manifolds.

I need some Longtubes and Highflows

 

Thanks guys. A lot of you are using the 6# lower and 3.25" upper but getting 4 psi less boost than I am. I hit 20 with that combo. I'm guessing there's an exhaust restriction somewhere.

Good info!

Jody