ZO6Ted

So if I'm making 9.5-10 lbs. does that mean my bp is likely 15 if it's linear? If I could get it dyno'd for free I'd go find out how much it helps but I'm fixing to do something more radical soon it looks like anyway.

Mark Johnson

iTrader: (1)

Couldn't answer that, Ted- but instead of all this conjecturing, just get that flapper outta there...…………..

smokeshow

iTrader: (16)

Without proper data, it is difficult to accurately say. But for anyone interested in the finer detail, a heavily filtered response pressure sensor or liquid filled analog gauge isn't going to tell you the whole story. After all, if exhaust backpressure was a consistent 5psi, or any positive number for that matter, the physics of scavenging would be non-existent. The sensor needs to be able to respond fast enough and with enough resolution to display the positive pressure wave 'peak' followed by the negative 'trough' that comes right behind it. That negative trough causes the valuable scavenging. If that 5psi backpressure peak, or even 50psi peak pressure wave returns back up the header only to hit a closed exhaust valve, what does it matter what that value is? This is a signal processing question where the answer is sort of lost in translation.

1redta

00pooterSS

iTrader: (40)

The less back pressure the better, especially with boost. You're pushing more air and pushing more air against a restriction causes a pressure increase so your pressure will be higher. I bet you notice a large increase from just removing it. Cost about $50 or less and takes a few minutes. Headers would help too but the flap is cheap and easy and by far the best bang for buck mod you can do on these trucks.

00pooterSS

iTrader: (40)

That must be pre turbine. Which is gonna happen with a turbo and is good for a turbo, helps spin the wheel and keep energy up in the housing. Pressure makes heat, part of what spins a turbo is kinetic energy. Another thing that spins a turbo is the amount of pressure drop pre and after the turbine so some back pressure there is good and essential.

Apples to ink pens here though.

ZO6Ted

Flapper gone $25 and I wanted to report back. I got antsy and couldn't wait on another track time so... I ran a log before and after. First I'm definitely NOT even a half *** tuner. Haven't done anything but transmission tunes. This is what I found 4.9 lbs of boost at 1k rpm, no change. But at 2k rpm boost dropped from 6.9 to 6.5. Engine temperature and iats, ambient same as before except amb was 5 deg. warmer. Doesn't this imply that exhaust restriction is less since I lost .4 lbs boost at identical rpm under same conditions? Full boost unchanged at 2400 btw and it is 7.5 not what I'd been told couple years ago. Don't know how that happened. Just thought this is a step forward. I will track it in a couple weeks still no mods except Whipple, Tune, flapper delete, Rancho 9000's. Hoping for 8.0-8.05 then forward with headers ory and probably 4" single, retune then more. Thoughts gentlemen?

Mark Johnson

iTrader: (1)

Cool- thanks for the update. Nothing worse than having pressure back there...………..

00pooterSS

iTrader: (40)

Lets see how it looks when Sam checks on the tune and touches it up. My headers and catback made ZERO difference until it was tuned for it.

It may however have a little better throttle response and fuel mileage. Have you noticed any change there?

ZO6Ted

Hard to tell because I just got the bypass valve on so haven't had a chance to get used to it. It is dramatically better mileage on the hwy since both. City not sure yet.