SamuelsonMotorsports

iTrader: (1)

MAP sensor was reading 93 KPA @ WOT (just called me) so maybe that stock airbox is a bad idea?

Said it was dropping from 99 down to 93 above 4,100 rpm.

Ideas?

Using the Airaid 200-712 "intake tube", K&N air filter with stock MAF and airbox, stock throttle body, stock truck intake manifold.
I understand the stock truck intake has been used for 550-600hp builds, but I've never used one until now on a motor that I was trying to make power with. Not sure what the limits of the stock airbox is? I didn't change the throttle body because its the same size as the intake manifold.

If I had to guess, possibly the Airaid intake tube- it has a pretty nasty transition at the throttle body IMO.

silver-mod-o

iTrader: (15)

Tell tale sign of an intake restriction somewhere... All you'd have to do to rule it out is pull the lid off the box and log it... If the MAP jumps up to where it wants to be then you've found the problem.

On the setups where I've kept the stock box I've taken a 3" hole saw and cut a couple holes in the bottom of the box. That usually cured it. I don't think the filter media or tube is the culprit here and yes... Your intake manifold and throttle body are good for plenty more...

I'd even consider your tuner doing away with the MAF and running it speed density. Gets rid of another possible bottle neck in the intake tract.

Vortec350ss

iTrader: (20)

Yea thats a fairly large restriction... get that sorted out and it will make a lot more power up top where than cam should shine.

black00chev

iTrader: (2)

Like these guys said, sounds like the stock box is holding you back some.

I have a much more mild setup with my 5.3 and I hit 95-99 kPa at WOT.

BadWolf

did you dyno your truck on this dyno when it was stock?

i know you said "these trucks" dyno 240 but what did yours do stock?

what type of dyno is it? a dynojet will read a lot higher (somethimes as much as 14%) then a load bearing mustang dyno. if its a mustang style dyno that could be part of the reason the numbers seem low

also when you consider that if 240 rwhp is common for these trucks. 300 hp stock crank hp minus 20% = 240. so the 4l80e isnt really that bad

RezinTexas

I have a similar chassis (except 10.5 vs 11.5 rear gear), and I can tell you that swapping out the Gen 3 intake/TB made a massive difference above 4500 RPMs. I don't have any dyno numbers, however it completely woke the engine up with the LSXRT. I also didn't loose anything on the low end.

something to consider

SamuelsonMotorsports

iTrader: (1)

Went out with a little obd2 reader with data on it to check the map sensor data while playing my newest favorite game called "find the restriction".

Took the airbox lid, turned it upside down and put the filter on top, took out the airbox and reclocked the tube so it would fit under the stock hood and...

nothing. Thats not it. Womp.

Thinking about going to Lowes and constructing a quick and dirty test tube in place of the airaid tube and seeing if maybe thats the issue.
edit: modified the airaid intake and opened it up some, which made me have to remove some of the fan shroud (no big deal) and still pulling vacuum @ WOT.

Gotta be the stock throttle body or stock intake manifold

1969x11

iTrader: (38)

Maybe the exhaust is the restriction?

Vortec350ss

iTrader: (20)

An exhaust restriction wouldn't cause intake vacuum.

1969x11

iTrader: (38)

Didnt say it would, Just saying the exhaust system may be contributing to lost horsepower.Looking for all out power out of a H/C 6.0 I would use a minimum of 3'' out of the headers y'ed into a 3.5'' tail pipe with a free flowing muffler.