I put a Pinnacle 4 inch exhaust on my truck and cruising at 70 on the highway it brought the boost up from 3 to 4 lbs to like 5 to 7 lbs. and it seemed a lot free'er, kind of like I had been pulling an empty trailer around and unhooked from it. Then last weekend I fabbed up a mechanical boost controller and now it runs up to 11 to 12 lbs before opening the wastegate if you have your foot in it or you're pulling a hill but still runs about 5 to 7 lbs at 70 MPH. I'm asking about additional boost being overrated because it's not like the difference between night and day from before I upped the boost. I haven't driven it loaded or pulling anything yet but I wanted to see what others thought. The truck does have 295,000 miles on it too.
Bob

My answer is simple:

Fuel & air + fuel & air = more power
Fuel & air + air = little to no improvement, depending on factory settings.

It goes a lot more in-depth than that, but that's a simple explination.

I know that when I put weight behind me I can actually pull it:D

You will max out your boost once you max out your fuel. So basically if you can cool the air and your engine can handle the boost, you might as well make as much boost as possible.

I mean, you can't lean out the motor, right?

RC, I see what you are saying. I guess I've been waiting for someone to offer a different opinion or dispute yours. I'm surprised at the lack or responses to this thread, I thought there would be more reply's.

I'm starting to buy parts from Walt at SS Diesel Supply and his sight says that they don't make a boost controller because of the fact that more air and the same amount of fuel doesn't make a difference. Of course if you increase fuel too then things happen. I'm sure its debatable but it kinda makes sense.

It seemed to make a difference to me with my truck. I do agree that you need to feed it more fuel to go much farther than you are, and you really need to have a Pyrometer and watch your temps. I pulled a 28ft boat up a pretty long steep hill the other day and held solid 20ps boost at 700 on the EGT guage all the way up the hill. My only fuel improvements right now are marine injectors and #9 resister. My next purchase will be a chip for my computer to add more fuel. I do recommend you get a intercooler before you try to go over 14psi of boost.

boost makes a big differance. take a 6.2L diesel truck for a test drive, then drive your 6.5L turboed truck because its basicly the same motor minus the turbo.

I hear you Red, when my vac pump went bad my truck was a dog. I just haven't noticed a big difference between where it was running and 11 lbs of boost. When I put the exhaust on it if you put your foot in it you would see it spike to 10 and immediately cut back to about 7, now with mechanical it will hold 11 to 12 I just can't tell much of a difference.

well since i put my manual boost controller on, i have seen a different in the water temp, is that because the more air going into it is cooling the motor down to?

your running the stock injectors right? as far as i know those injectors cant provide enough fuel to keep up with that amount of boost.

Red, I don't think that's comparing apples to apples. A turbo'd engine vs. a NA engine is definately a big difference but we're talking about raising PSI on an already boosted engine. The formula for how much boost pressure that is needed for optimum HP, combustion, etc. for the 6.5 was probably calculated by GM engineers and anything more with stock fuel I don't think will make a difference. Just my opinion.

more boost will cool your egt's, to a point. too much boost will cool your engine, after it explodes. Ed

fonecop, the reason that you didn't notice a difference in boost from 7-10 to 11-12 is probably, even at 7-10PSI you are burning all the fuel that is being sent to your motor from your IP. If you want more power, you will need to add more fuel. Simple as that.

So with marine injectors + added boost you can get more power, even w/o a chip?

Nick

Hey Bob. I didn't respond before 'cause RC had it in the first post. Once you have ENOUGH boost, adding more will not affect the power output, although (if you can keep the IATs down) more boost will keep things a little cooler.

There's a point of diminishing returns on that though, as higher EBP (back pressure) is the price you pay for higher boost.

Too much boost will obviously be bad, as an engine that normally develops 21.9:1 compression gets really interesting with more cylinder pressure, but there's a trade-off of sorts as increased boost keeps EGTs down, which limits thermal stress (at the expense of pressure stress).

Those who claim that "more boost doesn't help", or confidently state that "boost without fuel is just air" conveniently forget that the factory boost system on these trucks has some issues... when mine was factory (vacuum-controlled), I made sure my sensors, solenoids, hoses, etc were all nice and spanky, so things would work right. Then I put a trailer on the back, and pulled a big hill on a hot day.

"WHAT happened to my boost?" was the first thought that went through my head!

Why does the factory system tend to lose boost just when you need it most? Because the programming is wacky, because the PCM sees high IATs as a worse problem than high EGTs, because the engineers basically don't care if you can't pull this hill...

You shouldn't be pulling anything with this truck anyway.

That helps it last longer, in their minds.

If the factory system added enough boost for the available fuel in the first place, we wouldn't be having this discussion.

Thanks Guys, this makes sense. I don't have my EGT gage yet so I won't know a before and after as far as temps. I don't regret doing the mech boost controller because when the vac pump takes another dive I won't be left powerless. I have a lifetime wty on the vac pump but it was easier to install the boost controller than the vac pump.

In a diesel, we always have air, and adding fuel with your right foot makes us go faster, so adding more fuel with a chip or increased metering = going faster. More air is used to keep that added fuel from getting things too hot, and blowin out the tail pipe as a black cloud.

That's more or less expanding what RC said.

Now if you make that boosted intake air colder you'll notice more of a difference then adding 3-4 lbs of boost.

When I put in the MaxETork, I noticed a big power difference. When I added the manual boost control set at 14-15 psi...I did not notice a difference. Turned it down to 10, back up to 14...seemed the same to me.:cool:

Although..my truck does have some problems...:(

And yes, my WG control was working correctly before the WG controller...ran about 5-7PSI...