LB7 Turbo Downpipe

[Cumminalong]

Who here runs that downpipe and has dyno'd it, put it on the track, towed the 5th wheel, etc., with NO OTHER MODS?

Not a buddy of a friend who heard it from a guy, but ACTUALLY has one and has the dyno results. Not looking for the internet ninja's; I'm talking time slips, dyno charts, recorded data.

I have over 34 full recorded tuning pulls on my truck trying different products and settings, not including just random pulls to put down numbers in front of crap talkers. I don't run it like some of the dyno queens with their air box removed, or their exhausts unhooked, or cracking the valve on a nitrous bottle and spraying into the intake. I run it exactly how I drive it. Exhaust systems DO NOT create power, they are there to simply expell gases efficiently. There's only 2 things that add power.....AIR and FUEL. Everything else is a supporting mod.

10HP?....come on, you can fart in front of the intake and make 10 HP. 10 HP is nothing more than starting a dyno pull with one more pound of boost than the previous run. 10HP variance is actaully pretty consistent.

100* lower EGT's?.....do you REALLY believe that? Pre-turbo, post-turbo, NO other mod's other than that pipe?....

I'm not "comparing" that pipe to any other pipe, I'm looking at the system as a whole. I don't care if it's a 3" down pipe to a 4" front pipe or one that claims to be a 4" downpipe, but isn't truly a 4" down pipe. If it's doesn't offer a FULL 4" from start to finish, then you don't have a 4" system.

The argument that the gas can't expand is false. That's exactly what it's trying to do, that's what drives your turbo, it's a thermal machine. That's the same principal as putting a cam in the truck that opens the exhaust valves earlier....it uses that heat energy to spin the turbo. With your argument, you're saying that regardless of if you had a 2" pipe or a 5" pipe, it would still flow the same, this isn't true. A given diamter pipe can only flow a certain CFM before pressure must increase to move the gas.

Sometimes we want to believe the advertising to justify the money spent. What you need to be able to do is see through the cloud of BS the sometimes surrounds a given product.

If it was my truck, I wouldn't put the product on that claims something it isn't and won't have bang for the buck. But, if you want to drop that kind of coin on a pipe, it's yours to spend and I'll gladly get you the part. Some guys will sell ya the first part you ask for without knowing what you really want from the truck; I don't work that way. We try to understand what the end goal is for your truck and get you the products you need that will have the most impact for the money spent.

I'm not trying to make this a pissin' contest by any means, but "I", being someone who has access to almost any part I want and has a few builds, installs and tunes under my belt, couldn't justify that kind of coin for that pipe, especially being that I know what it actually costs to fabricate that kind of piece.

Again, not tryin' to piss in anyones Wheaties, but I give customers my honest opinion of a product. If I don't think the end justify's the means, I tell them. I try not to waste folks money on parts that won't live up the hype. There are products I won't sell and companies that I won't represent because I don't feel they have the customers interests in mind and I think their R&D is crap.

Trust me I've heard all the hype about this, that and the other. Everything gives you better mileage.....Everything gives you a bazillion HP......Everything lowers EGT's.....

 

[stacks04]

if the turbo down exit is 3", what good is a 4 " down pipe?

 

[Cumminalong]

if the turbo down exit is 3", what good is a 4 " down pipe?

Are you talking the actual turbo discharge?

That has to be matched to the turbine wheel. That is still energy being used and it's the last point in the system that you want pressure.

There are 3 main measurements on the turbine side. 2 on the wheel and 1 on the housing.

On the wheel you have the inducer and exducer and then you have the volume of the housing. Those three numbers determine if you get a slow spooling turbo with low back pressure (usually better on the top end) or a quick spooling turbo with higher backpressure (usually faster spooling and is common on a stock turbo.

After is leaves the exducer side of the turbine, you just want it gone.

 

[Diesel Tech]

Who here runs that downpipe and has dyno'd it, put it on the track, towed the 5th wheel, etc., with NO OTHER MODS?

100* lower EGT's?.....do you REALLY believe that? Pre-turbo, post-turbo, NO other mod's other than that pipe?....

The argument that the gas can't expand is false. That's exactly what it's trying to do, that's what drives your turbo, it's a thermal machine.

A given diamter pipe can only flow a certain CFM before pressure must increase to move the gas.

I already gave you the results from the dyno, sorry if you do not want to believe it. What I left out was that the boost also came up by 1-2 psi. The EGT was measure on a loaded pull on the dyno not a dynojet no load deal. Same test before and after, under the same test conditions. It was measured in the passenger side manifold for both test as was the drive pressure. First hand, no one else, no momma's brothers uncle crap. You need to go back and learn how to figure it all out because you are missing what truely goes on. Yes, it's not a ton of power but it's something that's real and can be measured time and time again.

Do you read what you type as first you say something is false, then you turn around and say it's trying to do it. Trying is NOT doing! It you allow the air to expand it slows down and drops temperature, that is just why a turbine housing squeezes the air down in the housing to increase the velocity and heat to turn the wheel! It uses the heat from squeezing the air down and the velocity and converts it to mechanical energy!

While I agree a given pipe can only flow so much air before pressure begins to rise let's look at what you've said. You want the pipe to be large at the turbo then reduce the pipe size as it goes downstream. So what your saying is make it big first to allow the air to expand, slow down and become more dense then squeeze it down into a smaller pipe to run it to the rear of the vehicle some 10 feet downstream. Sorry but that's not going to work nor is it what the TTS kit does. This is not about a pissing match but if you do not want to believe it that's fine but making the claims, the math says it will not work is dead wrong. If you did the math correctly then you would know it would work and why it works. Again this is not tons of power it's small increase and may not be for everyone.

 

[btfarm]

2 things:

1) Pouring water through a funnel was used as an example. That doesn't apply here. Water is not compressible and a given area will only flow a certain amount. Air (exhaust) is compressible.
2) Unrestricted, the turbo will flow a given terminal amount. Put a small exit path on it and there will be back pressure of a given amount. The turbo then flows less. Put a larger exit path on it and it flows more volume. Up the exit path (pipe diameter) to a point that the turbo continues to flow at its unrestricted rate. That then is the maximum size exhaust that will have an effect.

Now back to your regularly scheduled disagreement.

 

[Cumminalong]

I had something long and drawn out posted (not toward you btfarm), but after thinking about it......it's your money.

If you can justify $700 for 10HP, that's your choice.

I'll leave it at that; I'm done debating it.

 

[HoytBows]

2 things:

1) Pouring water through a funnel was used as an example. That doesn't apply here. Water is not compressible and a given area will only flow a certain amount. Air (exhaust) is compressible.
2) Unrestricted, the turbo will flow a given terminal amount. Put a small exit path on it and there will be back pressure of a given amount. The turbo then flows less. Put a larger exit path on it and it flows more volume. Up the exit path (pipe diameter) to a point that the turbo continues to flow at its unrestricted rate. That then is the maximum size exhaust that will have an effect.

Now back to your regularly scheduled disagreement.

Well then how do we find out what the LB7 Turbo needs to flow un restricted, and does the stock downpipe meet that flow need? If not what size pipe would. I really cant see any way that bigger isnt better in this case.

 

[btfarm]

Well then how do we find out what the LB7 Turbo needs to flow un restricted, I'm sure someone has that info but I don't. and does the stock downpipe meet that flow need? I doubt it due to emissions reduction requiring high temps.

I do, however, agree with Rich that the power gained is not going to be worth $700. $300 or so maybe, but not $700. Just for some freer flow.
If it was me, I'd just put a 4" downpipe on it that replaces the cat and leave the rest stock or go 4" all the way from front to back. I doubt the gain is going to be much though without a bigger tune.

 

[Cumminalong]

Okay, the way you figure out how much you need to flow is this.....

You take into account the engine displacement, expected RPM range, expected EGT range, forced induction or naturally aspirated (this helps determine volumetric efficiency), exhaust pressure and how much restiction is acceptable in the system.

Now with a 6600 cc engine, operating at up to 4000 RPM, with a max acceptable EGT of 1300, pushing approx 30 psi of boost, expecting 100 - 115% volumetric efficiency (typical of a turbo'd vehicle) you can expect to push 1916 CFM.

That is for a truck with a stock turbo.

Now, when it comes to the diameter of the pipe you need, you need to understand that a pipe will flow approx 115 CFM per square inch, you use 95 CFM when concerned about restriction. To figure out the square inches of the pipe, we go back to high school and use the old PI(R)2 formula.

The one thing this does not take into account is the length, number of bends, radius of the bends and surface friction.

What this gives us is this.

At 115 CFM per square inch, we'd need a 2.5" pipe to keep from causing a restriction.

At 95 CFM per square inch, we'd need a 3.1" pipe to keep from causing a restiction.

The stock downpipe DOES NOT meet the requirements due to it's shape. A 3" pipe however, does.

Again, this does not take into account length, bends, radius or surface.

 

[HoytBows]

I'm getting frustrated with this. What Im starting to get is that there is no point in bigger exhaust, bigger intercooler pipes bigger better flowing intakes because its not going to do much on the power end of things. It may allow you to run lower EGT's which would be handy for towing. SO am I ok to say that its a waste of my time and money to look into any of these air flow upgrades unless im looking to run big HP (bigger than my edge) or tow things a lot?

I get the whole every little bit helps but, right now it seems to me that any guy that put a 4" exhaust behind his stock downpipe pretty much wasted his money for the most part

 

[Cumminalong]

THE biggest restriction in your exhaust is the muffler.

That is part you want to replace the most.

Once you start pushing 500....550....600 HP or start looking at knocking 10th's of ET's, THEN the other air flow improvers start to shine.

BUT, on a truck with a stock turbo, the best bang for the buck is the stuff you already have.

Add a higher flow air filter and you're about maxed out for air flow until you add a bigger turbo(s).

 

[HoytBows]

yeah I already have a K&N in there....

 

[Cumminalong]

Then you're about maxed for what you can flow.

Unless you increase the engine displacement (i.e. stroker kit) or upgrade the turbo, you simply will not move more air.

You could replace that drivers side exhaust manifold and get rid of the crimped one, but even that isn't gonna get you a large gain.

HP upgrades get exponentially more expensive as you go. Every hundred HP (USABLE HP, not just 8 seconds of dyno HP) makes bigger and bigger cuts in the bank account.

You start out with the $1500 - $2000 to get that 400 mark.

Then you start looking at $5000 to get that 500 HP.

$12000 - 15000 to break 600.

700+ and it start getting crazy.

My truck for example is pushing over $24K in aftermarket parts, including the transmission. Trans ($7800), twins ($5000), dual CP3's ($3000), injectors ($1000), intercooler ($1200), FASS, head studs, valve springs, cam, gauges, water / meth, blah, blah, blah......it adds up fast.

Big boy power means big boy wallet.

It's a slippery slope.

Ya gotta ask yourself these questions and you have to answer them honestly....

How much power do I REALLY want to make and how much am I REALLY willing to spend?

Having an end goal is what makes that parts list cheaper.

 

[stacks04]

I had something long and drawn out posted (not toward you btfarm), but after thinking about it......it's your money.

If you can justify $700 for 10HP, that's your choice.

I'll leave it at that; I'm done debating it.

how did you go from disagreeing with me to agreeing with me. that is my point exactly, even 400 bucks its not worth it from a power increase pov. for other purposes 400 is justifiable though. never 700.

 

[stacks04]

I'm getting frustrated with this. What Im starting to get is that there is no point in bigger exhaust, bigger intercooler pipes bigger better flowing intakes because its not going to do much on the power end of things. It may allow you to run lower EGT's which would be handy for towing. SO am I ok to say that its a waste of my time and money to look into any of these air flow upgrades unless im looking to run big HP (bigger than my edge) or tow things a lot?

I get the whole every little bit helps but, right now it seems to me that any guy that put a 4" exhaust behind his stock downpipe pretty much wasted his money for the most part

your absolutely correct. dont get frustrated, nothing you can do about it. the system was designed correctly at the factory. it works fine, there is little things you can do to make it more efficient that you have already done.

now for big power, your going to need alot more, to invest in intercooler tubes and custom down pipes now wont do much, even if you decide later to put a bigger turbo ect. things need to be paired to one another, a new turbo may not be able to utilize what you already have. the biggest way to spend money and make power is a good tuneing tool and twin turbo setup. it allows you to retain much of the stock feel when normal driving, but it allows alot more in terms of get up and go for when you feel like it.

 

[Unit453]

Then you're about maxed for what you can flow.

Unless you increase the engine displacement (i.e. stroker kit) or upgrade the turbo, you simply will not move more air.

These aftermarket intakes do actually move more air but years of DMAX testing, dynoing, dragging, and everything else in between, it comes down to something simple:

Aftermarket intakes do flow more air. At stock or near stock power levels, your engine simply cant use that additional air flow. It just doesn't make enough power to sustain the need for more air. Sure, its breathing better, but if the engine cant use it; its a waste.

The only time that aftermarket air intakes have been proven to provide ANY gain is when your power levels are at 500 rwhp and above. Thats when the engine needs all the air it can get to sustain the additional fueling. Otherwise, the stock intakes flow more than enough and are pretty much the most efficient out there. Now, this is about 06-current generations as they've got the larger intake systems and are very different than 01-05 generations.

So, all these aftermarket companies "claims" of huge power increases are pure b.s. Its been tested on every generation truck since the conception. Intakes do not add any additional power. Sure, your seat-o-the-pants meter may say otherwise but the dyno and drag slip wont lie. On a truck with over 500 h.p. you'll be lucky to gain 15 h.p., but even then, its not about the minimal power gain, its to supply the modded engine with the air that it now needs for combustion.

Rich is also correct with the exhaust system. The muffler has been proven to be the biggest restriction. The cat flows quite well actually. Its been dyno'd that simply by removing the muffler, and the muffler only, you'll gain 11 h.p.

I think any truck, no matter if its GM, Ford or Dodge, can benefit from a 4" exhaust system. Its simply gonna be breathing better.

Great thread by the way.

 

[Cumminalong]

Let me break out some of my inner nerd-dom and show you guys how this actually breaks down when it comes to air flow.

There are certain things in the world that are know constants, they don't change, it's just the way they are.

Bigger is not always better.....it's just bigger.

The calculations below DO NOT take into account # of bends, radius of bends, or interior surface of the pipe.

As you can see below, from the point you hit a 2.6" diameter pipe your restriction is down to less than .5 psi.

THE main disadvantage of the OEM downpipe is the shape and sharp bends.

Here are our variables.....

Here are our constants.....

Here are the results.....

 

[btfarm]

So if I'm reading your graph correctly then you hit zero backpressure at around 4". Assuming a straight pipe w/o bends.

 

[Cumminalong]

For zero backpressure with no bends, you're looking at 4"

At 3.2" - 3.3", you're looking at 0.1 psi.

At 3", you're looking at at 0.2 psi of back pressure.

Again, this is assuming you're pushing 30 psi of boost, your EGT's are at 1300*, turning 4000 RPM's, so you're looking at MAX flow.

 

[trotorx2]

Very good thread. I can honestly say that I didn't notice any performance increase with my intake and 4" exhaust but, I'm pretty sure that when I bought my tuner they helped total performance.