Airflow mods: Additive or Proportional?

[DevinSixtySeven]

I always see numbers for airflow parts (filters, headers, cats, exhaust, pipe sizes, etc) which state things like "YOU will see a GAIN of ## HORSEPOWER over your STOCK CONFIGURATION!!" Adding things up, it seems to me that starting at stock (245hp), I could get somewheres in the neighborhood of (let's add these up, I'm using round & hypothetical #s so it's easier)

Stock: 245
Filter: 15
Headers: 10
Exhaust: 10
Cats+Pipes: 5

Total: 285hp at the engine

Adding a supercharger might kick in another hundred or so, therefore we'll say the total engine horsepower is 385.

This is assuming all these airflow mods are additive, ie adding another mod does not change the characteristics of a previous mod. Personally, something sounds amiss with this logic. If I add a custom exhaust providing me with 10hp over stock, I'm at 255hp. Theoretically, adding headers will give me 265hp, however it seems to me that adding one airflow mod on top of another should result in a larger gain than both mods considered separately, in other words, a mod will add an increase in power proportional to the power before the mod. For example (since this is hypothetical I'll pick easy numbers again, I know they're not realistic), an exhaust system might give me 10% power gain over stock, or stock+26.5hp, boosting the engine to 291.5hp. Adding headers to this might give me another 10% gain over *what's currently there*, or 291.5hp+29.15=320.65hp.
Let's add a touch of realism now...the performance gains are all probably under 5%, and only exhaust and headers will be even close to that 5%. Any of these mods will only sustain a given max flow rate before they actually hamper airflow due to boundary layer separation in the component, which means that at some point it might not matter how many airflow mods are strung together, you won't be able to get any more air through. I'm guessing that for the larger pipes downstream of the headers, this is a sufficiently high flow rate that we'll never need to worry about it, and even the headers should be immune given it's gas and not fluid flowing through them. With this in mind, it seems to me that an exhaust system should give me a few % over stock, headers a few % over stock+exhaust, and cats+big pipes a minute % over stock+headers+exhaust.

Watchoo people think?

-Sean

[mike.elmes]

Absolutely....

I feel the dollars spent vs. performance improved is minimal.

I am therefore limiting my mods to performance, rather than curb appeal.
I can't wait til the supercharger becomes available, as this for the money has tangible benefits.

I have installed the JBA headers and like how it sounds and feels.
I am about to change the exhaust too, but all these should contribute to the s/c 'd new Tundra with close to 100 hp above stock.

[KLS]

Sean,

Send me some of that stuff you're smoking. No, better not. One of us needs a clear head.

Filter? 0 to 1 hp gain
Helix Power Tower? nada
K&N FIPK? loss at low & mid rpms, gain at the peak
Headers? up to 15 hp depending on the rpms
Exhaust? 2-5 hp
Cat & pipes? A 2-3 hp gain at the top will lose that much or more at the bottom end.
Noise level? Plenty
Bragging rights? Plenty
Value for the money spent? Excluding the last two items, not much.


Ken

[red's tundra]

I don't think that you can really add it up that way and say the truck has 285hp. Those additions add power to different parts of the rpm range.

Let say you have 200hp at 4800 rpms and 245 hp at 4000 rpms. If you add a K&N intake that gives you say.....25 hp @4800 rpms, you haven't added 25hp to your max hp (which would be 270)...you only brought the hp up at the 4800 rpm range (to 225). That will definitely help with perfomrance....don't get me wrong, but you wouldn't really be able to say your truck had 270 hp.

This is just my observation...if I'm wrong, please correct me.

[DevinSixtySeven]

This is all good information. IMHO a lot of the hp gains advertised are at the peak of the curve on vehicles with overly restrictive intakes to begin with, ie Jeep Cherokees (that's what K&N was claiming an 18hp gain over stock).
I know the numbers are high, I wrote that in the original post. Everyone has been claiming (from manufacturers to owners) that their products boost torque or horsepower, but thus far I have yet to see something which claims to boost useful hp and torque, which is to say around 2000 rpm where we do the majority of our driving. Since these claims seem a little odd to me at times, I wanted to see what other people thought regarding these gains. All the round numbers below are based on various manufacturer's claims, not my own or apparently anyone else's 3rd party dyno tests. It seemed to me as well that one cannot add hp as I did below, however the correct method may be to add a percentage to the torque and hp curves.
As I am very curious as to the correct answer, I will return my air intake to the stock configuration (read: plug hole, reinsert tube, get a paper filter for 10$, get rid of the engine whistle plate ), and dyno the truck. I'll even do the first test this week if I can find a shop in Boulder or Denver to get me in, and I will graph the results in Matlab for all to see. Being an engineer, I am doubtful of the claims any marketing department puts on the outside of the box, and would rather get to the facts, which is why I posted this in the first place...lemme say it again if I wasn't clear enough in the first post: I think those numbers are incorrect, I think the (highly disputed) gains are not additive, they are proportional, and while they are not as high as 18hp for a K&N FIPK Gen II, I suspect they are high enough in the 3000-4000rpm range to notice a difference--same for a muffler.
This is the test I propose and will do, if only to satisfy my own curiosity and put a lid on the airflow argument.
I will dyno my truck stock at Denver's roughly one mile altitude, graph and post the results. I'll add in the highly criticized Helix, and see what happens. Next comes the airbox mod with the K&N drop-in. Perhaps I can get ahold of a Gen II kit for an afternoon, or I'll order one and send it back if it turns out to be pointless.
Since I want an exhaust at this point even if it only sounds better, I'll test that as well, but it will take longer since I'm getting new coilovers and such this month .
Headers and hi-flow cats will take even longer.
If dyno runs are cheap (like 3 for $50 or less), I see nothing wrong with spending an extra $50 on these mods to determine once and for all if they're really worthwhile on a Tundra.
If there are factors I need to take in to account during the dyno runs, please let me know, I am going to look around for a place to do it Friday or Saturday, and in the meantime, if anyone has dynoed their Tundra, please post either a graph or hard data on this thread with a list of your modifications so I can compare your curve to the stock curve.

-Sean

[red's tundra]

What exhaust are you going with? I had Flowmasters, but I ripped them off to get some warranty work done. I am not going to put them back on. Instead, I am going to get the TRD duals. I think their sound is good and I think that if any exhaust is going to give any gains, it would be the TRD exhaust. Also, I got a dealer to drop the price even more than the TS supporter cost.

BTW:When I ripped the Flows out, just for sh!ts and giggles I fired her up and took a lap around the block with no muffler. It sounded like a Big Block or something like it...very deep and LOUD!! I thought it would have more power, but it actually lost a bunch of power. I was VERY suprised!!! This proved to me that more flow isn't better....atleast not with the Tundra. Also, I got my exhaust leak fixed at the dealer and noticed some of my power returned and my gas mileage appears to be better. I've only got about 100 miles on since the fix, but I have definitely noticed a difference.

[DevinSixtySeven]

Actually, that sounds about right w/the airflow bit. I'm a little unclear on the concept of what exactly backpressure does to provide more torque, but it sounds like the reduced backpressure reduced the power of the engine. Perhaps there is a specific range of backpressure which will improve performance; below this the engine does not develop sufficient torque, above it, the engine stifles. That's my current hypothesis, I'm going to ask around in the ME dept on campus when I get a chance, because if you noticed a lack of power but a banana in the tailpipe doesn't help either, there's some sort of middle ground we're shooting for. Too bad I can't just call the engineers at Toyota .

I'm not certain which exhaust I'm going with, there are quite a few which people have put on. I'm considering a Flowmaster or a Magnaflow, 2.25" pipes from each cat to a dual-in muffler and a single 3" pipe out the stock location. Another member has this on his truck, and you don't even notice it isn't stock until you hear it turn over . Then there's SpiralTech, Bassani, and a horde of other manufacturers...I'm eventually going to look for something that sounds burly but with good manners and little or no resonance (the larger pipes will help minimize resonance as well). I'll just poke around the forums when I'm ready, there are quite a few threads of people describing their mufflers ...of course, I'm also hoping that I can get a measurable power increase, and I'm willing to trade sound for torque and hp.

Important question--when you took your test drive w/o the muffler, did you get a chance to feel what it was like in the power band through a couple of gears?

-Sean

[DevinSixtySeven]

I found a chassis dyno in Denver (and another in Evergreen, but that's farther), and will do a baseline test sometime in the next couple of weeks--stock air intake.

Then I'll start changing things, and I'll post the results.

-Sean

[KLS]

Originally posted by DeepStealth
Actually, that sounds about right w/the airflow bit. I'm a little unclear on the concept of what exactly backpressure does
......
-Sean

I'm just beginning my reading on exhaust system design. One thing to keep in mind is that the gas flow inside the system is not constant pressure--it's a series of pulsations. As each exhaust valve opens it sends a high pressure wave of hot gas into the exhaust system. These pressure waves travel down the system until they hit an obstruction or another pressure wave bouncing back, then they bounce back, etc. You want these pulsations in-phase so they travel in the same direction at the same time AND so there's a low pressure node when the next exhaust valve opens. If you think of organ pipes, the bigger diameter pipes have slower moving waves. Enlarging the exhaust pipe diameter will slow the waves and possibly reduce the low-end power. The complete piping and muffler is designed as a system. Changing or removing one part can upset the operation.

I have a lot more reading to do on this subject and there's not a lot of info available (and understandable) to the general public. I do know that it's very different from a flow system with non-pulsating flow.

Ken

[DevinSixtySeven]

I hadn't considered that yet. Thanks for the heads up! Keep us posted on what you find...I'd like to avoid reinventing the wheel if possible.

-Sean

[Jwitz]

red, when you pulled your exaust, what did you do with the O2 sensor, b/c if the O2 sensor (that for me is part of my rear exaust) was reading 20% O2 (which is breathing air), then the EFI would not work correctly, which may be why you lost power... back pressure as I understand it is the actual pressure on the pipes... What I mean is, I have learned in college that there are things called dynamic and static pressure when dealing with flow through a pipe... well, when velocity rises in the flow inside a pipe (exaust), then the pressure on the pipe (static) drops... Now, when you have a low restriction exaust, the flow of exaust gases needs to be as high as possible, this drops the pressure on the pipes and consequently the engine, which in turn creates its own vacum and draws more air in to the cylinder... this added air volume can mix with more fuel which creates more HP... now... I dont firmly understand how torque works yet, but as I understand it, having a low restriction exaust tuned for the 1000-3000 rpm range will give more low end torque... The point is, that as soon as the rpms become higher than this, the pipes physicaly cannot flow enough exaust and your high end pressure becomes to great and the engine must work much harder to "fight" this high end pressure...
NOW, manufacturers, in their infinite wisdom create products that will create the most hp in line with the engine... If you notice, all engines today create most of their hp at high rpm, possibly due to the advances in automatic tranny's which lets them work very well... this means that every one makes horsepower gaining products for the upper rpm range... I once read a issue of Truckin' which explained much of this to me, and the key for everything we are doing is to tune it to the rpm we want power at! cams head and exaust all have something to do with that... the only thing that doesn't is the intake... now I don't know about the K&N for the v8, but it seems to me that there is no way that you could ever have too much airflow... the more air the better... the only time that matters is when you get to the throttle body plate, in which high air velocity is important, but before that you want as little restriction as possible...
Everything you buy that goes to these goals improves hp and efficiency, but as you all have pointed out, a K&N filter BY itself may create hudge increases in hp, but when combined with headers and exaust, it's not additive!!! but rest assured that it will increase hp and efficiency, but not to the leaps and bounds that manufacturers claim...
(PS dont forget too that you can have as much air as you want through an engine, but if the fuel system can't keep up, it's nothing)

my .02

[KLS]

Originally posted by Jwitz

......
I dont firmly understand how torque works yet, but as I understand it, having a low restriction exaust tuned for the 1000-3000 rpm range will give more low end torque...
.....
a K&N filter BY itself may create hudge increases in hp, but when combined with headers and exaust, it's not additive!!! but rest assured that it will increase hp and efficiency, but not to the leaps and bounds that manufacturers claim...
.....
my .02

Forget all the talk about torque. It is just a unit of force that is measured and used to compute horsepower. Power does work, and horsepower is how we define it. Here's the formula: hp = torque (ft-lbs) x rpm / 5252. As you say, the only thing that counts is horsepower at the rpms you really use. We might talk about our Tundra's having a 245 hp engine, but that's at 4800 rpm. Who cares? What's the hp at, say, 3000 rpm? That's important!

There is NO air filter element or assembly that will give huge increases in hp unless the old filter has huge problems, and most don't. And don't be assured that it increases hp and efficiency, at least enough to notice.

Ken

[Mr. Ving]

Actually, in physics force does work, not 'power'.