enginjoe

iTrader: (11)

I think engineermike is partially right, but missing the point. We were talking about the power being lost by heat out of the exhaust pipes before it gets to the turbo. Lowering the amount of heat lost will give more power. Use the power/enthalpy equation Mike quoted to see how much power is being lost. Also, enthalpy is defined as H=U+PV, where U=internal energy (function of temp), P=pressure and V = volume. The enthalpy change of the gas from the inlet of the turbo to its outlet will not be just a function of temperature, but pressure as well. What we were talking about is the loss of internal energy before the turbo which can be prevented in varous ways.

We also know that there will be a limit to the total amount of power that can be made with restrictive stock manifolds, but none of us has gotten that far yet. We do know that there are front mount systems using stock manifolds pushing close to 1000rwhp. We should be able to get there too, a little more slowly...

BTW enginjoe = engineer joe

Zombie

iTrader: (2)

Not yet, tried to last wednesday but I got to the track to late and they wouldn't let me run. Don't know how comparable it would be though since when I ran 11.3@123.5 the DA was 4200 vs the 5300 it was on wed. I dunno when I'll run the car again. Last time was really good because the temp was way below normal that night due to rain (was only 85 degrees).

engineermike

I agree with everything in that quote except for the part about me missing the point. What I was referring to earlier was that insulating the exhaust "up-pipe" will increase the power the turbine makes at any give flow rate. This allows the wastegate to open, reduce mass flow through the turbine, and decrease exhaust pressure, which results in the engine making more power also.

True that h=u+PV, but PV=RT. Therefore h=u+RT, then we're back to enthalpy as a function of temperature only.

Mike

engineermike

What I'm saying is that the temperature delta and mass flow across the turbine determine the power it produces. For any given boost and compressor flow, more turbine delta T means less flow, which results in less exhaust pressure and more engine power. In short, hot exhaust gas = good.

I just thought of a great analogy to help people understand this! Think about the way a Diesel operates. They have no throttle valve, so the mass flow through the exhaust is the same at varying loads (aside from the small mass of fuel injected). However, if you hold a turbo Diesel at 2000 rpm under no load, they build no boost. Hold it at 2000 rpm under load, you get boost. If the mass flow is the same, then what changed? Under heavy load, the engine burns more fuel, thus producing more heat in the exhaust, spinning the turbo to a higher speed, producing boost.

Basically, the smaller exhaust housing caused greater pressure in the exhaust system. The result of this greater pressure is, you guessed it, higher temperature. The greater amount of heat is available to spin the turbine. Let's do a quick calculation.

During the exhaust stroke, the exhaust valve opens before the pressure is expanded to atmospheric. So, some expansion occurs into the exhaust system. A turbine holds pressure in the exhaust system, so the gas doesn't expand all the way to atmospheric 14.7 psi. So, you have a source of (guess) 60 psi hot gas in the cylinder after the exhaust valve opens. Assuming a normally aspirated engine runs an EGT of 1200 deg F at 14.7 psia exhaust pressure, we can calculate what this same gas would be at, say, 50 psi and 60 psi. Yikes, I get 2075 deg F at 50 psi and 2181 deg F at 60 psi AT THE CYLINDER (it cools before it gets to the turbine)!!! You can see where an additional 100 deg F will spool a turbo better. Just for comparison, my front mount creates about 35 psi exhaust pressure, which calculates to about 1891 deg F, but mine retains more of this heat because the turbo is so much closer to the engine.

I hadn't gone through this calc before, so it's sort of eye-opening for me too.

The turbine makes more power on hot gas, so it has more power to accelerate itself. So, yes, it is related to heat.

Hotter gas will result in a drop in backpressure. Forget about velocity.

Mike

Zombie

iTrader: (2)

Maybe i'm using the wrong term. Does the exhaust gas exit the system better due to the difference in temp being bigger?

Jammer

iTrader: (1)

Great info...Great...
fwiw, when i want to increase boost, i was lucky, I turned the Alan head on my lil wastegates...10lbs to 20lbs, with just a few turns...LOL... Tis was one of the few simple things in life that actually worked for me. And it holds steady and doesnt creep. Me was lucky I guess.

Jammer

iTrader: (1)

And now lets apply bernoulli's principle that says that a rise (fall) in pressure in a flowing fluid must always be accompanied by a decrease (increase) in the speed, and conversely, if an increase (decrease) in , the speed of the fluid results in a decrease (increase) in the pressure. This is at the heart of a number of everyday phenomena.
Further, the physical principle formulated by Daniel Bernoulli that states that as the speed of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases. The phenomenon described by Bernoulli's principle has many practical applications; it is employed in the carburetor and the atomizer, in which air is the moving fluid, and in the aspirator, in which water is the moving fluid. In the first two devices air moving through a tube passes through a constriction, which causes an increase in speed and a corresponding reduction in pressure. As a result, liquid is forced up into the air stream (through a narrow tube that leads from the body of the liquid to the constriction) by the greater atmospheric pressure on the surface of the liquid. In the aspirator air is drawn into a stream of water as the water flows through a constriction. Bernoulli's principle can be explained in terms of the law of conservation of energy. In physics, basic laws that together determine which processes can or cannot occur in nature; each law maintains that the total value of the quantity governed by that law, e.g., mass or energy, remains unchanged during physical processes. Conservation laws have the broadest possible application of all laws in physics and are thus considered by many scientists to be the most fundamental laws in nature. As a fluid moves from a wider pipe into a narrower pipe or a constriction, a corresponding volume must move a greater distance forward in the narrower pipe and thus have a greater speed. At the same time, the work done by corresponding volumes in the wider and narrower pipes will be expressed by the product of the pressure and the volume. Since the speed is greater in the narrower pipe, the kinetic energy of that volume is greater. Then, by the law of conservation of energy, this increase in kinetic energy must be balanced by a decrease in the pressure-volume product, or, since the volumes are equal, by a decrease in pressure. So, would a smaller exhaust pipe equal greaer velocity and lower pressure... and does that even matter... would not a higher pressure possibly equate to more heat?

engineermike

Trying to apply Bernoulli's will only confuse matters. If the velocity of the gas increases, then the pressure will decrease, but the velocity-head will increase. In other words, if you look into the exhaust stream, the pressure hitting your face would be equal to the stagnant pressure of the gas. If you looked at it from the side (i.e. a pressure tap), then the pressure would measure lower. This all doesn't matter, though, because once you get into the turbine, for any given density and flow rate, the velocity will be the same. Exhaust velocity around the valve, in the exhaust port, header tube, or up pipe does not affect velocity in the turbine.

Mike

Jammer

iTrader: (1)

Thanks Mike... Im gonna try to absorb that, contenplate that, and someday apply that Good info.

LS1Formulation

iTrader: (13)

Ok, so I understood a lot of these concepts here, but I have a specific question. I plan on buying an STS turbo kit this winter for my car but I'm also in the process of installing a set of stainless edelbrock shorty headers to replace my restrictive '98 model year manifolds. Since these are shorties, the total area of the headers can't be much more than the stock manifolds so I can't imagine it losing that much heat, not to mention stainless retains heat better than mild steel. I was thinking the flow increase over those manifolds would help make more power. Any thoughts on this? Also, before anyone flames me for buying these headers... I got them brand new off ebay for $91 so I figured it was worth the expenditure. My goals for the car are mid to high 11's, just to add a bit of info here. I don't plan on getting into the motor other than valvesprings and maybe LQ9 heads if I can get them cheap enough. Are my goals possible? (Sorry for hijacking this thread but it was quite relevant to my plans.)

one eyed willy

iTrader: (1)

i havent heard anyone say what size turbo or trims?how much cfm does your turbo push at 13 psi compared to 15 psi?different turbos will spool at different times depending on trim and size.seems the ultimate goal for best hp would be to increase volume(headers) and increase pressure(heat).stock exhaust to increase back pressure seems like a band aid.too much back pressure decreases hp,which is what you have done,but at the same time added more boost and alot more heat(detonation?).no doubt you feel a increase from the added boost,i would be worried about the ill effects on the motor,heat is the biggest cause of detonation.i would think that using headers and free flowing exhaust makes more since and just going down a notch or 2 on the turbo turbine would be a better solution,it will let it boost quicker.although going too small it would run out of boost up top.just depends on the mapping of the turbo.

just my 2 cents,im building a 396 to run 12psi,so i dont think back pressure to spool the turbo will be a issue,ill be using full custom exhaust.

engineermike

That's not exactly how it works. You install stock manifolds to hold heat in, not to increase backpressure. Hotter exhaust at the turbine will reduce the pressure needed to spin it. The engine see's this reduction in exhaust pressure and makes more power at the same boost level.

Mike

one eyed willy

iTrader: (1)

your taking XXX amount of air,heating it up to increase volume.wouldnt it be more efficent to just reduce the amount of air needed to spool the turbo?leaving your exhaust temps lower?

i have no ideal?lol

1320

iTrader: (6)

its not heat that is being added, just kept instead of disapated. The heat is always there, it just doesn t make it to the turbo as energy.

BTW, i did the stock manifold to header experiment. With stock manifolds no boost limit really, 14 psi in first gear etc.....unwrapped (coated titec) edelbrock victor headers, no boost......I mean nada....it would make maybe 6-7 psi in 3rd gear @ 1300 ft. 1st gear....wot...1-2 psi, 2nd.....wot 2-3 psi.....

I thought there was a problem....tested, tested tested, no problems no leaks.

Remove headers and exhuast, panted all white, wrapped with fiberglass tape (1 inch wide headers, 3 inch wide exhuast) all the way to the turbo. (My rearmount system that I make) Painted the outside of the wrap, mostly to make it crusty and hold the shape better. Painted the turbo housing white as well. (bbq paint) First drive.......boost, lots of it......14 psi no problem in first gear.

nothing but paint and wrap, about 65$ total. I have since put on skid plates to protect the wrap since my wife drives it to work everyday and parks in an underground garage with a high point in the driveway. Not bad for a l11 sec car with 2.73's now.....and a stock motor, stock cam etc.

theredone2b29

I would trust engineer Mike on this one, you can't argue with math. It makes sense - just find a way to minimize heat loss between the turbo and the engine, if you do so your turbo will be way more efficient. Looks like a little paint and wrap is the cheapest way to do this.

Stoichiometric

iTrader: (10)

What material would make an ideal insulator? Ceramic coating or fiberglass wrap, or both? Is there any advantage to wrapping or coating the turbine housing for HP gains?

67Firebird455

iTrader: (27)

Heya Zombie, I'm with you, sold my LT's and am going back with stock 01 manifolds, and exhaust wrap. Hope to have the same results as you!!!