DarkblueTA

No, you're talking 3d here = cubed. 2d=area 2d exhaust pipe err.....yeah...nothing would get through it. *being a smart ****

DarkblueTA

Bankz27

Well I may be off alittle bit but I would think of it the same way the charge pipe would be. Well if you have a smaller pipe wouldnt it push more air to the turbo quicker then a larger pipe? Samething with the Charge pipe...smaller pipe quicker flow of air into intake. I dont know about the white paint though....sounds interesting just got to test it to see if it works..

I may have to agree with heat as well more heat the better the turbo might be of spool quicker and creating more boost...but best way to find out ways to help would be to test it.

Zombie

iTrader: (2)

Why is everyone so hung up on volume / velocity, it has very little effect. Turbo's work off of pressure, nothing else.

The swap from manifolds to headers test has been done with results showing a loss in spool and ability to build lots of boost on 1320's car. On my car I swapped from LT's back to manifolds and it resolved all of my boost issues.

1320 should have his car running again this week with a fully painted exhaust and wrapped headers, so we will see what kind of difference it makes.

GTObsessor

iTrader: (2)

Zombie, what are you doing for a y-pipe (I think I saw someone else ask if you've done something for it but didn't see an answer) did u go back to stock and paint it or what? I was thinking a jet-hotted one may be a good idea?

buldogg

iTrader: (1)

same question here.

Also what are you doing for or about the CATS? I have mine gutted and I took them to a muffler shop so they can cut the empty CAT box off and weld in a pipe or make me a whole new pipe to go from the manifolds to the y-pipe.

Zombie

iTrader: (2)

my exhaust is stock with gutted cats and it's all painted white.

If I hold 50% throttle in 2nd or 3rd the car will get to 15psi quicker than I expected it to. Spool up to full boost is awesome!

engineermike

Actually, turbo's work off of heat and mass flow - nothing else. The power produced by a turbine to drive the compressor is represented in the following equation:

Power = mdot x (h2 - h1) x n

mdot = mass flow rate
h = enthalpy of the gas
n = turbine efficiency

Enthalpy of exhaust gas is a funciton of temperature only. Most have a hard time grasping this concept (myself included), but proof is in the nearest Thermodynamics book.

That said, the hotter the gas going into the turbine, the more power it will produce for any given flow rate.

As far as painting goes, I believe that it has insulating properties that are helping you. However, I highly doubt that he color of the paint makes much difference. The color certainly doesn't affect the "conduction" or "convection" rates of cooling. The emissivity factor may be different and thus radiate less heat, but "radiation" heat loss is going to be an order of magnitude less than the others.

I do agree that the difference between manifolds and headers could be significant due to the heat transfer area difference as well as the thickness difference. Hell, LT headers sort of look like a big air/air exchanger now that I think about it.

Wrap everything with header wrap. I expect you'll see more of the same results. Don't be picky on the color though.

Mike

Got Me SOM

iTrader: (2)

I wonder if you would have kept the headers and just did the paint and would have seen gains.

switching to a more restrictive manifold and making more power makes no sense. You are probably seeing higher boost due to more restriction not exactly making more ower.

Zombie

iTrader: (2)

It seems that we are basically describing the same thing. Hotter gas = more pressure.

We did some unscientific testing the other day with some pieces of header, the white paint and some wrap. The results were quite good, the paint does an amazing job.

Zombie

iTrader: (2)

How is the manifold more restrictive? My car had the opposite problem of most, not enough back pressure, not the typical too much back pressure you see most people posting about.

Painting and wrapping the headers would most likely have made a big difference in spool, but would have done nothing to help my car get over speed bumps. I'm quite happy with the stock exhaust system, it's performing very well at 700+ crank HP.

No matter what the science, i'm very happy with my exhaust setup now and the way it boosts (and I can finally drive over a speed bump without those POS SLP long tubes and y-pipe dragging like a mexican low rider).

CHRISPY

Zombie, when are you hitting the track and dyno? I am really looking forward to seeing your results. How do you think cats would affect things? Cats in themselves hold and maintain tremendous heat. I am wondering if you think that would hurt or help?

Cheers,
Chris

Got Me SOM

iTrader: (2)

SLP's do hang low but your theory on not enough back pressure is completely whacked. The more you open up your exhaust the better your turbo will run. That is Turbo basics 101.

CHRISPY

I think you might be confused That is after the downpipe

With the STS the stock exhaust manifolds and intermediate pipe is essentially the UP-pipe to the turbo

What you are referring to is the downpipe "tailpipe" on the STS kit

You want the downpipe to be as free flowing as possible. You can definitely go too big with the up-pipe to the turbo and also material selection is important to keep heat in the pipe. (that is why stock cast iron manifolds and painted/wrapped pipes work better)

engineermike

From Engineering Thermodynamics, Chapter 4, Section 2, "the conclusion that the internal energy of an ideal gas is a function of temperature only is known as Joule's law. . . we can also show that enthalpy if an ideal gas is a function of temperature only."

You're right, but for the wrong reasons. You have plenty of backpressure. One of the dissadvantages of an STS type turbo is they create more backpressure than a conventional front-mount. What you were lacking is heat. You got that by insulating the exhaust. I'd be willing to bet that your exhaust pressure actually dropped (at the same boost level) AFTER you insulated it.

It works like this: As I posted earlier, the work that the turbine does is proportional to mass flow rate and temperature drop (NOT pressure drop) through it. So, when the exhaust was not insulated, the gas was cool by the time it reached the turbine. The wastegate recognizes that the boost level is not as high as it wants, so it closes off. This causes the mass flow rate through the turbine to increase. The side effect of this is that in order to get more mass flow through the turbine, it requires a higher pressure drop. This higher exhaust pressure is a bad thing because it reduces the power the engine makes. Clear?

Okay, so you insulated the exhaust system. Now, the temperature of the gas entering the turbine is higher. The turbine makes more power and drives the compressor up to a higher boost level. The wastegate says "Oh no! Too much boost!" and opens to bypass gas around the turbine, thus decreasing mass flow through the turbine. Less mass flow through the turbine means less pressure required to push the exhaust through it. So, exhaust backpressure drops and engine power increases.

Mike

longrange4u

iTrader: (2)

Ummm actully what is being said directly supports what he is saying... we are not talking the air flow / restriction... we are talking much less surface area on manifolds vs: LT Headers (I think it was said 5X less) which retains heat... the heat maintains volume (**** I gotta read Mike's post to make sure I have this right). So in short... the same amout of air will pass through the turbo regardless... but the hotter the air is the more volume it has so the faster the turbo will spool.

I belive that you will even see increased boost pressures with the increased efficency. So if your running the identical amount of exhaust from a 346 LS1, but you increase the temp efficency all the way to the turbo, you may see 11PSI 500-750 RPM (example only) earlier. Nothing changed with your engine... it is not producing more exhaust.. just the exhaust temp.

Zombie

iTrader: (2)

Yes, that makes sense to me, especially after doing some more reading on the subject, but just raises more questions as to what the system was doing before. I'd need temperature and pressure data to know that though and I was way to lazy to go through that effort.

What you are saying is that temperature delta across the tubine wheel is what deterimes the work done at a given pressure.

Maybe you can make sense of what was happening before.

This is what my car was doing.

.84 turbine housing it would make 6 psi of boost reliably and would make it pretty fast. I got annoyed with my inability to make more boost so I swapped out the housing for a .70, my boost would now go to 12.

Was this change in work done due to temperature change or pressure change? I'm going to say pressure since nothing was done to retain heat in the gas, unless the smaller scroll caused a much greater temp delta across the turbine, but I don't see the smaller scroll having much effect on temp. I do see pressure having a greater effect though, but I could be wrong.

Let me also add that while I was able to attain more boost my rate of climb for the boost stayed about the same (is that related to the heat?). The rate of climb is MUCH higher now.

Is it possible that I did not have enough pressure to enable the heat to do it's job better since they are related?

If the gas is hotter like it is now and and i'm making more boost, did this cause a rise in back pressure or a drop? Did the velocity of exhaust increase due to the greater temperature/pressure differential?

You got me questioning everything now Mike. Is there a engineer in the house?

GTObsessor

iTrader: (2)

so if there's nothing special about your y-pipe (except for the white paint), wouldn't jet-hot coating work even better at containing more heat? I mean, even if it was in a 3" dia.

Pro Stock John

iTrader: (34)

Did you make before and after passes?

longrange4u

iTrader: (2)

I would say yes... the difference between the stock and 3" pipe is not dramatic for the surface area.... nothing like LT's vs: Manifolds