Zombie

iTrader: (2)

Had two changes done to my car recently and recieved it back yesterday. Converter got swapped for a much tighter one, car feels almost like a stock auto now but will foot brake to 2700, it's very nice.

The other change was my switch from SLP long tubes back to stock exhaust. With SLP long tubes I could set the wastegate to stay closed and it would struggle to make 13psi. After the swap back to the stock exhaust it comes up to full boost of 15psi at 50% throttle (verified by loggin). It's a HUGE difference. The SLP LT's suck very much, not just for a turbo application but because of ground clearance. Sold my old ones for $200.

The wastegate actually opens and makes noise now, car feels great. Only major change left is to swap to 2.75 gears and the car will be just about perfect.

Another thing that was done to my exhaust was it was painted with high temp white paint. Why white, because white reflects the heat.
We were told by my friends father (literally a rocket scientist LOL) to paint the pipes to help them retain exhaust energy. The results on a quick measurement he made at idle was very impressive. At the primary tube of a header his idle temp went down 45 degrees (from 530 to 485) from about 2 square inches of white paint only applied to the top of the header tube. If the heat isn't being radiated off the header then it's staying in the pipe. I've played around with charles's law calculations (p1/t1 = p2/t2, i'm a nerd, so sue me) and found that if you have 15 psi of exhaust pressure at 800 degrees before the turbo, raising that temp to 900 degrees will give you 17.3, a 2.3psi increase! Raise the temp to 1000 degrees and it's now 19.7 psi! Shows you how important it is to keep the heat in the exhaust. Long tubes + ehxuast have over 2 times the surface area of stock exhaust.

He's doing some more experiments with header wrap and painting the ehxaust to see if he can get the headers to work as good as or better than his stock manifolds did.

trtturbo

iTrader: (25)

great info!!

Reject

iTrader: (24)

kick ***! science finally dose something right! lol

67Firebird455

iTrader: (27)

Wow, had no idea, hadn't thought of it that way... Guess I'll get rid of my flowtechs, gonna end up getting jacked in CA for having longtubes to begin with... =( I would LOVE to have massive boost under 1/2 throttle, sounds great.

Pro Stock John

iTrader: (34)

Maybe boost went up because you went to a more restrictive exhaust setup?

smoke20

iTrader: (2)

hey zombie here is some more data for you. i took my car for a 45 minute drive at lunch. when i got back i took an infared temp guage and checked both lt and rt headers - averaged at 280-290 degrees. at the collector for each header temp was at 275. at the y-pipe single pipe temp was at 270. then as it went to the borla stainless steel is where the big drop came. only 12 inches from y-pipe temp was at 170 stayed that temp all the way to turbo. car was at idle with ac on . im going wrap y-pipe back with header wrap and try to keep heat loss to a minimum. if anyone has an infared thermometer and get a reading on stock exhaust manifolds i would like to compare the temp.

dubs6

iTrader: (1)

so you got more psi without turning up the boost. you added a more restrictive exhaust increasing pressure before the turbo. do you think this translates to more power? i could see how this translates to less lag b/c higher exhaust speed at lower rpm but i would think it would more restrictive for higher rpm's.

mahhddgtp

No kidding.. Something just seems screwy here... Requesting explanation.

Skunkworks

The important factor here is rear mount... Allot of temperature and velocity is lost by the time you get to back.

LT have a very large surface area by comparison to cast manifolds, also cast manifolds will hold heat better. The LT's dissipated allot of heat which hurt performance.

jamnut

iTrader: (4)

I is not very well edumacated, but I have a little theory about this.

We all know that turbo's work on exhaust gas pressure & heat, the amount of heat that the exhaust manifolds retain compared to the heat that LT's retain is enough to get more efficiency out of his turbo. The new heat efficency that he's found is enough to over ride any restrictions that the manifolds may have caused. Also if he's running 01 or 02 manifolds they are much better flowing than 98 - 00 manifolds.

CHRISPY

That is exactly what I thought would happen. Great testing man!!

Have you heatwrapped the Y pipe and intermediate pipe? That with the cast stock manifolds will make a BIG difference to heat retention in the pipe.

Zombie

iTrader: (2)

Nope, has nothing to do with restriction and everything to do with thermodynamics. The size of the pipe before the turbo doesn't really matter (within reason, no macdonalds straws of course). Making the pipe before the turbo smaller or larger doesn't matter, the pipe will NEVER BE ABLE TO FLOW MORE THAN IT'S MOST RESTRICTIVE POINT. In this case the turbo is the biggest restricion. If I had an 4" exhaust it wouldn't matter because the opening on the turbo is still the same size. The time needed to fill a 2.75" pipe vs a 3" pipe is mesured in milliseconds (i could probably figure out the math if someone really needs me to, just have to find the formulas. I've seen the math done before though).

The problem I was having was too great of a temp change from exhaust outlet to turbo. The exhaust system had a lot of surface area and the headers do not retain their heat. Everyone one knows that something hot trys to make itself the same temp as the environment. Cast iron on the other hand takes forever to cool off compared to any header based car. If the cast iron gets hot and takes a long time to cool, then there is less of a temp change between the exhaust gas and the iron manifold. That means the hot exhaust gas has to go further down stream to get rid of it's energy, which in a rear mounted turbo setup is great news.

There are 3 types of heat transfer that we need to worry about:

Conduction: how well does the exhaust pipe transfer heat from the inside to the outside

Convection: how much airflow do we have over the pipe cooling it.

Radiation: how much heat is being radiated off the surface of the pipe.

Conduction is determined by the type of metal used, convection and radiation can be solved by insulating the pipe with coatings and insulation and keeping it's surface area to a minimum.

I'm hoping this makes some sense, it's not the easiest of topics to understand, lots of variables. I'm still trying to figure all of it out but have a pretty good grasp on it now.

Let me give another example using charles law to illustrate how important the heat retention is.

1st the basics, a hot gas takes up more space than a cold gas
2nd, if the volume doesn't change that the gas is occupying, pressure will increase.

So we use the formula p1/t1 = p2/t2 to figure out some things on a front mounted turbo setup first.

We will say that a front mounted turbo system running a tubular manifold and producing 10psi at the intake manifold has a pressure ratio of 2:1. That means in order to produce that 10psi of pressure on the intake it takes 20psi of pressure in the exhaust before the turbo.

In the example we will say the exiting exhaust temp out of the port is 1600 degrees under load and has cooled to 1400 by the time it reaches the turbo. So the 1400 degrees of temp produced 20 psi of pressure in the exhaust manifold. If we now insulated the manifold and were able to keep the temp drop to 1500 degrees, our back pressure would increase 1.8 psi.

If we now move that same turbo 12 feet away from it's source the exhaust gas has more volume to fill, more surface area to radiate and conduct to and more exposed air flow to cool the piping itself.

Now I have not measured or calculated the exhaust temp at the turbo inlet at the back of my car so i'm just going to assume it's around 1000 degrees under load for my example.

That is now a 400 degree drop from the front of the car. Our original 20 psi of back pressure has now become 12.5 psi. I think you guys can see where this is going now. It's pretty tough to make more boost than you have exhaust pressure pushing on the turbine wheel.

If I had only wanted to run 5-7 psi this probably would have been fine, but I want to get closer to 20 psi. There are only two ways of doing that. Increase the velocity of the gas in the turbine housing by using a smaller housing, or increase the pressure in the exhaust pipe by raising the temperature. Since i'm already running the smallest housing for my turbine wheel my only solution is more heat.

Wrapping the exhaust is the next step, but I don't think I'll need it unless I can't hit my boost target of 22psi. Right now my waste gate is pretty loud at 15psi.

98turbls1

iTrader: (17)

Wow, this is some great reading Zombie... I learned a lot from your experiments... Are you going to be doing a dyno comparison??

solobaric

iTrader: (5)

Could we have some info on the paint itself? Where can you purchase it? What temp is it rated to? Are you going to paint the Y as well? Do you still have cats?

kp

iTrader: (34)

I would have guessed the tighter converter would have had something to do with it also..

DarkblueTA

That's what the guys at work said. The Rocket Engineers... Crazy thermo guys.

Zombie

iTrader: (2)

Converter didn't help me get over 13psi when I was 6spd. Car would never make more than 13psi when it was stick, wastegate never opened. Converter has no effect other than making the car much nicer to drive.

enginjoe

iTrader: (11)

This is great stuff.

The ideal gas law can be used to get the above equation (P1/T1=P2/T2) if we are assuming that the the volume doesn't change much from the exhaust port to the turbo inlet. Ideal gas law: PV/T=mR=constant. So, P1V1/T1=P1V2/T2. It is probably reasonable to a point to assume that V1 ~= V2 given low enough flow rates that any restriction in the system does not cause the exhaust gas to compress much. This allows us to come up with the equation P1/T1 = P2/T2. This equation would be pretty much be exact once the turbo is spooled to some constant speed. During spool up, however, the pressure in the system rises quickly due to the restriction caused by the unspooled turbo. I believe it is in the <0.05 sec range as far as time to get to pressure. So, woop de do, we have to keep volume as part of the equation during spool as above: P1V1/T1=P2V2/T2. Temperature is still the key in this equation anyway. I think Zombie's test gives us some good data to prove that this is true.

FWIW, Boyle's law (P1V1 = P2V2, given a constant temperature ideal gas) actually doesn't apply here because the exhaust gas isn't a constant temperature. It would acually be more suited to a front mount system.

kp

iTrader: (34)

You said you switched to a much tighter converter, didnt mention anything about a 6 speed..

I think the turbo is too far away from the manifolds for them to make that much of a difference but I'm no engineer. Whatever works for ya

mahhddgtp

I failed to notice he said he was rear-mounted... sorry