turbo question

[Turbo Thom]

A friend and me were talking about turbos and he said the inside dimensions were the same no matter if your turbo was a 12 -14-or16 cm, with a 4" outlet. Therefor a down pipe larger than a 3" was of no use since the inside of the turbo was a set size. My question is, is that so?If that is true I can see where he would be right.



Also on another subject does anyone know anything about the Excide battery that is of the same makeup as the Optima. The battery is sold at NAPA. 84 mo. warranty with 100 CCA. $100 each.



Thanks



Preston

 

[illflem]

Preston, folks have posted here before that Excide batteries are junk, I have no experence with them and can't say. I did buy four Optima style Champion labeled batteries for two tractors and a Ram, they've been working great for over 18 months and were only $63 each.

 

[EMDDIESEL]

A similar question was asked recently and it basically is the same in this situation, your friend is wrong. As exhaust cools, it becomes more dense, more dense means more volume, therefore a larger exhaust will flow more volume. So a larger exhuast and downpipe will make a difference since the engine can get rid of more exhaust faster, which means faster spoolup of the turbo plus lower EGT's. So to say a 4" exhaust gives no performance gain is ridiculous.

 

[Cooker]

Exide batteries are junk.



I agree with EMDDIESEL, except I'd stick with the 3" downpipe and wrap it with header wrap and run 4" the rest of the way.



Just my opinion,

Ryan

 

[BigUgly]

EMD;

As the air cools, it does become more dense, yet wouldn't greater density cause LESS volume? Same number of air particles packed in tighter (higher Density), leaves the same amount of air is less space.

Just wonderin?

Josiah

 

[EMDDIESEL]

I guess i was not using the right word when i chose the word "Dense" but the total volume of exhaust is increased which is why you see so many large exhaust systems on High Perfomance engine both gas and Diesel.

 

[Coop]

The bigger diameter pipe would have less friction losses as the gas escapes, therefore, there would be less pressure downpipe of the turbo. This creates a higher differential pressure across the turbo, allowing it to spool-up faster and rotate faster. Theoretically.

 

[NVR FNSH]

EMD - the volume of exhaust is not increased down stream of the turbo. For a given mass flow (mdot = lb/sec) increasing the pipe diameter will decrease the velocity of the gas & thus reduce the pressure loss (frictional losses). Pressure loss is proportional to velocity squared. mdot = density*velocity*area >>> increased area results in a decrease in velocity.



My bet is that there is not a big difference in exit diameter between the 12/14/16 turbine hsgs with the same flange size - they are designed for the same turbine wheel. I may be wrong as I've never measured any of the hsgs.



Brian

 

[TXRam]

Just to add to what NVR FNSH posted, just think of the turbine side of the turbo as a backwards compressor. High pressure in, low pressure out, high temp. in, lower temp. out, lower volume in, higher volume out (this is where I think NVR FNSH did not use the right words).



The turbines "expands" the gas, as the pressure drops across the turbine, the volume increases.

 

[NVR FNSH]

TXRAm - there's a reason I prefer mdot, same on both sides of the turbine wheel.



Did all the EIT problems in SI units since I didn't have to worry about that pesky little Gsubc constant... . Does NASA use SI?



Brian

 

[Ram_Kowboy]

Your turbocharger is basicly an air pump. The larger the diameter of the exit pipe the quicker the air pressure will move away from the turbo. The idea is to unload that pressure as quick as possible.

Imagine if you had a air hose with a air nozzle on the end of it. You blew the nozzle into a 3" hose or a 4" hose. Which would move the air faster? The one with the least restriction. Another benefit to moving the air out quicker is lower Exhaust Gas Temperature.



I kinda know where your friend is coming from. If you had a 4" exhaust system and a 3" muffler, there would be no advantage to the 4" exhaust. The maximum benefit would be 3".



I asked a similar question when I was brand new to the turbo diesel world. Ted Jannety ( whom I have learned to respect on the horsepower subject ) was kind enough to explain the benefits to me!

 

[klenger]

I think we need a poll to see who's explanation makes the most sense... or how about a poll to see if we should have a poll?

 

[Coop]

I'll poll for whether or not we need a poll.

 

[Max340]

Originally posted by EMDDIESEL

I guess i was not using the right word when i chose the word "Dense" but the total volume of exhaust is increased which is why you see so many large exhaust systems on High Perfomance engine both gas and Diesel.

The total volume of the exhaust gasses is the same.



The Turbo depends on the velocity of those gasses to spin. Thus, forcing the exhaust gasses through a narrow (small diameter) pipe or housing means they will be moving faster. Faster movement means more shaft speed on the turbo, and more boost.



However, on the downstream side of the turbo, you want a larger diameter pipe, since the exhaust gasses will need a free flowing area to go after exiting the turbo.

 

[KWIKKURT]

Let me try to explain in Laymans terms.



Yes the 12,14 & 16 cm Turbo housings do have about the same size output hole. After all they are all using the same wheel. So why does larger exhaust tubing offer "More Flow"?



Rather than try to explain why (Venturi ---- Higher speed = Lower Pressure ... etc) it works and further confuse everyone especially myself. Let me state a few unknown facts about Flow and restriction. I will put in my . 0000000000002 pesos worth and then the Rocket scientists can explain more



If you take a 10ft 4" tube and restrict the first couple of inches to 3" (ie: Turbine Wheel & Housing) it still will flow with less restriction Much MORE EXHAUST gasses then a 10ft 3" tube. It is just the way it works.





And why does 4" make such a difference over 3". It is not 33. 3% more flow like you would think. When working with flow (gasses or liquids) thru Pipes & Tubes the math you use is diameter increase X 3. 14 Pie ( I Think)



While working with Jet Fuel, Avgas pumping systems I learned that if you double the size of pipe (2" up to 4" = 100% larger in inches of diameter) But it almost Quadruples the flow at the same pressure.



I hope this helps some of the regular Down to earth thinkers like me a little.



The rest of you Superbrains feel free to tear apart my opinions with scientific fact.



Meanwhile I will play it safe with 5" to Dual 5" stacks



MY exhaust guy Greg. Mighty Muffler in PHX AZ.

 

[TXRam]

Kurt explained it pretty good. Restriction in piping is directly proportional to the length of the restricting piece (for example, even though the stock system has some bends that make the system more like 2" than 3" at those points, the flow through it is still very close to what it would be if the bends weren't "crushed", and far more flow than if it was all 2"). Also, when considering flow through a system, it's the area, not the diameter, that's used. A=Pi*D*D/4 - let's use a 3" system and a 4" system to compare. The Area of the 4" is 3. 14*4*4/4 (12. 5in^2) vs. the area for a 3" is 3. 14*3*3/4 (7in^2) - therefore, Kurt's statement is right on (double the diameter, quadruple the flow). We only changed the diameter from 3 to 4" (25% based on the 4"), but the flow area almost doubled.



Pressure is what causes flow, flow drives the turbine, and as the pressure drops across the turbine, the volume, not mass, increases.

 

[Deezal Man]

You guys are too much . .



Here's the deal. . in terms everyone should be able to understand. .



Air is no different than any other gas I can think of... and/or metal.



Heat creates expansion, cold promotes compression.



Ever hear of the byrometer? High pressure systems mean sunny, low pressure means cool rainy weather.



Increase density, decreases volume. vise vera. A hot air balloon EXISTS on this relationship.



Anyway, you get the point. A PERFECT exhaust would be largest at the manifold and very slowly taper to a smaller diameter to the tail pipe. As air cools, it becomes more dense, and therefore requires less volume.



This taper would place even pressure on each exhaust pulse as it exists the pipe, and therefore you would create a balanced push/pull configuration. Meaning, about as little resistance as you could possibly have.



I don't know of anyone doing this, simply due to the cost of manufacturing and engineering. . It just isn't practical. Best way around this is to keep the exhaust pipe as short as possible. Like the ones found on a drag car. But again, this isn't practical for daily use.



Bottom line, a larger diameter down pipe will provide far more benefit than a larger tailpipe.



As far as your turbo question, I can't offer much.

 

[NVR FNSH]

Has anyone actually instrumented their exhaust system for pressure & temperature and done a comparison between 3", 4" & 5"?



Brian

 

[Turbo Thom]

Well folks:

Now I know why the space shuttle goes so fast. It has a Cummins 5. 9 with a 6 ft. turbo and 3 -3 ft exhaust pipes.

I'm an older man with limited knowledge of physics but I think y'all have explaned to a point as to what my question was. I am going to cut part of the 3" down pipe off, weld on a 3 to a 4 bell to the exhaust brake, and from there turn out in front of the rear wheels with a 5" tube , and let the air flow.



Thanks.



Preston

 

[KWIKKURT]

Turbo Tom, You figured it out except this is how you should exit the exhaust IMHO