More boost at lower RPM's with smaller exhaust?

[Fiorelli]

I was wondering if I'd gain anything buy going to a smaller exhaust.

The smaller exhaust should create more restriction and heat. I would think the restricted exhaust would increase the velocity of the exhaust gas leaving the turbo hopefully driving the turbo faster. Heating up the exhaust would make it expand increasing the volume of exhaust again hopefully increasing the velocity.

I'm 5inch now and was wondering about going to a 3 inch. I don't get much exhaust heat I've pulled it 12 times now and never got the exhaust to heat up enough to burn the paper with the part number off the exhaust pipe.

 

[falcon60]

No,a turbo likes the largest exhaust that you can run.The thing that drives the turbine is the difference in pressure between the outlet side and inlet side of the exhaust turbine wheel.If you're having slow-spooling or late-spooling problems an exhaust housing with a smaller A/R will help since it is physically smaller on the inlet side of the turbine and will have greater pressure difference and velocity. If you're happy with the power now,then the lack of exhaust heat after the turbo is not a problem.....in fact it means the pipe is big enough.
I love those old modded tractors!

Terry

 

[drag-200stang]

Waste gate leaking?

Turbine AR too large. What is it?

Compressor too small, to provide enough boost?

 

[757-A_V_8_R]

Turbos want the biggest exhaust possible. Turbines run off heat hot exhaust flow. Greater heat coming out of the turbo would indicate a loss in efficiency...... which is bad. In a 100% efficient turbo, the exhaust would come out of the turbine at a cool temp. Retaining heat would be helpful between the engine and the turbine, not after. Look into header wrap and turbine insulator blankets. A/R has the most effect on spool time.

 

[Bort62]

Turbines run off pressure differntial, not heat.

You can have all the hot air in the world upstream of the turbine, but if it's not at a higher pressure than the air downstream - it won't flow through it and thusly, it won't do crap.

It just so happens that in this case, the way we are raising the pressure of the working fluid (exhaust) is by heating it...

 

[757-A_V_8_R]

Turbines run off specific enthalpy differential
Work Out = Enthalpy Defferential

For the sake of a more direct explaination i was meerely stating that energy working on the turbine system was provided by heat content(ethalpy), .... though pressure is part of that equation. But the majority of my response was meant to quell Fiorelli's concern that the exhaust pipe was not getting very hot.

 

[Fiorelli]

The turbo is not waste gated. And it is not in very good shape it was pulled off an 855 CID cummins and thrown in the scrap pile. I really need to put a pressure gage on it and see what it is really building for bost but it has to be 5 to 8 psi at 1800 which is all I want. I need boost at the lower RPM's. I really need a smaller wastegated turbo something that will build at least 5psi at 1000RPM's and still have 8 buy 1800. I just don't know how to figure out what I really need.

 

[Bort62]

Turbines run off specific enthalpy differential
Work Out = Enthalpy Defferential

For the sake of a more direct explaination i was meerely stating that energy working on the turbine system was provided by heat content(ethalpy), .... though pressure is part of that equation. But the majority of my response was meant to quell Fiorelli's concern that the exhaust pipe was not getting very hot.

Well, okay... if you want to go there...

I also was trying to oversimplify

However, without a pressure differential you get no mass flow, independent of what your enthalpy differential may be.

 

[LUCKY13]

If it can be done a smaller diameter pipe between the turbo and exhaust mannifold will help. Also you can try putting heat wrap around this pipe to help hold heat in which will drive it harder.


On the remote mounted turbo's wraping the pipes make a big diff in spool up so that should help if you cant do anything else. The exhaust after the turbo needs to be big, so dont make it smaller.


If you can find a exhaust housing that has a smaller A/R that fits your turbo this can help.



Jess

 

[Bort62]

If it can be done a smaller diameter pipe between the turbo and exhaust mannifold will help.

Jess

That's not going to help either, but hey - what do I know?

 

[TCIC 300ci superbeast]

if put ing a smaller pipe on it wont work then how does a VG(variable geometry) turbo work.

 

[XPC66]

Turbines run off specific enthalpy differential
Work Out = Enthalpy Defferential

For the sake of a more direct explaination i was meerely stating that energy working on the turbine system was provided by heat content(ethalpy), .... though pressure is part of that equation. But the majority of my response was meant to quell Fiorelli's concern that the exhaust pipe was not getting very hot.

Specfic enthalpy in and out is a good way to measure isentropic process, but it is still PVT that matters here and it's the pressure differential and density across the turbine that is of consequence, thus why turbocharger turbine selections are made via intercepts of mass flow and pressure ratio on the maps.

Even the first step in the calculation is to determine the expansion ratio. So the smaller the drop the smaller the expansion ratio. The more restrictive the dump pipe the smaller the ER.

 

[XPC66]

if put ing a smaller pipe on it wont work then how does a VG(variable geometry) turbo work.

By manipulating the boundary layer and angle of attack on the blades.

 

[Bort62]

Finally Xecute and I agree on something

 

[wallaka]

if put ing a smaller pipe on it wont work then how does a VG(variable geometry) turbo work.

They change the pitch of the blades on the compressor wheel, that's how. A different angle of attack gives different flow and spool characteristics. It all works on the cold side, anyhow. Nothing to do with exhaust piping.

 

[TCIC 300ci superbeast]

ok then take a hose and then put your thumb over it same CFM at higher psi

 

[wallaka]

ok then take a hose and then put your thumb over it same CFM at higher psi

Not with air or water, or any other hose I know about. Take the shower head off and see how much water comes out when you turn it on. Put the plug in and measure, if you want to be scientific. Then do the same but leave the shower head on. I bet you a million bucks that the shower head restricts flow. Same thing with the aerator on the kitchen sink. It's a restriction; take it off and the water comes out way faster. It has the same pressure driving it. Get an air hose and put a blower on the end of it. That's a lot of air, right? Well, next just put one of the quick-connect fittings on it. Again, a lot more air comes out because it's less restrictive.

I don't even see how the remotest application of logic would make a person believe that a smaller outlet would increase flow and pressure. Physics (and easily demonstrated empirical evidence) says it ain't gonna happen.

 

[fb71]

if put ing a smaller pipe on it wont work then how does a VG(variable geometry) turbo work.

They change the pitch of the blades on the compressor wheel, that's how. A different angle of attack gives different flow and spool characteristics. It all works on the cold side, anyhow. Nothing to do with exhaust piping.

actually, you've got that a bit turned around. The compressor doesn't change at all. Also, its not the vanes on the wheels that move. There's a collection of vanes that surround the turbine wheel, and basically modify the flow path of exhaust gases over the turbine, effectively changing the volume of the turbine housing.

 

[wallaka]

Oops. My bad. For some reason I had thought I'd seen one with a variable compressor technology. Might have been just a concept.

I've seen the ones (Cummins/Holset?) that have like a sliding collar in the turbine housing, though the Garrett ones do indeed have movable vanes inside the turbine housing.

Anyhow, looks to me they're like having a variable A/R scroll. At lower RPMs, they present a smaller housing for quick spool, and at higher RPM they open up to allow the gasses to escape yet keep the turbo spinning at an optimum rate.

 

[Bort62]

ok then take a hose and then put your thumb over it same CFM at higher psi

Well, since I am making a concerted effort not to be rude with people on this forum, I won't even respond. I will just let those familiar with my typical ridicule of clearly ignorant statements imagine what I might have said here.


Enjoy.

(You are about as wrong as anyone who still thinks the earth is flat)