When running the piping from the turbo into the carb on a blow-through setup, would there be any advantage or disadvantage to using larger or smaller diameter pipe? Would larger pipe have more volume and less pressure? Would smaller pipe have more pressure but less volume? Is there a way to calculate a happy medium? What is your goal with the piping? Thanks.

 

the pressure will be the same.
the smaller the pipe is the more restrictive it is(restriction = bad anywhere in turbo setups).
causing slow spool up times.

EDIT: read all of this (6 pages)
http://www.turbomustangs.com/forums/...0&pagenumber=1

www.turbomustangs.com
i

what is your setup going to be?
turbo size?

 

Turbos are spun from high velocity, hot, expansive exhaust gasses.

So your goal would be to maintain the exhaust velocity, and heat, from the engine to the turbo. Larger pipes will provide a velocity decrease, and in turn, more turbo lag (and often, some very odd swirly currents in the larger tube where it mates with the smaller tubes from the head, reducing scavaging).

Having made many different styles of exhaust manifolds for turbocharged engines, I've found the best "overall" method is to run the four exhaust tubes from the header plate right to the turbo flange in parallel, and have the "collector" be the turbo housing itself.

Use tubing a hair larger than your exhaust port for the highest velocity.

 

That is very helpful info, thanks. Does the tubing from the turbo to your carb or efi intake matter as well? What benifit do you get from using larger tube? That was the question I was trying to ask.

 

The benefits of a larger tube, is that it holes more volume, acting more like a plenum than a tube. Turbo systems like larger plenums.

The disadvantage of larger tubes is the velocity of the incoming air slows down as it has to fill the additional volume.

Fitment without leaks is more important than tubing diameter, so I'd worry more about that.

Plenum volume helps, I've increased my plenum volume of my 460 motor by welding together an "ugly gooseneck mounted box" with two 4.6L throttle bodies, which coincidentally have the same OD as the OD of the turbo outlets - meaning that I can use one hose from turbo to TB, without any annoying adaptors, shims, spacers, or such.

 

yes is does.
Read all of this thread to find out why.
http://www.turbomustangs.com/forums/...0&pagenumber=1

here's the post that you are looking for.

"If I could interject an idea. . . a restriction between the turbo's compressor and the intake plenum can cause high backpressure also.

I just put together a turbo (T-76 GTS) in my 383 LT1 Camaro and was dissappointed with the results. It lost 20 hp as compared to the T-trim Vortech, at the same boost, that I just sold. After doing some thinking, I replaced a piece of 2 1/2" pipe between the intercooler and TB with 3" and, with the same boost controller setting, picked up 6 psi boost.

Then it occurred to me that, with the restriction in the intake side, the boost controller was forcing the turbo to overcome it. The compressor doesn't have a problem doing this, but it takes alot more energy (pressure) from the exhaust to spin the turbo fast enough.

Check out your intake side plumbing for restrictions. Piping, intercooler, air filter, MAF, throttle body, etc. . . should all be 3" id or so."

does it make sense now?

a Leak free system is very important if you want it to spool fast.

 

Fred
I don't see how a large in intake tube before the carb/T-body is going to act like a plenum. An intake intake tube that is too large will only reduce spoolup time by a very small amount(likely not noticeable).
An intake tube that is too small will act like a restrictor plate and will increase exhaust backpressure and can reduce intake pressure too. This causes power loss.

Doesn't the exhaust pressure and the turbo housing speed up the air to spin the turbine anyway?
Kind of like air in an shop air line accelerating when force through a small blower tip by pressure. It doesn't matter if the air line is 1/2" or 1" before the tip, the same amount of air (mass) is coming out the tip at that pressure no matter how much volume is in the line behind it.

 

Daniel,

Your description of an airhose, is a correct statement. However know that you're not comparing apples to apples here... fluid dynamics (air is a fluid) is very different between an air compressor and a turbo system. An air compressor might provide 10cfm @ 120psi. A turbo system might provide 800cfm @ 15psi.

I was talking about exhaust tubing mostly, so my apologies if there was some confusion. Often I cannot verbalize what it is my head. I'll get to intake related bits later... allow me the opportunity to clarify my exhaust related comments.

First, know that I cannot draw even if my life depended on it. So while looking at this drawing, use your imagination based on the text.



Essentially what i'm describing, is to have exhaust runners from the head, right to the turbo flange, using the turbo housing as the collector. This ultimately will minimize back pressure, as the pressurized airflow is introduced from each runner, right into the turbo's turbine wheel. This minimizes (under boost) reverberation, as the mix of airflow is in the more aerodynamic turbine housing. This is in leu of a collector area, when then feeds the turbo.

While it is true that mass is mass regardless of volume, there is more to this than just mass. There's scavanging effects you want to try and maximize, even though the turbo being a large cork will significantly reduce. This is why I suggest using the turbine housing as the collector, and running exhaust tubes slightly larger in diameter than the exhaust ports. If you have 1-7/8" ID exhaust ports, 2" ID tubing would be about right more or less. The reason for this is.... boundry layers, like so:



The black rectangle is a section of pipe. All off the arrows left to right represent airflow. The larger, green arrows indicate a higher velocity. The black arrows indicate a slower velocity. This is because the air flowing through the pipe, has some resistance from the pipe itself, mostly around wall of the pipe. If the tubing is polished like glass, this is significantly reduced but still exists.

This is also true for your air hose analogy BTW, except its not really measurable since the ID of the hose is so small, in comparison.

Now this is not to say that if you don't follow my idea you're going to have a crappy turbo system - that is far from the truth. Turbocharged systems are fairly forgiving actually, so if you're "off" in your design a little bit, it's nothing to worry about. If you were going to compete with your vehicle at 200mph at 10K rpm, I'd say okay, worry about the tiny details. But for the average man, even log manifolds work fine. I am sorry if I caused any confusion.

This is a correct statement. However, your maximum airflow is determined by the ID of the TB, the ID of your MAF if you're using one, the ID of the airbox in and out, the ID of the intercooler inlet/outlet, and the turbo itself. Using larger tubing between any of these really does nothing for you.

Yes, of course. But, you want this to occur without effecting other things, like scavaging, blowback when the exhaust valve opens, etc. You want to eliminate these things as much as is reasonable.

On the fresh air side, I'll add a final comment that's irrelevent, but might be interesting. We all know that longer runners are better for low-end torque, and shorter runners are better for high RPM.

On a rover V8 block, with antique aluminum Buick 300 heads, I brazed together an aluminum intake with no intake runners of any kind. Essentially, the "intake" was a huge plenum, with "holes" in it that lined up with the "holes" in the head And you know what? It worked darn good with the T3 turbochargers.

 

How would you do the crossover pipe on single turbo V8?

 

There is more than one way. But on my truck, I have a pipe running from the stock exhaust manifold on the drivers side, back around behind and under the engine, connecting to a log style manifold I built for the passenger side.

You can also run both manifolds straight foreward and run them together right at the turbo flange. But there just aint enough room for me to do that on my truck.


Marlon

 

Hey you guys rock! This is all very great info. Thanks also for the link to turbomustangs. I am reading it every day. I have another question. The headers and flanges should be built with steel, but can you use aluminum tubing after the turbo? I was wondering if the compressed air is hot enough to warp aluminum tubing? Also, would 3" tubing all around be ok or would it be "too big?"

frederic

Are you welding your header tubes directly to the exhaust side of the turbo housing?

 

There are several ways, looking at my 351W powered crewcab. You could go down in front of the crossmember, undernreath the oil pan, and up on the other side.

In my truck, I'd have enough room to run it back and over the transmission, I have a good 5-6" between the top of the tranny and the firewall edge.

A friend of mine did something bizarre on his dodge truck - he ran the two manifolds forward, came up over the valve covers and over the intake, and mounted the single turbo right there, clocking it so the fresh air outlet aims at the throttle body (which he relocated by turning the intake around). He'll need a hole in the hood but it's one way I guess.

Not sure how he'll change valve cover gaskets in the future... lol

 

Steel is fine for the headers and flanges. Stainless steel is even better.

Aluminum tubing is great for intake charge pipe. The air coming out of the turbo is hot, but its not near hot enough to warp aluminum. On my Freightliner, all the pipe from the turbo to the intercooler is aluminum, and then its rubber hose from the intercooler to the engine. It makes 40+ psi and it doesn't hurt the aluminum.

3 inch for intercooler pipe sounds good. It really depends on how much power you are gonna be making, and how big the inlet is on your throttle body. There isn't really any advantage to using bigger pipe than the TB, or carb. Now if you mean 3 inch for header tubes, thats just too big.... unless its between the collector and the exhaust housing.

And I dont think anyone welds header tubes directly to the exhaust housing. Just weld the tubes together at the flange that bolts to the exhaust housing.

Marlon