Why are Compressor Outlets so small?

[johnl]

My S-60 outlet ID is about 1 3/8" while the OD is 2" and the wall thickness of the compressor outlet casting is more than 1/4"

Then we go and put 2.5" or 3" IC hoses and pipes on a 2" outlet? WTF?

Why is there such a big step there?

What about the flow?

[Frank]

Mainly because of the flow interaction inside the compressor housing. The air is continually being put into a smaller area. The outlet is only relative to that.

[88_pacifica]

Would there be any performance gains from "opening" that up some. I know they do it on the exh side but what about the compressor side?

[Frank]

Because if you drop the velocity off to quickly by expanding the pipe, you can have adverse flow effects.

[johnl]

Because if you drop the velocity off to quickly by expanding the pipe, you can have adverse flow effects.

Right. And that is what the standard set up does. I mean the ID of the compressor outlet, in my turbo, is 1 3/8" and then the ID of the stock hose is 2." So, I presume there is an adverse flow effect caused by that.

How about a transition inside the hose - so there isn't a step for the air to flow past? How about a section or ring made of 2" ID pipe that is wedge shaped - thinned to the ID of the hose at the downstream end and left thick at the upstream end to match the compressor outlet ID?

[Frank]

I have seen some foot long transitions from 2" to 3" or something like that. Those are good off the compressor. I recommend maintaining the same size pipe from the compressor to the intercooler... say all 2" including the intercooler inlet. Then on the outlet go 3" with 3" pipe to a nice 70mm TB and intake neck! hehehe

[devlish]

that's what i did on my DSM. used 2.25" pipe to the FMIC, then 2.5" up to the throttle body. however, i have also had 2.5" all the way, exact same setup, and noticed no difference. but i like the first idea better so i went back to it for some reason.

[3Bar_Mopar]

Forward Motion's Enforcer turbos have the compressor outlet polished and enlarged (as well as compressor housing) to make a smooth transition to the compressor to IC hose.
I have less than a quarter inch of meat left on my compressor outlet on the end.

[johnl]

OK, good info - FM ports its compressor covers/outlets.

What is going on with the physics of air flow inside the compressor housing?

Tell me where I am wrong; it's hard to describe -
The compressor housing consists of a scroll or curled horn with the inducer/exducer in the center. The horn has a cut out/slot in the side of the horn to make room for the inducer/exducer to spin and to transfer/pack air into the horn. The curled horn, as a horn, starts with a small ID and the ID increases as it progresses to the ID at the end of the scroll/compressor outlet. So, what happens to the physics of that horn when the rate of progression of the horn shape ( the degree of flare) is accelerated - when the end of the horn/compressor outlet is ported (to match the greater ID of the IC pipe)?

[BadAssPerformance]

...So, what happens to the physics of that horn when the rate of progression of the horn shape ( the degree of flare) is accelerated - when the end of the horn/compressor outlet is ported (to match the greater ID of the IC pipe)?

As mentioned it slow the velocity down if you open it up too soon. Mildly porting the comp housing outlet will make a smoother transtition to connection hose so I'd bet the two would offset eachither for a benefit. OEM comp housings are thick in this area, aftermarket comp housings are thin for a better housing to hose transition.

So if you have a thick walled stocker and want the best performance, just polish the ID but dont port it, then get a custom hose or turn down the OD of the outlet...

...but honestly, unless you are looking for 1/16 of a HP, it is not worth the time. you guys wouldn't beleive how F-ed the transition between the 52mm throttle body to intake is on my shadow!

[johnl]

Yeah, guess I knew it's a gnat on an elephant's A** kind of deal.

Just bugs me to see that big cavitating step there while I'm sweating port matches and other stuff in the intake.

[devlish]

Yeah, guess I knew it's a gnat on an elephant's A** kind of deal.

Just bugs me to see that big cavitating step there while I'm sweating port matches and other stuff in the intake.

just remember though... that step goes from a small compressor outlet to a larger IC pipe. NOT the other way around (large > small)which would be more of a problem. like mentioned above, there are easier ways to get that 1/16 of a horsepower. don't eat one, not two dbl cheeseburgers for lunch ... empty the glove box... etc. do a good job porting the exhaust manifold where we KNOW there are gains to be had from that. just my $.02

[shadow88]

I was thinking about this for a spring project. If I've read everything properly, the air goes from 1 3/8" to above 2" (the flared end of the stock lower intercooelr hose), then down to 2" for the rest of the hose then flared back out again to 2 1/4" or 2 1/2" then into the cooler.

Using Franks' guide of enlarging the flare after about a foot, why not try to go up to 2 1/2" and onto the cooler?

I'm planning on using scraps of exhaust tubing that will cost nothing and weld them all together with the bends required to clear the trans.

What if it's worth alot more than just 1/16th of a hp. more like 10-15hp? Wouldn't it be worth a try?

Any further thoughts on this?

[Speedeuphoria]

well the larger diam pipes will let the air be cooler by a few degrees(5 or so) it all depends on the setup, if its nearly stock then prob a waste of time, your better off opening the exhaust or getting a better IC or using W/I

the reason the outlet is small is because they are mostly focused on the A/R of the compressor and not the outlet

[puppet]

A lot of businesses offer "ported" outlets ... frankly I don't know what, if anything is to be gained or lost by it ?? The scroll itself produces the pressure. The scroll starts out very small ... low pressure. As the air moves around the housing on it's way out it picks up more air along the way, increasing the pressure.

Maybe Frank would know how much you can port this out before you kill/improve the turbos pressure building characteristics. Got to be more to this considering that there are at least 3-4 sizes of T3 comp wheels (stocker, the 16v, MP+ and the S60 ) ... each able to produce a little more pressure ... yet all working with the same housing geometry.

[shadow88]

It's not even close to stock anymore.

I didn't even consider the cooling advantage of allowing the air to expand a little, good point.

I was thinking because I spent alot of effort last winter making the air move through the engine more efficiently, with very good results. There should be another increase in making it a larger volume of air right from the turbo rather than the nech up and neck down of the stock lower hose.