Let's talk about stepped tubing and funnels.

I don't know all of the fancy fluid dynamics terminology, but I know that it's better for air to accelerate a little more gently than suddenly. So it follows that there would be some benefit to replacing a 2.5" intake elbow with one that started around, say, 4" and tapered to 2.5".

Discuss.

 

preferably with a velocity stack on the end.

 

I noticed zero difference in switching to a velocity stack with no filter vs running no stack and no filter.

 

I've heard from knowledgeable folks that velocity stacks are meant to be mounted in a place where the air will be flowing towards it (like the front of the car) and be pushed at it, otherwise they are nearly useless.

 

velocity stacks do what their name implies. they change the cross sectional flow are from infinite (not really but how else would you calc it?) to the diameter of your pipe.

This gives you a flow velocity gradient at the inlet of the pipe that reduces the boundary effects of sticking a pipe into a volume (yer intake tube into the earth's atmosphere).

air does not like to turn corners or make bends or be radically compressed or decompressed. doing this slows down the net velocity and thus its mass flow rate in the case of a motor.

the velocity stack reduces (almost but not quite eliminates) the radical ramp of velocty entering the pipe from nearly infinite (as it goes from still atmospheric to the velocity inthe pipe at the sharp edge) to something more reasonable across the horn shape.

HOW EV ERR

putting a filter on ***** this pipe-in-a-reservoir flow problem up a little. Your fitler creates a turbulent gradient of flow that "fixes" the boundary condition problem somewhat.

a better comparison would be:

pipe with no filter
pipe with velocity stack

but since we all use filters... it doesn't matter as much.

 

Are you talking about a stack pre-compressor inlet? For real world impact, I'd say that perhaps that could have some effect on spoolup but not after that. Probably the difference is negligible.

Doesn't fluid dynamics stuff change when a system is pressurized vs. sucking?

 

That's why big dog turbo dragsters have front facing turbo's with a velocity stack on the front bumper/headlight/nose with no filter and a straight shot into the compressor.

I believe in those types of applications it would actually help.

 

the stack and front facing are independent... anything front facing (ie facing higher pressure) is good. velocity stack is good.

the velocity stack helps most when flow velocity in the pipe is most different from environmental conditions. ie redline vs. atmosphere.

go look at your OEM mazda air box (at least on the 01)... the snorkel has a mild flare to it.



note that the oems use a pretty idealized setup. smooth flow in to a tuned pipe and then to a large panel filter (less pressure drop) and on to your motor.

 

**** I thought this was about funnel cake which is worth it.

As for the funneled intake, the performance difference in our application would probably fall within the error tolerance of the dyno.

 

tell you all what, when i dyno again ill do it with and with out the stack

 

There is a guy here in MD that runs a twin turbo OPS car when he had his turbos mounted with the inlets in the hood he made xx psi I don't recall the actual number but when he took the same exact car and set up and moved the turbos forward so they were right out front with stacks on them he gained 4 psi of boost at the end of the track this would be at around 210mph I do not see them making a big difference on our cars unless you are doing a salt lake flats build or something that will trap 175 mph or more.