It would be cool if K&N actually followed that same principal in the design. I doubt they did, not many automotive aftermarket companies do.

Looks a little restrictive to me.

Look how big of an airbox they use in WRC

https://www.miataturbo.net/attachmen...ine=1426268176

You routed your hot side IC pipe through your cold air source. Reroute that hot side pipe and find power with a cold air box.

I messed up math. Intake plus turbo equal 270f. 270 x .9 = 27f

550/577 = .953. Vs .984

Somewhat trivial gains.

Yes, I agree. I might just have to reclock the turbo and route it down.

But, it wasn't me!... It is a BEIG kit for an MSM. Apparently, they tried to follow the OEM hotside route in their kit.

In it's past life, I solved this problem by using the hollow frame member to route cold air from a filter stashed just behind the bumper cover. (You can see the old route the from the picture). Since then, I ended up plating this opening and used the structure to mount a nerf bar.

http://https://www.miataturbo.net/me...2151018a-4052/

Really interesting read as I'm just now thinking about this. :D

Flame suit on.. :lowdown::rofl:

Soooo.. The calculations were on 180 degree engine bay temps v 90degree outside temps yes? And so at 6psi, it would be about a 10hp difference?

Does this take into account how others are talking about the size of the charge pipe making a difference? If not, is there an even smaller difference with a filter right on top of the turbo v a 1 or 2 foot long charge pipe?

Does colder air move more slowly enough to make a difference in this situation?

Not 10rwhp.

If you assume 10hp per psi.

Then 9.5 x 6 = 57hp. Vs. 9.8 x 6 = 58.8hp from the turbo at 6psi.

Measurable difference but very trivial. Intercooler is key.

What is missing from your calculation is the fact that if you're running the same "boost" in each scenario, the turbo has to work harder (more energy into compressor) to get the same boost from the hot air, as it's less dense. So that means more energy out of the turbine, so to do that the wastegate clamps down to raise turbine pressure to get the extra energy.

So two identical engines, one with cold air intake, one with hot air, the cold one will actually flow more air since the turbine pressure goes down, less likely to detonate (turbine pressure goes down). It's more than just boost and intercooler temps.

I have a back to back of this exact filter, with and without the end piece that you can put a hose on.
No hose either run, both runs had the enclosure in the power steering reservoir location.

GT2560, well flowing cast log, 2.5" exhaust. 20ish psi tapering on.

This is 285rwhp, and the difference where you can see it averages 5rwhp.

https://fbcdn-photos-g-a.akamaihd.ne...338c4c84fdda1d

Adding to what brain is saying, the math shows its trivial, and that's before what no one has yet mentioned.. Delta T.

If the intercooler is fed hotter air, the difference in intercooler surface temp compared to ambient air temp cooling it is greater, (greater Delta T). The greater the difference in temperature the faster the heat transfer.


Ie, when the air into the cooler gets hotter the cooler gets more efficient.

I really don't bother with cai ever on low boost setups, I just add one click on the MBC.

Dann

Does the length of the charge pipe also have resonance effects like the intake?

Imagine if you had a huge fan in the engine bay, and all it did was suck up engine bay heat, and blow it into the mouth of the car at the heat exchangers.

This is exactly what your turbo is doing when you have a hot air intake. Makes all the heat exchangers from the intercooler back less effective since they are getting warmer air.

There is no question that a CAI is the better way.

To try to put numbers to how much it helps, to do it somewhat close, you'd need a map sensor before and after the turbo, temperature before and after turbo, temp after intercooler, turbine inlet pressure, and preferably a MAF sensor too. And if you want to put numbers to how it affects say, radiator effectiveness, it would get even more complex as then you'd need water temp in/out of radiator and air temp before/after radiator for both setups. To measure heat soak, you'd have to datalog all of this and graph it, and measure time between cooldown after a set of runs or something to accurately know how much it matters.

Or you could just accept the physics that cold will make more power and make the engine less likely to detonate and build a CAI accordingly.

Sorry, I edited my question while you were answering it.

His math is wrong, it's not trivial! See my post right above this. Leafy touched on it too, the pressure drop upstream of the turbo is a big deal too! Having a good flowing CAI is much better than sticking a little filter on the inlet of the turbo.

my math on the inlet has been corrected. if you're going to bring up the turbine efficiency, show us a math formula that factors it in.

a 90°f intake delta, plus the 90°f turbo delta, after intercooler would be an extra 27°f on a day 90°f day assuming a 90% effective IC.

you're only 18°f degrees more likely to detonate from intake temps. in the grand scheme of things that nothing and the compressor/turbine efficiency difference between the two is also going to be negligible.

I'm not saying CAI isn't better, but im saying it's not a make or break big deal, assuming you have a good IC. I made efforts to source ambient temps myself. But I'd be more worried about living in the rocky mountains vs. the dead sea really...

Brain there are other math that uses the turbine work to determine the temperature increase across the compressor. But the math going on with the turbine, the efficiency and rho is a whole lot more difficult to do. You're into the case where you have to solve a non linear equation. Either using matlab or brute force in excel like a child.

The equation for the turbine is the change in Enthalpy across it. Enthalpy is denoted H, and H = U + P*V, where U is internal energy, P is pressure, V is volume. Thus you need all the stuff i posted above (temps, pressures, MAF sensor) to measure it.

Like leafy said it's several things changing, not just one. When you change one, it changes all the other things. Kinda like how if I put a turbo on my car, more air goes in, but then air gets hotter, and then cooler from IC, and then denser, and then need more fuel, and then have to change timing now, and so forth. One thing changes other things in the system.

I'm not going to makeup 14 assumptions for temp/pressure and try to solve it, I don't have a software that will do it worth a crap.

But I'll at least show you this to help everyone understand. Say it's an 80*F day. With a CAI, temps going into the turbo are 80*F, with a hot air intake, lets just say 100*F HIGHER, so 80 + 100 = 180*F into the turbo.

I'll assume we're running the same boost before/after, and that the boost reference is at the intake manifold.

And let's just say we're at sea level, 40% relative humidity.

Case 1: Density Air at 80*F, 0. 0727 lb/ft^3
Case 2: Density Air at 180*F, .0569

So if you have a 300whp miata, you're flowing about 30 lb/min through the compressor.

At 300whp, airflow is 30lb/min, so with a 3" inlet pipe hooked to the inlet of the turbo, air speed is

Case 1: 30 lb/min / .0727 lb/ft^3, = 412.7 ft^3/min, or CFM
Case 2: 30 lb/min / .0569 lb/ft^3 = 527.2 ft^3/min.

So at this point, we can see that with a hot air intake, the CFM going through the compressor inlet had to go up by 527.2 / 412.7 = 27.7% just to match the same mass flow rate of air.

This is not without consequence. I said we have a 3" inlet pipe, so at 3" ID, Area is A = pi*r^2 = 7.0868 in^2. One foot of pipe would be 12", so one foot has 7.0868 *12 = 85.04 cubic inches. There are 1728 cubic inches in a foot (12x12x12) so 85.04 cubic inches is 0.04921296296 cubic feet in 1 foot of pipe.

So case A, 412.7/ .04921296296 = 8386 ft/min, 5280 ft in a mile, so 8386/5280 = 1.58826 miles/min, times 60 is 95.3 mph. Speed of sound is 761.2 mph, so 95.3/761.2 = .12 mach

Case B, 527.2/.04921296296 = 10713 ft/min, 10713/5280= 2.0289061833 miles/min, times 60 is 121.7 mph, so 121.7/761.2 = 0.16 mach, or 0.16/0.12 = 33% faster air.

Pressure drop vs speed is not linear, it's squared!

I'm not keeping units anymore, but lets say you have 10 units of crickets worth of pressure drop in Case A, Case B is going to have 16.31 crickets worth of pressure drop, or 63.1% higher pressure drop!!!!!

If inlet temps are more than 100*F higher (say your turbo is bolted to a hot exhaust manifold, for example) the numbers get worse. Or if you have anything smaller than 3" pipe for your inlet, again, it gets worse.

I would like to point out that I ONLY did some of the calculations for pressure drop upstream of the compressor. I did not touch anything else!

And just in case it's not obvious, asking your turbo to flow 27.7% more pushes you to the right of the compressor map, and most people here are already right of the "sweet spot", so then the compressor is becoming less efficient (more heat in charge, more turbine inlet pressure to get energy to drive compressor).

There is a reason that every turbo engine in production in the world has a cold air intake from the factory.

that doesn't really touch on anything I said.

It's my opinion that you use the largest intake pipe you can fit to reduce the pressure drop between the filter and turbo.

one example of a warm air intake on a turbo car: the mazdaspeed miata.

You said it's trivial, I showed you why it's not. You were only looking at one aspect of it, not all of it. Even I didn't look at all of it, just another aspect that is a lot more significant than the one you considered when you stated CAI is trivial, intercooler is key. No disrespect, but you can't draw a conclusion looking at just one part of the picture. Even my math is only one part, I didn't consider the turbine, compressor efficiency, etc.

You also asked for the equation for the turbine so I posted that too.

The point is that CAI does in fact make a difference, it is significant, and there is a lot more benefit than just 3* colder AITs as you posted. I want people to realize that and not assume that is the ONLY consequence of a hot air intake. There are in fact many reasons to run a CAI, and 3* or whatever cooler AITs is not the only reason.

you're ignoring a lot more than i am. and yes, you really lost track of your units, conversions, and relevance there.

you're forgetting how much a good IC equalizes the density ratio of the air that the motor ingests on each gulp, and that's really the most important factor when talking WAI vs CAI. Yes, the turbo will have to work a little bit harder to compress that air, but I don't you're going about determining that correctly.



here, this one factors in most:

Not2Fast: Turbo Calculator

it agrees that the change from 26.6*C to 82*C intake temps doesn't change the HP significantly once you input the rest.