L28et Swap Cold Air intake placement with large FMIC

[halokilller]

I have a large fmic on my 71 240z right now. The previous owner installed a small cone air filter right behind the radiator and I was thinking that it cannot be a good place for it because it will be breathing hot air. Will the fmic make the cold air vs hot air intake negligible? Where do you guys mount your intakes to make them breathe cold air?

[Tony D]

Changes in air density change the surge points of the compressor quite a bit.

You really need to look at the compressor map to see what changes it will make in compressor flow and surge characteristics.

 

If the FMIC is properly sized, any changes in compressor density temperature increase should be handled readily and your output from the FMIC should be within 10C of ambient.

 

The change you get from 40C air, as opposed to 60-80c air under the hood is really more of compressor map shift and surge points moving around.

[Kash]

You can pull out the slide rule and the magna-flux to figure out the optimal intake air temp and intake placement to minimize compressor surge while maximizing your air density prior to compression or you can go with your gut check that the coldest possible intake air you can start out with is the best solution.

[240zphilly]

Ive always run the intake out in front of the rad or in the wheel well for this purpose, I didnt know the science behind it other than that it seemed like a good idea.

[winstonusmc]

I run the intake out of the smaller hole under my FMIC cold pipe. The intake temps are around 15 to 20 degrees above ambient at full boost. With no cold air intake, it was more like 30 to 40 above ambient.

 

 

[Tony D]

Winston, your FMIC is sized poorly, there shouldn't be that. Kind of spike on after-cooler temperatures just from moving the inlet position to the turbo unless you were sucking air right from the exhaust manifold area under the intake right at the turbo inlet...

 

Even then, the additional turbo discharge heat should easily be taken up by the intercooler.

[winstonusmc]

Well the turbo was just suck air under the exhaust manifold. I really didn't log too many times without the cold air intake. And a intercooler will cool so much, so cooler air in equals cooler air out to a certain point.

[ctc]

Well the turbo was just suck air under the exhaust manifold. I really didn't log too many times without the cold air intake. And a intercooler will cool so much, so cooler air in equals cooler air out to a certain point.

 

Wow that is an over simplification.  Did you put and engineering or thermodynamic thought into that statement.  You totally missed Tony's point.

 

A properly sized intercooller will extract enough heat to get the charge air down to almost ambient or even sub ambient, depending on the cooling medium chosen, regardless of inlet temperature.  The key ratio is the cooling medium temperatre to the charge air inlet temperature for a given intercooler design.

 

In the case of the above FMIC example, with proper sizing, it will remove the heat added to the ambeint air from not only the turbo, but any additional heat introduced by the engine bay. 

 

Being simplistic, an intercooler by definition takes the intake air at an elevated temperature and extracts as much heat as the cooling medium and thermal losses allow.

[winstonusmc]

So what you are saying is there is no reason to have a cold air intake if you have an efficient enough intercooler? I am not an engineer, but it seemed like common sense. So can we see some examples of this in a calculation or formula. I am just trying to understand how a cold air inlet doesn't lower the temps out of the intercooler. I was just sharing my experience with my setup. No I didn't spend $1000 on my intercooler, but my intake temps are right at 90degrees at .9bar in Socal on the stock turbo. With the J-pipe it was around 215 sucking out from under the turbo, around 150~160 with CAI and the J-Pipe, 115 with a CX racing core and no CAI, and 90 with FMIC and CAI. Hard numbers for my setup.

Edited October 15, 2013 by winstonusmc

[Kash]

Wow that is an over simplification.  Did you put and engineering or thermodynamic thought into that statement.  You totally missed Tony's point.

 

A properly sized intercooller will extract enough heat to get the charge air down to almost ambient or even sub ambient, depending on the cooling medium chosen, regardless of inlet temperature.  The key ratio is the cooling medium temperatre to the charge air inlet temperature for a given intercooler design.

 

In the case of the above FMIC example, with proper sizing, it will remove the heat added to the ambeint air from not only the turbo, but any additional heat introduced by the engine bay. 

 

Being simplistic, an intercooler by definition takes the intake air at an elevated temperature and extracts as much heat as the cooling medium and thermal losses allow.

At times we know too much to be dangerous...all you did here was to validate his simplified (correcet) statement.  Engineer here...ME

[Kash]

My current set-up:

[ctc]

So what you are saying is there is no reason to have a cold air intake if you have an efficient enough intercooler?

 

Yes

 

I am just trying to understand how a cold air inlet doesn't lower the temps out of the intercooler.

 

It does, but I was addressing Tony's point that your intercooler was sized poorly.  If it were properly sized, you would not have seen the change in after cooler temps when you moved your air intake to another location.

 

So can we see some examples of this in a calculation or formula?

 

Go look at an good intercooler site, they have sizing equations posted or call them direct.  I will leave the math as and exercise for the student and those interested.

 

To Kash, as an ME, I think you would like people to be more precise in their understanding of thermodynamics, especially those that do share the foundational knowledge we acquired in school.  Generalizations belong on other sites, not this one.  Rules of thumb, depend on the thumb.

 

To simply state "cooler air in equals cooler air out" neglects the cooling medium being used.  In some instances, I bet I could get an intercooler to heat the air from the turbo further.

 

Based on your knowledge base, I am supprise your first post didn't recommend properly sizing the intercooler first, then getting colder air into it (both inlet and cooling air).

 

TO THE OP's ORIGINAL QUESTIONS;

 

Will the fmic make the cold air vs hot air intake negligible? Yes, if adequately sized.

 

Where do you guys mount your intakes to make them breathe cold air? Outside the engine bay or boxed to shield the intake from engine bay heat with a fresh air supply.
 

Edited October 15, 2013 by ctc

[Tony D]

"With the J-pipe it was around 215 sucking out from under the turbo, around 150~160 with CAI and the J-Pipe, 115 with a CX racing core and no CAI, and 90 with FMIC and CAI. Hard numbers for my setup. "

 

As stated, you just proved you have a crap intercooler!

 

The Delta-T across the turbine at a set Pressure Ratio EASILY explains the difference in temperature on the J-Pipe numbers. But the difference with IC is HORRID! BOTH of those should be within 9 degrees of Ambient. Any decent cooler should drop mass air from 270 to 104 without much airflow at all.... 215 is child's play.

 

You picked the wrong core, bud!

 

 

As to the 'under ambient' you can't get that with Air-Air, and likely you will need chilled water to accomplish better than perfect intercooling. The math is out there all over the internet. In it's most basic form: PV=nRT Boyle's Law. But that's very basic. VERY basic. The turbocharger sites can get you a better understanding of what inlet does to outlet temperatures. Similarly, intercooler function can similarly be quantified. You need to know the sizing for peak horsepower, pounds per hour for horsepower, and then the prospective worst case btu rejection scenario. Size it properly using that, and the vagaries you show will not make a blip on the screen.

 

For instance, JeffP runs consistent 43C inlet temperatures. At 8, 17, 21, 25 psi.... It's strange how it doesn't heat soak and temperature rise... Because even though everybody who sees it says "that intercooler is way too small" it works.... Because he did the math beforehand.

Edited October 16, 2013 by Tony D