Thoughts on hot air vs cold air intakes
 

Hot air vs cold air intakes seems to always be argumentative. I think everyone will agree that cold air is better, it just comes down to how much better and some feel it's not worth it. The hot air guys seem to think that as long as you have a decent intercooler it doesn't matter. I think they're full of hot air :p:

All of us notice the difference in power of our turbo cars between a cool summer night and a hot summer afternoon and that difference is soley due to intake temps! If the difference in intake temps didn't matter you wouldn't notice a change in power. Anyone running a hot air intake is not making the power they should be. End of story.

I have the pettit hot air intake and it sucks and blows. I also have the ASP large IC and while cruising on the highway in 70f weather my intake temp on the PFC was 105f. Thats with hardly any boost.

A while back I used a temp gauge with a remote sensor to see what the temps were like around those filters and its terrible. As soon as you come to a stop the air just bakes. Easily double ambient. It cools when you get moving, but slowly. My intake temps on 80+ days are at least 120+. Worst $/benefit ratio of any mod I've done. The extra $50-$100 for a box seems well worth it.

I absolutely agree. But, the theory goes that, the only time it makes any difference is when the engine is running while the vehicle is at a stand still--e.g., at a traffic light. At all other times, air is flowing through the front of the vehicle and is essentially allowing cool air to enter the intake. I just think 'why make the engine suffer at stops while making it suck in hot engine bay air?'

Although I basically agree with what you said, there IS another factor:

The ability of the IC to cool the air after the turbos compress it. That is also directly related to the temperature of the air passing through it, and may have an even bigger effect than the intake air temperature.

BTW, I run a cold air intake, and a larger IC - see my sig.

having a cooler "starting" temp is a no brainer.

Wow, a new topic!!! Just kidding Damon ;)

I agree. Even while driving at highway speeds, a "hot air intake" wil be sucking hot air that comes off the engine, intercooler, and radiator. That can easily be 50 degrees hotter than ambient. At a stop, air intake temps can be 150+ over ambient.

Well, I do have a "hot air" blitz intake, but I was going to try and fabricate a cool air box just to see what happens. Has anyone tried this before and have any pointer for me?

thanks,
-josh

If that were true I could drive down the highway for hours and immediately pull over, pop the hood and find that the air around a hot air intake under the hood is no warmer than the air outside the car. Wrong!

Well you'd need to be pretty fast, because our little cookers heat the engine bay asap.

Seriously, I cannot argue with you. I have a cold air intake setup and I see it no other way. Traffic these days keeps you idling at lights too many minutes on any trip or commute. Maybe someone can rig up a digital thermometer in the intake to measure intake temps and we'll all know.

Guys, intake temps were measured YEARS ago! http://www.fd3s.net/intake.html#COM

The M2 intake listed was the metal one, not the C/F one. As you can see, even the M2 is much hotter than the stock intake, but much cooler than an open intake. This is why I think the PFS intake is actually the best intake available, it's unfortunate it has to steal from the IC duct to get it's air. And it also makes working on the car a PITA, which is why I run an rx7fashion box now.

Bottom line, IMO, running an open intake is a bad move. There is no reason to, as the box intakes get plenty of air and run much cooler.

I have a similar set us as you: Large M2/ASP SMIC and with 2 4" K&N filters. I also added 3" ducting to channel cold air from the nose up through the gap between the frame rail and the raditator to them along with a home made heat sheild. It sucks hot air from the engine bay into the engine while at a stop.

Does anyone know if an M2 or PFS "enlcosed" intake box will fit with an ASP/M2 Large SMIC?

I don't think anyone argues that there IS a difference in intake temps, but the hot air guys often insist that these differences don't matter because they happen to have a "big" intercooler. Rubbish.

start lower. end lower. physics owns you.

Agreed. Cooler, denser air to the turbos means more efficient (more rapid output rise to controller limit, more output-pressure capability, etc.) turbo operation.

Period.

Won't the IC work more effectively also given cooler ambient air? Meaning that, yes, the cool night air is providing colder intake temps, but I would also expect that the IC is cooling the post turbo air more than it would on a hot day. Plus everything along the path (intake manifold, engine, exhaust, turbos) is going to get better cooling given cold ambient temps.

I'm not speaking to the hot air vs. cold air debate, but I would make an uneducated guess that the difference is probably not soley due to intake temps.

By intake temps I mean pre-air filter...

Is there anyway of getting air from the standard front bumper to the filters. I have the HKS Racing Suction kit but would love to get them some cold air!

I also have twin oil coolers so they're both out.

I've said this many times on this forum, yet people still want to argue with me saying that a big intercooler is just as good!

Good point....and I fully agree with you, of course. :)

yes,there is a way to get cooler air. someone on this forum runs piping thru/under sleek headlight unit, right to the duct for oil cooler.I bet it lower the temps quite a bit.

The old metal M2 or rx7fashion box will....John, give Rick a call. He's running the rx7fashion box with an ASP large now. He is still running the PC680 on the side of the IC.

The PFS should work but it would need to be modified quite a bit.....

Quote :'the PFS intake is actually the best intake available"

You must be on crack, its a horrible unit. One its seriously old technology, second its so restrictive and it just cooks the air. I called it the the PFS hot box.

I have a single turbo with no air box just a K&N filter. My air intake temps are 15c lower then when I ran the PFS equipment.

When my Fd is running the intake pipes on the turbo side are very hot, but on the other side going to the TB its cool to touch. Guess my FMIC works :)

I have the carbon fiber M2 air box. I wonder if it's better than the old metal one. I'd assume the carbon fiber does not asorb and radiate heat as much as the metal box would?

Here is some info on Carbon Fiber for you guys! :)

http://www.everything2.com/index.pl?node=carbon%20fiber

Here are some pipe guards for motorcycles. I would say that the heat protection properties of Carbon Fiber would be substantial.

http://www.motoworldracing.com/wb-06...pe-guards.html

In this link K&N talks about the heat resistance in paragraph 2.

http://www.knfilters.com/Racing/crbnfiber.htm

It is the resin that is laminating the Carbon Fiber fabric that is the weak link for heat. Now a days we have vinylester resin, a cross between polyester and epoxy resins. It is formulated to be extremely heat and chemical resistant. Maybe I need to make a duct that comes from the front bumper straight to the intakes and with a good heatshield for the intake, you should get much improved air flow and intake temps. Also what do you guys think a vented hood would do to change the equation?

I think (imo) the best intake ever made for the FD was the one that was hand made of welded pieces of titanium piping that went down to the corner vent in the front bumper, where the oil cooler in the R1 resides. I cannot for the life of me remember who made that, I havent seen him post in months, and I cant find the thread w/ Search.

The best intake for the FD is a modified stock airbox, with 2 sources of cool air: The original source, and a source for cool air from under the airbox. No aftermarket cold air intake (that I have seen) offers this. The only problem with the stock airbox is that it won't work with a very big intercooler.

If only someone made some sort of a kit to modify a stock airbox ...................... :D

Is there anyone currently selling new box style intakes? i know the store doesn't have any.

Once you figure out how to make the stock airbox SMALLER and fit IC's (as you saidyourself), you'll be a millionaire :)

very simple! back in 98 I put a water to air intercooler system in my FD, A radiator made from a Cadillac heater core, a pump from a boat catalog, A resiviour tank from a Summit catalog, and a intercooler from Turbonetics, put it all togther, and works fine, come on guys. does it work?? if you dont turn on the switch for the pump, On the dyno it will run, almost a full A/F ratio richer, it leans out when you use the cold air ,YES it works, at least on the Hiway and drag racing at night, I dont road race on courses much!

I have a heatsheild that is open to the now removed bottom side of the foam it's not the best but I think it is better than not having one.

Wouldn't the best intake be to have a sealed box with tubing to the mouth of the front bumper?

Alex

I was looking into the Rotary Extreme intake box to later accomodate my future ASP or Vmount IC since it was completely aluminum-made but their business has halted (hopefully not indefinitely!).

You can buy it elsewhere here but with the intakes only: http://www.shaneracing.com/sr93intk.html
The RE version appeared to be completely aluminum wheras this one the sides aren't but top is? All intake boxes I've ever seen are same design though.

very simple! back in 98 I put a water to air intercooler system in my FD, A radiator made from a Cadillac heater core, a pump from a boat catalog, A resiviour tank from a Summit catalog, and a intercooler from Turbonetics, put it all togther, and works fine, come on guys. does it work?? if you dont turn on the switch for the pump, On the dyno it will run, almost a full A/F ratio richer, it leans out when you use the cold air ,YES it works, at least on the Hiway and drag racing at night, I dont road race on courses much!

I think the deal is this: Cold air is great, MORE air is better. That's a simple way of saying cold air IS what you want and DOES make a difference, but shouldn't be acheived at the expense of good flow... so if you've only got a 1" x 8" opening of fresh cold air and that's it, that's not going to work better than an open, less restricted "hot" air intake.

What we don't all know is at what point those two competing factors meet in in a compromise. Is a little restriction OK for a LOT of cold air? ... or a LOT less restriction worth a hotter charge? I don't think anyone has a definitive answer.l

I agree with ya Peter.

I have a 'hot air' intake. K&N filters with minimal piping.....the front turbo filter clamps right onto the small black 90 degree bend piece off of the compressor, and the rear turbo filter clamps onto a custom mandrel bent pipe that I bought from chuck westbrook. Here is a pic:

https://www.rx7club.com/attachment.p...hmentid=176685

I decided to delete the hard pipe kit and go this route after my experience with a friend's FD. He owned it for about 6 years out in Texas and ran the same intake configuration. His car always boosted well, ran strong, and his intake temps (on the pfc commander) never were any higher than mine.

I've never had any problems, plus I can hear my turbos spool up much better now, hehe. I am sure some in the 'Ice Cold Air' camp will take potshots at me, so here is something to aim at :D ------> :buttslay:

Im glad all you have twins still :) For my single im going to have to fab up a cold air intake because having the K&N on the turbo itself next to the engine isnt helping much.

I've always wondered if the Odula hoods would help cold air boxes.

The look of the scoop isn't that great...but I could imagine removing the top of a M2 or rx7fashion box and have foam placed around it to create a tight seal to this hood scoop.

https://www.rx7club.com/forum/attach...d=180449&stc=1

http://www.odula.com/page/frame.htm

The box that SR Motorsports sells is the rx7fashion box. It's all aluminum. I run mine with the top removed -- I gained 5 rwhp on back-to-back runs on the dyno with the top removed and no other changes. I don't think having the top removed hurts much from a "sucking hot air from under the hood perspective", but I could be wrong. :)

Rynberg,

did you have the hood open during the runs?? It may not represent real life conditions as the car is static.

And DamonB, what got your panties all in a wad to start this thread! ;)

True, but I think it's safe to say that more air will hit the filter with the lid off than on, under any conditions.

He's got a newborn, enough said... :D

Damon, congratulations on the new addition to the family, BTW. :)

From a thermodyamic stand point, the cooler the air coming into the compressor, the less work (equating to horse power used in the turbine) to compressor the air and push it. This is of course purely textbook so I don't know how true that holds to real life results.

Does, anyone know what cold air boxs will fit with a small v-mount? Does the pfs fit with the rotary extreme normal vmount?

Thanks,
Josh

How about mating the A/C with the IC? Cooling the air inside the IC instead of cooling the inside of the car? I remember reading about a concept Mustang with this system.

anyone who thinks hot is better than cold is an idiot. go drive your car on a cool night then come talk to me. YEP!

My buddy and i did alittle testing comign back from the track one night. we both have smic;s but he has hot and i have cold air intake. the intake temps as measured by the power fc were dramatcally cooler in my car. i cant remeber exactly what they were as it was a few yrs ago but there was a big difference.

How much of this change in power is attributed to cold air flowing through the intercooler (which will vary based on type), rather than ambient temps reaching the filtered intake, which is super-heated anyway after compression? Also, what method was used to test and verify your conclusion?

Would you say a more efficient component of the intake system can make up for the shortcommings of another? Say for example, the greater flow point that ptrhahn raised, as opposed to a colder but more restricted setup.

I more than agree with the logic concerning the efficiency of the turbo, as we've all experienced sharper boost response, but what happens afterwards tends to be a rather large debate as well, and is responsible for making or breaking a lot of power. I can't help but think this is a large(er) part of why we make more power on those cold nights.

The only debate comes from those who don't know what they are talking about; people can't see the forest for the trees. I have not said a hot air intake won't work, will hurt your engine, blah blah blah I'm saying a hot air intake is losing you power and I don't care what kind of intercooler you're running or what the weather is.

For example some say that the cool air is making more power not due to temperature at the intake but because the intercooler works more efficiently in the cool air. Let's look at the flip side of that coin. Let's say that it's a hot day and the intercooler therefore is less efficient. Wouldn't you want to do everything possible to get cool air into the turbo and keep intake temps down since the intercooler now can't contribute as much? Of course you would!!! But this is also true in every situation! This doesn't somehow magically change just because you have a bigger intercooler or it's a cool day!

I agree completely! Logic rules!

Dave

Ok, so the intake air temps have either 2 or 3 temperature changes to go throgh:
Cold Air Intake: Air enters the Intake Piping at X degrees (where X is outside air temps). The air then enters the turbochargers and is compressed. The air temps are then raised Y percentage degrees based on turbocharger adiabatic efficiency (my spelling may suck, sorry) at whichever boost point you are running. This air is then pushed through an intercooler where it is cooled Z percentage degrees (depending again on which point of the efficiency range it is running, which will depend on OAT's, IAT's, Boost Level, and Airflow). So this actually gives us an equation that if given the values of each variable, we can determine the ending IAT (notated by I) at the throttle body. For the equation to work, all percentages must be noted in an additive fashion, meaning to see a %10 increase, X must be multiplied by 1.10)
I = X * (1+Y) * (1-Z)
Hot air would add one variable to this equation. The percentage increase determined by Air movement in the engine and heating of the air underhood. This term will be represented by H.
I = X * (1+H) * (1+Y) * (1-Z)

Any increase at any point in the equation will result in higher ending IAT's.

Another thing to factor in the equation: Intake Air Flow restriction of a cold air, versus a Hot Air. With turbocharged vehicles, it really means that it would take just a little longer to reach boost if there is any noticable restriction. Since the turbos will spool to a certain point above atmospheric, which will not be affected.

I honestly believe filter design will play a more important role in restriction that cold air intakes or hot air intakes.

I understand the importance of cold air on turbo function, but what I'm refering to is the importance of the intercooler, and if it has greater effect, nullifying effects of cold air entering pre-turbo. Heat soak is a problem, so I figure that because of this, the effects on the intercoolers ability to alter air temp before it hits the manifold, is now more dramatic, and thus requires more concern.

Putting it another way, is there any consistent evidence out there which shows that colder air hitting before the turbo, provides substantially more power, even with a heat-soaked intercooler?

DaveW,
I believe this mimics what you stated ealier. "The ability of the IC to cool the air after the turbos compress it. That is also directly related to the temperature of the air passing through it, and may have an even bigger effect than the intake air temperature."

Any input?

u guys are reading too much into this. It really is very simple, on a cool day the car performs better. why cause starting ambient is cooler. The cooler u start with the much much better off u are.

Yes...the fact that every OEM production turbo application has an intake that draws air from outside the car, not the engine bay.

You're making the subject of heat-soaked ICs the issue here, not intake air temps before the turbo, which is what this thread is about.