I agree, the old Mazdaspeed hood and FEED hood are about the only hoods that I would even consider using on my car and even then I still don't like the way they flow with the rest of the body.

 

It makes a big difference IMO, if they are painted body color.

 

I'm glad to see old threads get brought back to life. There hasn't been any new thought-provoking stuff in quite some kind, just lots of 'pics' and 'help' threads.

 

With all due respect to Kevin and the ASP setup (I have a medium kit), I'm not that enthused about the provided "extension" piece to the duct mouth, which already comes in a pretty severe angle due to the FD engine compartment's design. The extension I was provided with in the kit is basically a crude 90-degree scoop attachment, and while I'm sure this helps direct some airflow in there, it's still a pretty severe angle, and the airflow is going to take a path of lesser resistance (i.e., the radiator-- which has a much thinner core specifically for that purpose--and any gaps that may be next to it). I think that may be the reason for the "1-3 mph" airflow speed readings Howard found, not so much the lack of exit area for airflow in the engine compartment.

I think an extension with smoother angles that extends all the way to the front of the radiator opening (to help separate the airflow/pressure of the IC and radiator) would help airflow speed through the IC tremendously. I'm going to try and fab something up in the near future.

I did something like this for my Greddy SMIC a while back, and while I don't have any testing numbers, the temperature of the IC body was significantly improved at lower speeds when I opened the hood.

 

oops, I meant to post that quote in a different thread...the one about the thermal blanket.

 

Damian and Andy might be breathing life into something I wanted to do years ago but never had time. Should be pretty awesome in form and function if it works out like I envisioned.

 

wouldn't taking off the weatherstriping off the fire wall do the same thing? what about do the above and blocking off the hole above the stock innercooler intake? would that have any effect? or you could just put spacers on the hood hindges to raise the back of the hood up a little. just a thought if you don't want to cut holes in your nice expensive hood.

 

There are good many threads that explore this idea, but it all of them have come to the conclusion that because of the low pressure area next to the windshield it would hinder outflow and actually cause the air to be sucked in at speed. I have wondered about the FEED designed hood if the same would also happen.

 

To me.....the ultimate in radiator airflow optimization (with respect to directing it OUT of the engine bay) is to make a custom duct that connects the back of the radiator to the top of the hood and directs ALL of the airflow coming out of the radiator directly out of the engine bay. That's the way it's done in professional racing and should be highly efficient . It's the way a V mount SHOULD be done. Pictured below is the JGTC skyline engine bay and you can see the duct that I am talking about.

 

Is it a secret?

 

Is that an AST on a skyline or something that just looks similar?

 

The reason for ducting the airflow on the exit side the radiator is not to "direct ALL of the airflow coming out of the radiator directly out of the engine bay", but to use the negative pressure created by the duct in the hood to help increase airflow speed through the radiator, making that heat exchanger much more "efficient". If you can create enough of a negative pressure area on the exit side of the engine bay (or create more positive pressure on the face of the heat exchangers), the duct wouldn't be necessary.

It's more important to increase airflow through the IC since it has the thicker core, so it's easier to mount it on top and use a duct in the hood for that purpose, due to lack of room in the FD's engine compartment. It's the same reason that car pictured has the IC on top.

 

This will be hard or impossible to do given the way an FD is packaged. It could be done with a v-mount though.

 

Correction. HIGH pressure area in front of windsheild.

 

There are other dividends as well. It also sends the air exiting the radiator up over the car rather than allowing it to exit under the car. Another option many use is to duct the radiator exit into the front wheel wells, achieving the same goal.

 

I understand that the primary goal of that setup is not to direct the heat out of the engine bay but rather to improve the overall efficiency of the cooling system through manipulation of pressure. It just so happens that by the way it is set up is ALSO directs all of the heated air exiting the intercooler out of the engine bay thus not contributing to a hot engine bay.

 

Yep...ala the vast majority of the prototype cars running at LeMans. In most cases it is actualy more desirable to exit it out the side as you described above rather than through the top of the front body (on prototype cars anyways) due to trying to maintain attached flow over the top surface of the vehicle so that they can get clean air to feed into the rear wing.

Anyways....if you could go to a V-mount or a \\ mount and direct the airflow out through the top of the hood, that would help considerably in decreasing underhood temperatures. Unfortunately, this all costs $$$$....which by being FD owners, none of us typically have that much to spare!

 

That and to help prevent heating the air headed for the wing and making it less dense.

 

True, good point, forgot about that.

 

The engine in and of itself will contribute far more to underhood engine temps than the heated air exiting the IC and/or the radiator.

 

Interesting point, Kento. I understand that the exhaust components will have a higher surface temperature (>400F), but I'd think that the size of the radiator would make up for the lower surface temps (130-210F)? I'd like to hear your justification for this (not that I doubt you, but I'm an electrical guy who'd like to learn more about heat transfer and that sort of thing).

-s-

 

^ I think his simple point is that when discussing underhood temps the engine/turbos etc have a tremendously greater ability to heat their surroundings then the intercooler could ever hope to. Removing only intercooler exit air from underhood isn't going to show any difference in underhood temps, although the intercooler itself may become more efficient.

 

You're forgetting about the engine block, the turbos and their associated manifolds, etc., radiating serious amounts of heat with actual surface temps that are far hotter than the exhaust airflow temps from the radiator/IC. At least the exhaust air from the radiator and/or IC provides "cooling" airflow through the engine bay. The exhaust airflow from the radiator/IC doesn't just "build up" and continually increase underhood temps; it has to go somewhere. Take that airflow completely out of the engine bay and you'll end up with nice mobile oven.

 

Thanks Kento (and DamonB), that makes perfect sense.

 

IIRC, the general rule of thumb for an IC engine is the fuel's energy goes to useful power, waste heat and pumping losses in roughly equal amounts. Guessing that the rotary does a bit worse on useful power versus waste heat seems pretty safe, so I'd say that ducting the radiator's exhaust might have some benefits. But, as Kento pointed out, that air is much cooler than the turbos or downpipe, and it can help to cool them. OTOH, I doubt the shortblock or heatsoaked UIM will benefit significantly from the rad's output.

I'll play with the heat in the intake charge after I eat.