Seoul Seven

So..I dont know if this has been talked about or not but, I removed my hood and was fiddling with some things and decided to go on a quick run around the town. I didnt have my hood on and wanted to see if i would feel any difference.

When i did a few pulls i definitely felt a noticable oomph.
I got home and touched the motor out of curiosity. Usually with my hood on after a run my TB and pretty much everything is hot enough to where its somewhat untouchable. When i touched this time, everything was just cool. but warm.

The intake filter and elbow were not hot at all and were quite cold.


I also wondered if running with my hood off defeated the whole ventilation thing the RX-7 has going on meaning hotter internal temp? im just curious if having proper ducting if i had a hood on to feed cold air to the right places really would make that much of an improvement.


If its worth anything,
I've still got the undertray and fanshroud on.

Non Turbo
Spectre Air Filter (cone)
Streetport
RB Catback

anyone have any thoughts or opinions on this?
Are there charts and data showing just how much a good CAI adds?

KrazyRX-7

Here is a basic car fact, for every 10 degree's you drop the intake temp, you should pick up ONE HORSEPOWER, this has been proven by many sources, However i dont think anyone has tested this with a rotary, but it is true with a piston engine. That being said keep reading!

On the other end, when talking about Efficiency it has been said by many automakers, and engine builders that there is a such thing as to cold. If a engine never reaches "optimum temp" it "may" cause more emmisons, use more gas, and be more problemmatic. this is why alot of mid 90's GM's run at 235 F...(including the 32v northstar v8's and 3.8 V6's. insane right? if you would like to know how i found out about this. PM me. its kinda funny.)

I have no idea if any of this applys to a rotary, but its food for thought on the subject. I would like to hear some rotary guru's chime in. Personaly, once you have let the car(rotary) warm up properly colder engine bay tems should mean it will live longer right? all i have heard is heat kills rotarys fast.

There is also the constant debate, weather or not e-fans work right/well, weather the under tray is needed or not(the plastic pice under the engine), ect., ect. would love to have some of this cleared up:P And in my deffence I stongly dislike ANY GM product

Hypertek

iTrader: (3)

Try the raised hood method and see if you like it.

oakback

Is your cone air filter sucking in engine bay air, or do you have it blocked off (with a box/shield), and fed with "outside" air? This will make a very noticeable difference.

Hypertek

iTrader: (3)

could be the mental idea esp if your hearing the engine more.

Seoul Seven

My Air filter sits unmodified. so yes. its sucking yummy warm air lol.

i also never really noticed how strong the clutch fan pulls air...EVEN at a standstill.

i snatched a couple leaves and placed them right by the entrance of the bumber and the fan sucked them right in lol

kiyoshi

Yes, indeed.

Seoul Seven

This always bugged me, even if you have your filter boxxed in, your intake elbow is hot as F**** since its completely exposed to the motor. wouldnt the intake temps raise as soon as it began traveling throw the tube? Or does the motor move air fast enough for it not to effect it?

KrazyRX-7

Should be able to move air pretty quickly, However there are those guys that wrap their Cold Air Intake with exhaust wrap or some other insulation, claiming it help's lower intake temp. Never seen this one dyno proven.

arghx

iTrader: (3)

The stock intake elbow is rubberized. It doesn't absorb that much heat.

Wrapping an intake with heat wrap is exactly what you DON'T want to do. Header wrap is meant to keep heat in.

mikeric

iTrader: (20)

When I lived in Atlanta, AG I had a first gen Miata with a 1.8l motor swapped in. The car was pretty quick in the usual GA heat, but on cool fall or spring days, that thing would really come alive! It was almost like driving a different car.

My current turbo engine in my RX-7 is too strong to notice any difference--although I have seen about 5hp differences on hot dyno days. For all practical purposes, driving at 90%, I can not tell the difference.

You also have to take into consideration the aerodynamics. At high speeds, it will not benefit you to not have a hood. At low speeds losing a 40lb hood along with the accompanied engine noise may combine to make you a little faster yet feel even faster than actuality.

Get a friend to sit in the passanger seat with a stop watch and make some runs to 80 with and without the hood and go from there.

oakback

Or keep the hood, and make and airbox with air fed from outside.

Get some of those election signs from the side of the road, duct tape them together, even that will be better than sucking hot engine bay air. Run some flex hose from the front grill or brake cooling duct to the "box".

Once you're happy with it, get some aluminum sheet from home depot and replicate it.

Seoul Seven

doing pulls from 30 to 80 would be able to catch any power increase? you think?

ofcourse id be doing several runs each to get an average

Evil Aviator

Yes, it was talked about in the late 1800s. It has since been determined that hot air does in fact tend to expand.

It doesn't add, it multiplies. The exact multiple depends on the engine mechanics and its tuning. Also, inlet air temperature will tend to affect an engine's performance differently across the rpm, temperature, and pressure ranges. SAE J1349 gives a general guidance for typical power increases with changes in ambient air temperature, pressure, and humidity.
http://wahiduddin.net/calc/calc_hp_dp.htm

Many sources are full of crap. See SAE J1349 above. While not perfect, it is a good basic gauge. The important thing to understand is that hardly anything related to engine performance is a simple additive or subtractive value. Performance parts dealers use this to confuse consumers and legally lie about their products. For example, if I were selling a cone air filter that usually increased engine horsepower by 1%, I would attach it to a 1,200hp V12 engine, take a dyno reading, and then legally advertise that it was dyno proven to add up to 12hp.

Yes, and just like the engine operating temperature, the inlet air temperature can also be too cold. If the inlet air temp is too cold, then the fuel will not atomize properly, which reduces both power and economy. However, this usually will not come into effect until about -60F.

Despite what the $4,000 carbon fiber hood dealers will try to tell you, underhood temperatures don't matter much unless they are frying your wiring and plastic parts. Just try to keep the hot air from getting sucked into the engine intake.

Once the stock configuration is modified, the result will depend on the nature of the modifications. Sorry, but there literally billions of ways to modify the front end of your car, so unfortunately there is not one answer to your question, which is why it is in constant debate. In most cases, e-fans are not as strong as a properly-working stock fan, and the undertray usually helps with both cooling and aerodynamics.

Seoul Seven

Thankyou aviator for throwing some of your personal knowledge in. I think im beginning to understand.

So with intake, intake upgrading in general, there is a such thing as too much and too little. DEPENDING on the way your motor is tuned. as one motor may see bigger gains with one intake temp vs a different tune with the same temp. im not saying thats correct, but that is the general idea?

so to really get the most bang strictly speaking CAI, you would have to find the best way to flow outside air directly to the filter, keeping the intake temps colder so that the air is denser?



on the e-fan debate part, after seeing my clutch fan suck paper and sticks/leaves through my bumper at stand still, i think the stock setup is more than strong enough to pull alot of air. I'd see e fan being a replacement more than an upgrade. Like if you upgraded to a bigger rad, the shroud and clutch fan combo wouldnt work, you'd get an e fan to replace it.

Evil Aviator

Yes, that is the general idea. For temps, it is pretty hard to get down to -60F, so I wouldn't worry about too little temp. Intake manifold size, on the other hand, can be too small or too large for a given engine rpm, which is why you see variable intake technology like VDI and Renesis on the 1989-later 13B NA engines. Engines without variable intake systems are optimized for a certain rpm range, and rpms above and below this range will suffer performance losses.

Yes, but unfortunately a convoluted CAI may cause a drop in air velocity or incur a pressure/suction loss that reduces engine performance. Also, a CAI may increase aerodynamic drag, or block off cooling air to the radiator or brakes. The trick is to get ambient air into the engine without screwing up everything else.

Other common reasons for replacing the stock fan:
- Replacement clutch for the stock fan is expensive
- E-fans allow for custom settings through a manual switch, thermostat, fan controller, or EMS.
- E-fans can operate when the engine is off
- "Clean up" the engine bay for show cars