Hi,

I live in Vegas and I know the Rx8 is a little warm under the hood, but 150 to 160 degree intake temps on a 110 degree day seems excessive. This is assuming that the intake temps that the Torque Android App is correct.

Short of cutting a hole in the hood, does anyone have some recommendations on how to lower this? The car is basically stock.

I haven't had the bumper off yet, I'm sure when I do some ideas might pop up. I was also thinking about getting creative with aluminum tape on the intake tube and maybe the airbox. Any other ideas are welcome.

Thanks

 

Those are some crazy high intake temps. Did you try the throttle body coolant bypass? Might help a bit. Not much if you're seeing 150+ but could help a bit.

 

remove underhood insulation, the aluminum hood will dissapate heat.

 

Considering the temperature is measured from upstream of the throttle body this will not change your temperature readings whatsoever.

Apart from venting the hood there is little else you could probably do. I'm assuming you're seeing these temps while the car is stationary? Being 40F over ambient isn't anything crazy unusual, especially when its 110!

 

Try putting a washer between your hood mounts. Maybe 2 and see if that will give you any additional flow.

 

Typical when standing still once everything gets heat soaked.

 

Thanks for the responses. I did the hood washer thing on my Subaru before cutting a hole for the top mount intercooler. It helped a lot. That same mod also allowed the ac to work at stop lights on my wife's Mazda speed protégé. I might try that and see how it works. I had an aveo that I was actually able to drill holes where the fender folded under the hood. It was a very stealth way of venting but the same method won't work with the 8.

The hood insulation removal is a good tip. I doubt I would notice the extra noise. Price is decent and also a good point about the giant heat sink that is my hood.

As for when I see the Temps, it's driving around mostly 45 mph streets and even the freeway. If I sit in traffic during the day the floor really heats up. Even at night if I go down Las Vegas Blvd, my legs get hot.

 

?? what year subaru did you have?? But on the side note.. On my rx8 vented hood and Removing stock air intake with the box helped me some with under hood temps.. and a little with coolent temps.. nothing to shake a stick at though..

 

If your legs are getting hot id take a look at the CAT could be starting to clog this could be some of your exses heat under the hood too.

 

Um,

30 to 40 degrees higher is not uncommon given where the air comes from, above the radiator, in a cramped space, running through that stupid tube.

I pulled the hose off my VAFD, and the valve piece as well. that made a pretty significant difference. The hose was kind of a long air heater tube given its location.

Other than that, the REVI duct will route in cool air.

I also insulated my stock air box. that helped a bit too. I used the foam tape with aluminum on the back from Home Depot.

 

Thanks for this. After reading this comment I searched to see what a VFAD is and yeah this is pretty much the first mod on any car. Modifying the intake before the airbox. I found this simple mod which I already have some tubing for. I expect this to drop the intake temps significantly.



I'll give this a try next time I get some garage time.

 

Let me know how it works...

Also, a pick of what you did inside the engine compartment meeting up with the airbox would be cool as well.

 

all I can say is that accordion is going to make your intake turbulent as all hell

Posted From RX8Club.com Android App

 

@ Paul,

I would say turbulent up to the air filter, then it will smooth out going through the filter, the cone and the magical screen... Right? Isn't the goal to just pack air into the air filter box faster than it will need to come out?

 

It was a 93 with a 2.0 ej20 block, 1.8 intake manifold and 2.2 heads which combined with an E-Manage, allowed me to run up to 17psi on 91 octane (tuned on a 110 degree day). I lowered this to 14psi for reliability purposes. I tracked the car frequently eventually selling it after I got married. The Rx8 was purchased to basically replace that car. On a side note, that car also put me in the internet with my "Subachad UpPipe". Unique Motorsports AKA Subachad UpPipe | Unique Motorsports


Back on task..
I added a couple washers to the hood allowing it to vent a little. I realize this might actually hurt airflow at freeway speed but should work for around town use. The outside temps have cooled off to 80-90 which seems to make the car much happier. My fans don't run for nearly as long shutting the car off.

I also read up on the VFAD thing and while I haven't setup the "turbulent hose setup" yet, I did cap the vacuum line. It's been a week and I'm happy to note my check engine light is not on. I agree with 04 green regarding the turbulence, besides, if there are 2 3" ducts going into the airbox, I seriously doubt there will be a lack of airflow into the box.


I haven't had a chance to test the results yet since my OBD2 plug was loaned out. I did get it back today and will post up the results though with ambient temperature changes dropping 20 degrees I realize they will not be overly scientific.

 

And, um, Pictures of the inside, how you spliced the hoses into the air box....

My nose is coming off over the holidays to straighten out the headlights, I might be copying your setup.

 

Yea the economy readings are way off on any of these obd2 readers, the reason is because their method of calculation isn't exactly accurate. I have found that many software obd2 readers calculate fuel economy from the following equation:

MPG = (14.7 * 6.17 * 4.54 * VSS * 0.621371) / (3600 * MAF / 100)
= 710.7 * VSS / MAF

MPG - miles per gallon
14.7 grams of air to 1 gram of gasoline - ideal air/fuel ratio
6.17 pounds per gallon - density of gasoline
4.54 grams per pound - conversion
VSS - vehicle speed in kilometers per hour
0.621371 miles per hour/kilometers per hour - conversion
3600 seconds per hour - conversion
MAF - mass air flow rate in 100 grams per second
100 - to correct MAF to give grams per second

The problem I have found is that these tools never really compensate properly for coasting and they average in the MPG of a coast which by this equation slowly makes its way towards a crazy large mpg number.

 

Thats a good point, I was a bit trigger happy with my post. My thoughts were really wondering what would happen to the airflow as the tube starts to flex and vibrate with speed

 

i use an ultragauge for mpg. it has a calibration process and a coast "injector cutoff" guessing function. after a few tanks, it stays pretty accurate for mpg.

 

That picture with the tubes is not actually my car. When I get around to this, I'll be sure to post up some good pictures.

Android Torque app + Elm 327 Bluetooth MPG test - Spot on! I wasn't expecting it to be correct, but the one tank I actually checked the miles and divided it by the gallons, it was 15.something. Torque at that time told me 15.1. It really doesn't get any better than that. Oh and Torque goes up to 255mpg during coasting and seems to be fairly accurate overall.

Torque temp readings - I'm confident in the reading, but even if it's wrong, I'm using the same tool to measure so the changes still apply.

Results - I'm not sure if adding the spacers to vent the hood did anything. I can say that simply capping off the VFAD absolutely did. The 150 degrees on a 110 degree day was actually driving around and on the freeway. Now I'm about +20 degrees on the freeway. Driving around town tonight was 88 degrees and I peaked at 138 degrees sitting in stop and go conditions on Las Vegas Blvd. Whats most noticeable is how quickly it cools off during normal stop light to stop light driving. The temps were consistently 120ish degrees. So basically a 10 degree improvement. Not bad for capping a vacuum line.

I'm still waiting to get my new I was hoping to be in this weekend, but the insurance is slow to get back. Once I do, I'll actually get some more mods done. Basically focusing on general drive ability, nothing too extreme.

Chad
Unique Motorsports | Cars, Tech, and Other Ramblings

 

fyi the coasting showing 255 is actually the limit of the byte value of the metric (aka 0xFF).

Posted From RX8Club.com Android App

 

I'm curious why CAIs have the tendency to be closer to the ground in our cars, is that just because of the location of the grill opening?

 

Its all about feeding the intake the best air. The mazdaspeend/Aem system is made to go through the chessis and fit right into the large opening of the front bumper so it can both get the most air and is far away from the heat of the engine bay.

 

@ subachad, if you ever get the front off, go ahead an pull all the VAFD stuff out. There are 2 air paths, one heats it up a lot, the other is more of a straight shot. With VAFD open, it still uses both. The pipe that runs over the radiator is something the definitely belongs in the garage.

 

Because hot air rises...