150+ Degree Intake Temps
 

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.

https://www.rx8club.com/attachments/...d-dsc01303.jpg

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...

See, that's bad logic. The temperature close to the ground is always hotter than air two feet off the ground, unless the ground is frozen or wet or something. Heat radiates off of what is emitting it, that means that the hot air near the radiating body rises to a cooler region. Air further from the road is cooler than air close to it in dry conditions.

Agreed, which is why not having a splash tray will cause your ac core to get heat soaked quicker. I think a lot of it has to do with packaging, reliability, driving conditions, etc. Having it point forward will have it pull air that is not heated from the radiator area but will also make the air box get dirty quicker. Making a turn down into the bumper opening will avoid grasshoppers in the airbox, but could make for higher intake Temps.

My last tank was 17.7 mpg. That's a big difference but I also kept the traction control on the whole time.

Agreed, and two feet of the ground is somewhere near the top of my engine and the hot air radiating and rising off of your engine is much hotter than the air radiating off of the road, hence why the cold air intake drops below the engine bay closer to the road

The under tray keeps the hot air (been through the radiator) from sneaking back in front of it in slow traffic. This issue is also the reason for the foam around the radiator mod.

The lower pickup is because, at low speed, there is a trapped volume inside the nose that guarantees that any hot air will be sucked in first, either through the tube, or the VAFD opening.

Close to the grill is the coolest air. The Racing Beat intake is the best for this. It mounts to the grill. The rest of it is the subject to debate, but the Duct is a definite win.

I moved the intake pickup and posted the info on my site. It was getting pretty late after trying to fix my broken headlight and removing the light reflectors from my foglights so I basically used a subaru bracket and some 3" universal auto ducting to relocate the pickup. It really needs to be a little forward so it's not in the turbulent heat mess when the fans are on but even still, prior to this it wouldn't have been possible to see intake temps less than 15 degrees above ambient on the freeway.

http://www.uniquemotorsports.com/wp-...2-47-04-AM.jpg

http://www.uniquemotorsports.com/wp-...2-38-21-AM.jpg

http://www.uniquemotorsports.com/wp-...2-47-11-AM.jpg

Results: Highly recommend it. While there can still be a 40 degree spread between the outside air and the intake air, it’s overall much better. Prior to doing this, I would not be able to get close to the ambient air once the car was warmed up. Now it’s about 15 degrees over in flowing traffic and 25 to 30 degrees over in heavy stop and go in town traffic. One more thing to note is by replacing the "preheater" tube like this, I think the intake temps will actually improve with the VFAD reconnected.

Here is a link to the write up I posted on my site along with a lot more pictures.

Rx8 Airbox Mod – Lowering Intake Temperatures | Unique Motorsports

Thanks for the pictures, and especially for the temps. I need to start watching those again and see if the tubing will help over just having the box open and maybe re-directing air upwards..

Thanks again

Thanks for all your well done posts. I just got the 8 in march and still doing "fix mods". Your post regarding "congrats on the 8" has helped me a lot. I still haven't pulled the plugs, aside from that, insulating around the radiator and A/C reprogram, I pretty much did everything you mentioned. Fixing the threads for the ESS, I managed to scratch my cornea... wear safety glasses when taping threads under a car kids.

I'm moving into my new garage this weekend, I'll update this thread when I get a chance to modify the intake a little more. Most likely, I'll mount it forward a little so it's cool when the fans are on and hook the VFAD back up.

i updated this. Here are the highlights I posted on my site.

Changes I wanted to make

-Hook VFAD back up, allowing the main pickup to be the relocated intake
-Move the pickup tube forward a little so its out of the turbulent air produced by the radiator fans

Results: With the pickup moved, I now see the following temperature differences.

Stop and Go Traffic – Intake temps are usually 20-25 degrees higher than ambient.
Free flowing Traffic – Intake temps are usually 10-15 degrees higher than ambient
Freeway – Intake temps are usually ambient to 5 degrees higher than ambient

The bracket

https://cimg8.ibsrv.net/gimg/www.rx8...cce3e2f183.jpg

The bracket installed

https://cimg0.ibsrv.net/gimg/www.rx8...023a2aef67.jpg

The end result

https://cimg9.ibsrv.net/gimg/www.rx8...cab0c69003.jpg

don't hit any deep rain puddles ....

Nice... But I echo the deep puddle concern. Nice work on the bracket.

I don't see me fording any creeks deeper than 8 inches. If I do, I can floor it to initiate the vfad. It's also turned a little, behind the bumper plate to help keep out rain, dust, grasshoppers, etc.

It's not necessary to reinforce that you have no idea about the situation ...

Oh god, the damage that will do.

For some perspective, if you drive through a puddle at 4500RPM, your engine will attempt to suck in and compress about 100 liters of water into 10 liters of water in the span of one second.

Don't forget that water is incompressible.

That would be bad. There is no direct path though to the intake, it's not a ram air setup as it's behind a cover. I would actually have to submerge the entire front of the car at which point, the intake box is not perfectly sealed where it goes through the core support so it wouldn't be able to suck up water anyway.

Another interesting point about this is I moved it down and forward so it would be out of the turbulent air from the cooling fans. I have since installed a Koyo radiator and now when the cooling fans finally kick on, they don't create that turbulence of hot air in the front bumper opening.

I have my radiator all insulated with pipe insulation, heat reflective material on my intake and airbox, and a fully sealed up Racing Beat ram scoop connected to the stock intake. My intake temps are usually about 10 off ambient when driving around. Obviously when sitting still its going to go up.

Great write-up and pics for your handy work. I personally see very high intake temps but that it because I have an AEM intake that has to be a short ram, since the previous owner was in a front end accident and the support beam is bent backwards so I could not install the "S" curved piece that goes from inside the engine bay between the beam and the firewall and put the filter outside of the bay. I see temps of 143-149 while driving and then 150-160+ when sitting at idle with no airflow. I saw one up to 175 yesterday when the outside temp was 92 degrees out.

I just have the VFAD connected as it came, but with a short ram intake instead. I like this idea of the intake tubing/accordion style and planned to see about ripping out the VFAD system and capping the manifold and route my filter where it is supposed to be outside of the engine bay but use the accordion to wedge between the bent support mean instead of the metal piping that came with the intake. Would basically make it like yours but with a filter on the end of the accordian hole.