Wildcard

While I don't believe there is really any ram air effect from this mod, it is a fact that with the VFAD in, my intake temps were consistently 10deg above ambient (as read by my scanalyser). Anyone with a scanalyser can confirm this for themselves. After the mod, my intake temps were only 5deg above ambient.

Hymee

iTrader: (1)

Thanks Wildcard, that sort of real life experience tech info is valuable amongst all the theory :D

Cheers,
Hymee.

rotarenvy

so what is more importaint to power, air flow or air temp? you could have lowered air temp and still lost power due to less air flow. did you log the air flow meter?

takahashi

Me too me too.

I don't think there will be more air going into the air box --- or the RAM air they talked about. If it does great... at least it is a colder air into the box (proven by sCANalyser)

Wildcard, have you ever do under the ambient temp? My index temp once recorded 1 degree lower and 1 degree above - in the whole trip of 20mins :D

Wildcard

I do have scanalyser plots of air flow (grams/sec) with the new intake, but not with the VFAD. I honestly don't think there would be any difference though, since the engine is SUCKING in as much air as it needs, vice having air forced into it. It doesn't really care where the air comes from. In this case though it's a little bit cooler.

Also, mass air flow for identical engine operating conditions is going to vary due to the density of the ambient air, which is constantly changing as temperature and pressure changes. So for a comparison to be truly accurate, the air density at the time of each measurement would have to be identical.

Wildcard

Never less than ambient...

Maybe your outside air temp sensor got a little bit heat soaked from the engine bay and warmed up slightly. The only way to cool air below ambient is to force it to expand.

takahashi

I agree with Wildcard to his explanation.

I doubt is any difference either. Since the common dinominator is the inlet mouth of the standard OEM air box - which is the same with or without the intake nose :o.

Wildcard, you explanation re: temp could be right; but the below reading is from cold engine - maybe it is from the garage air. Anyhow I am getting a lot of close intake temp cf. ambient last weekend when the outside temp is over 24 degree. Had you have a 35 + degree logging yet?

rotarenvy

here are a few to ponder;

if a engine sucks as much air as it can, then why tune the intake?

people replace the air filter with one with less restriction yet your happy to replace a smooth pipe with a corigated one? wouldn't a corigated pipe pose more restriction than a smooth one and have the same effect as using a dirty or restrictive air filter?

takahashi

Jarl,

Based on your statement you are assuming the cloth side tube from the VFAD is smooth and not defracting air travelling from a closed enviroment.

For your record, my Odula tube is smooth, but has a matt surface inside (not corigated); as explained in Japanese that to minimise water along the length of tube.

Revolver

I've noticed that rotarenvy plays a good devil's advocate with various mod suggestions. This is good because it forces you to re-assess what is being proposed and challenge any information it is based on (e.g. he made me re-think the whole mag wheel thing).

But let's turn this thing around for a bit so we can learn something from someone who speaks with a reasonable amount of authority (not to hijack the thread of course ). What mods have you done to your car rotarenvy? Pros and cons of each??

rotarenvy

QUOTE=takahashi]Jarl,

Based on your statement you are assuming the cloth side tube from the VFAD is smooth and not defracting air travelling from a closed enviroment.

For your record, my Odula tube is smooth, but has a matt surface inside (not corigated); as explained in Japanese that to minimise water along the length of tube.[/QUOTE]

I think the cloth tube is a problem with the std intake and I can't quite see why mazda did it. I think something like the odula intake is what people should aim for. don't take my comments the wrong way as I believe this type of mod has merit. cold air is good but has it been at the expense of something else?

I would agree most of the intake tuning is done by the air box and the std snorkel is more for noise control. yet when I removed the intake I don't believe I got any benefit.


I have no real mods. I have 2 Defi gauges oil and water temp. I also replaced the wheels. not a major weight saving only 2kg per wheel. They are 18x9 +39 offset and I'll freely admit I think they have dulled the steering somewhat. I can't say if this is due to the tyres or the offset alone. one perceived benefit is that I haven't noticed the same nervous twitch from the rear under hard braking on the track. I don't have to fight the car for control to stop the rear stepping out. maybe my driving has just improved and I'm not braking on turn in.

I tried removing the VFAD as I dearly wished for gains. I tried it out for a week and decided it didn't work without proper ducting. I was relying on air entering the bumper and looking for the easy way out and filling the standard VFAD area;. hence colder air to the air box. any ducting should help but I'm sceptical about gains.

I have a r-magic filter that felt good but I have removed it and returned to std as I was worried about it's filtration. I'm now oiling it to see if it helps.

I would like to do more testing but I'm to lazy to set up the pressure and temp sensors :P

Revolver

Thanks for that.

I've also noticed a rear-end twitch under heavy braking from speed and agree it is more noticeable when the car isn't straight. I think I'd prefer to keep the steering feel and work on my braking technique rather than go to 9.0's.

Indeed, the more I look at wheels, the more they seem a vanity thing. The OEM set-up is pretty damn good considering the chassis isn't exactly overloaded with torque. I'm starting to think that instead of replacing the wheels I may experiment with different tyres instead when my OEM tyres wear out. If I use some of the money saved on not buying new wheels and spend it on good quality 225/45 tyres I reckon I will keep the steering feel, avoid the tyre squirm some have noticed with 245/40's and perhaps get better grip wet and dry.

As for the CAI - yet to be convinced it has more than a placebo effect. There are so many competing views out there. I also distrust what some of the manufacturers are saying about their products. The DIY jobs that Eric and Wildcard have done make sense but I think both say there is only a marginal difference in the butt dyno and I'm a bit gunshy about whether or not such a system might cause problems with the engine - not suggesting it will - I just lack the knowledge to be confident about doing it to my own car. :o

Wildcard

First of all I need to correct an earlier statement. The intake temp sensor is effected by "wind chill factor" from the air flowing over it, so a reading below ambient is possible, as Taka has seen. That's what I get for trying to sound like a smarty pants earlier.

I have the Mazda USA Renesis computer based training package on my computer, and in that, the cheesy commentator states that the main purpose for one part of the VFAD being closed below 5500rpm is to reduce intake noise. This is a production car after all - not everyone who buys this car is an enthusiast.

I used to have a pod filter on in place of my airbox, and the intake noise was as noisy as hell. Noise comes out of that throttle body like a loudspeaker when the airbox is removed. It's like having another aftermarket exhaust up the front. No ****. I think one of the reasons they might have chosen a cloth tube for the VFAD is so that it can absorb some of the intake noise. I also think this is why it is burried deep under the bumper - for further sound proofing.

I'm not for a second claiming big gains from a CAI. I can assure you though that my car has definately not lost any power. I also don't believe that turbulent flow through the tubes is a problem, because the air filter and the two MAF screens in front of the MAF straighten any turbulence out of the intake air.

Modding a naturally aspirated RX-8 is all about small cumulative gains. On their own, one single mod is is unlikely to register a butt dyno reading. But add a few small gains together and you have something worthwhile.

EZZY

im not a qualified automotive mechanic..... :o

i wouldnt call the factory cloth piping smooth, and i think it soaks heat easily

i dont think a smooth pipe would matter much, as long as the filter is in a good shape. any type of air flow would have to travel through the air filter itself, and then the air flow meter determines how much air has passed through... ie. air/fuel ratio thingo....

im happy with the end result, even with the stock exhaust.... now i just need to "service" the k&n more often

Gerael

Not sure if anybody here is a mechanical engineer... but.. after taking fluid dynamics.. and learning about pipe flows...

I can say this about the cai's...

First of all.. almost every factor about the pipe matters... from size... shape... interior smoothness.. like the ridges on ezzy's pipe... opening shape... how many bends it has.. length.. and more that I probably do'nt even know about..

I can say this about Ezzy's pipe.. The opening looks good... because it has a funnel shape.. this would be improved a little if it was attached to a plate with a hole in it...

The ridges in the pipe interior.. are terrible... this will slow down air flow tremendously... imagine two pipes.. one hollow smooth tube.. and ezzy's pipe next to each other...
put water through both... and low flow rates... see which one will flow faster?? or even in high flow... the ridges create turbulent flow.. which will slow down the air flow like crazy...

or better yet.. you know those soda straws at magic mountain or whatever.. with the ridges.. when you blow really hard.. there is sound... sound = kinetic engery being transfered into turbulent flow which is the sound... which means the energy of motion is lost.. and not getting out the other end very fast....

I would also try to reduce the amount of bending.. or at least the angles...

I don't really know how fast the air flow is... at low flows.. it wouldn't even matter...

I'm not trying to say diy cai are terrible... just wanted to have some input on the design of it... I think any mech eng. whos taken fluid dynamics can back me up...

EZZY

oh yes... i can see where you are getting at
the smooth interior surface will allow much faster and free flow water travel, but for the air flow application, would those ridges encourage then produce some sort of turbulance, which gives you a stronger air flow?

the factory tube sits straight after the air flow meter is also a ridge designed.... so if a smooth pipe is so important, then this pipe should be of other design

BMC air filters have similar ducting piping
http://www.bmcairfilters.com/infoCDA.asp

S-Spec have similar ducting piping also
http://www.s-spec.com/s-spec_products_coldairfeed.html

Pipercross have similar ducting piping also
http://www.pipercross.net/viper_product.asp

alternatively, for the DIYers, there is always the option of using PVC pipes for a smoother interior surface.
have tried both setup on my last MR2 import, and to be honest, there is no difference. they both worked well as long as you have the opening sitting at a proper location

Wildcard

I agree that the airflow in the DIY tube(s) is probably more turbulent than the stock tube, but remember that the DIY tube is also shorter and wider. I can't see turbulence being a problem unless the intake tubing is working to full capacity. Having driven both, there is no real world evidence to suggest that there is any restriction at all. The only thing we know for sure is that the intake temperature is lower, because we can measure that.

As for the stock tube, I would be surprised if the flow remained laminar all the way through that tube, especially given the friction that the cloth walls would be creating. It's been too long since I calculated Reynolds numbers, so I will stop before I embarrass myself. I studied aero engineering and fluid mechanics once too....

This is all good discussion though! We all benefit and learn from challenging each others assumptions and ideas.

Gerael

Hrm.. I just learned something from talking to my brother yesterday whos studying to be mechanic...

It seems to me that the stock intake has different lengths.. like.. a long one with a flapper valve that switches to the short intake.. is this right?

Anyway.. he informed me that the long tube actually is needed for low rpms.. where flow is a slower... the longer tube can build up more air "momentum"... which allows air to keep being sucked in at a more constant rate... but to really breathe...in high rpms.. it switches over to the short intake... which is just straight.. with the funnel on the end...

I don't really know if this is how the rx8 intake works.. but from the pictures I've see now.. it would seem so... I gotta check service manual and read more about its operation..