This has been covered here before but I really want to address this towards intakes for the RX-8. I am also going to give you guys a tip as to why the cars idle rough with some intakes.

First of all, I believe no one's claims as to 9+ hp gains from an intake. If it is more than about 4, they are either lying or there is an inconsistency in the test. There is one such intake system on the market right now who I am going to use as an example. I'm not going to name any names but their initials are "K" and "N". If we take a looks at their dyno chart for the RX-8, we see that they show a 9.5 hp increase over stock. Impressive from just a filter right? Let's look closer.

The original base line run was done 3 days before the aftermarket filter run. If a dyno comparison isn't done the same day, it isn't valid. You need to establish a number at that temperature and humidity level. If we look at their dyno closer we see that this in fact was an issue for them. On the test day of their product, it was 10.7 degrees F colder. You can also rest assured that the humidity was lower too. Also, we don't know what temperature the engine was at in each test. The RX-8 ecu does some really weird stuff to the timing depending on what temperature the engine is at. If they had retested the original setup again on this day, they would have still shown an increase in power over the previous run. Am I saying that they didn't get a gain at all? Nope. What I am saying is that it isn't 9.5 hp. It is probably closer to 3 or 4. Sorry, that's all you'd get with NO filter at all so how could they get more? They can't. What they do get is unbearable intake noise which may make the car vibrate like it is alot more powerful. Butt dyno's lie. A 4 hp gain can't be felt unless your car only makes 4 hp and weighs 8 pounds. At the weight and power level that the RX-8 has, you can't feel it acceleration wise.

Another problem with aftermarket intakes is the fact that they make the car idle rough. We've seen this many times with many systems. Many forced induction kits are suffering the same fate. Sadly most still haven't figured out why. Here you go guys. The problem is that the length of the intake pipe between the air filter and the maf is too long. This length is very critical. It seems strange but it is. This is why Rotary Extreme said their long arm intake didn't work. This is why another one in development will also suffer from the same problem. Luckily if yours is too long, you can fix it. I am not saying any more as I don't want to take responsibility for someone modifying their own parts and messing up. This is where the problem lies though.

 

I agree with most of that, however I would like to point out the vast majority of dyno's out there correct hp according to temperature and pressure according to SAE-J1349 specs. Usually a "CF" for correction factor will appear on the dyno sheet.

 

beh, don't matter. even having "smart" dynos, your graph can vary so much from run to run even when they're back to back it's not a credible claim to say that you'll get 2 more horsepower as variability can make up for that.

 

Reality destroys everything.

 

That implies they actually did use the correction factor and didn't just post the results as they were. This is an option. There is no mention of this and another reason why dyno claims by manufacturers shouldn't necessarily be trusted. I'm not saying that all are lies. I'm just saying that it is safer to be a sceptic than to trust everyone.

 

what are your opinions regarding the dyno charts for the rotary extreme intake?

 

Sounds like rotarygod have created more problems then solutions

Great info as ever. Enlighten lay man like Taka

 

High HP gain = Increased sales

Marketing fodder!

Trust quote a 10hp gain on their intake, which is somewhat optimistic considering its setup:

http://www.trust-power.com/mazda/rx8.../airinx_b.html

 

Correction factors only correct for differences in ambiant air density and humidity. It does not compensate the loss of power caused by to retarded spark / increased fuelling due to high intake temperatures. So even if it is corrected to SAE-J1349, there still is a hit due to higher intake temperature.

And there is nothing mysterious about why it affects idle regulation.

And, long time ago, I've worked in the UK for a aftermarket filter and direct induction system manufacturer. There were no design work other than adapting an existing filter to the OEM intake using a silicon hose. You however can sometimes measure a 4 hp increase at very high RPM (and a dip at midrange!!!) provided it does not ingest hot air from the engine bay.
Also, after a while, it either clogs up (if not washed regularly) or loose some its cotton filter medium (if washed regularly) and therefore becomes more like a "rocks and pigeons"* filtering device...


* copyright : Andreas E. who worked there too!

 

Well when I read the Dyno results the HP gain was all at the top end.

8 grand or higher. So how valid is a 10 hp gain when you can never use it?

Oh I forgot everyone who has an 8 always shifts at 8 grand and never below.

A 1 hp gain for normal driving is all your going to get.

 

I know hp seems to be the issue here. However, I have my K & N system sitting in the box, in the garage and I'm thinking why would I want to install this after reading the above posts. Well, I've installed the K & N filters on my 1998 Jeep Cherokee and my 1997 Harley Fatboy. Even if I can't feel the difference, what I can feel is the cost savings in filter replacement. Do the math and the concept is a winner. As for rough idling, nothing idles worse than a hardmounted Evo with a hot cam and headwork. So I'll take the one or two hp that you guys think I'm getting and enjoy a great filter that only needs to be cleaned in 40,000 miles rather than buy a new one every 5,000.

Thank you for your ear.

 

The correction formula is still just basic adjustment. Car's still dyno more when its colder and less humid, regardless of the formula. The SAE correction just "attempts to" normalize the numbers. They'll still be off, I'd gander 5%...which falls within the range of rotary's argument.

When we had CP-E dyno the mazda 6 intakes, we made them dyno the stock first (best of 5), then swap over to their intake (while the car was still strapped down) with about a 30 minute pause, then dyno'd again (best of 5). I gander thats about as close as you can get. Same dyno, 30 minutes apart, same temp, same humidity, same coolant temp, same straps. Still doesn't mean any of the other cars will see exactly the same gain. Both turbo magazine and sports car compact have both had extensive articles on the falacy of dyno testing, and how its extremely easy to "cheat" dyno's. One of the more frequent tricks is turning on the AC while the stock setup is dyno'd, and shutting it off while the aftermarket setup is used.

One thing to remember with these "cotton gauze" filters, is that they filter less dirt then stock paper ones. If your willing to live with that, thats fine, but just realize they do have their drawbacks. Even K&N's own website points out their loss of efficency vs paper filters (you have to dig to find the actual papers). I think its to the tune of 6% additional silicon contamination...which directly effects lead, copper, iron, and alumnium wear.

http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm
http://www.bobistheoilguy.com/airfilter/airtest1.htm

 

RB intake, I beleive. RB reputation + quality, that's why I returned my K&N when I heard they were coming with one this late fall.

Just installed the RB catback and I do not need the Boss system anymore. I just want to heard my 8. LOVE IT!

Coming up soon, RB springs and intake when out....

another beautiful day with my 8.

Simon

 

Is that only for rotaries? Because I have a cold air intake on my 240SX and the air now has an additional 6" or so to travel from the filter to the MAF sensor compaired to the stock intake and my car idles just the same.

 

Actually for reasons unknown, this is only a phenomenon that has been seen with the RX-8 maf sensors.

 

Yes but is your MAFS hot wire/film? I wouldn't think so. That makes the difference.

 

Mazda has addressed this in an MRI


AFTERMARKET AIR INTAKE SYSTEM - ROUGH ENGINE IDLE
Applicable Models
Model Starting S/N Ending S/N
2004 RX8 00000000 ZZZZZZZZ

Some customers may complain of rough or poor idling condition. The RX8's airbox N intake system is specially designed to eliminate restriction N create a smooth airflow over the MAF. If the customer has installed an aftermarket air cleaner or intake system, the airflow stream to the MAF element may be disrupted N cause an improper MAF signal. This erratic signal results in a rough idle condition. Also, aftermarket air cleaner elements are sometimes coated in oil to better filter the incoming air. The oil from this type of elemnt may damage theMAF resulting in a poor idle or MIL related to the MAF. If a customer complains of a rough engine idle, see the repair instructions below. 1. Check for aftermarket air intake system or aftermarket air filter element. (Replace with factory system if necessary.) 2. If rough idle continues, check for additional bulletins / M-tips, workshop manual troubleshotting. 3. Confirm repair.

 

they are all accurate as it was my car and there were 4 or so other forum members to confirm this data.

 

when i installed my k&n i didnt notice any change in the idle except on cold starts it jumped up to about 2300rpm for the first 30 seconds upon warm up. i notice a considerable change in the way it drives, but im also curious about the dyno claims. i just got finished with my dyno install today so i will make several runs on it with the intake and then try it back to stock. i will post the info, if anyone has any requests on some variables they would like me to try or change let me know

 

In "guestimating" dyno results for comparisson purposes, you mihgt want to try to make note of what kind of ventilation/fans the dyno shop has availble and is using to push air over the car for cooling etc. It's my understanding, particularly with many of the newer cars, this can greatly affect results, and makes it particularly difficult in trying to compare results from different dynos with different cooling fan capabilities and set ups. OTOH, since you plan on doing your runs on the same dyno, the potential for test equipement "varriation" is greatly reduced. From my dyno experiments with the light weight flywheel, one gets different results based on the gear you select to do your test in as well.

 

the dyno is a dynojet and all the variables such as cooling fans will always stay the same. as far as gear choices im not really yet sure what the 1:1 gear is in the 8 but im assuming 4th, so i will try all the runs in this gear. after i get some consistent runs i will continue to dyno the car after every mod that is claimed to produce power.

 

Silicon causing wear is not a good assumption to necessarily make. Silicon is actually put in the oil as an anti-foaming aditive and has shown not to cause wear, only negatively effecting air release properties which may or may not be important on a particular application.

 

Idle problems with K&N, sound like installation issues, not design. I haven't had any problems.

 

There is a discrepancy between cars. Some have issues. Others don't.

 

Yeah, and lead is a very effective lubricant.