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Hey, so there are a lot of questions/misconceptions about this car and I'm feeling a little myth busterish. I finally got my hands on my old obd2 bluetooth reader and have done some logging with the torque app.

The first thing I wanted to address was the resonator delete. I drove around until the car was fully heat soaked and stopped off at a gas station. I popped the hood and unhooked the resonator from the air box (you can just pull down on it and pop it out of the fitting). I drove around comparing iat (intake air temp.) to ambient air temp. The whole time I was driving ambient air temp was fluctuating between 49-50. I did two or three pulls merging onto the highway redlining 2nd gear and pulling to about 70 mph in third. The lowest iat I saw during all three pulls was 63 degrees. So I went back to the gas station and popped the resonator back on. After performing the same pulls on the same stretch of highway I was seeing temps down under 58. Pretty big difference if you ask me but maybe its worth the heatsoak for the extra grumble. If you do take the resonator off I would definitely block off the hole or youll just be shooting yourself in the foot.

I would also like to add in that while I was driving I monitored manifold pressure, but even with the stock filter, air box and the resonator on, I was seeing 12.3 psi all the way to redline.... which is strange because barometric pressure here was 12.09psi (also read from the ecu). but the point of that is that there is no noticeable change in airflow... well other than the air gets hotter w/o the resonator haha.

The last thing I measured was peak torque timing. This car has a massive peak torque band due to the dual variable cams, so it was pretty easy to see what peak timing was just while running the app. Right now I am running a tank of 100% 91 octane and I was seeing 16 degrees of peak torque timing...

so the next phase of this post will be my findings once I fill up on 87, and further even 85. I'll keep you posted. until then, here are some good reads;

Air Filtration Test
http://mazda3revolution.com/forums/2010-12-mazda-3-engine-performance/12745-free-mod-skyactive-intake-resonator-delete-block-off.html
 

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This is a great thread. I was getting ready to do somethign similar. I wanted to test how far the car CAN advance the timing and then find out how far it DOES advance it using 87 and 93 octane.
 

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Discussion Starter #5
Measure mass air flow with and without the resonator hooked up.

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I did for a minute but torque has some funky calculations for cfm, it was saying like 450 cfm haha. idk either way it is a representation of airflow regardless of how accurate it is. I think I might do it anyway. but I do know that these cars are throwing down 100% volumetric efficiency which is why I was just looking at temp and manifold pressure.

This is a great thread. I was getting ready to do somethign similar. I wanted to test how far the car CAN advance the timing and then find out how far it DOES advance it using 87 and 93 octane.
I can't wait to run out of gas! my theory is they have the timing capped because they are super afraid of knock. hence why our motors have so much less power than a brz/fr-s with almost identical engine specs. Not sure how I feel about the whole piston cavity thing though... I feel like that would be the #1 contributor to weak timing, there's a lot more surface area to absorb heat from combustion.
 

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I can't wait to run out of gas! my theory is they have the timing capped because they are super afraid of knock. hence why our motors have so much less power than a brz/fr-s with almost identical engine specs. Not sure how I feel about the whole piston cavity thing though... I feel like that would be the #1 contributor to weak timing, there's a lot more surface area to absorb heat from combustion.
FR-S doesnt have an atkinson cycle engine designed for highest fuel mileage possible. Thats comparing apples to oranges

If you wanted a performance engine you went way wrong with a skyactiv lol
 

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hence why our motors have so much less power than a brz/fr-s with almost identical engine specs.
Bore-stroke ratio is significantly different, compression ratio is different, fuel injection is different, VVT is different, and boxer and inline-4 are totally different species.
 

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Um no, don't give up

I subscribed to this thread and everything!
 

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Interesting. 16 timing advance sounds retarded, I'm super curious what it'll run with some custom tuning.

FR-S doesnt have an atkinson cycle engine designed for highest fuel mileage possible. Thats comparing apples to oranges

If you wanted a performance engine you went way wrong with a skyactiv lol
The Skyactiv does not use an Atkinson cycle engine. A slight delay in intake timing is not Atkinson cycle.

There's some trickery involved and it makes significantly less power than a regular Otto cycle engine. The Fusion hybrid uses a 2.0L and it makes closer to 120BHP. Total power is 141BHP including the electric motor. HowStuffWorks "How an Atkinson Cycle Engine Works"
 

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Discussion Starter #13 (Edited)
haha no... I have a company vehicle so the 3 is just sitting there all week. I'll try and get some driving in this weekend.

and for the record I'm not trying to make this car faster.... it will probably be a biproduct of making it more efficient though. If I wanted a fast car I wouldn't have sold my 320 whp wrx to buy this one.
 

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Discussion Starter #14 (Edited)
here it is folks, there is indeed benefit to running 91 octane. about a degree of timing advance. seems pretty solid across the board... there are a lot of unrecorded variables but I don't think this type of consistency is a coincidence. I wish I had a dyno to measure this :-/ I cropped them to the same size for comparison.


I'll let it learn some more and make another log.
 

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While I'm sure I can't fully interpret your data, that does look interesting. Between the two logs what were the weather conditions, and human input again? I don't think the ECU retards timing on 89 due to knock (it could, but mine has not ever knocked yet even running hard into the redline) so is it sensing the octane of the gas? I'll probably have more stupid questions for you.
 

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While I'm sure I can't fully interpret your data, that does look interesting. Between the two logs what were the weather conditions, and human input again? I don't think the ECU retards timing on 89 due to knock (it could, but mine has not ever knocked yet even running hard into the redline) so is it sensing the octane of the gas? I'll probably have more stupid questions for you.
it learns timing based on knock, but this kind of knock would be very slight and only detectable to a really trained ear, or a knock sensor. weather was about 60 degrees clear @6000ft and that was a 3rd gear pull from 2k to about 5500 rpm. The computer is always trying to find its optimun timing and will always be riding the very edge of knock to get the most power/efficiency. so when we put 91 octane in the car pushes itself a little further until it hears knock then stops. and vice versa for lower octane it will pull timing out until it quits hearing knock. at least this is all assumed knowledge based on how most modern cars work but I don't know for sure if this is the case.
 

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This engine has ways other than timing of controlling knock. That is what makes it interesting. This engine can also control knock with A/F ratio. By making the trim richer, it can cool the combustion chamber more and reduce knocking without changing timing.

I believe this has become very common in the euros. I'm hoping running 91+ octane not only advances the timing slightly, but will also lean out the A/F ratio a bit which would help combat fuel dilution in the oil.
 

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This engine has ways other than timing of controlling knock. That is what makes it interesting. This engine can also control knock with A/F ratio. By making the trim richer, it can cool the combustion chamber more and reduce knocking without changing timing.

I believe this has become very common in the euros. I'm hoping running 91+ octane not only advances the timing slightly, but will also lean out the A/F ratio a bit which would help combat fuel dilution in the oil.
That's badass! I never knew that it did that. I really think running 91 octane is every bit worth the money... people that say it isn't probably only ran one tank and didn't let the car learn to it's full potential. man I should be logging afr too huh? from what I looked at, it seems that this car has a wideband built in. Is that correct?
 

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So what do you get out of running 91. Slight more power? Slight better economy?
 

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In non-ideal conditions you could probably get more power out of the engine as the computer can just keep pushing the AFR and timing to maximize power per cycle rather than saving the engine from blowing itself up. I personally don't notice any difference but it's entirely reasonable for 91 to make an improvement, say on a hot day at the track.

Economically speaking though it will be a hard sell, as you have to save quite a bit of gas to make up for the price difference (5-10%) between 87 and 91 here in SoCal.
 
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