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Old 10-06-2009, 09:10 AM   #1
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Default IRTB inside plenum, creating a rich AFR mixture.

Hullo oh learned ones
I seek some advice from the brains-trust.
I recently fitted a genuine Mazdaspeed IRTB kit on my '94 NA8.

This:



Without changing the tune on my MegaSquirt, she has been running VERY rich on idle, and light throttle acceleration.
In other words, plumes of smoke (black in colour) billow out the exhaust up to 3,000RPM and around 90-99KPa.

I would have assumed that, because the IRTB is still housed inside a plenum, and going through the MAF and associated intake tubing, there would be little change, and with the increase air-flow, I kinda expect it to run a little bit on the lean-side.

Can anyone explain why it has been running rich?

I have since leaned-out my fuel map to compensate.

Thanks in advance

PS: anyone care to share (or sell) a good MSQ file for IRTB in and/or out of plenum?
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Old 10-06-2009, 09:17 AM   #2
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Very short runners don't flow well at low rpms and subsequently make less low rpm torque. You are flowing less air at low rpms now. You are also probably flowing a little more air at high rpms and might need to add richness there. If the runners have a larger throat diameter, that will also contribute to less efficiency and flow velocity at low rpms.

Cliffs: You have fundamentally changed one of the design features of your engine and will need to completely reevaluate your tune.
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Old 10-06-2009, 09:36 AM   #3
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No offense, but isn't the point of a MSPNP so you can tune? To me it sounds like you added a restriction and lost power since it's not tuned correctly.
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Old 10-06-2009, 11:11 AM   #4
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So um... some pics of the setup up close and on the car?

I have to admit... I do find that kit pretty sexy F FujiRacing
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Old 10-06-2009, 07:43 PM   #5
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Thanks Six

You made me remember that I forgot about the basics of fluid dynamics

I was so excited about getting the car up and running, that I had my blinds on and was so focused on the assumption of increased air-flow and seeing more power across the whole rev range, that I forgot that there has to be a compromise somewhere.

For the curious, here is a photo of the setup:



There's a few touch-ups I need to do until it's 100%.

Keep the advice coming please guys and girls
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Old 10-06-2009, 08:38 PM   #6
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I do like.

I wonder if that plenum is big enough for a turbo application?
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Old 10-06-2009, 09:30 PM   #7
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Quote:
Originally Posted by gospeed81 View Post
I wonder if that plenum is big enough for a turbo application?
In what way would adding a turbocharger change the volume airflow through the intake plenum or throttle(s)?
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Old 10-06-2009, 09:49 PM   #8
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Quote:
Originally Posted by gospeed81 View Post
I do like.

I wonder if that plenum is big enough for a turbo application?
Thanks mate. It's a second-hand item that has been modified for the better, so it looks alot rougher than the pretty picture of a brand new set.

The plenum is pretty much as big possible without having to remove/relocate things.
The end is literally 1mm away from the lip of the clutch fluid reservoir (my car is right-hand drive), the fuel hard-lines sit a few mm apart, and you can't clip/unclip the TPS plug without undoing some bolts and levering the plenum out of the way.

The measuring tape and vernier calipers at Mazdaspeed were working overtime on design day

BTW: I'm not going artificial aspiration
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Old 10-07-2009, 09:49 AM   #9
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Quote:
Originally Posted by Joe Perez View Post
In what way would adding a turbocharger change the volume airflow through the intake plenum or throttle(s)?
In... what... waaaaay... does the author's use of the prison symbolize the protagonist's struggle, and how does this relate to our discussion of the uses of irony?
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Old 10-07-2009, 09:50 AM   #10
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Quote:
Originally Posted by Joe Perez View Post
In what way would adding a turbocharger change the volume airflow through the intake plenum or throttle(s)?
Other way around...how would adding this to a turbo application change the volume airflow through a turbocharger?

That's what I was getting after for the few folks I have heard considering indis on a turbo setup. Too complex to me...but it might be a neat setup.
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Old 10-07-2009, 01:26 PM   #11
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Quote:
Originally Posted by gospeed81 View Post
Other way around...how would adding this to a turbo application change the volume airflow through a turbocharger?

That's what I was getting after for the few folks I have heard considering indis on a turbo setup. Too complex to me...but it might be a neat setup.
It would likely have the same effect - more high rpm flow and more peak hp with some sacrifice in low rpm torque. Some light reading:
HowStuffWorks "How do tuned intake runners work on your car?"
Pretty good powerpoint:
http://www.eng.fsu.edu/~shih/eml4421/student%20presentation%20EML%204421/2006/Manifold%20Tuning.ppt
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Old 10-07-2009, 01:41 PM   #12
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Good light reading...we've hit on a few of those points in class.

I got an A in Fluid Dynamics...but it's amazing how much there is still to understand.


I was mainly asking the original question to gauge how the plenum compared to the stock manifold we all consider to be too small (in volume..disregarding runner length/diameter).
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Old 10-08-2009, 03:52 AM   #13
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You're a champ Six. Thanks for those links mate.
The Mazdaspeed plenum is considerably bigger than the stock one.
I would guess that it has about 75% greater volume, because it's a "box" (to put it simply) and it doesnt have parts of inlet runners and other castings inside.

If I were to remove the IRTB trumpers/velocity stacks/ram tubes that is housed inside, then it would make a great big space ideal for forced induction.
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Old 10-08-2009, 04:35 AM   #14
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let me get that
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Old 10-08-2009, 06:56 AM   #15
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I've been driving my car a few times each day, for the last few days, morning, afternoon, night and been leaning-out the AFR little by little.
Although the plumes of fuel smoke has decreased, I don't really want to lean her out more than what I have.
Idle mixture is fine now.

I don't feel like I've lost power due to the overly rich mixture, and everything is nice and smooth, so I'm just gonna bear the extra fuel costs
She my weekend toy, so fuel $$ it's not really a big deal
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Old 10-08-2009, 10:16 AM   #16
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Quote:
Originally Posted by OZMX-5 View Post
If I were to remove the IRTB trumpers/velocity stacks/ram tubes that is housed inside, then it would make a great big space ideal for forced induction.
The radii on the velocity stacks are still just as necessary on a forced induction engine. Air flows in just the same manner as with a naturally aspirated engine, the pressure differential is the only real change. Fluid dynamics remain in effect as air bends and turns to enter the cylinders. Fluid dynamics may actually become more important from an efficiency standpoint as you are trying to move an even greater volume of air through the same orifice.

Where would someone be able to find one of those manifolds? They aren't readily available in the states to my knowledge.
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Old 10-09-2009, 04:27 AM   #17
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Quote:
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... Fluid dynamics may actually become more important from an efficiency standpoint as you are trying to move an even greater volume of air through the same orifice.
Although I agree, I was also thinking about the law of diminishing returns. I just thought simply that if air is forced into the plenum, then perhaps there is more to be gained by having a physically larger space (thus more air can fit into it) and the venturi effect (is it venturi effect? It's been so long since I looked into this stuff) of the stacks become less advantageous.

Either way, I'm sticking to NA power. Too many have gone to the Dark Side.

Quote:
Originally Posted by sixshooter View Post
Where would someone be able to find one of those manifolds? They aren't readily available in the states to my knowledge.
Neither are they in Australia.... and AFAIK, anywhere in the Galaxy
I've googled "ITB", "IRTB", "Quad Throttles", "Throttle Bodies" for the last couple of years, and this landed in my lap by happy chance.
At the same time, there was another, fairly identical set, being auctioned on Yahoo Auctions in Japan.
What's the saying, "It doesn't rain, it pours" ?
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Old 10-09-2009, 05:03 AM   #18
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Quote:
Originally Posted by sixshooter View Post
Where would someone be able to find one of those manifolds? They aren't readily available in the states to my knowledge.
im working with BMC on making cheap gsxr-based kit for you bitches. it will be available for FI people too.
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Old 10-11-2009, 09:24 PM   #19
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Still being adventurous and leaning the fuel map bit by bit. It's getting better, but still drinking fuel. Oh well.
Last couple of nights I was brave enough to really open her up in 1st, 2nd, and 3rd gear, and WOAH! Does she rev or does she REV!!

As other IRTB owners can attest to, the response of these things are ... hmmm how do I put it.... envigorating and the sound.... oh my, very anti-social indeed
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Old 10-12-2009, 12:43 AM   #20
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Quote:
Originally Posted by UrbanSoot View Post
im working with BMC on making cheap gsxr-based kit for you bitches. it will be available for FI people too.
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