IRTB inside plenum, creating a rich AFR mixture.
#1
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?
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?
#2
Moderator
iTrader: (12)
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 20,652
Total Cats: 3,011
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.
Cliffs: You have fundamentally changed one of the design features of your engine and will need to completely reevaluate your tune.
#5
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
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
#8
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
#11
Moderator
iTrader: (12)
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 20,652
Total Cats: 3,011
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
#12
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).
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).
#13
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.
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.
#15
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 $$ it's not really a big deal
Although the plumes of fuel smoke has decreased, I don't really want to lean her out more than what I have.
Idle mixture is fine now.
I don't feel like I've lost power due to the overly rich mixture, and everything is nice and smooth, so I'm just gonna bear the extra fuel costs
She my weekend toy, so fuel $$ it's not really a big deal
#16
Moderator
iTrader: (12)
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 20,652
Total Cats: 3,011
Where would someone be able to find one of those manifolds? They aren't readily available in the states to my knowledge.
#17
Either way, I'm sticking to NA power. Too many have gone to the Dark Side.
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" ?
#19
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
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