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Discussion Starter · #1 · (Edited)
Finally got the car Dyno-tuned. Results are not what I had hoped for, even though the car performs very nicely.

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Problems are that he couldn't run more than 20º of cam gear advance, or rather there was no point.

There seems to be excessive back pressure, causing problematic system AFR readings. Under WOT in the VTEC range - I see 12's on my AEM WBO2, when the software is showing 14's (!) I don't know where to go with that

JDM K24a3/K20Z3 40º limiter in gear. TSX cams. Exhaust is 2" header runners into 3" collector, then 2.5" exhaust with Stainless Works 'turbo' muffler from there. I made a test pipe & removed the cat, it made no difference I could discern besides more flames out the tailpipe.

I have the K-tuned 70mm TB, but my intake is a modded RBB. I can't see how that would be the issue at the moment, though

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Can you elaborate? I don't get how the AFR's are skewed.

Mid engine creates packaging constraints on the intake & exhaust



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I know it’s probably the only way to make things fit, but that area where it transitions from the plenum to the TB could be constricting flow. A 24/20 frank engine should want more than 20 degrees vtc and even in mid or rwd applications I would expect 200+ whp. If I remember correctly you have slightly higher compression pistons as well ?
 

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And for the AFR differences , I would trust the kpro readings over the aftermarket wideband depending where the sensors are placed. 12-14 is a pretty big difference.
 

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I know it is hard to compare, but if you look at his results and description, it seems to fit well.

Only the RRC intake, an RBC would have likely done the same, woke up his engine at the top end.
 

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Discussion Starter · #7 · (Edited)
Thank you for the input.

The plenum / TB neck is wide open - it does look tapered in that first pic

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The O2 sensors are staggered - just clocked to avoid any flow overlap. I could try swapping locations

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Someone else questioned whether K-Tuner goes open-loop for VTEC, and whether that would explain why the AFR is ignored/not recorded in software logs? I dunno. There has to be a rational explanation as to why the system isn't showing actual AFR's. I trust the AEM WBO2 - I've never seen them be erratic like that.

I do have Nippon Racing 11.13:1 pistons, also TSX cams - I am more interested in the wide torque band, which I have, I just expected better VTEC performance.
 

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Can't you tell by smell which one is correct? If the Kpro AFR is reading ~14.7 and the AEM reads 12-13 you should be able to smell the exhaust if the engine running rich if that's the case.
 

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Based on your pictures, your output is 100% limited by your intake and exhaust configurations. You obviously have constraints to work within, but you can't expect your changes to not have a negative impact on output.

Regarding your AFR readings. Are the O2 sensors the same? have you tried switching which sensor is plugged into ECU/AEM? Have you tried switching sensor locations with each other? Assuming the sensors are the same and the readings of each individual sensor does not change with it's position, start looking at the voltage/resistance output of each to determine if they are giving different information.

 

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Discussion Starter · #11 ·
Based on your pictures, your output is 100% limited by your intake and exhaust configurations. You obviously have constraints to work within, but you can't expect your changes to not have a negative impact on output.

Regarding your AFR readings. Are the O2 sensors the same? have you tried switching which sensor is plugged into ECU/AEM? Have you tried switching sensor locations with each other? Assuming the sensors are the same and the readings of each individual sensor does not change with it's position, start looking at the voltage/resistance output of each to determine if they are giving different information.

I understand my setup creates limitations. No one has clarified what concrete changes would need to happen to alleviate that. Just saying it's limited is not very helpful.

No factory or aftermarket intake or exhaust is gonna fit my chassis, so no matter what I have to chop/mod whatever I use. Again, I'm not after screaming high rpm HP. I kept the TSX intake & cams becuase I want the even wide torque band. I'm just trying to figure out what is going on with the system AFR's so I can run a little more cam advance, and maybe make a little more power :D

The sensors are not the same. AEM WBO2 controller uses an LSU4.9, the Honda system uses a standard Denso WBO2.

I could swap locations, not swap which one feeds the system.

I ran the car with no cat, and that made no difference to the discrepancy. I ran the car today with the downpipe open - no connection to the cat, muffler or the rest of the exhaust. That made no difference either, system still shows 14 AFR's. Clearly, the system isn't really running 14's under WOT, there would be other resulting problems were that true. Again, the AEM WBO2 controller appears to be displaying the actual AFR's - 12's under high load/rpm certainly seem appropriate for a safe tune.

The main issue is figuring out why the system doesn't properly indicate actual AFR's under the high load conditions.
 

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May I suggest you ask LotusElise for a quote to run a 1D simulation on your engine. He would need main dimensions of your intake and exhaust system plus engine data. A data log of a dyno run is also helpful. He would be able to tell you from the simulations if intake or exhaust are a major factor or the cams. Just from your pictures, I do not like the transition from the TB to the intake manifold too much, but doubt you would lose more than a few Hp from this.
In general short 4-1 headers provide little help anywhere in the rev range. If large enough, they won't restrict, but do not provide positive resonance effects. It would generate a rather flat torque curve across the range. If you would supercharge your engine, this would work just fine.
Long runner intake manifolds shift the torque curve to lower rpm. The relevant resonance peaks (6th to 3rd) all occur at lower rpm. The 2nd harmonic will eventually kick in, but usually only at very high rpm. And in between there is a low torque valley. Again, a simulation will tell you where these peaks are.

My suspicion is that you need longer duration cams in combination with a suitable intake manifold for higher up peak power.
A k24 needs longer duration cams compared to a k20 for the same rpm power band.
If space is tight, you might even look into a PRC intake or a RSP intake. The PRC is really compact and about as short regarding flange to end of manifold dimensions as it gets.
 

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Discussion Starter · #13 ·
May I suggest you ask LotusElise for a quote to run a 1D simulation on your engine. He would need main dimensions of your intake and exhaust system plus engine data. A data log of a dyno run is also helpful. He would be able to tell you from the simulations if intake or exhaust are a major factor or the cams. Just from your pictures, I do not like the transition from the TB to the intake manifold too much, but doubt you would lose more than a few Hp from this.
In general short 4-1 headers provide little help anywhere in the rev range. If large enough, they won't restrict, but do not provide positive resonance effects. It would generate a rather flat torque curve across the range. If you would supercharge your engine, this would work just fine.
Long runner intake manifolds shift the torque curve to lower rpm. The relevant resonance peaks (6th to 3rd) all occur at lower rpm. The 2nd harmonic will eventually kick in, but usually only at very high rpm. And in between there is a low torque valley. Again, a simulation will tell you where these peaks are.

My suspicion is that you need longer duration cams in combination with a suitable intake manifold for higher up peak power.
A k24 needs longer duration cams compared to a k20 for the same rpm power band.
If space is tight, you might even look into a PRC intake or a RSP intake. The PRC is really compact and about as short regarding flange to end of manifold dimensions as it gets.
Thank you for the input.

My main concern is the discrepancy between system & controller AFR readings - and the fact that it is limiting my cam advance potential

I know the RBB intake limits top end, however I don't think that is the cause of the skewed AFR's& the subsequent cam advance limit.

I want the nice even torque the TSX cams & intake provide - the main goal here is just to make sure I'm not loosing untapped torque/hp due to malfunctioning / faulty items.

I did remove / disconnect the cat & run the exhaust open off the collector extension - almost made my ears bleed - that made no difference to the system AFR values being logged, whilst the WBO2 showed 12's under WOT/VTEC load range. The issue I'm concerned about cannot be backpressure, acknowledging that the exhaust in general is a restriction in terms of making optimal power for the setup..
 

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Swap the O2 sensor locations and see if they read the same. If they do, find the specs for each O2 sensor and use a multimeter to verify the output from each sensor is matching what each gauge is reading. You will just have to diagnose each piece to figure out what is going on.

Regarding you intake and exhaust compromises. Starting at the throttle body, the transitions look okay, but the restriction down to the narrowest portion of the intake manifold looks small. What is the effective diameter in the intake manifold? 60mm? A 70mm throttle body will only flow as well as your narrowest point. Your intake manifold looks cobbled together in places. The transition from the throttle body flange to the plenum is no longer smooth. Unknown how well you lined up the runners with the cuts and welds. A bore scope camera will tell you how well all the new transitions were done. The exhaust header primaries are way too short to make good torque. Without torque, you will loose HP. The bends and transition in your header are too abrupt and short, and will reduce the flow/add restrictions.
 

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In general short 4-1 headers provide little help anywhere in the rev range. If large enough, they won't restrict, but do not provide positive resonance effects. It would generate a rather flat torque curve across the range. If you would supercharge your engine, this would work just fine.
Exactly this. The scavenging phase is essentially for the NA alternation of load. If there is no suction form exhaust side there will be no acceleration of the air column before the piston runs down. So you loose around 100° of the cycle to create significant VE. The engine clearly tells that it see it the same, no more VTC advance then 20° is a heavy number. It's like you cut the cam duration by around 30°-50°, and - if that would help - in a negative way.

Swap the O2 sensor locations and see if they read the same.
Would be also my first approach after verifying they show same results in an other operation point. This could indicate a heater issue of one of those two. AEM source their controller stuff in China. I am not saying China stuff is low quality in general, but some of the controllers showed issues from the beginning or after some hot events. The controller board get heated to much and electronic parts got grilled. I've saw many who made it a typical race engine living and some broke during tuning or even before. Beside that, if one injector is not feeding right it could be that a flow scheme in that exhaust system doesn't mix up fast enough and the different angles and location of the two sensors lead to different measurements.

Regarding the placement of wideband's. The position of the blue sheltered one is a bid disadvantaged, the black one sheltered (guess the AEM one) has an better postion, but is still not optimal. The purpose is to measure the exhaust gas of all in the exact same flow scheme. To reach that you should use a bottleneck (which I won't recommend personally, but many do) or go about 100 mm more upstream, where the flow is forced to uniform a bit more than at the merger end.
 

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Discussion Starter · #16 ·
Swap the O2 sensor locations and see if they read the same. If they do, find the specs for each O2 sensor and use a multimeter to verify the output from each sensor is matching what each gauge is reading. You will just have to diagnose each piece to figure out what is going on.

Regarding you intake and exhaust compromises. Starting at the throttle body, the transitions look okay, but the restriction down to the narrowest portion of the intake manifold looks small. What is the effective diameter in the intake manifold? 60mm? A 70mm throttle body will only flow as well as your narrowest point. Your intake manifold looks cobbled together in places. The transition from the throttle body flange to the plenum is no longer smooth. Unknown how well you lined up the runners with the cuts and welds. A bore scope camera will tell you how well all the new transitions were done. The exhaust header primaries are way too short to make good torque. Without torque, you will loose HP. The bends and transition in your header are too abrupt and short, and will reduce the flow/add restrictions.
Thank you for the detailed input, I appreciate it.

I have ordered a new Denso O2.

I think the runner transitions are clean. The TB neck is the narrowest point - I hogged out the TSX DBW neck to go with the 80mm TB I had originally.

I'm going to have to look into making a new header with longer runners - they will have to loop upwards and then down - there is no room to extend downwards. Thing about that is, other X1/9 users use the crappy 'shorty' header off eBay & make over 200WHP - so I still don't see it being the immediate problem, albeit not optimal.





 

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Discussion Starter · #17 ·
Exactly this. The scavenging phase is essentially for the NA alternation of load. If there is no suction form exhaust side there will be no acceleration of the air column before the piston runs down. So you loose around 100° of the cycle to create significant VE. The engine clearly tells that it see it the same, no more VTC advance then 20° is a heavy number. It's like you cut the cam duration by around 30°-50°, and - if that would help - in a negative way.

Would be also my first approach after verifying they show same results in an other operation point. This could indicate a heater issue of one of those two. AEM source their controller stuff in China. I am not saying China stuff is low quality in general, but some of the controllers showed issues from the beginning or after some hot events. The controller board get heated to much and electronic parts got grilled. I've saw many who made it a typical race engine living and some broke during tuning or even before. Beside that, if one injector is not feeding right it could be that a flow scheme in that exhaust system doesn't mix up fast enough and the different angles and location of the two sensors lead to different measurements.

Regarding the placement of wideband's. The position of the blue sheltered one is a bid disadvantaged, the black one sheltered (guess the AEM one) has an better postion, but is still not optimal. The purpose is to measure the exhaust gas of all in the exact same flow scheme. To reach that you should use a bottleneck (which I won't recommend personally, but many do) or go about 100 mm more upstream, where the flow is forced to uniform a bit more than at the merger end.
Thank you for your input.

I'm going to investigate a longer runner header - the problem is this is the space I have to work with



This is how I have the collector merge setup with the O2's in the taper back to 2.5". I could move the system (blue sheath) O2 into the collector before the V-band.

 

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My 2 cents are, 194hp at the wheels is not terrible for essentially a compromised stock k24.

People get too caught up on numbers, some dynos just read lower or higher. Don't get discouraged by the numbers if it performs well.
 

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Discussion Starter · #19 ·
or go about 100 mm more upstream, where the flow is forced to uniform a bit more than at the merger end.
Should I put it up here? When I was reading about sensor placement, I thought they needed to be 18" or more from the head ports? As it is they are closer than that

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I could probably move them back just before the flex coupler - but that seems to be the opposite of what you are suggesting
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THB, I agree with that you a got decent result. If you improve he header and cams, you can squeeze a little bit more out of it.
If you want to add a lot of torque and power, just supercharge the K24. It'll cost you as much as redoing your intake, exhaust and cams. For these power levels, you don't even need charge cooling.
K24s respond really well to even mild boost (4-7PSI) and your header design won't matter anymore as it is well dimensioned for low back pressure.
A 2nd hand JRSC or CT-E supercharger will get you straight to 270 to 300 wHp without even trying too hard.
I am not too fond of these types of muffler. I'd try a straight through design, maybe a bigger one or two in a row for routing reasons. K-series engines respond really well to low back pressure. You will find you'll need higher VTC figures.

Here is my current 4-1 on my Elise. It is suboptimal for a NA engine and could life with bigger primaries, but shows what some people can do with pipes.



 
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