My 2.4 CVT Low end power exhaust job + dyno

4 posts in this topic

    Recently my complete exhaust overhaul was completed, therefore putting it up here. From what I gathered over the years, looking at other exhaust jobs for 4B12 engines, there is one general pattern to all of them. Mostly it ends up in getting 4-1 exhaust manifold, getting rid of cats or replacing them with metallic catalytic converters and going for the 2 1/2 inch or larger  piping. As a result it yields best max power readouts on dynos, however this approach is far from the  best for CVT applications.  Often CVT owners correctly chooses 4-2-1 type manifold design over 4-1, however still decides to go with aftermarket axle backs and generally bigger tubing sizes. 

   So from the start, my concern was to make the perfect exhaust for CVT transmission. First I made a decision to go custom instead of aftermarket, which probably was cheaper and better choice from what I later found out about those aftermarket parts. I started with exhaust manifold and for obvious reason went for 4-2-1 design. It was correctly designed by engineer on solidworks, with all proper flow measurements to make it equal volume runner manifold. Since there were couple exhaust manifolds out there that claimed to be equal length, at first he tried to replicate those designs, however they possibly could not work as equal volume. I guess person who buys such shiny manifolds would not bother to volume test them. Therefore mine was designed from scratch. After it was made, I decided to maximise its  potential by getting it ceramic coated. I went for most over the top solution which was performance white coating from Zircotec (  ) 

   There were 3 main benefits on doing the coating. First one, when opening hood on warmed up engine, there is no more of the OEM heat levels that immediately hit you. Now you can feel the same heat as before only if leaning inside, close to engine cover. All I mean is that you dont need any temperature testers to tell that engine bay temperatures are way down. Second one was knowledge that inside the exhaust manifold temperatures were now much higher and resulted in higher velocity and better cylinder scavenging efficiency. Third benefit was better catalytic converter work due to receiving hotter gases initially, which helped chemical reactions within the cat. Obviously exhaust gas analysis were done to see cat efficiency.  Since my exhaust build consisted of 2 parts. Making exhaust manifold and the the rest of the exhaust later, I had opportunity to drive with new manifold, but with stock, rest of the exhaust. At that point stock exhaust limitations became very obvious.  First issue was noise, similar to one pressure valves make when slowly getting opened. Two shops checked entire exhaust for leaks just to conclude that it was simply due to exhaust gas velocity increase and overall exhaust resonance change result. The bigger problem was rough vibrations when RPM needle hit around 1000 rpm and on idle 750rpm. As I found out later, it was result of extra small piping diameter inside factory exhaust back end. It had valve inside it that opened way for gases to larger pipes if there were enough pressure or stayed closed and routed gases through really small piping at idle . In my case the valve was starting to rust and did not work properly, thus causing slight bottleneck situation at slightly opened or closed throttle. I did however put the car on the dyno with that setup. 

Dyno was done on 4WD mode, what you see in graphs is wheel hp in kilowatts. 1kw = 1.341 hp and Newton meters 1Nm = 0.737 ft lb

Mods at the time of a dyno: Works p1 flash tune , TGS Aluminum crank  and water pump pulleys. OEM Throttle body bored from 60mm to 63mm inside diameter. Works drop in filter(stock air box) TGS intake middle pipe, ralliart snorkel, 4-2-1 coated exhaust manifold. Engine oil Millers cfs 5w40 nt. No internal engine mods. 

Max hp registered was 119.5kw / 160whp and 228Nm / 168 foot pounds torque. 

Impressions from driving were as if there is a noticeable pull from around 2000RPM that was later confirmed by dyno, but was not present before installing exhaust manifold. There was not however feeling of more power in higher RPM range. 

     Then the car was given back for work on the rest of the exhaust. 

It started with new catalytic converter choice since OEM was too restrictive. Since where I live, we have to pass emission test each year, getting rid of the cat was not an option. Basically there were two choices as for aftermarket cats. One was cheap and widely available magnaflow cats and other one was going with German HJS tuner cat. There is a quite good Russian post on comparison between both cats that I will maybe translate and put up later. Based on that I went with HJS and got the HJS Nr. 90 95 0192 HD  It had inner joint diameter of 57mm, exactly what I needed, and double the precious metals of OEM cat. New cat exhaust gas analysis showed significant improvement over OEM one.   As for the rest of the exhaust, 57mm or 2 1/4 inch inner diameter tubing was used. With 54mm / 2 inch parallel tube inside rear exhaust bundle. It was replicated and tested in engineering software, even with spare for future mods. Therefore, anything bigger in diameter for this engine in Naturally Aspirated application is completely useless or even counter productive.  As for materials used, similar to SUS404 grade metal was used to make tubing, resonators and rear bundle, including internals. Material was pre-treated chemicaly, so that exhaust would not change colour over time. I cannot remember correctly, but I think that thickness of the tube walls were double the commonly used ones. (difference between inner and outer diameter) Although exhaust was made as a copy of the OEM, thicker tubes gave a somehow unique sounding exhaust. Soon I will try to get it on film, just need to get something better than my old phone.  One really important note on the rear bundle internal valve I was mentioning before. Its purpose is not only to make exhaust more quiet during idle and pressure buildup, but although to sustain back pressure for such period ( - 2000 ) RPM. In my case, valve mechanism was copied from stainless steel, but with larger diameter accordingly.  None of the aftermarket axle backs ( at least to my knowledge ) are not utilising same mechanism, therefore I can say with confidence, that putting one on would most definitely  rob some low end performance, or in best case would not give any benefits there. Making a custom axle back with upscale internals would yield not only same benefits for high RPM, since in full throttle ( valve open ) positions there is not much restrictions, but although maintain the low end power.  Aftermarket axle backs sure would sound louder, however as I stated before, I managed to get a nice sounding exhaust at full throttle and near OEM silent at city cruising and idle only because of thicker tubing. 

     After exhaust was completed, I immediately noticed the difference in performance. That pull that I noticed after installing exhaust manifold was still there, but it switched to lower RPM range. Now it starts from about 1600RPM. More so, it would pull much more confident till the 6000RPM from standstill. That was my prediction before going to the dyno for the second time and as I suspected it was confirmed.  Other than that, no more exhaust gas leak sounding noise or low RPM vibrations, all smooth and silent. Probably the best out of that RPM switch was the feel of gas pedal when switching from FWD to AWD. Those with AWD CVT lancers probably know the feeling when, after adding the rear wheel assist , car becomes somewhat sluggish as if you can actually feel the power loss from rear axle. In this case I had to relearn my driving habits, since even the slight touch of gas pedal on AWD mode gave immediate response. Feeling of sluggish gas pedal was completely gone. CVT itself tends to maintain RPM around 2000 mark, especially while driving within city limits, therefore any power shifts prior to that mark would yield the best possible results. 

    Second dyno showed max 126.5kw / 170whp and 238 Nm 175.5 foot pounds torque.  At this instance, max hp rating is not the important one, rather the low and mid range overall gains. As this engine ECU is known to do , including my case, the Air fuel ratio is getting rich mid way through. Tuner offered to lean out afr from 4000 onwards, which would net extra  3 to gradually increased to 6 whp at 4000- 6500 range, but we decided to leave it till the next visit. Besides, in my plans there is a custom valves in the near future, that should deliver more air at those ranges, thus leaning the mixture out by itself. But as I said, max top RPM power numbers were not my goal for that day. In case the afr log file successfuly was uploaded, anyone interested can view it with the help of this software :

To summarise: After watching some dyno graphs, including the ones with cat deletes, in my opinion my approach was the most beneficial to CVT application. Nevertheless, it would be nice if someone else could share and post their dyno results after exhaust mods for the sake of comparing them. 

First diagram will be the first dyno after exhaust manifold installed; second one with full exhaust and third is both graphics compared.




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Log file innovate fuel.log

flash tune + ex manifold.jpg

flash tune + complete exhaust.jpg


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More photos

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Right on dude, this is awesome.  About how much has the custom work cost? Would love to hear a sound clip or two


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Love the write up, always nice to see stuff done on a 4b12 engine. I plan to do mostly aftermarket parts (4-2-1 from SuperCircuit and Magnaflow cat-back) for the exhaust system when I pay off the Lancer (or if the exhaust system goes bad, w/e comes first)


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