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Let's keep this thread focused on GMS 3" exhaust and talk more about ECU tunes and graphs here: GMS Stage I ECU
GMS - Modular Exhaust System 3''
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Working on my installation today....
I have gotten the Capristo Exhaust, Midpipe, and Intercooler hose removed, and all of the bolts for the shroud. However, I can't get the darn shroud removed. I have been wiggling, cajoling, and some minor forcing, but it resists being removed.. I removed the upper heat shield bolts for the fuel tank and it has given me more wiggle room, but there is some cooling pipe that is VERY VERY close to the shroud that is making removal very hard.
I have gotten the Capristo Exhaust, Midpipe, and Intercooler hose removed, and all of the bolts for the shroud. However, I can't get the darn shroud removed. I have been wiggling, cajoling, and some minor forcing, but it resists being removed.. I removed the upper heat shield bolts for the fuel tank and it has given me more wiggle room, but there is some cooling pipe that is VERY VERY close to the shroud that is making removal very hard.
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Yup. Passenger side top? And then you’ll suddenly move it one way and it will pop free. You’ll wonder if it will ever go back on, but it does.
My dealership took the whole heat shield out to get access, but that probably takes a proper lift to get out under the car.
All could have been simplified if only Alfa had spun that clamp 180 degrees.
Best of luck with it!
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I never installed OEM downpipe with cat back again, so now I honestly do not even remember anymore exactly how I removed it, but I can now easily access GMS downpipe V-band with ratchet extension, with having shroud on, from below the car. Any writing here won't help much as I believe with the OEM V-band clamp is rotated differently from car to car so I guess some access it easier, other harder.
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Got most of the parts reinstalled (shields, cooling duct, and most of the exhaust clamps preliminarily placed and attached. Should be much easier to adjust now that I don't have to remove the cooling shield to do any work on it...
My helper approved of the reassembly too...
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My helper approved of the reassembly too...
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BTW.. This is the bane of your existence.. Technically it doesn't NEED to come all the way out, but I took it out just to be sure. I was finally able to force it out once the Cat was removed. Getting the cover back in place was a less than 10 minute job.
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What do you guys think of incognito ceramic coating? Black or white? Another step towards droping the engine bay temps that I'm thinking of for some time now. It just breaks my heart to have the exhaust components in its shine and rainbow look all covered by coating...
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It is a felony to hide those welds, but in my opinion, this is not a beauty contest, so if it works good, I think it should be an option. I would consider it strongly if there are data that proves function, when time comes for exhaust. And I like the trade off with slightly less low end, in return for a better top end, so a replacement seems highly interesting.
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Black, white, silver, grey, all available.
Both wrap and coating do the same job. The wrap has tendency to trap condense that turns to moisture under the wrap so standard mild steel exhaust tend to rust which in our case with rust free T304 material is not really an issue. The ceramic coating is not as effective as heat wrap is in terms of heat control. Let's say the coating is another minor upgrade but if I had to choose between two, I'd go with wrap.
It is a felony, indeed. I guess I'll give it a try on my car and we'll see how it works out.
Regarding the top end, the 4C's stock turbo is running out of breath at higher rpm range, so replacing OEM restrictive exhaust with the free flowing exhaust, does help a lot by reducing the backpressure and therefore gaining top end power. Also on remaped ECU's there is a lot of turbo surge on stock exhaust as the turbo is pushing more air in, than the engine can flow at the low-mid range rpm and this effect is only heating the charge air and putting stress on turbo, so we don't want it. Again free flowing exhaust does help with this issue too, but we still had to decrease maximal boost on our tune in this low-mid range to further reduce the turbo surge. Porting the head would help with this and increase overall engine power but let's not get to much off the topic here.
OEM turbo is squeezed(as is should be for a good setup). But when reducing back pressure, increases power, it means that turbo isn't really "out of breath", because we cannot get more than compressor will give. The turbine might choke the engine on hotside, but thats not the same, although it steals power. And when reducing exhaust pressure increase power, it means that at least a part of the choke, was not down to turbo itself.
I've not seen numbers anywhere for Volumetric efficiency, MAF readings or turbine pressure of our engine. Before we have these data, we are really searching for power more or less blindfolded. We cannot even "guesstimate". This is the reason I suggested that a tap for pressure reading at both sides of turbine, it would at least be a start.
I assume you have plenty data at MAF, but do you have estimates for Ve and maybe data for turbine pressure ratio as well? When playing in MatchBot, it seems like parameters must be quite good to get much above 300Hp.
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I am aware of turbo characteristic and terminology so I wanted to simplify things a bit to make it more understandable. Perhaps I simplified it a bit too much for those of you who are more knowledgeable regarding the turbos and the word "out of breath" wasn't the most appropriate. For us, mere mortals I'll try to make another simplified, but more precise explanation.
Two turbo related things are happening once we boost our 4C engine beyond OEM setup (1.5 bar):
At low-mid range rpm and increased boost we are experiencing compressor surge as the turbo cannot push as much air as we are requesting into the engine, so part of the air is now escaping back through the compressor. Less backpressure (free flow exhaust and head porting) or reduced boost are the solution. Smaller compressor would help but we would sacrifice top end then, so no.
If we can flow the same amount of air into the engine at less boost (less backpressure) we are lowering air temps allowing us to advance ignition timing, gaining hp, but even without any change to ignition timing, the power increase at high rpm is notable between OEM exhaust, GMS 200 cell cat and GMS decat. The only logical connection I see behind this, it could be a rather small housing (AR) of our stock turbo and therfore lots of backpressure, but the spool is quick. Of course this is just a guesstimate until someone makes proper measurements. However, 3" exhaust should be spot on for 350hp figures, so no need to worry about exhaust being the bottleneck and the temperature drop in the engine bay and around the turbo is noticeable, allowing more stable engine power.
Two turbo related things are happening once we boost our 4C engine beyond OEM setup (1.5 bar):
At low-mid range rpm and increased boost we are experiencing compressor surge as the turbo cannot push as much air as we are requesting into the engine, so part of the air is now escaping back through the compressor. Less backpressure (free flow exhaust and head porting) or reduced boost are the solution. Smaller compressor would help but we would sacrifice top end then, so no.
If we can flow the same amount of air into the engine at less boost (less backpressure) we are lowering air temps allowing us to advance ignition timing, gaining hp, but even without any change to ignition timing, the power increase at high rpm is notable between OEM exhaust, GMS 200 cell cat and GMS decat. The only logical connection I see behind this, it could be a rather small housing (AR) of our stock turbo and therfore lots of backpressure, but the spool is quick. Of course this is just a guesstimate until someone makes proper measurements. However, 3" exhaust should be spot on for 350hp figures, so no need to worry about exhaust being the bottleneck and the temperature drop in the engine bay and around the turbo is noticeable, allowing more stable engine power.
If this flow map below is correct, 1.6Bar is perfect to get maximum mass out of the compressor:
Are you going higher than 1.6?
And what pressure do you have between cylinder head and turbine inlet, did you weld some ports so it can be measured? Say that there is 2Bar here when exhaust valve close, thats 2Bar that is fighting air coming in when inlet valves are opening. Too much pressure here, and we know that we have to back off. Obviously too much to discuss with a keyboard, but just trying to mention it for the common knowledge, and in case it has slipped from your attention
It can also be mentioned that boost pressure number is kind of overrated, what really matters is the weight of new fresh air coming in. For example, with a supercharger, changing a cam result in lower boost, but still increase power output. Most would assume that reduced pressure = less power, but actually opposite result. I have close to no knowledge regarding cam, but I do not think we have adequate knowledge to be sure porting is the next logical step, maybe there are better options before this? As you kind of say, everything affects everything, and I feel that we only have scratched the surface for now...
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Well, I got 20 minutes to drive with the exhaust installed with the Stock ECU. "All" that is installed is the main turbo pipe, Cat, Midpipe, and the Akrapovic adapter. I do not have the GMS muffler, as the shop will be using the Akrapovic adapter to adapt to my Capristo Exhaust. I was able to reuse both of the O2 sensors, and so far, I haven't tripped the "Check Engine" light with the stock ECU. Fingers Crossed on that one! I have a Porsche Clube HPDE in 2 weeks, so I hope it keeps working "normally"
I took it VERY easy to drive to the race shop. I did get some smoking early on, as I assume the wrap needed to "cook" some. It is quite loud, and cold start is an "event". It is loud enough for my neighborhood, that I am very glad I have the Capristo valved exhaust to be adapted to the GMS exhaust. The Capristo is a 2.5" Exhaust, so it shouldn't provide much flow constraints.
I took it VERY easy to drive to the race shop. I did get some smoking early on, as I assume the wrap needed to "cook" some. It is quite loud, and cold start is an "event". It is loud enough for my neighborhood, that I am very glad I have the Capristo valved exhaust to be adapted to the GMS exhaust. The Capristo is a 2.5" Exhaust, so it shouldn't provide much flow constraints.
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In 20 minutes, you will not have completed a full driving cycle and the e-test parameters will still show "not ready". No code means not ready to decide if you get one or not!
But the good news is that if you do throw an emissions code before or at the track, just reset it with an OBDII reader, and pull the negative on the battery for a moment. That will reset the test cycle, and give you 100 miles or more of code-free (and Dynamic/race mode lockout free) driving. However, the fuel trim tables will not be properly written until the test is ready, so about the time that your car will start behaving at its best, you may go back into code / limp mode. Reset as above again as a temporary solution. Have EC program your ECU to block the code is the longer term answer.
Hoping that you don't get the repeating code that I did - let us know either way, please, as it means that I would need to troubleshoot the new O2 sensors that went in with my exhaust to see if there is a problem with my installation if yours is trouble free.
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@4Canada - Thanks for the info! I was pondering taking the car on a hour plus drive to make sure everything is 100% prior to the track day, so you just convinced me that I better do that. I'll have my OBDII Reader at the track (I always do), and likely the EuroCompulsion Phase 2 ECU with me too (just in case).
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It's the same family turbocharger map but there could be some differences so not exactly comparable. Turbo map is presenting optimal working range without any restrictions which we have (exhaust, head flow, etc.). It helps us select optimal turbo for our application (mostly on engine displacement), but entire VE (volumetric efficiency) depends on the engine components, not the turbo itself. VE with help of turbo will dictate then the power.
In our case we are surging on WOT (wide open throttle). Large compressor, matched to a small turbine (for a quick response) and high boost and low airflow conditions (in low to mid range rpm) cause the surging (air separates from the compressor blades, allowing some air to escape back out through the compressor). Many solutions for this. 1. Decrease boost, 2. larger turbine wheel (slower spool), higher AR - larger housing (later spool), 3. less backpressure (exhaust or head porting) together with decreased boost. Obviously, decreasing the boost is the smartest solution, but if we fit free flowing exhaust or port the head we will allow more air flow at lower boost, so no more surging, yet the same hp and quick turbo spool. Only fitting free flow exhaust or porting the head, but keeping the same boost will increase airflow and gain power, but will still cause surging effect as the ECU is told to get to the same boost. With GMS Stage I ECU tune, we decided to reduce surge and not to go for max hp and torque at low-mid range rpm, so we lowered the low-midrange boost request to the ECU. Because of that, we are heating the air less which is allowing us to advance the ignition timing in the upper rpm range and gain hp.
Regarding the high rpm range and free flowing exhaust. In most of cases and it seems in 4C too, now that we connect all the facts (quick spool, low-mid range surge), the conclusion is that turbine side is rather small and when you add restrictive exhaust with lots of backpressure, the exhaust side of turbo is the restriction. Jamie, from Alfaworks was experimenting with hybrid turbos and his conclusion was that changing compressor side only didn't gain much and by changing the turbine side as well, the boost increased but power not all that much, which again means, that there is a lot of backpressure due to limited flow. I'm quoting Jamie's words: "You can get a lot more boost pressure out of the hybrid with both compressor and turbine wheels changed, I got up to 2 bar of boost pressure but the power just wasn't any greater than with 1.85 bar of boost. When I just changed the compressor wheel, the turbo could not flow any more." Free flowing exhaust does help significantly and dyno numbers prove it. More air flow, less heat and advanced timing is resulting in higher rpm range hp.
Backpressure is not needed at all and should be nullified if possible, but it's not, especially on turbocharged cars, where the turbine itself is representing a huge restriction. Now add poor flowing head design and restrictive exhaust and you will have a poor breathing (poor flow), low VE (volumetric efficiency) engine, which will require a lot of boost to make any decent amount of hp. All the turbo engines, except racing turbo engines, don't bother with the flow capacity, as it is far easier to add more boost than have high flowing engine head (expensive) and quality exhaust system (expensive). Ported head and free flowing exhaust also hurt the emissions due to less exhaust recirculating effect, so once again not a viable choice by today's standards. However, any decent racing engine builder will aim for the highest possible flow of components (exhaust, engine head) to achieve the best possible VE and rather keep low boost to achieve responsive and temp stable engine.
Regarding boost. Yes I agree, the airflow matters and the boost is actually only telling us how much of restrictions we have.
Regarding the cams, cam overlapping and cam timing. I have quite some experiences with it. On my S50B32 engine which in it's N/A (natural aspirated) stock form achieved a healthy 94hp / liter and showed 300hp on dyno, when we put a centrifugal supercharger on it, we yielded a 400hp with only 0.4 bar of boost. We later moved to larger supercharger but couldn't get past 1 bar of boost, because the cams had too long intake duration and were overlapping too much so we were actually pushing and wasting the supercharged air through the exhaust valves. With revised overlapping setup we gained some power, but the duration of the cams didn't allow us the best solution. This is a problem you get into if you are converting the N/A engine to supercharged setup. This is the problem that is only happening on the supercharged cars, where you have none of the restriction in the exhaust system. Short intake duration and long exhaust duration cams with least possible overlapping are needed. Cam timing should be set for late intake opening (there will be enough time to fill the cylinder with fresh air as the air is now forced in by supercharger) and exhaust opening should be as early as possible (a lot more exhaust fumes must be scavenged now). The engine will flow greatly and yield a lot of hp on minimal boost, making it a perfect race engine with strong high rpm achieved by centrifugal supercharger but rather weak low end torque. It's an expensive and very emission delicate engine, so not much of supercharged engines on the market today. Powerful in top end and very responsible and easy to drive on the limit.
N/A engines like long intake duration and short exhaust duration cams with a lot off cam overlapping. At low and mid range rpm, the overlapping is minimal, but at high rpm range it's significant (the exhaust valves are still opened, while the intake valves are already opening as this helps to drag the air into cylinder by using the exhaust). Cam timing should be set for early intake opening (to extend the time of the air flowing in to the cylinder) and late exhaust opening (not all that much of exhaust fumes to be scavanged). Engine will be lacking the torque compared to FI (forced induction) engines and will have a lot of hp only with lots of revs, which will make the engine very responsible and easy to drive on the limit, but expensive to run due to increased rpm wear and tear and requirements of lightweight components to make high rpm operation possible. The most expensive engines are racing N/A engines. Their hp/price ratio is not very viable.
Turbo engines like short intake duration and long exhaust duration cams with some cam overlapping. At low range rpm, the overlapping is significant (to help with the turbo spool), but at mid and high rpm range it's minimal (to prevent wasting of the fresh air through the exhaust, but it's not as critical as with the supercharger setup is, as by having a turbocharger in the middle of the exhaust system there is also a significant backpressure preventing this effect). Cam timing should be set for late intake opening (there will be enough time to fill the cylinder with fresh air as the air is now forced in by supercharger) and exhaust opening should be set to somehere between N/A and supercharged engine (not late, not early, somewhat "normal"). Torquey, powerful, cheap, emission efficient but hard to drive on the limit due to the turbo lag. No wonder this is the most common engine setup today. Excellent power/price ratio.
Of course the timing and overlapping can also greatly affect the emissions, so all the upper statements are valid for race application where emissions are not so important aspect of engine tuning.
Head porting is expensive and takes a lot of time but surely is the best way to gain VE. Except the emissions, there are absolutely no benefits of having poor engine head flow as it has no benefit of having restrictive exhaust. Changing the turbo and increasing the boost would gain more hp, but if you do the engine porting first and then upgrade the turbo, you will outperform someone with upgraded turbo and without ported head later.
@GMS Have you tested what the pressure is before and after turbine, and are you willing to share it? What charge/boost pressure during the test is of course equally interesting.
If you don't want to reveal, no hard feelings.
Example,
forum for my other car, 13.5psi boost, resulting in 19psi over turbine(engine sensitive for back pressure)
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![113037]()
If you don't want to reveal, no hard feelings.
Example,
forum for my other car, 13.5psi boost, resulting in 19psi over turbine(engine sensitive for back pressure)
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