There was a thread on the old forum on increasing the performance. A larger fuel injector and an unrestricted manifold were mentioned. I'm going to need to do these things. Any help, Guys?
Hey redgalvin, ya know, this here's a pretty big topic we're talkin' about. But don't worry, I'll give ya the know-how you need once again, just give me a few days. Gotta admit, though, I'm still bummed out that the old forum ain't around no more.
My SR been gathering dust for quite a while now, I've been thinkin' 'bout tweakin' the compression ratio lately.
Thanks, Took 3 months to get a reply. Appreciated. I've got 3 '78's was recently given a 2015. No comparison to my hot rod '78 but I can live with 72 mpg.
First, let's take a moment of silence for the fact that the old forum just "disappeared". And then it took a full three months to get a "response". Really unfortunate, huh? After losing the old forum, I try my best to come here often, you know how it is...
Now about the performance upgrade for the SR400 FI, I've written quite a lot on this in the past. I'll put it all down again in the hope of enriching our conversations here.
First off, we gotta recognize that the SR400, regardless of the type, always leaves a bit of a bitter taste in the mouth, since it's essentially a "modified" SR500. Actually, if you consider the carbureted SR400, it ain't half bad—once you upgrade the carburetor, it's like the thing finally wakes up. It's just a shame that the fuel-injected version gives many riders a real headache.
So, no matter how folks spin it, I'll say this—the SR400 and the SR500 are apples and oranges in a lot of ways. On paper, the SR400 might seem to have a smidge less torque, a smidge less horsepower, but the difference when you're in the saddle is night and day. That's why I always say, if you got the chance, the means, and the will, making the jump from the SR400 to the SR500 is a solid move. Maybe some wise guy would ask, why not just get the SR500 from the start? The answer's a mixed bag—first off, the SR500 has been out of production for a good while, and secondly, it's not street-legal in some spots. That's why there's always a market for bumping an SR400 up to a 500+.
Alright, let's cut to the chase—how do we save the SR400 FI? I'm sorry for the dramatics here. I gotta stress this—if anyone's happy with their SR400, be it carbureted or fuel-injected, then they're living the dream, really living the dream, no BS, and your wallet ain't gonna be bleeding red.
The first step in improving the SR400 FI is the ECU. I've tried a few solutions, like the PCV coordinator, a small interventional coordinator without an interface, and an air intake temperature sensing stick. To my knowledge, there are a couple more interventional coordinators out there in the world, along with some real professional ECU flashing options. But for now, the only one I can recommend is the PCV. Note, that's the Power Commander 5, not the 6. The 6 is compliant with California's emission regulations. I haven't personally used it, but according to friends who have, the range of adjustments is more limited. Well, it is California legal after all, so I guess that's to be expected.
In fact, based on my experience with ECUs, the best option out there is a flash-tuned unit, like Harley's Power Vision. That thing is incredibly powerful, only surpassed by a full ECU replacement. But sadly, such a thing doesn't exist for the SR400. I do know a flash-tune developer, though. I hope I can pay him a visit this year and see if I can persuade him to make something like that. Considering the number of SR400 FI users worldwide, there's probably some market for it.
So, for now, when it comes to the SR400 FI, I only recommend the PCV. And very importantly, it's best if you add an Autotune to it, probably the AT-200 model. A PCV plus Autotune will let you auto-tune based on the AFR settings you've put in and make trims to the fuel map.
That's step one. But now, I gotta tell you about another unfortunate reality of the SR400 FI that's even worse than its carburetor counterpart. Even if you use a PCV and Autotune, set the perfect AFR, and even adjust the ignition map, sadly, the response just won't be as good as expected. Yes, there's something to blame for this, and the culprit is the fuel injector.
The stock fuel injector for the SR400 FI is actually a small injector meant for a 250cc displacement, the part number indicates that it's the same as the one used in early R1 models and certain WR250s. How fascinating is that? Now about fuel injectors, there's something you should know. Unlike carburetors which are linear, injectors are binary – they're either open or closed, 0 or 1. The principle of injection is that the computer tells the injector how long to spray for. So now you know why the SR400 FI's response is even more sluggish than a carburetor model, this is the reason.
Theoretically, if we need a certain value, any injector, big or small, can meet that value. But the major difference lies in - how long it takes to supply that amount of fuel. So if it's a big injector, the need is met almost instantaneously, while a small injector has to work hard to gradually get there. So here's my second tip for boosting the performance of the SR400 FI: the second thing you need to do is replace the fuel injector. And the prerequisite for this is to have at least a PCV, otherwise the stock ECU won't be able to properly control that injector, and your riding experience will be nothing short of a disaster. How do I know this? Because my friend did just that, didn't heed my advice and rode out on it. It took less than five minutes for me to win a bottle of Heineken.
As for purchasing fuel injectors, I've tested three options so far:
1 - Buy an XT660 injector separately and install it on the SR400's stock throttle body. 2 - Buy an XT660 throttle body assembly (includes injector). 3 - Buy an OVER 46mm throttle body assembly from Japan (includes injector).
I've tried all three options myself and each has its own specifics you've gotta pay attention to. Let's kick off with the first one:
Option 1 - Using the XT660 injector only
Truth be told, I reckon this solution is the most fitting for the stock SR400 FI engine. It's super cheap and the effect is remarkable. Even if you upgrade the engine to an SR595 FI, theoretically, the stock throttle body size should still be okay. I've seen folks in Japan converting their SR400 FI to SR595 FI and still use the stock spec throttle body. But one thing I'm pretty sure of, if you don't change the injector, the engine's responsiveness will be limited by the injector's size. Anyways, without considering throttle body size, using the XT660's injector on the SR400 FI is absolutely feasible.
But since the XT660 injector is physically a bit longer than the stock SR400 FI injector, when you fit the XT660 injector onto the SR400 FI throttle body, the screw locks on both ends of the fuel rail need to be raised a bit. I've got a picture detailing it. In short, it's not hard.
Tip for Option 1 The spot marked with the arrow is where you gotta jack it up yourself. It’s pretty simple, for thickness, just use your common sense.
Option 2 - Using the XT660 throttle body assembly
This one is the trickiest, but it's the one I'm currently running. The XT660 throttle body measures 50mm, it's not small. But if you remove the heating assembly underneath (I heard it's there to deal with cold weather in North America and Europe), it gets a lot smaller. However, even without the heating assembly, there's still a lot of issues you have to overcome to fit the XT660 throttle body on the SR400 FI. Here's what you'll be up against:
A. The intake manifold of the cylinder head The intake end of the SR400/500's cylinder head is way smaller than the XT660's diameter. So here you'll need to pair it with a reducer pipe, and have a physical interface at the cylinder head's intake end. Otherwise, even with the reducer pipe, you can't secure it properly. B. Even with the XT660 throttle body assembly, you'll still need to use the SR400 FI's stock fuel rail. That's because the XT660 throttle body assembly doesn't have a standalone fuel pressure regulator or a fuel pressure regulator port. The SR400 FI's fuel pressure regulator is connected to the fuel rail. But once you connect the SR400 FI's fuel rail assembly with the XT660 throttle body assembly, the height will be a bit too much. This will cause a physical conflict when connecting the fuel line between the fuel rail and the fuel pump. It's doable but you have to be super careful. The best solution is to custom-make a new fuel line to connect the fuel pump and fuel rail. I've got a picture detailing it. Again, be careful with this because it involves fuel. If you really want to go with this, you've got to be extra careful. C. The most important thing: when you’re trying to combine the SR400 FI’s fuel rail assembly with the XT660’s throttle body assembly, because of several physical differences between the two, you’re gonna need to custom order an extension pipe to connect the fuel rail and the throttle body. I strongly recommend bringing both to a CNC for onsite fabrication, because there’s no room for error. We’re talking about high-pressure fuel injection here.
Tip for Option 2 1 The connector pipe in the picture is used to link the fuel rail and the throttle body assembly with the injector. 2 The spot the arrow’s pointing to is for the intake pressure sensor pipe. Connect the SR400 FI intake pressure sensor to that spot. 3 The arrow’s pointing out how to connect the gas pump and the fuel rail after you’ve finished putting it all together.
Option 3 - Using the SR-specific throttle body from Japan's OVER
This is definitely the easiest solution. Physically speaking, it's "almost" completely compatible. But there are still some things you need to watch out for:
A. It's the priciest, seriously expensive. Compared to the XT660 solution, it's like a high-roller's kind of pleasure. B. The diameter is slightly smaller than XT660, but I reckon, unless you're doing some extreme engine mods, it won't make much of a difference. C. The throttle cable position is on the flip side compared to stock, it's on the right, so you gotta be careful how you route the cable. D. Now, this is a drawback. This throttle body can't use the stock TPS sensor because the throttle cable position is different. The rotation direction of the TPS is completely opposite to the stock one. Therefore, the TPS sensor that comes with this throttle body is a custom piece. In theory, you can find its part number, but sadly I haven't yet. So, this is a concern. If for any reason you need to replace the TPS sensor, you might need to hit up the dealer. But I can tell you, the throttle body is a KEIHIN product, and the TPS sensor is also produced by KEIHIN, so in theory, you can look for it from KEIHIN's parts supplier. Why do I mention this? Because a buddy of mine, when using this throttle body, had the TPS damaged due to some unexplained current issue, and that's when he realized this part isn't easy to find. E. This is related to the fourth point. Since the TPS sensor's rotation direction is opposite to stock, there's a step in the throttle body installation manual that instructs you to switch the positive and negative terminals of the TPS sensor connector in the main harness. This step is really a pain in the neck. There's a trick to it, in theory, but honestly, it's d**n difficult. Pushing out the positive and negative terminals from the sensor connector is tough. Before you figure out the trick, this process could waste your whole evening.
Tip for Option 3 The positive and negative terminals of the TPS sensor in the main harness need to be switched (FYI: a TPS sensor usually has three wires, positive and negative provide voltage feedback, and the middle one transmits data.)
Plus, although I don't have the numbers to back it up, I've got this gut feeling that the injector on the OVER throttle body assembly is smaller than that on the XT660. But hey, that's just my sense of things. Still, this doesn't take away from the performance of the OVER assembly—it's got more than enough oomph, no doubt about it.
All the solutions above need the ideal PCV + Autotune setting. From what I see, Autotune is almost absolutely necessary, unless, you have the freedom to use a dynamometer for tuning. Because the XT660 injector size is quite large, with high instantaneous fuel efficiency, so without an ideal fuel map, it would be pretty rough to ride. So, that's why I said you need the Autotune to help with setting the AFR. But the process of PCV + AT is another story, let's not go there for now. Also, please plan the placement of the PCV well, try your best to shield it from vibrations. Any means that could avoid direct contact or provide buffering, you should give it a go, 'cause the PCV is still a small computer.
So there you have it, my ultimate choice for fuel modifications on the SR400 FI. So far, the methods I've tried are: 1 - Stock SR400 FI with XT660 injector paired with stock throttle body (fuel map tuned with Autotune) 2 - SR400 FI upgraded to SR500 FI with OVER throttle body assembly (fuel map tuned with a dynamometer) 3 - SR400 FI upgraded to SR585 FI with XT660 throttle body assembly (fuel map tuned with Autotune)
From my experience, as long as PCV or PCV + Autotune is set up ideally, even the stock SR400 FI can have a pretty sensitive and good response. Pair it with the SP TADAO (Japanese：SP忠男) front exhaust pipe and the performance gets even better.
Last Edit: Jun 19, 2023 9:29:12 GMT -5 by porkhere
You've got this, for sure. Although mastering the way of jetting takes some time to study, the truth is I only started learning about it with the SR400 FI. If you put aside those "tiny" electronics, it really isn't that different. When I get the chance, I'll continue to share more about modifications, especially the tuning or settings of the PCV, which are particularly crucial.
First, let's take a moment of silence for the fact that the old forum just "disappeared". And then it took a full three months to get a "response". Really unfortunate, huh? After losing the old forum, I try my best to come here often, you know how it is...
Now about the performance upgrade for the SR400 FI, I've written quite a lot on this in the past. I'll put it all down again in the hope of enriching our conversations here.
First off, we gotta recognize that the SR400, regardless of the type, always leaves a bit of a bitter taste in the mouth, since it's essentially a "modified" SR500. Actually, if you consider the carbureted SR400, it ain't half bad—once you upgrade the carburetor, it's like the thing finally wakes up. It's just a shame that the fuel-injected version gives many riders a real headache.
So, no matter how folks spin it, I'll say this—the SR400 and the SR500 are apples and oranges in a lot of ways. On paper, the SR400 might seem to have a smidge less torque, a smidge less horsepower, but the difference when you're in the saddle is night and day. That's why I always say, if you got the chance, the means, and the will, making the jump from the SR400 to the SR500 is a solid move. Maybe some wise guy would ask, why not just get the SR500 from the start? The answer's a mixed bag—first off, the SR500 has been out of production for a good while, and secondly, it's not street-legal in some spots. That's why there's always a market for bumping an SR400 up to a 500+.
Alright, let's cut to the chase—how do we save the SR400 FI? I'm sorry for the dramatics here. I gotta stress this—if anyone's happy with their SR400, be it carbureted or fuel-injected, then they're living the dream, really living the dream, no BS, and your wallet ain't gonna be bleeding red.
The first step in improving the SR400 FI is the ECU. I've tried a few solutions, like the PCV coordinator, a small interventional coordinator without an interface, and an air intake temperature sensing stick. To my knowledge, there are a couple more interventional coordinators out there in the world, along with some real professional ECU flashing options. But for now, the only one I can recommend is the PCV. Note, that's the Power Commander 5, not the 6. The 6 is compliant with California's emission regulations. I haven't personally used it, but according to friends who have, the range of adjustments is more limited. Well, it is California legal after all, so I guess that's to be expected.
In fact, based on my experience with ECUs, the best option out there is a flash-tuned unit, like Harley's Power Vision. That thing is incredibly powerful, only surpassed by a full ECU replacement. But sadly, such a thing doesn't exist for the SR400. I do know a flash-tune developer, though. I hope I can pay him a visit this year and see if I can persuade him to make something like that. Considering the number of SR400 FI users worldwide, there's probably some market for it.
So, for now, when it comes to the SR400 FI, I only recommend the PCV. And very importantly, it's best if you add an Autotune to it, probably the AT-200 model. A PCV plus Autotune will let you auto-tune based on the AFR settings you've put in and make trims to the fuel map.
That's step one. But now, I gotta tell you about another unfortunate reality of the SR400 FI that's even worse than its carburetor counterpart. Even if you use a PCV and Autotune, set the perfect AFR, and even adjust the ignition map, sadly, the response just won't be as good as expected. Yes, there's something to blame for this, and the culprit is the fuel injector.
The stock fuel injector for the SR400 FI is actually a small injector meant for a 250cc displacement, the part number indicates that it's the same as the one used in early R1 models and certain WR250s. How fascinating is that? Now about fuel injectors, there's something you should know. Unlike carburetors which are linear, injectors are binary – they're either open or closed, 0 or 1. The principle of injection is that the computer tells the injector how long to spray for. So now you know why the SR400 FI's response is even more sluggish than a carburetor model, this is the reason.
Theoretically, if we need a certain value, any injector, big or small, can meet that value. But the major difference lies in - how long it takes to supply that amount of fuel. So if it's a big injector, the need is met almost instantaneously, while a small injector has to work hard to gradually get there. So here's my second tip for boosting the performance of the SR400 FI: the second thing you need to do is replace the fuel injector. And the prerequisite for this is to have at least a PCV, otherwise the stock ECU won't be able to properly control that injector, and your riding experience will be nothing short of a disaster. How do I know this? Because my friend did just that, didn't heed my advice and rode out on it. It took less than five minutes for me to win a bottle of Heineken.
As for purchasing fuel injectors, I've tested three options so far:
1 - Buy an XT660 injector separately and install it on the SR400's stock throttle body. 2 - Buy an XT660 throttle body assembly (includes injector). 3 - Buy an OVER 46mm throttle body assembly from Japan (includes injector).
I've tried all three options myself and each has its own specifics you've gotta pay attention to. Let's kick off with the first one:
Option 1 - Using the XT660 injector only
Truth be told, I reckon this solution is the most fitting for the stock SR400 FI engine. It's super cheap and the effect is remarkable. Even if you upgrade the engine to an SR595 FI, theoretically, the stock throttle body size should still be okay. I've seen folks in Japan converting their SR400 FI to SR595 FI and still use the stock spec throttle body. But one thing I'm pretty sure of, if you don't change the injector, the engine's responsiveness will be limited by the injector's size. Anyways, without considering throttle body size, using the XT660's injector on the SR400 FI is absolutely feasible.
But since the XT660 injector is physically a bit longer than the stock SR400 FI injector, when you fit the XT660 injector onto the SR400 FI throttle body, the screw locks on both ends of the fuel rail need to be raised a bit. I've got a picture detailing it. In short, it's not hard.
Tip for Option 1 The spot marked with the arrow is where you gotta jack it up yourself. It’s pretty simple, for thickness, just use your common sense.
Option 2 - Using the XT660 throttle body assembly
This one is the trickiest, but it's the one I'm currently running. The XT660 throttle body measures 50mm, it's not small. But if you remove the heating assembly underneath (I heard it's there to deal with cold weather in North America and Europe), it gets a lot smaller. However, even without the heating assembly, there's still a lot of issues you have to overcome to fit the XT660 throttle body on the SR400 FI. Here's what you'll be up against:
A. The intake manifold of the cylinder head The intake end of the SR400/500's cylinder head is way smaller than the XT660's diameter. So here you'll need to pair it with a reducer pipe, and have a physical interface at the cylinder head's intake end. Otherwise, even with the reducer pipe, you can't secure it properly. B. Even with the XT660 throttle body assembly, you'll still need to use the SR400 FI's stock fuel rail. That's because the XT660 throttle body assembly doesn't have a standalone fuel pressure regulator or a fuel pressure regulator port. The SR400 FI's fuel pressure regulator is connected to the fuel rail. But once you connect the SR400 FI's fuel rail assembly with the XT660 throttle body assembly, the height will be a bit too much. This will cause a physical conflict when connecting the fuel line between the fuel rail and the fuel pump. It's doable but you have to be super careful. The best solution is to custom-make a new fuel line to connect the fuel pump and fuel rail. I've got a picture detailing it. Again, be careful with this because it involves fuel. If you really want to go with this, you've got to be extra careful. C. The most important thing: when you’re trying to combine the SR400 FI’s fuel rail assembly with the XT660’s throttle body assembly, because of several physical differences between the two, you’re gonna need to custom order an extension pipe to connect the fuel rail and the throttle body. I strongly recommend bringing both to a CNC for onsite fabrication, because there’s no room for error. We’re talking about high-pressure fuel injection here.
Tip for Option 2 1 The connector pipe in the picture is used to link the fuel rail and the throttle body assembly with the injector. 2 The spot the arrow’s pointing to is for the intake pressure sensor pipe. Connect the SR400 FI intake pressure sensor to that spot. 3 The arrow’s pointing out how to connect the gas pump and the fuel rail after you’ve finished putting it all together.
Option 3 - Using the SR-specific throttle body from Japan's OVER
This is definitely the easiest solution. Physically speaking, it's "almost" completely compatible. But there are still some things you need to watch out for:
A. It's the priciest, seriously expensive. Compared to the XT660 solution, it's like a high-roller's kind of pleasure. B. The diameter is slightly smaller than XT660, but I reckon, unless you're doing some extreme engine mods, it won't make much of a difference. C. The throttle cable position is on the flip side compared to stock, it's on the right, so you gotta be careful how you route the cable. D. Now, this is a drawback. This throttle body can't use the stock TPS sensor because the throttle cable position is different. The rotation direction of the TPS is completely opposite to the stock one. Therefore, the TPS sensor that comes with this throttle body is a custom piece. In theory, you can find its part number, but sadly I haven't yet. So, this is a concern. If for any reason you need to replace the TPS sensor, you might need to hit up the dealer. But I can tell you, the throttle body is a KEIHIN product, and the TPS sensor is also produced by KEIHIN, so in theory, you can look for it from KEIHIN's parts supplier. Why do I mention this? Because a buddy of mine, when using this throttle body, had the TPS damaged due to some unexplained current issue, and that's when he realized this part isn't easy to find. E. This is related to the fourth point. Since the TPS sensor's rotation direction is opposite to stock, there's a step in the throttle body installation manual that instructs you to switch the positive and negative terminals of the TPS sensor connector in the main harness. This step is really a pain in the neck. There's a trick to it, in theory, but honestly, it's d**n difficult. Pushing out the positive and negative terminals from the sensor connector is tough. Before you figure out the trick, this process could waste your whole evening.
Tip for Option 3 The positive and negative terminals of the TPS sensor in the main harness need to be switched (FYI: a TPS sensor usually has three wires, positive and negative provide voltage feedback, and the middle one transmits data.)
Plus, although I don't have the numbers to back it up, I've got this gut feeling that the injector on the OVER throttle body assembly is smaller than that on the XT660. But hey, that's just my sense of things. Still, this doesn't take away from the performance of the OVER assembly—it's got more than enough oomph, no doubt about it.
All the solutions above need the ideal PCV + Autotune setting. From what I see, Autotune is almost absolutely necessary, unless, you have the freedom to use a dynamometer for tuning. Because the XT660 injector size is quite large, with high instantaneous fuel efficiency, so without an ideal fuel map, it would be pretty rough to ride. So, that's why I said you need the Autotune to help with setting the AFR. But the process of PCV + AT is another story, let's not go there for now. Also, please plan the placement of the PCV well, try your best to shield it from vibrations. Any means that could avoid direct contact or provide buffering, you should give it a go, 'cause the PCV is still a small computer.
So there you have it, my ultimate choice for fuel modifications on the SR400 FI. So far, the methods I've tried are: 1 - Stock SR400 FI with XT660 injector paired with stock throttle body (fuel map tuned with Autotune) 2 - SR400 FI upgraded to SR500 FI with OVER throttle body assembly (fuel map tuned with a dynamometer) 3 - SR400 FI upgraded to SR585 FI with XT660 throttle body assembly (fuel map tuned with Autotune)
From my experience, as long as PCV or PCV + Autotune is set up ideally, even the stock SR400 FI can have a pretty sensitive and good response. Pair it with the SP TADAO (Japanese：SP忠男) front exhaust pipe and the performance gets even better.
PLEASE Guys We dont need the 'quote c/w all the pics' Over and Over (bang head); ie, We All Know What is Being Talked About from the original post! It just burns up space and is a drag to scroll through.
Last Edit: Nov 18, 2023 20:00:43 GMT -5 by gcrank1
1981 SR500 lonnggg term cafe racer / 2000 Kaw W650
