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Discussion Starter · #1 · (Edited)
I recently added the chimera cold air intake. I already have some cheap Kemimoto Exhaust - it sounds great. The exhaust was perfect. However, while I knew the chimera would change the sound - I didnt expect it to be that much.

I feel as if I lost a bit of pep in mid mid and low range as well.

Anyone swap back to stock or Im missing the”key ingredient” to bring this all together? So that these two forces combined, and whatever else, will give me the pep and top end I desire. Im also not sold on the sound of the chimera over the sound of the Kemimoto exhaust.

Yes, Ill probably add 2 teeth to the rear of my bike. I dont want to lose too much top end.
 

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Intakes make as much, if not more sound than the exhaust unless you run a wide open pipe that doesn't have packing or chambered design.

If you want more mid to low rpm power you want a longer intake.

Lastly, intake and exhaust mods together you'll want to address tuning of the ECU to make sure you are getting the right amount of fuel flow for maximum performance.

ECU flash would be easiest.
 

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Discussion Starter · #3 ·
I understand the need for a proper fuel to air mixture. Flashing the ECU vs a PCV or other similar software, Im sure would be ideal. I just wasnt expecting this type of overall change.
What is the fuel mod system that constamtly monitors air and fuel mixture as you ride it?
 

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Discussion Starter · #4 ·
To be honest, with the chimera it sounds like the bike is underwater under throttle. I dont like how it sounds and so far Im not picking up any substantial power difference.
 

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I understand the need for a proper fuel to air mixture. Flashing the ECU vs a PCV or other similar software, Im sure would be ideal. I just wasnt expecting this type of overall change.
What is the fuel mod system that constamtly monitors air and fuel mixture as you ride it?
ECU uses the narrowband O2 sensor to monitor. The fueling needs to be close to optimal for proper adjustment/operation.

I'd get a flashed ECU or have yours flashed to get the close baseline setting that the narrowband O2 can handle the rest.

You can also use the stock airbox and get a better flowing filter plus bigger diameter tube that connects to the throttle body. Less noise but more capability to make power.
 

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You can check out my modified Grom airbox in other posts of mine. There is a thread over in the Monkey forum covering it. I posted lots of pictures. It looks factory. I’m running the Koso outer intake tube, a BMC filter, Koso connecting tube, and DHM adapter. I hate that loud reverberating sound of an aftermarket intake. Mine has none of that sound, yet it flows really well. I’d be surprised if the Chimera flowed much better at all.
 
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Here is the Monkey thread where I was discussing my airbox setup. You can read the whole thread or skip ahead to post #32. Posts #37 and #38 are where I posted photos. This is one option you might consider if you are unhappy with the Chimera intake.

 

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Discussion Starter · #8 ·
Here is the Monkey thread where I was discussing my airbox setup. You can read the whole thread or skip ahead to post #32. Posts #37 and #38 are where I posted photos. This one option you might consider if you are unhappy with the Chimera intake.

This is really awesome, I will take a look at it and see if I can’t adopt it for for my GROM thank you.
 

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Here is the grom air box mod thread aswell. Done on the OG but would be the exact same as SF except you don't need to drill out vent holes in front of where the snorkel is.
 

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I originally started with the basic airbox mod of removing the small section of tubing behind the air filter and running a BMC air filter. I guess it helped some. Probably not much, because you still have that tiny stock connecting tube down to the throttle body from the airbox.

Taking the little bit of extra effort to install the huge Koso outer intake tube and then the larger Koso connecting tube with the DHM adapter takes it all to whole new level. Pretty close to an aftermarket intake. I’m planning to port (back cut) the throttle body soon to really finish this off right. This will completely smooth the transition from the connecting tube into the throttle body increasing velocity.
 
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You can also save a few bucks on the koso intake tube and fab your own with a Radiator Hose too. The go to seems to be a dayco 71863. believe it's a lower rad hose off of a 96-00 Plymouth voyager? Could be wrong on what it's from though. Just cut it down to more or less match the factory intake tube bend. I've got this sitting in my shed waiting to be put on. I'm gonna put a few more miles on my 2018 grom then do the basic airbox mod and then change it to the rad hose with a v-stack behind the filter to see if my butt dyno can really tell any difference. After that I'll be putting in an EFIE as well to help with the AFR. Rather than spend way more on a pcv or the like.
 

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I got a second, reflash for My ECU after installing the Koso tubes. I think it changes the air flow enough to justify it. I had also just installed the Yoshimura ST-2M cam, so a different tune was needed anyway.

I’ve yet to see a real good way to attach the radiator hose to the airbox. Maybe there is a good way, but the ones I’ve seen were terrible. They appeared to leak air like crazy. An intake leak could lean out your AFR.

I’d say the radiator hose easily moves plenty of air, but it is the connection to the air box that I never have liked. The Koso tubes and DHM adapter are about as good as a stock airbox can get. Throw in a BMC, DNA, or maybe the Koso filter, and it makes for a nice setup. If you want to take it all the way, port the throttle body with a taper (back cut).
 

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Nothing some good epoxy and attention to detail can't seal up ;) I don't plan on going with a cam for a good long while so the $50 efie to my door should do me well enough until then. Once I have enough spare change laying around to justify a cam I'll be going with a high compression piston and a good tune for sure though and then I'll be able to justify a full intake too.

I have a velocity stack for a Toyota Ae86 Coming on the slow boat. Should be close enough to the right size I can get it into the rad hose with the flange cut off. fingers crossed Cheaper than buying a 3D printed or the Brock's v-stack, and if it doesn't work I just won't use it.
 

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Start at post #88 and it explains the efie with some good testing involved as well.
 

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I originally started with the basic airbox mod of removing the small section of tubing behind the air filter and running a BMC air filter. I guess it helped some. Probably not much, because you still have that tiny stock connecting tube down to the throttle body from the airbox.

Taking the little bit of extra effort to install the huge Koso outer intake tube and then the larger Koso connecting tube with the DHM adapter takes it all to whole new level. Pretty close to an aftermarket intake. I’m planning to port (back cut) the throttle body soon to really finish this off right. This will completely smooth the transition from the connecting tube into the throttle body increasing velocity.
People neglect to realize that the outer tube of the airbox is actually a measured part of the intake system. There's a lot to be gained by conservatively modifying the stock airbox. I would also be skeptical of taking too much off of the throttle body. Smoothing out the outer lip so the air has a smoother transition I could see helping to some extent, but I'd speculate that most of these guys that are opening up and tapering the bore all the way back to the butterfly are taking a lose in the low end for minimal gains up top.
 

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People neglect to realize that the outer tube of the airbox is actually a measured part of the intake system. There's a lot to be gained by conservatively modifying the stock airbox. I would also be skeptical of taking too much off of the throttle body. Smoothing out the outer lip so the air has a smoother transition I could see helping to some extent, but I'd speculate that most of these guys that are opening up and tapering the bore all the way back to the butterfly are taking a lose in the low end for minimal gains up top.
Do you think tapering the bore to the butterfly is ok as long as your aren’t enlarging the bore itself at the butterfly? I would think there is a difference.

Yeah, maybe the fact that my intake is long is why I didn’t notice any loss in low end performance after installing my Yoshimura ST-2M camshaft.

I’ve been emailing with Cameron Jones about the throttle body work. I’m waiting to hear back from him again.

He offers a back cut, which tapers the bore and he also offers an over-bored throttle body which he exchanges for your existing throttle body. I assume the over-bored version is bored out at the butterfly to about 26mm from the stock 24mm.

I’m probably just going to do the back cut version to smooth the transition out. It is currently a terrible transition, but you could say that about all aftermarket intakes too. This should, in theory, keep the air from tumbling, increasing velocity. I want to combine that with some head port matching, just to clean up the flow. I guess it would be ok to match my exhaust port with the inside diameter of my exhaust too? What do you think?

If I remember correctly, the Venturi effect increases velocity, but typically a compressible fluid’s density would only increase if upstream pressure was increased. This would explain why turbos and superchargers have their benefits. I can’t help but wonder if there is a point where velocity is increased, but density of the air/fuel charge is decreased so much that you have gained nothing or even lost performance. It seems there is likely a sweet spot.

I ordered DHM titanium valve spring retainers to install while I have the head off. I may have Cameron Jones bump the rev limiter up another 250rpms. I’m running titanium tappet adjuster nuts already. I’m told that the stock valve springs can be pushed all the way to 11,000rpms once the titanium retainers are installed. My rev limiter is currently set at 10,000rpms. I think setting it at 10,250rpms or 10,300rpms would be a little more on the conservative side, but could continue to take advantage of the ST-2M cam’s high rpm performance. It really starts pulling above 9000rpms, but is quickly stopped at 10,000rpms by my rev limiter.

I welcome anyone’s thoughts on any of this.
 
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Do you think tapering the bore to the butterfly is ok as long as your aren’t enlarging the bore itself at the butterfly? I would think there is a difference.

Yeah, maybe the fact that my intake is long is why I didn’t notice any loss in low end performance after installing my Yoshimura ST-2M camshaft.

I’ve been emailing with Cameron Jones about the throttle body work. I’m waiting to hear back from him again.

He offers a back cut, which tapers the bore and he also offers an over-bored throttle body which he exchanges for your existing throttle body. I assume the over-bored version is bored out at the butterfly to about 26mm from the stock 24mm.

I’m probably just going to do the back cut version to smooth the transition out. It is currently a terrible transition, but you could say that about all aftermarket intakes too. This should, in theory, keep the air from tumbling, increasing velocity. I want to combine that with some head port matching, just to clean up the flow. I guess it would be ok to match my exhaust port with the inside diameter of my exhaust too? What do you think?

If I remember correctly, the Venturi effect increases velocity, but typically a compressible fluid’s density would only increase if upstream pressure was increased. This would explain why turbos and superchargers have their benefits. I can’t help but wonder if there is a point where velocity is increased, but density of the air/fuel charge is decreased so much that you have gained nothing or even lost performance. It seems there is likely a sweet spot.

I ordered DHM titanium valve spring retainers to install while I have the head off. I may have Cameron Jones bump the rev limiter up another 250rpms. I’m running titanium tappet adjuster nuts already. I’m told that the stock valve springs can be pushed all the way to 11,000rpms once the titanium retainers are installed. My rev limiter is currently set at 10,000tpms. I think setting it at 10,250rpms or 10,300rpms would be a little more on the conservative side, but could continue to take advantage of the ST-2M cam’s high rpm performance. It really starts pulling above 9000rpms, but is quickly stopped at 10,000rpms by my rev limiter.

I welcome anyone’s thoughts on any of this.
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Imo the throttle body is just an extension of the Intake manifold, and to taper the bore out to its maximum limits would be like trying to port match a 34mm throttle body onto a 24mm manifold. Sure, the tb can flow more air more efficiently, but its gonna cost power on the low end and it's still not going to flow as well as if the TB was mounted on a matched intake. That bore in the throttle body was left that way by honda because it helps to increase velocity before the butterfly.. Now if your a legitimate racer like Cameron Jones who probably rides at higher rpms on a track you might see gains, but for most of us who ride street I think it would negatively effect anything below 8k rpm. But this is all just my opinion and I very well could be wrong, but I would love to see some dynographs showing before and after the modified TB install. Now if we were to go forced induction, that would be a totally different story!

As far as the exhaust port goes all I did was match it to the header and cleaned up the casting flaws from between the back of the valve seat up and out the port. Blending valve seats (int/exh) and matching the intake manifold to your head and TB seemed to be the worst areas on the stock setup in my case.
 

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I also went with Ti retainers and have had zero valve float issues at 10k, or when holding it over 9k for extended periods of time. Imo the dual springs are just increasing parasitic driveline forces and should only be used in the most extreme of engine builds.
 

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Sorry for the thread Jack OP! Seriously though buy both the intake and outer tube from Koso (takegawa makes an outer as well) if you can't live with the intake noise.

Lots of people here swear by the rad hose mod too, personally I use a piece of 32mm central vaccum hose and am happy with the results when compared to the stock intake tube.
 

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Discussion Starter · #20 ·
I’ll be giving something a try. She is getting her forks rebuilt and still waiting for other goodies. So I’ll be getting after it soon.
 
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