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Discussion Starter #1
I’m looking for a cam to fit a stock bore engine. I already have intake, exhaust, reflash, etc. I don’t want to lose a bunch of bottom end. I ride some steep roads in the mountains.

I thought maybe a Yoshimura ST-1M would be a good choice because I’ve read that it adds power everywhere, instead of focusing all of it at the top end like the TB Cam.

The ST-2M looks like it adds more top end with a little bit of loss in the lower rpm ranges. Does the ST-2M work ok in stock bore engines? I can’t find much info about this cam.

Any other cam suggestions? Takegawa maybe?
 

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Discussion Starter #2
Does anyone know if the Yoshimura ST-2M cam would be similar to the TB cam? Anyone?

Just can’t find much feedback about the ST-2M cam.

Thanks!
 

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I'm sure you looked at the dyno charts that yoshimura post on their website. Sounds like you hit the nail on the head as far as power delivery between the two cams.

I don't like the hit to torque and horse power below 8k

Yoshimura ST-2M Cam
 

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Discussion Starter #4 (Edited)
You are correct, I did look at Yoshimura’s dyno results. According to that, they look like pretty good cams. Not really any significant loss over stock in the lower rpm ranges then a pretty good boost up top.

I wish the TB cam wasn't based on a regrind. For whatever reason, I’m not in love with the fact that the base circle diameter is smaller, I guess causing the screws to contact the valves at an angle.

I‘m beginning to wonder if you can trust any of the specs posted by manufacturers regarding lift and duration.

When you look at that chart floating around the Grom forum here, it seems to have different numbers in some cases. The Yoshimura ST-1M cam being one of them.

Honda Grom Cam Research - Google Drive
 

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You are correct, I did look at Yoshimura’s dyno results. According to that, they look like pretty good cams. Not really any significant loss over stock in the lower rpm ranges then a pretty good boost up top.

I wish the TB cam wasn't based on a regrind. For whatever reason, I’m not in love with the fact that the base circle diameter is smaller, I guess causing the screws to contact the valves at an angle.

I‘m beginning to wonder if you can trust any of the specs posted by manufacturers regarding lift and duration.

When you look at that chart floating around the Grom forum here, it seems to have different numbers in some cases. The Yoshimura ST-1M cam being one of them.

Honda Grom Cam Research - Google Drive
Yeah I've been following any and all info cam related lately as thats going to be my next step after finding someone to port my head. I dont care for all my power to be up high. I'm looking more at the ST-1M based solely on the fact that from the dyno numbers appears to follow a similar curve as the stock cam but just a bump in power. The only thing Im not sure about is my intake and exhaust combo and what the ST-1M will do with it.
 

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Discussion Starter #6
Sounds like we are in a similar situation. I feel like I’m at a crossroads. Not sure if I want to go further down the rabbit hole and get a Kitaco Neo 181 kit or do a cam, ported head, and higher compression piston. After you buy a nice ported head, high compression piston, and a good cam, it’s not that much more to get the Kitaco Neo big bore kit.

I’m determined to stay with the stock airbox. I don’t want the additional noise of an aftermarket intake. I did the airbox mod and have been running a BMC panel filter. I’m wanting to adapt the larger Koso connecting tube from the airbox to the stock throttle body. I hope I can find a way to make that work.

Exhaust is the Anodizing Racing exhaust from Amazon (surprisingly a pretty nice exhaust for $80.00). Zero complaints. I may get a Hindle or something else one day.

Running a Cameron Jones Racing reflashed ECU.

I like the looks of a DHM ported larger valve head. Drowsports does a sweet looking CNC ported head that is out of stock and unfortunately only sized for the Koso 34mm throttle body.

Even if I do a Super 125 type build or the Kitaco Neo 181, I really should probably get an ARacer ECU like a Mini 5. At some point, I’m not sure if reflashed ECUs are enough.

Maybe just a cam, new reflash, and trying to adapt the Koso intake tube, would satisfy me for a while.

I already have many other supporting mods. A long list. The bike is way overbuilt, considering it is barely making any more power than stock.
 

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Yeah it does sound like we have a similar end goal as far as power delivery. I was going to go big bore but am concerned about the connecting rod. I figured if I stay 125 I’d be less likely to have to address that part of the engine.

i currently have a dinger built long tube intake (not even sure he makes them anymore, all I see is medium and short advertised), moriwaki exhaust and a DHM reflash. I’m pretty sure my exhaust is definitely the weak link in my current setup. It’s nice and quiet (my intake is way louder) but doesn’t flow as much as other exhaust. I have a hindle on order and will be passing my moriwaki down to my GF.

After that I’m going to look into getting the head ported, high compression piston and a cam then call it a day.

The grom is a money pit, I’m trying to keep my hands off the shovel if you know what I mean.
 

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Discussion Starter #8 (Edited)
Someone told me that David Hugh-DHMotoring, “activ3” on this forum I believe, was working on a way to adapt the Koso tube to the stock throttle body. I emailed him today to inquire when he might have a solution.

David emailed me back tonight with a link to the product on his website. He said he just posted it yesterday.

I ordered one! Perfect timing.

 

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Discussion Starter #9 (Edited)
Yeah Phoenix, the Grom sure is a money pit. I kind of don’t like to think about how much has been spent on this bike. The nice thing is that I do a little bit at a time. It’s fun and pretty easy to work on.

The connecting rod concerns me too. That is why I would probably do the Kitaco Neo kit if I went big bore. Splitting the case might be more than I need to be diving into right now.

Reliability is really important to me. I don’t want a bike that breaks down regularly.

I wonder how hard a high compression piston will be on the motor?

It looks like my intake situation is about to be the way I want it. That DHM adapter with Koso tube should work good. My exhaust may be holding me back too. I like my exhaust though. I like the way it looks, it’s compact, pretty quiet.

I need to decide on a cam next. The Yoshimura is definitely at the top of the list. I just wonder if the ST-2M would be a better choice than the ST-1M?
 

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Im with you on not wanting to split the case. Maybe down the road but Its year round riding here in AZ and I really dont want my bike down any longer than it needs to be. I have an Africa Twin to ride while the grom is down but its not near as fun for screwing around. I want to take the 125 as far as I can before going any bigger.

Connecting rod is still a concern for me too even with a high compression 125. I plan to keep the revs under 10k so hoping it wont put too much stress on the rod. Guess time will tell once I get this all together.

Your exhaust is most likely holding you back but probably not near as much as my current one is. I'm curious to see what switching to the hindle does for my performance. Wondering if Im going to lose some power down low because the hindle is more free flowing. Im thinking the moriwaki is building some back pressure due to its restrictive nature. Guess we'll see what the outcome is next week.

Im leaning heavily to the Yosh ST-1M just so I retain my bottom end. It appears to be the best option for that very task. Maybe someone else will chime in on the subject.
 

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Discussion Starter #11

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Your stock crank shaft is fine with the 125 build and even up to the 170cc build but anything bigger I would go with the Kitaco HD crank/rod plus this upgrade you can not go back down to a 125cc because the cylinder shirts will hit the rod arm.

Your biggest improvement will be the oil catch can to get rid of CCV "Crank Case Pressure and heat", this I consider your best investment to gain max power from your engine. I've been building/testing/blowing up grom engines since the groms came out in 2013-14. Too me this is the key to keep your engine happy. Been there since 2014.

The best 2v engine I ever had was the old BrianS 170, we used re-ground oem cam, we did a duel valve spring setup, ported the head, added valve stem caps to help with the stem contact to the reground cam, we added spacer to the cam chain plunger to increase the tension on the cam chain, the manual adjustable cam chain unit by GFZ is a better choice. For all around ECU I would go with Aracer mini-5, best proven ECU for the common wanna-be grom engine builder.

Good luck on your builds and ride safe. A stock Airbox with the front cover on even with the BMC filter will reduce your HP on the engine, been there I have a open mouth front cover like a shark's mouth and it does make the grom louder but it works for my build, everybody else uses the various after market airbox but when I'm on the road with other groms my grom keeps up with the BBK kit groms or walks away from most of them. Check out some of my old posting from 2014 till now and you will see from 2018 till now I have the same setup with slowly improving the grom from PCV-WB02 to Aracer, sprocket selection, and porting heads, intake tube, and throttle body porting and polishing of butter fly valve and so on, but my biggest saver of my engine has been the Takegawa oil catch can setup and external oil cooler.

Ride safe and ride it like you stole it
 

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Your stock crank shaft is fine with the 125 build and even up to the 170cc build but anything bigger I would go with the Kitaco HD crank/rod plus this upgrade you can not go back down to a 125cc because the cylinder shirts will hit the rod arm.

Your biggest improvement will be the oil catch can to get rid of CCV "Crank Case Pressure and heat", this I consider your best investment to gain max power from your engine. I've been building/testing/blowing up grom engines since the groms came out in 2013-14. Too me this is the key to keep your engine happy. Been there since 2014.

The best 2v engine I ever had was the old BrianS 170, we used re-ground oem cam, we did a duel valve setup, ported the head, added valve stem caps to help with the stem contact to the reground cam, we added spacer to the cam chain plunger to increase the tension on the cam chain, the manual adjustable cam chain unit by GFZ is a better choice. For all around ECU I would go with Aracer mini-5, best proven ECU for the common wanna-be grom engine builder.

Good luck on your builds and ride safe. A stock Airbox with the front cover on even with the BMC filter will reduce your HP on the engine, been there I have a open mouth front cover like a shark's mouth and it does make the grom louder but it works for my build, everybody else uses the various after market airbox but when I'm on the road with other groms my grom keeps up with the BBK kit groms or walks away from most of them. Check out some of my old posting from 2014 till now and you will see from 2018 till now I have the same setup with slowly improving the grom from PCV-WB02 to Aracer, sprocket selection, and porting heads, intake tube, and throttle body porting and polishing of butter fly valve and so on, but my biggest saver of my engine has been the Takegawa oil catch can setup and external oil cooler.

Ride safe and ride it like you stole it
Cisco, would the catch can be beneficial even if I were to stay at 125? Everything I've read seems to be in reference to BBK.
 

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Cisco is just stressing that you vent the crankcase properly. Whether that's into a catch can, or a terminal filter.

I'd agree its useful even with a stock bore build.

In my opinion, the GomFatherz Cam Cover with a hose and filter does wonders, as does the NCY GY6 decompression kit which replaces your dipstick with a hose barb piece that you can run hose and filter to.
 
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Cisco is just stressing that you vent the crankcase properly. Whether that's into a catch can, or a terminal filter.

I'd agree its useful even with a stock bore build.

In my opinion, the GomFatherz Cam Cover with a hose and filter does wonders, as does the NCY GY6 decompression kit which replaces your dipstick with a hose barb piece that you can run hose and filter to.
So I should run both or one or the other? Sorry Im new to this type of stuff.
 

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Cisco, would the catch can be beneficial even if I were to stay at 125? Everything I've read seems to be in reference to BBK.
If you look at your stock engine setup on the right side crank upper there's a tube outlet with a rubber hose that normally goes to your air box, this is to help vent out the pressure in the crank case and also capture oil mist, as you go up in compression "BBK kit" " adding more after market parts and running at high RPM heat builds up inside the crank along with pressure and to keep the engine from failing the excess pressure needs to be vented off some how or else you'll get oil puking out your engine via the airbox, "oil coming from the vent hose to the airbox" when this happens you'll have loss of oil and less cooling which will cause engine failure. If I had know that from the beginning I think I would have stuck with the BrianS 170 and the Finbro 183 2V engines but now that I'm up to the 181-4v engine I'm slowly learning what works with those type of engine and what engine material works best with the grom.

Hint, cast piston is not as great as forged piston, all my engine failures on my 181 engine has been cast pistons coming a part.

A adjustable cam chain unit is a must if you are planning to ride in the upper 6-11K rpm range and also the Koso cam chain arm kit with the metal sprockets.

Your drive chain should be replaced with a o-ring style chain, it will last longer and EZ to clean and oil.

sprocket selection is a must to learn, use gear commander because it will give you the approx amount of speed you'll get with the F/R sprocket teeth setup and rear tire size setup using a stock 4sd transmission. I use gear commander as a guide of how fast my grom will go with my 5 sp transmission.

Another good upgrade is the 4th bearing support that goes on the fly-wheel side of the crank and also the Kitaco clutch side cover.

Good luck and ride it like you stole it.
 

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Discussion Starter #17 (Edited)
Yeah Cisco, I’ve read through hundreds of threads here on the forum. I appreciate your contributions and that you are not afraid to try new stuff to see what works. Sometimes you blow it up, pick up the pieces, learn something, rebuild, and move on.

It sounds like if the crank case pressure is too high, it starts working against the piston from the bottom side. Does the stock vent tube just not provide adequate ventilation?

I think for now I’m just going to add the DHM adapter, Koso connecting tube, Koso outer snorkel, a camshaft, and new reflash. I’ll see how I like things after that. If I still want more power, I’ll add a Kitaco 12.2:1 high compression piston, a DHM ported larger valve head, aRacer Mini 5, Hindle exhaust, etc. I’ve just got to figure out which cam.
 

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Discussion Starter #18
Ended up ordering the Yoshimura ST-2M cam.

I need to get my ECU reflashed again now. I probably need to step up to the aRacer Mini 5 soon, but good grief it is expensive when you add in the AF-1.

I hope I like it. Looks like you don’t really lose much at all on the bottom end and midrange, but gain quite a bit up top.
 

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Ended up ordering the Yoshimura ST-2M cam.

I need to get my ECU reflashed again now. I probably need to step up to the aRacer Mini 5 soon, but good grief it is expensive when you add in the AF-1.

I hope I like it. Looks like you don’t really lose much at all on the bottom end and midrange, but gain quite a bit up top.
Let us know what you think of it when you get it installed. I’m still shopping for a cam myself.
 
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