[426john]

If you mod the standard airbox , benefits , might be incremental , but small.
Expect a very small amount of low RPM improvement.
Maybe a small incremental increase in induction noise.
But in doing so , your building the foundation , with other performance mods , to improve both power output & torque .

 

[426john]

I picked up a spare stock air box for my 2020 Grom. I have both Koso tubes and DHM spacer. I’m going to mod the box and install it. Does anyone have this mod on an otherwise stock bike? What can I expect I specifically I am wondering about noise and if I will lose any low end torque. My plan is to do this first then if I like it to add the tb cam. I have it left over from a 2020 monkey I had. If I remember correctly I think the cam lost low /mid torque and woke up at higher RPM’s.

Depends on the spec & characteristics of your camshaft.

 

[426john]

How did you get on ?

 

[426john]

I finally got to check out the mod. 50 miles tonight. I want to be as accurate as possible for future readers that might consider this mod. My bike is stock except I am running 15/35 I added a tooth to the rear because there just wasn’t enough torque to get going with stock sprockets and I couldn’t pull 3rd gear past 8.25k, 4th was even worse and pulled to 7.5k max. I do have the 12oclock speedo healer installed and dialed in. I rode the same roads I’ve been riding for years and know what to expect from the setup before this mod. First let me comment on the noise. I hate induction noise and removed a chimera intake after a 5 minute ride because it was too loud. This was a pleasant surprise. Yes it is louder than stock but if you didn’t know what stock sounds like you wouldn’t know it was louder. I could hear it over my stock exhaust but the wind noise in my helmet was louder. About as loud as a cat purring vs not. I have no problem keeping this mod on for good. As mentioned earlier I am 1 tooth shorter than stock for a tiny bit more torque Below 5k. With this mod I would say I lost about half of that gain. I can live with it but may go up to 36 to get it back. I was able to pull 3rd gear to 9k @56 mph. That’s a little more than pre mod. Fourth was still below 8k but there was no loss of performance. My bike reliably gets me to 53 mph sitting straight up. If I need 55 I have to tuck. After the mod I was able to go 54 mph sitting up. That’s a huge improvement when I only hope to make small gains. Top speed in a tuck was 63. I haven’t tuned the ecu for this ride. I’m going to install a Tb cam next and get a stage 2 ecu tune. The cam will lose a bit of low end torque but wake up around 6k. By adding another tooth in the back i hope to compensate for the cam profile and I think I may be able to hit the limiter in 3rd and pull 4th higher. I don’t expect any more noise from the tune so this may be the 55 mph with staying power I’m looking for. Parts are on order.

Great news , i have another bike , with air box removed , but the grom i want to keep that refinement.

 

[426john]

I did take the next step and installed the Tb cam and DHM ecu stage 2. 57 mph sitting upright wasn’t a problem and 3rd gear did 57 before the rev limiter so I do see the improvement with the cam and ecu but idle seems to hang up above 2k and I don’t like that. I’ve cleared and reset A few times but after 10 or 15 miles the idle issue pops back up. There is no annoying noise and I can feel a slight decrease in torque so if I keep this setup I will add a tooth to the rear I emailed David asking about the idle issue. I want to solve that first.

Defiantly some advantages to keeping the stock air box , its very water proof , keeps induction noise down to a minimum , it can , help improve torque & here in Spain its essential for the safety check every year.

The hanging idle , is certainly a pain , but I'm sure , some further calibration & consulting with David ( DHM ) will result in a better , settled idle.

Thanks for your feedback & lets hear about your final setting , cheers.

 

[426john]

I have been very happy with 14 / 34.
One down on the counter sprocket is equal to 2 on the back.
I have found the sweet spot with this set-up.