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I got a 2015 Grom, 5400 Miles, equipped with a mnnthbx intake(I don't do metal intakes, heat transfer does not agree with me), DHM ecu reflash, Grom Fatherz speed spacers, and cheap high mount exhaust. Besides a cam or changing sprockets, what else could I do to gain some more top speed and top end power?
 

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I'm running high mount exhaust, Mtake, CJR flash and tb cam. The cam is definitely worth it for top end, I'd do that next. You did say besides cam though. Check your tire pressures?

I think your next step is high compression piston or bbk etc.

I'm done with engine mods now myself. Diminishing returns in my mind as everything starts to get more expensive and reduces reliability...
 

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I'm running high mount exhaust, Mtake, CJR flash and tb cam. The cam is definitely worth it for top end, I'd do that next. You did say besides cam though. Check your tire pressures?

I think your next step is high compression piston or bbk etc.

I'm done with engine mods now myself. Diminishing returns in my mind as everything starts to get more expensive and reduces reliability...
That's honestly my concern. Reliability, cause I beat the hell out of it day in and day out.
 

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Aftermarket cams are great if you constantly pin the throttle and run your engine at redline all the time. But they're not so good for regular daily transportation riding, because in order to gain high rpm horsepower you have to give up low rpm torque. A slower turning engine that pulls strong at low rpms without lugging is more reliable and lasts longer than a high redline screamer.

For reliability and convenience I also run a self tuning ECU that never needs reflashing so I can make all the changes I want any time I want. The gas mileage always drops for the first fill up after making any changes as it's learning the new operating parameters, and then pops back up to normal by the next fill up. A high torque slow turning engine also gets really good gas mileage. Summer average is 145+ mpg and Winter average is 132 mpg.
 

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Convert 145 Miles / Gallon (US) into Kilometers / Liter
61.6458375875


61,6 KM/L AVERAGE



It's a lie.
Honda certifies 134 miles per gallon for a stock Grom, which converts to a little under 57 kilometers per liter.. Here are the factory specs:


I get a little bit more gas mileage than a stock Grom by modifying the engine to get more low rpm torque. I also lightened the bike 21 pounds down to a 208 pound curb weight, and I weigh 138 pounds. Add about another 10 pounds for clothes helmet and any extras and my combined bike and rider weight is under 360 pounds. This is LESS than a Honda CBR300R bike ALONE. Bike weight is why a Grom gets DOUBLE the gas mileage of a 300, which is a PIG.

86181


I'm just a regular daily transportation rider so my riding style is totally different from everyone else. My engine pulls really good between 3,000 to 6,000 rpms because I modified it to do that. So I don't need to wind out the engine or pin the throttle just to get the bike moving.

One mile per gallon does equal .425144 kilometers per liter, so you're right on the math. ;)
 

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port the intake port, port and polish the exhaust port, port match the I/D of the intake pipe and the exhaust pipe, open up the intake port to about 26-27mm and do the same for the inlet tube and plastic spacer and polish the inside of the inlet tube. Port the throttle body and polish the butter fly valve.

take the intake and exhaust valve and polish the stem and add a duel valve spring and also do a valve lapping.

Yes added wt loss on the Grom and the rider will help out the grom.

good luck and ride safe and ride it like you stole it.
 

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Discussion Starter #13
port the intake port, port and polish the exhaust port, port match the I/D of the intake pipe and the exhaust pipe, open up the intake port to about 26-27mm and do the same for the inlet tube and plastic spacer and polish the inside of the inlet tube. Port the throttle body and polish the butter fly valve.

take the intake and exhaust valve and polish the stem and add a duel valve spring and also do a valve lapping.

Yes added wt loss on the Grom and the rider will help out the grom.

good luck and ride safe and ride it like you stole it.
I planned on port and polish but that's when I said screw it and dig into the head along with cam, valve upgrades and such. Its seeming like I did the most I can with what I got besides shedding weight but even then, its not much of a gain. Thanks
 
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