Power Now! MXR's VHM Cylinder Head & Pipe Combo Test
What's up my people! I hope your Monday has been nothing short of amazing so far!
I'm wearing a particularly large shit-eating grin today because, as promised, I threw down some moto's with the new 250SX mods yesterday!
For those just joining in, I own a 2017 KTM 250SX that I have been tweaking over the last year/ year and a half and it just keeps gatetting better.
So, let's get into it!
A fresh top end was installed along with the VHM & P.C. pipe. 4 heat cycles were completed before riding the bike.
Mods on this bike before the addition of the VHM Cylinder Head w/ MX Insert & P.C. head pipe:
-Moto Tassinari V4R Reed Cage
-Pro Circuit R-304 Silencer (with stock head pipe)
-49 T rear sprocket (50 stock)
-I'll leave the bling-bling out of this blog for now
THE VHM HEAD (with "MX" insert):
Look, I know I said I'd leave the bling-bling out of this blog BUT COME ON! The gorgeous gold hue of the VHM head just slaps you in the mouth right off the bat. I love the way it looks. It's am mini work of art.
For a lot of us, that's enough to seal the deal. I am no different than a lot of you & I have dropped senseless coin on plenty of shit that may have even made me slower when I was younger & understood less about bikes/ how they work/ etc.
However, I am happy to report that the VHM head works quite well!
Being older & smarter allows you to hit the bling and the zing? with the same dollar!
The VHM Head also comes with 3 insert options. The shell of the head is exactly that, just a shell. You need the insert to use the head.
You can choose from:
-An "MX" insert (tested)
-An "SX" insert
-A blank insert that you can have an engine builder tuner cut to suit your needs. I'm not that guy.
FIRST LAPS. Pay Attention, Lectron Owners:
At first I was a bit discouraged when the bike bogged & surged erratically off the bottom, then literally exploded to life out of nowhere. It's hard not to be when we're so accustomed to "gimmie now" these days, but that's reality!
What does it mean? Well, like adding a pipe to a bike, there's usually some jetting or mapping changes that follow. Especially if you want the most out of your investment.
The VHM Head was no different.
Thankfully, the Lectron is SO easy to adjust. It's one of the reasons I love it and decided to sell them after my initial purchase. The thing has no jets, doesn't care much about elevation or temp changes, what pipe you're running and so on. They come pre-set for your machine from the factory.
You can adjust: your idle, your "low end" fuel delivery with the flick of the wrist and lastly, your "high end" fuel delivery externally.
Here's the take home message for the Lectron owners: The bike was LEAN off the bottom. Soft/ weak bottom end followed by a violent surge is your indicator. You need more fuel off the bottom.
In this case & to adjust this w/ a Lectron, you simply turn your metering rod clockwise to "richen" that bottom end circuit.
I started by "adding" fuel, just .25 turn richer and gave it a go. Better but still far off the mark. the engine was rattling and making sounds you really don't want to hear as they indicate DAMAGE will follow if untended to. Lean death rattle...
Another .25 turn.... yeah baby, the bike is starting to level out and pull hard off the bottom again. I was so satisfied by this that I was able to complete the whole 20 minute moto and "listen" to the bike through the RPM range.
I had hopped onto my other bike during moto one after a few shitty laps on the 250SX, knowing it wasn't ok to ride at that moment. Needless to say I was pumped as positive feedback was present after an adjustment.
SO, HOW DOES IT RUN??
To answer your question, quite honestly, the bike shreds! It has much more HIT off the bottom than it had previously.
This is great because the bike had very poor over-rev when it was new. This is what prompted the 49 tooth rear sprocket.
The 49T allows you to stretch the bikes RPM range out but there's always a trade, and that would be giving up some bottom end in this case. It's not a ton. The 49T is a needed & positive change. But, I am not a ultra-skilled 2 stroke rider & you need to be prepared to keep the bike on the pipe a bit more when going to taller gearing, generally speaking.
The VHM put the grunt back where I lost it from the 49T. That's great because I did not feel a loss in over-rev that I gained from the taller gearing!
Overall it is angrier, snappier & more willing to blast out of turns or up hills.
I intend to play with the "high end" fuel circuit next, to see if I can coax a little more over-rev out of the bike. I will likely try a bit richer a setting on the "low end" too, until it starts to produce a negative effect (too rich).
For now, a great baseline ended up being one-half (.5) turns richer on your Lectron metering rod (clockwise). DON'T FORGET TO RE-POSITION THE FLAT SIDE OF YOUR LECTRON'S METERING ROD TOWARDS THE ENGINE WHEN YOU'RE DONE!!!!!! You dummy! Haha.