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Squish and the Pursuit of Optimal 2 Stroke Engine Performance


ThumperTalk

Nobody can deny that 2 strokes are in the midst of a revival. While professional MX is still dominated by 4 strokes, the simplicity, lightness, & character of 2 strokes makes them dominant in the off-road world. Because of this, we’re seeing a resurgence at local races, events like RedBull Straight Rhythm, and those riding just for fun.

Recently, we had a chance to talk with Matt Denecke, a die-hard 2 stroke rider & owner of  Apex Technical Innovations (ATI), a small but passionate manufacturer of innovative billet cylinder head kits based out of Faber Virginia. Apex cylinder heads are designed to have increased combustion efficiency and feature interchangeable domes that allow riders to tailor power characteristics to suit various riding conditions.


TT: Matt, thanks for taking the time! What’s up with your 2 stroke cylinder head kits; are they just another high compression option? 

ATI
: Our heads are much more than a high compression head. In fact, many of our domes are lower compression than the stock heads they replace. The goal with our heads is to increase combustion efficiency to get an all around healthier running engine. There are several aspects that we optimize, these include the squish clearance, squish velocity, compression ratio, the overall shape of the combustion chamber, etc. The end result is a quick, complete deflagration that uses as much of the fuel available without giving it a chance to detonate.
 


TT: What benefits should riders running an Apex head expect?

ATI
: While more power is certainly a benefit of these heads, it goes beyond that. Carbed models benefit form much more consistent jetting, 6000ft elevation gains and 60℉ temperature swings without changing jets are a huge plus with these setups. Usable power is also key. We noticed particularly with TPI models the throttle response does not necessarily feel connected to the response you get from the engine; there's a bit of hesitation off idle at low throttle openings, then the torque comes in as the engine builds some momentum. Our XC dome adds to the smoothness of the stock bike by adding torque in this area and giving a more linear response to throttle inputs. More control, more traction, and less stalling are what the user would gain. More detonation resistance is another benefit, along with most users reporting increases in fuel economy, particularly on carbed models. Oh, you want arm ripping power? We can get you that too, and everything in between!


TT: How do the different domes change the power characteristics? 

ATI
: We change several aspects of the combustion chamber design to give the unique power characteristics of each dome:

The SX dome will have the most aggressive power. Hard hitting low to mid with the most peak power and torque. It generally works well for supercross, arenacross, aggressive woods riding, general motocross, and high altitude. 

The MX, or MXC in the case of the 300, is designed for linear power with an emphasis on top end and overrev. It is smoother than the SX but more aggressive than the XC, and revs the fastest. It generally works well for desert riding, general motocross, flowy woods, and play riding.

The XC dome is designed for smooth, linear power with an emphasis on low end luggability and traction. It is best suited towards enduro, single track, technical hill climbs, slick conditions, or for anyone wanting a smooth, torquey response. 


IMG_4056.JPG
 Interchangeable combustion chambers (domes) allow riders to dial in the power characteristics to suit their riding style & conditions.
 

TT:  Can I just have my OEM head cut for the same benefits? 

ATI: You can have your stock head cut, but beware of who you go to. We offer OEM head machining services, which use the same CNC precision as our billet heads. While generally you will see improvement with a basic manual lathe head mod, there’s more to it than “what compression ratio do you want?” You also miss out on the extra cooling and the interchangeability of the billet heads which is a big plus in my opinion.

TT:  How will these work with a TPI model? 

ATI
: Long story short is these heads are designed to get the most out of the stock map without a re-flash. The combustion efficiency allows the head to burn as much of the available fuel as possible, which pairs well with the generally lean stock map. We recommend making sure you have the most recent dealership updated OEM map (Apex head or not). These are KM557EU2125102 or KM557EU2125103. For those interested in having ECU’s re-flashed, we are in the process of developing our own maps.

 

MG_7072_50.jpg
TPI 2 stroke power delivery can still be tailored to suit rider preferences (Husqvarna TX300i pictured).

 

TT:  How will these heads affect reliability? Do they require race gas?

ATI
: These heads were designed with pump gas in mind. Generally MX and XC domes are 91 octane friendly (US AKI rating) and SX domes are 93 octane friendly. Over 2000 ft altitude the SX dome is 91 friendly as well. All of our standard 125cc and smaller domes are safe on 91. For those who want to run race gas or are at high altitude, we have custom setups available or can make new custom setups to fit your needs.
 

TT:  What models do you support now and what's on the radar?

ATI: In addition to these KTM/Husq/GasGas 300 heads, we also have heads available for the YZ250, YZ250X, YZ125, YZ125X, RM250, Beta 125RR and KX85. We are currently working our way down the KTM lineup and hope to have heads available for all of their full size bikes by the end of the year. We also have YZ85 and CR250 heads in the works, along with a few other projects to look out for.
 

Brandon Ricks - IMG_2742.1.jpg
Apex XC head making a 2006 YZ125 more competitive in the Open Vet Class.


TT: Matt, the floor is yours. What else would you like riders to know about Apex and its products?

ATI: I think the big thing I want to express to riders is how important finding the right power delivery is to them. Just like having your suspension set up for your weight and riding conditions, having an engine that works with you instead of against you is a much more enjoyable riding experience. We work very hard to make sure each customer gets exactly the setup that will benefit them the most for their specific riding style. Pair that with increases in peak power and torque along with almost eliminating jetting changes and you're getting a ton of benefits with one bolt on part.

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If you have questions for Matt Denecke at Apex Racing, tag him in the comments section below using @Matt at Apex Racing

 

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@Matt at Apex Racing if you get a OEM head cut/modified, is just the squish adjusted, or squish adjusted and bowl shape modified?  Let’s assume a 2018 KTM  300 XC (Carb) bone stock used for fast woods riding racing at 1200 feet ASL

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10 hours ago, mmc205 said:

@Matt at Apex Racing if you get a OEM head cut/modified, is just the squish adjusted, or squish adjusted and bowl shape modified?  Let’s assume a 2018 KTM  300 XC (Carb) bone stock used for fast woods riding racing at 1200 feet ASL

The squish would be adjusted as well as the combustion chamber CNC machined to match the riding conditions its being used for. For fast woods, the chamber would look noticeably different.

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5 hours ago, RedmistNZ said:

@Matt at Apex Racing

I am interested in the CR250 ('06) version. Extra cooling over stock would help in the slow stuff.

do you ship internationally ?

That's a model we hope to have soon, we do ship internationally

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