{"product_id":"synchrotech-k20-6-speed-mainshaft-civic-si-rsx","title":"Synchrotech K20 6 Speed Mainshaft for 06-11 Civic Si\/DC5 RSX","description":"\u003cul\u003e\n\u003cli\u003eFactory Ratios, No Change In Driving \u003c\/li\u003e\n\u003cli\u003e3.266 First, 2.13 Second \u003c\/li\u003e\n\u003cli\u003eComplete Mainshaft Assembly Meeting OEM Specs \u003c\/li\u003e\n\u003cli\u003eCompatible with DC5 RSX and 8th Gen Civic Si \u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003c!-- split --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli\u003e\u003ca class=\"active\" href=\"#Description\"\u003eDescription\u003c\/a\u003e\u003c\/li\u003e\n \u003cli\u003e\u003ca href=\"#VehicleFitment\"\u003eVehicle Fitment\u003c\/a\u003e\u003c\/li\u003e \u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\n\n\u003cli class=\"active\" id=\"Description\"\u003e\n\u003ch3\u003eSynchrotech K20 6-Speed Mainshaft (SG-K213-MS)\u003c\/h3\u003e\n\n\u003cp\u003eThe mainshaft carries first and second gear, and on a K20 6-speed those are the two gears taking the worst of everything. Launches, hard 1-2 shifts, and the highest torque multiplication in the box all land here. If yours has been damaged, or you're building a transmission properly from the case up, this is the Synchrotech replacement, built to OEM ratios with materials and tolerances meant to outlast the factory part.\u003c\/p\u003e\n\n\u003ch4\u003eSame Ratios As Stock\u003c\/h4\u003e\n\n\u003cp\u003eWorth saying plainly, because it's the first question people have. This runs a \u003cstrong\u003e15-tooth 3.266 first\u003c\/strong\u003e and a \u003cstrong\u003e23-tooth 2.13 second\u003c\/strong\u003e, which are the factory ratios.\u003c\/p\u003e\n\n\u003cp\u003eThat means the car drives exactly as it did before. Same gearing, same shift points, same speeds in each gear, no tuning adjustments and no relearning the car. You're replacing a damaged or worn component with a stronger version of the same thing, not changing how the transmission behaves.\u003c\/p\u003e\n\n\u003cp\u003eIf you wanted a ratio change, that's a different product. This is the one you buy when the gearing was never the problem.\u003c\/p\u003e\n\n\u003ch4\u003eWhy First And Second Fail First\u003c\/h4\u003e\n\n\u003cp\u003eWorth understanding, because it explains why this is the part people end up needing.\u003c\/p\u003e\n\n\u003cp\u003eThe lower the gear, the higher the torque multiplication through it. First and second see dramatically more load than fifth and sixth, and they see it in the most abusive way, on launches and on hard shifts where the driveline is shock loaded rather than gradually loaded.\u003c\/p\u003e\n\n\u003cp\u003eAdd power to a K20 and that gets worse fast. A transmission that was fine at stock output starts damaging teeth or shafts once you're making real torque and using it. That's why mainshafts and gearsets exist for this gearbox, and why they're what serious builds go through.\u003c\/p\u003e\n\n\u003ch4\u003eBuy The Assembly, Not Just Gears\u003c\/h4\u003e\n\n\u003cp\u003eThis is a complete mainshaft with first and second, and that matters more than it sounds.\u003c\/p\u003e\n\n\u003cp\u003eThe shaft itself is a wear item. Splines and bearing surfaces take load every time you shift, and a shaft that's been through a gear failure often carries damage you won't spot until it costs you a second time. Starting with a fresh assembly removes that variable entirely rather than gambling on a used shaft you can't fully inspect.\u003c\/p\u003e\n\n\u003ch4\u003eBuilt Stronger Than Factory\u003c\/h4\u003e\n\n\u003cp\u003eSynchrotech manufactures these to meet or exceed OEM specification, using quality materials and tight tolerances so the shaft holds up where the factory part gave out.\u003c\/p\u003e\n\n\u003cp\u003eThey've spent decades working specifically on Honda transmissions, developing materials and heat treat alongside metallurgists, which is why their name comes up constantly when someone's gearbox lets go on a car making real power.\u003c\/p\u003e\n\n\u003ch4\u003eWhile You're In There\u003c\/h4\u003e\n\n\u003cp\u003eReplacing a mainshaft means the transmission is fully apart, which is nearly all the labor on this job. Use the access.\u003c\/p\u003e\n\n\u003cp\u003eInspect your synchros, sleeves, hubs, and bearings while everything is exposed, and replace what's past spec. Anything that ran alongside a damaged gear has likely taken debris or abuse, and closing the case up with a fresh mainshaft next to worn synchros means doing this again sooner than you'd like.\u003c\/p\u003e\n\n\u003cp\u003eIf you're finding wear throughout, a full rebuild kit is better value than replacing pieces individually.\u003c\/p\u003e\n\n\u003ch4\u003eFitment\u003c\/h4\u003e\n\n\u003cp\u003e2001-2011 Honda and Acura K20 6-speed transmissions, including:\u003c\/p\u003e\n\n\u003cp\u003e2002-2006 Acura RSX and RSX Type-S\u003cbr\u003e2006-2011 Honda Civic Si\u003cbr\u003eAcura Integra Type R (DC5)\u003cbr\u003eHonda Civic Type R\u003c\/p\u003e\n\n\u003cp\u003ePart number SG-K213-MS. 6-speed transmissions only.\u003c\/p\u003e\n\n\u003ch4\u003eWho Should Grab One\u003c\/h4\u003e\n\n\u003cp\u003eThis is for the builder who's opened a K20 6-speed and found damage on the mainshaft, and for anyone assembling a transmission for a car making enough power to justify doing it properly. Factory ratios mean nothing about how the car drives changes, you're just replacing a weak point with something stronger. Inspect everything else while you can see it, and close it up once.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eFits:\u003c\/strong\u003e 2001-2011 Honda and Acura K20 6-speed transmissions (RSX, RSX Type-S, Civic Si, DC5 Integra Type R, Civic Type R). \u003cstrong\u003ePart number:\u003c\/strong\u003e SG-K213-MS. \u003cstrong\u003eRatios:\u003c\/strong\u003e 3.266 first (15 tooth), 2.13 second (23 tooth), matching factory. \u003cstrong\u003eType:\u003c\/strong\u003e complete mainshaft assembly, direct OEM replacement.\u003c\/p\u003e\n\u003c\/li\u003e\n\n \n\u003cli id=\"VehicleFitment\"\u003e\n \u003cp\u003e2002-2006 Acura RSX Type S\u003cbr\u003e2006-2011 Honda Civic Si\u003c\/p\u003e \n\u003c\/li\u003e\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\u003c\/ul\u003e\n","brand":"Synchrotech Transmissions","offers":[{"title":"Default Title","offer_id":46745273630754,"sku":"SYN-SG-K213-MS","price":439.95,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/2218\/5701\/files\/SYN-SG-K213-MS_u3r8.jpg?v=1788287010","url":"https:\/\/www.hybrid-racing.com\/products\/synchrotech-k20-6-speed-mainshaft-civic-si-rsx","provider":"Hybrid Racing","version":"1.0","type":"link"}