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My 2014 SR Viper MCX 270 project sled

Bruce Jardine

Veteran
Joined
Mar 9, 2016
Messages
44
Age
50
Location
Tremonton, UT
Country
USA
Snowmobile
2010 Yamaha Nytro MTX Turbo
Two years ago, I lost the bearings in the turbo on my 2010 Nytro MTX so I looked around to see what else was out there and I found a 2014 SR Viper XTX that had a lot of work done to it. It was stretched to 162 with a Van Amburg tunnel and from what I can tell has the newer Viper MTX rear suspension. It has a MCX 270 kit installed and it was such a good price, what I thought anyway, that I bought it headed home. Needless to say, it didn’t perform anywhere near like my Nytro and I was a bit disappointed. It was the end of the season and I only rode a couple times before we put the sleds away for the year. Last year, I was still unimpressed but kept riding. It has a Koso X-2 boost/AFR/Temp gauge and it would always boot up and shut off time after time. The battery was on its last leg and I thought that was the issue but after I replaced the battery, it still did it. Found out the ground connection was bad and after I made a good ground for it, the gauge worked fine. Next time I went riding, I switched over to boost and was shocked to see it read zero. I rode around and didn’t move at all. Then it was time to put the sleds away again. This year when I pulled the sleds out and got them ready to start riding, I chased down the gauge’s connections figuring it was disconnect but it wasn’t. This is what I found instead:
 

IMG_5469.JPG
 
So I thought if I replace this, my gauges issues will be fixed and my performance issues will be fixed too. This line going to the gauge sensor tee'd off from the vacuum line going from the throttle bodies to the MCX ECU. Before this, the sled wouldn't pull the proper RPMs. I could only get it to hit 7200-7300 max. I've read that target is 8,900-9,000. I thought that this huge hole in the vacuum line right next to the MCX box was giving the box in inaccurate reading and no wonder it didn't run right. So I fixed the line and went riding. Still disappointed. It maybe ran slightly better but we were riding at a lower elevation than where I normally ride. So I was determined to dig into the sled and figure out what was wrong. Watching the boost gauge I was lucky to see 1 psi on the gauge. I've watched tons of videos on YouTube of guys on their SR Viper's with the MCX 270 kit and I should be riding with skis in the air everywhere! I recently upgraded to an enclosed trailer so now I could tear the sled apart inside without being out in the elements. Gone are the days of snowmobile covers and working on sleds in the dark and cold. I read a few turbo forum posts on diagnosing turbo issues and decided to build a plug for the intake before the turbo and pressurize the whole system. I turned the regulator on my compressor down to about 18 psi and started airing it up. Here’s my homemade boost pressure tester:
 
I wanted to add a pressure gauge to it but I figured with the regulator turned down, it was safe and I wanted to know what was going on. As I started blowing air into the intake, I could hear a pretty decent leak coming from under the MCX intake. I felt around and could feel air blowing out around one of the injectors. I figured that the oring seals on the green injectors must be bad so I started disconnecting everything so I could pull it out. I made plugs for every hole in the intake/intercooler so I could test it by itself. Put some foamy hand soap all around the injector bosses and aired it up with the compressor regulator turned down:
 
Sure enough, the first injector had enough air coming out that it blew the soap bubbles away. So I went about finding orings to replace them for all the injectors. Figured I’d pull them all out, replace them, and put it all back together. But looking closer, it didn’t seem like the leaking air was coming from the injector oring after all. This is what I found when I looked closer:
 
I couldn’t believe it. This was down under the injector where I didn’t see it at first and it wasn’t until I put my finger on the hole and the leak would stop that I figured out it was a manufacturing defect. Once I cleaned it up and took a closer look, I could see it was just a bad weld. I can’t believe that this came from MCX like this. When I aired it up on the sled with 18 psi, the whole system wouldn’t hold more than about 5-6 psi. So even though the whole wasn’t huge, it was a big deal. Not sure how the original owner who had the sled built was ever happy with its performance. Maybe he wasn’t and that’s why it was sold to the guy I bought it from. So I know a guy that owns a welding shop and had one of his guys tig weld the hole and took it home to test it again. Put all the plugs back in and aired it up. Sounded like there may have been another leak but may have been coming from one of my hoses and clamps so I dunked the whole unit in large tub of water. Found a small pin hole leak coming from a joint of one of the intercooler vertical runners and the tank at the bottom. No way to weld it so I pulled the fin back a little bit, put some tape on one side, and mixed up so JB weld, packed the JB weld into the spot between runners next to the tank and let it set and cure for a day. 24 hours later I aired it up again it was holding 18 psi. I was stoked. Surely this was my problem solved.
 
I thought I might want to check the exhaust system too. I made a makeshift gasket and a block of wood and clamped it on the end of the header pipe. I had drilled a small hole in the wood block just large enough for the rubber tip of my air nozzle to fit in and blew in to it. It just blew and blew. Kept blowing for a little while and pulled the air nozzle away. Not one bit of pressure built up. I browsed the Viper FAQ pages and found the thread on cracked headers. Sounded like it was an issue for 2014 Vipers. Mine's a 2014. Could it be? So that night I tore into it after I got the intercooler/intake all put back on. This is what I found:
 
So no wonder I wasn’t getting boost. Almost all the exhaust was dumping out the one side. I thought it was kind of loud but it always had been. Maybe it had gotten louder. Hard to tell over two years with too few rides spaced out. So I had a dilemma. Do I have the header welded up? It was in really bad shape. There were cracks going across the bottom, not just down the side like in the pics of other peoples’ posts. I decided I’d look for an aftermarket header and see what was available. I found a great deal on an MBRP stainless header. I read everything I could find on them and what people were saying is that it didn’t give any horsepower gains like they claim. I decided that didn’t matter to me because I’m not running a NA sled. In fact, they called this a “shorty” header and I thought the shorter the runners, the less volume to fill and pressurize which would make the turbo that much more responsive compared to the stock header. That was the biggest selling point for me. So I pulled the trigger and got the new header:
 


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