**(reprinted with permission from Dyno Tech Magazine)

Evolution of the VMAX

Many snowmobile enthusiasts consider the 1981 SRX to be a milestone for Yamaha, and snowmobiling in general.  Yamaha’s bold new Darth Vaderish styling concept featured exposed individual front suspension struts and squared- off, three-piece hood.  To many, this was a refreshing departure from the previous generic hood and front suspension designs.

The 1981 440 SRX had a chassis very similar in appearance to the current V-Max.  With some lighter driveline components (e.g. aluminum drive axle0, a smaller cooling system, and shorter travel rear suspension, the 1981 SRX weighed an actual 483 lbs. With three gallons of gas on tour DynoTech scale.

While we’ve never dyno tested a stock 1981 440 SRX engine, other testing facilities have reported very peaky horsepower in the high eighties at 9000 RPM.  Many 1981 SRX owners had problems with poor low RPM performance, belt wear, and fuel mileage.  Others experienced more severe difficulties with crankshaft life.  Some engines were evidently not holding up well to continued high RPM operation.

In 1982, Yamaha increased the SRX’ displacement to 550cc, and horsepower was reportedly in the low nineties, again at 9000 RPM.  But the 82 models never made it to market.  Instead, Yamaha’s 1982 model line lacked an official high performance sled, and in 1983 upped the SRX’ displacement to 535cc and renamed it the V- Max.

The V-Max featured all- new, more moderately ported chrome- bore cylinders and longer/larger diameter twin pipes that lowered the power peak about 750 RPM.  While the maximum horsepower is not any higher than the 1981 SRX, the V- Max enjoys a considerable toque and midrange horsepower advantage over its smaller, higher revving predecessor.  In addition, Mikuni 38mm round slide power- jet carbs replaced the old, difficult to tune butterflies that cursed the earlier SRX.

Our stock V- Max was also tested with shortened; chassis fitted stock pipes (a modification that Bender Racing performs only for highly modified V Max engines), Aaen twin pipes, and PSI twin pipes.

Several years ago, an aftermarket CDI box was advertised for the stock V- Max that’s was supposedly good for a five HP gain.  We obtained one of those, tested it on a stock 1985 V- Max, and lost several horsepower.

For those of you who monitor exhaust temperature, out experience on the dyno and in the field shows that the V- Max shouldn’t be run on 92 octane gas at much over 1150 degrees.  For our dyno analysis, unleaded 100 octane VPC10 was used.  Stock 290 main jets were retained, and the power air jets were removed.  This resulted in a safe BSFC for known high-octane pump gas at our80 degree F Carb Air Temperature.  Winter operation with this fuel flow may cause trouble during extended high-speed operation.

After the Yamaha Exciter was introduced in 1987, the V- Max was eliminated from Yamaha U.S.’ production line Yamaha Canada, however, has continued to make it available to its customers though it will most likely be phased out of production after 1991.

All Data for 22.92 inches of Hg, 60 F dry air

Test:  100 RPM/  Sec Acceleration

Fuel Specific Gravity:  .750

Stock V- Max Stock Pipes

Stock V- Max Cut Stock Pipes

Stock V- Max Aaen Pipes

Stock V- Max PSI Pipes

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