400c Rumors… or just internet trolls.
- Thread starter JKendrick87
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Well , yeah thats why i square grind my ported 357xp . Its a beast for a 57 cc saw
5 yrs don't feel bad , i spent the better part of 2 decades critiquing powersports powertrain protocals . Drive clutch design & optimizing was rather straight forward , driven clutch tuning was much more involved . The balancing or phasing of two clutches is imperative . Much is made of the primary drive clutch spider & roller & weights , where as the proper helix clocking & spring combination & axile offset within the driven clutch is just as important for proper transition & efficency between the two clutch systems . As Ben mentioned a simple weight or spring rate change will significantly change the rpm shift pattern & overall achievable peak rpm range of any engine & power train system . That also plays into proactive engine design & timing perimeters & aggressive carburation tuning to optimize or balance & enhance what the engine & chassis are capable of on the track , trail or mountain . Ever since the introduction of IFS & liquid cooling & computerized engine monitoring & calibrated onboard fuel management systems , sleds have evolved into a highly refined recreational vehicle , from the early power tobbagan's of the 50's . Of course the same can be said of cycles & saws to a similar degree !
In your day clutch tuning must have been a nightmare. The belts, clutches, etc sucked compared to what I was dealing with in the mid 90's. Not to mention the motors had much cruder cylinders and pipes, which much complicates tuning.
I did mess around helping a friend with a Yam SRX440, which I believe was a 79. It went like hell when the jetting and clutching were bang on, but sucked if they were even a hair off.
Actually clutching of the RXL & Indy Starfires in the 70's was World class . Solid rubber Goodyear gold or Gates Belts of that vintage stood up to the horsepower & clutching of the day within the early free air 500 & 600 triples e.g. Centurian .Todays 200 +hp sleds would shread them in 2 laps .The carburation was suspect back then Tiltison & Kehien until 75 . Mikuni's became the norm thereafter , which solved the carb bowl foaming on the big triples . Actually Jim Bernats 440x 75 triple was the 1st Mikuni liquid triple with IFS at Anchorage Alaska testing. . The 1st generation liquid cooled 75 & 76 Starfires & later 77-78 RXL models all had Fugi power plants which were extremely efficient engines . Engine tuning & pipe design was world class & competitive within today's standards . Suspension for 25 lap ovals would still be competitive , however endurance oval or cross county action today would be prehistoric brother 4-6" max. I actually bought Steve Thorsons RXL 650 Midnite Blue Express via Polaris Industries in Roseau in 78 . I still have it , I think the 78 RXL chassis was the sexist Snowpro sled ever built . As for the Yamaha SRX 440 sleds , 77 was the fastest model they produced dyno'd at 98 hp . 78 thru 79 they detuned the engine from its track tuning to a modest trail tune of 80 hp . Smaller carbs & timing numbers produced better fuel mileage @ a performance cost . The 1980 Black & Gold SRX was the sexist but slowest @ 78 brake hp . I ran a 76 340 & 440 SRX as a Independant in Michigan's UP (MISA) for 2 seasons as a top Independant in class , prior to running professionally in Canada in Peterbourough & Thunderbay 250 & 3 times @ the Soo's I-500 . All with Team Polaris colours . Anyhow , I still love my sleds & wrench on buddies sleds every yr . I intend to be buried with my 77 RXL650 factory sled lol.
My friend had 3 sets of cylinders. The oem ones where spares. The other were earlier Yamaha race team pieces (76,77maybe?). Intake port layouts were different
. One was bridged. Pipes were Aaen, a set of factory team pipes and a set from a guy that worked with Aaen. Carbs were 40mm Mikunis. Ran Phillips B35 oxygenated fuel with a little or a lot more MTBE added when we could. Made peak power north of 10k. And that's about all I remember. Had a belted/cleated track and a racing suspension(Wahl I think).
Aaen pipes were reliable aftermarket pipes . We developed our own piping systems , with power cans before they were available for consumer sleds lol. Aaen clutching was world class , ran a few of their units on a few ZCats & Liquid Twisters to replace the oem Salisbury units on their 1976 model sleds . Our fuel was all proprietary "Polaris Race Fuel & Mix" although I know for a fact its was Quaker State which was Polaris's Team Primary Sponsor or Kendall oil which was a secondary oil sponsor in the 70's .
Yeah , my Titanium chassis 650 RX-L runs peak horsepower between 8500-9300 rpm , which was the factory set up which dyno numbers indicated produced 125 hp . The only 77 RX-L that ran high numbers was the 440X sleds of Jim Bernat & Jerry Bunke , which spun up to 13,000 with its monoblock triple engine mounted directly to the magnesium bulkhead sans motor mounts . This lowered the centre of gravity by 3" & provided additional engine stiffness to ensure no crank twisting . Dial indication showed +/-.001 degree of crank runout up to that rpm . producing a conservative 100 hp . The 340 & 250 RX-L. Factory sleds of Brad Hulings produced 88 hp & 65 hp on the factory dyno . P.S. my 76 340 & 440 Srx's produced 70 hp & 100 hp on a local shop dyno . The Yamaha had great engine performance & clutch efficiency however their suspensions were obsolete & fragile . I only raced ovals for that reason . P.S. I had a chance to run Gille Villenerves 650 Skiroule IFS in 75 with its monster Kohler starburst cylinderheads . It was actually faster than the Polaris HQ sleds in Time trails what a beast , just could not hang with the Titanium chassis & Magniesium Bulk head sleds from Polaris or Scorpion in the 2 yr era in the endurance oval events over 250 laps .
He does seem to have thing for those 79xx, don't he?
Rhetorical
I chase grunt and can gear up for felling if needed. Building cylinders for milling changed things a bit for me. Less is more given enough area and corrected port lengths. Found a few ways to cheat the numbers with more area.
Kevin does sweet work with 7900' s . I have a 6100 heading his way but have not broke it to him yet !
That is a judgment call depending on the gear box and spread of said gears hooked to it.
Four gears is going to warrant a very wide useful curve with meat under the spread. An eight speed stick in the hands if a skilled user just became a narrow peak run HP game if the driver can maintain being withing the operating range. I know what engine is going to last longer and I've made no reference to valving, two strokes or four or any of the component costs.
Send it filthy!Kevin does sweet work with 7900' s . I have a 6100 heading his way but have not broke it to him yet !
Can you say it again then?
You going to get there eventually from time served.
2 stroke chainsaw , a wide torgue band is preferred over a peaky horse power curve . 6 speed manual tranny on my Cummins makes for stump pulling torgue , with modest horsepower numbers & thrifty fuel mileage numbers brother
What year is the Cummins truck?2 stroke chainsaw , a wide torgue band is preferred over a peaky horse power curve . 6 speed manual tranny on my Cummins makes for stump pulling torgue , with modest horsepower numbers & thrifty fuel mileage numbers brother
Don't think many new grinders consider port velocity or broad band grunt. When I started building milling saws chasing overrev went away. Chasing anything but pure mid range to about 10k was an education in less is more. The timing numbers changed and the intake track got bigger everywhere once all things were considered. Same old adage though. More in equals more out if you can keep the velocity up during dynamic flow conditions.2 stroke chainsaw , a wide torgue band is preferred over a peaky horse power curve . 6 speed manual tranny on my Cummins makes for stump pulling torgue , with modest horsepower numbers & thrifty fuel mileage numbers brother
Gearing up was now an option so I put an eight pin 28 404 on the milling saw 660. It ran out of chain again. Depths are at 0.055 on RS round ground. It's either go to square cutters or put on a ten pin and test that using stock off the reel chain and go from there. Honestly though 0.045-50 is about it. The chatter starts slowing things down again in big oak logs.
No
You act as though it’s possible. Please see step 1
2001 Wolfy , low mileage truck !
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