November 28, 1999
Dear Ralph:
It seems that since you know so much about snowmobiles that maybe you can help me with a tow vehicle. Why are the Turbo Diesels so powerful in the mountains pulling trailers? I’m considering buying a Ford Super Duty truck, do you know anything about the “High Altitude Principal Use” option (option code 428) offered on the gas engine? My local Ford dealer isn’t much help (no surprise there). Or, am I better off with a 7.3 Power Stroke diesel?
Scott Florence
Just like the engine in your snowmobile, normally aspirited gas engines in tow vehicles loose between 3 & 4 percent of their horsepower for every 1000 feet above sea level. This means that at 7000 feet, the gas engines have lost over 20 percent of their rated horsepower and torque. In contrast, trucks with turbo diesels (like the Ford Super Duty F-350 7.3L Power Stroke) maintain full horsepower and torque up to about 10,000 feet. The turbocharger maintains a full fuel/air charge to all cylinders, maintaining full horsepower and torque. Above 10,000 feet, even the turbo can’t keep up with the thinning of the air.
The High Altitude Principal Use option 428 is a no-charge option for Super Duty F-Series trucks with gas engines and consists of some revisions to the EEC-V calibrations and often a change in the rear axle ration to provide greater towing capacity with the reduced horsepower that will be produced at higher elevations. This option is recomended for trucks that will be operated primarily at elevations above 4000 feet.
This is also the main attraction of turbos for use in snowmobiles. The power robbing nature of high altitude isn’t as apparent, and sleds with turbos running at altitude make almost as much power at 8000 feet as they do back East. The issues of reliability and stresses on the drivetrain are something to consider, but the attraction of making an actual 150+ HP at 8000 feet is tempting, very tempting.
November 28, 1999
Dear Ralph:
I read in SnowTech Magazine that the Cat 500, 600 & 700 will have Hemholtz resonators on them this year. I own a ‘98 ZL 500 which is a great sled with the exception of the noise levels. I have tried to get a fix but have had no luck. Do you think the system on the 2000s would retrofit onto my sled? Do you know wether the resonator is on the exhaust pipe or exhaust canister? Would both have to be purchased? Any other changes that would have to be made?
Peter Young
The Hemholtz resonator that Arctic Cat is refering to, which little information was available in the Spring, turns out to be an airbox change that was made to many of the ‘99 600s. The internal dimensions and ports of the airbox are altered to “trap” the primary firing frequency of the engine, resulting in a quieter intake noise level. This modification is now being adapted to a large number of 2000 Cat models, and you should be able to add this to your ‘98 500. I don’t believe you can get the internal airbox components seperately, so you’ll likely have to order a new airbox. It would be wise to emulate the carb jetting specs of the 2000 model 500 engine to compenstae for any airflow changes, and then make final calibration adjustments from that point.
November 28, 1999
Dear Ralph:
I have a ‘99 ZL 600 EFI along with an extended (non-manufacturer) warranty that expires in 2004. Neither the Arctic cat warranty nor the DFS extended warranty cover “pre-ignition” nor “detonation”. My manual says to use a minimum fuel octane rating od 88.
My objective is to maximize engine life/reliability and I don’t give a ____ ___ about a loss (or gain) of a two-three horsepower. If my manual recomends a “minimum” octane of 88, does this imply that a high octane is better? I’m told higher octanes contain more alcohol and that alcohol burns hotter (which is bad)? What are the trade-offs in using higher or lower octane fuel? (A/C dealers tell me one thing, experienced mechanics tell me another).
Neither warranty covers damage resulting from air or water in the fuel, so which method is best for insuring any and all water is removed from the fuel, the “bag” or Isopropyl alcohol? Or both?
My A/C dealer tells me air cannot get into the fuel line because my EFI “automatically pressurizes the system”. How do I prevent air from getting into the fuel line; how do I check for air in the fuel line; how do I remove air from the fuel line?
Your input would be great,
Chris Kinson
Fon du Lac, WI
One at a time Chris, we’ll take care of your concerns. Your warranties specify they do not cover pre-ignition or detonation as an “out” if something really weird happens. The intent of a warranty is to protect you from defects in components or workmanship, not to provide you with “free service”. Engine failures on a snowmobile are far too often caused by things like improper jetting, fuel quality, fuel system icing, things that are more environmental and not the result or fault of the manufacturer. A good relationship with a servicing dealer is far more important than a piuece of paper in my opinion.
On fuel octane, lower octane fuel burns hotter, higher octane fuel burns cooler. Higher octane is generally considered “better” because it a) keeps the engine running cooler, hopfully avoiding reaching the melting temperature of aluminum in whatever condition you may encounter, b)if you start out with higher octane fuel, despite aging or whatever condition the fuel may be in, by the time it runs through your engine it hopefully will be volatile enough to still be the minimum 88 octane. Fuel that was 91 octane in November when it was dumped into the tank at the filling station may not be 91 in Janruary by the time it is burned in your sled!
Higher octane fuel MAY contain alcohol, it may not. Alcohol does raise the octane of any fuel it is added to, but you can get 91-92 octane with or without alcohol. Buy high octane fuel from a busy station and you should be OK. Alcohol actually burns cooler, not hotter. The confusion with this is that alcohol increases the oxygen in the fuel/air ratio, so a sled may display hotter combustion temperatures, thus the logic in running larger main jets or using your EFI jumper to increase the fuel delivery.
Trade-offs in octane? I don’t want to get into a detonation vs. pre-ignition article here, but lLower octane makes slightly more power, higher octane makes slightly less power. More important is the flame speed and ability to resist detonation. Higher octane resists detonation, and whatever power loss (if even detectable) isn’t worth worrying about. Your sled asks for 88, run fresh 89 and don’t worry. If you add pipes or higher compression heads, run 91-92. Octane is very motor (and elevation) dependent. You can get away with lower octane fuel at higher altitudes due to the reduced cranking compression. Ever wonder why you can buy 85 octane out West? An engine that is happy running 87 back East at low altitude is happy running 85 out West at higher altitudes.
Removing water from fuel; the in-tank absorbers, or “bags” as you refer to, work fine at removing fuel from the tank. They do absolutely nothing to remove water thas has been sucked in through the air intake. For this reason, although more inconvenient I prefer Isopropyl, as it will remove water from both the tank and the engine.
Yes, you can get air into your EFI system. If your fuel level gets low enough and your fuel pump starts sucking air, you have a problem. If you ever suspect you’re running put of gas on an EFI, you want to shut it down. This holds true for most all injection systems, autos too. How do you prevent air from getting into your fuel line? Keep enough gas in the tank! How do you check for air? By looking at the fuel line for air pockets. How do you get it out? Get some fuel in the tank and run the sled at idle until all air is purged from the line. Hope it works, or you do have a problem!
November 28, 1999
Dear Ralph:
I have some problems with my ‘98 XCR 440. Last year I used it bone stock, only rejetted to MJ 340. I used R8 helix and silver/blue sec. spring (stock) and S53R weights and almond/gold spring (also stock), drive belt OEM -67. It ran pretty good, more top end than most ‘98 ZR 440 SnoPro’s. I could even reach almost 110 mph @ 8500-8600 rpm on the speedo in absolutely ideal conditions, 100 mph in most every condition. It usually revved at 8300 rpm.
By the end of last season it started to behave funny. I slowly lost my top end, and my back-shift decreased. I thought it was due to the warm weather, causing my soft -67 belt to stick to the clutches, since this was at the very last days of the season. But when I used it this year I had the same problem in cold weather, decreasing rpm’s when approaching 60 mph, dropping to approx. 7400. By then it refuses to go above 80-85 mph. Terrible back-shift.
I’ve tried a lot of things, changing to a harder -66 CVT belt improved my backshift and raised my rpm’s a bit, but still no top end. I’ve changed my primary spring to a brand new, which took care of some of the problem and raised my engagement a couple of hundred rpm’s. I’ve tried new weights (a bunch of them). With 10MBs I have a snappy engine, but it overrevs to 8700 rpm. So far it seems like 10M works OK, but my backshift could be a lot better, the engine has rubber band feeling and I have a 300-400 drop in the rpm’s in midrange. Now I can reach at least 95 mph at good conditions, @ 8300 rpm.
I suspected a power loss, but I’ve dynoed it to approx. 97 hp. which is I believe is OK. What has happened with my trusty XC racer?
Swedish regards,
Tomas Fahlen
Instead of trying to fix the problem with calibration changes, I would concentrate on finding what changed that is causing a good working set-up to not work any more. How many miles do you have on this sled? It sounds like you’re convinced that the engine is in proper condition based on your dyno verification, but I’m not so sure. 97 HP sounds way too high for that engine, I’d expect more like high 80s, low 90s. I wouldn’t be surprised if you need a new set of pistons and rings. Remember, this is a little 440 being squeezed for about all she’s got, and what you’re describing sounds about right for loss of compression. Anything over 1000 miles and I’d be very suspicious.
Once you have eliminated the engine power for sure, then you would need to concentrate on the drive train. All the way from the drive clutch to the track and suspension. Have the clutches been cleaned and serviced? Bushings OK? Any binding? Belt deflection, ride height, side clearance all OK? Button condition? Are the clutches shifting out as far as they used to? Driveline bearing condition? I’m not convinced your engine is making full power. If it is, then one of these basic components is likely the cause of your woes.
November 28, 1999
Dear Ralph:
I have a 1997 Arctic Cat ZR 440 that I am trying to get the clutches set up on. I have just recently installed V-Force reeds and Black Magic twin pipes. My question is, Black Magic says engine should run at 9200 RPMs peak, and to me that seems a little high. I have already seen my friend lose a motor due to overreving. I’m currently running about 8600 RPM with notched 47.5g weights and a 54/48 helix with red secondary spring in first hole, sled pulls 8600 RPM out of the hole, but falls to 8400-8500 RPM with top end speed at about 100 mph. What do you suggest I do? Thanks and keep up the good work.
DCMT50
For you to question if 9200 RPM is the correct RPM to run at is one thing, questioning it from a reliability / durability stand point is a totally different issue. Each and every exhaust system is designed to produce maximum power in a very specific RPM range. If Black Magic told you that pipe set on your engine was designed to operate at 9200 RPM, then I would trust their expertise and experience. If you want to get the best performance out of your sled, clutch it to spin at the RPM specified by the pipe manufacturer unless you have proven that it works better at a different RPM. Start with the recommended clutching specs for your temperature and elevation from Black Magic, and perform the fine tuning adjustments from there. If you’re really that worried about engine durability, you can always put the stock exhaust back on.
If your sled was in my shop I’d hook it up to our DynoJet track dyno and we’d find out what engine RPM puts the most power to the ground. I’ll bet it’d be in the 9000-9200 RPM area.
November 28, 1999
Dear Ralph:
I would like your thoughts on replacing pistons and which ones to use. I burnt a piston due to a carb freezing or something, it was not a lean set-up. It has been suggested to me to replace both pistons at the same time. The sled is a ‘94 ZR 580 with almost 3,000 miles. Compression at the start of the season was 120 PTO and 119 MAG. Is it best to use OEM pistons, or Wiseco, or other aftermarket, jobber parts? What are the pro’s and con’s of those options? Can the cylinder plating take a light honing if needed?
Wes Moore
Prince Albert, Saskatchewan
Most important here is that you follow the specifications and recommendations based on the type of piston you install. Cast OEM pistons can be installed with much tighter skirt clearances than forged pistons (like Wiseco). Forged pistons tend to expand a bit more than cast, and need more skirt clearance. Forged pistons also tend to withstand heat better, and are typically more durable. OEM cast pistons are usually less expensive.
Considering that the engine has almost 3000 miles, it is prudent to replace both pistons. More important than mileage is the condition of the piston and cylinder; specifically the critical specifications like piston skirt to cylinder clearance and piston ring end gap. There are very specific service limits, and regardless of how the piston and cylinder “look”, these measurements should be performed and the decision based on that information.
The ‘94 580 engine with plated cylinders would need to have any aluminum stuck to it removed, then it could be lightly honed with 400 grit silicon carbide SOFT stones (Ammco #3955 honing stones). The ‘94 ZR 580 had a tendency to run at too high RPM in the midrange, which caused some piston seizures. Arctic Cat addressed this in Service Bulletin 94-08, recommending the installation of a new cam arm and drive clutch spring kit (p/n 0637-069) to keep the engine spinning at 8000 RPM.
Other areas to pay attention to on the 580 engine that scuff or seize pistons are the cooling system, it is extremely critical that the cooling system be properly filled. If air remains in the system, piston scuffing can start to occur when the water temp reaches 190 degrees. Check the outlet of the silencer, make sure it isn’t bent, partially closed from hitting a stump or something. This would cause piston heat to be excessive. You should also remove the silencer and shake it, checking for loose internal baffles. Loose baffles will have the same effect as a blocked outlet, restricting exhaust and causing piston heat.
