PLUGGED EXHAUST VALVES
I was all for this mod until I read some things on DTR's reports. Kraven is 100% correct, in that you have to ensure you are matching the fuel curve to the opening of the valves. The airflow actually drops as the valves open, and the ECU in turn is programmed to cut fuel to match the drop in airflow. If the valve lines are plugged off, and therefore open earlier, the ECU thinks the valves are opening (and therefore expecting a drop in airflow) and cuts fuel to match....however, what really happens is NO drop in airflow, but there IS a drop in fuel, therefore the motor is now lean during the ECU valve transition. I would guess that the stumble at 7000 when on/off the throttle is actually a rich missfire condition due to the valve closing early from a drop in cylinder pressure.
On the non-efi models, the carb jets would deliver fuel "on demand", and were not subject to this valve opening transition fuel delivery problem.
We REALLY need a closed loop EFI on these sleds....too many variables to ensure consistency with a "one map fits all" mentality, IMO.
On the bold, agreed.
Auto-tune + PC-5 is as close as we can get for now. Only the FST -WEBER 4-stroke has the closed loop as far as I know.
With respect to DYNO TECH RESEARCH (Jim's comments) he was referring to the
INCONSISTENCY in the
timing of the opening of the exhaust valves possibly affecting the fuel curves (and his revised PC-5 maps) on the 800's, which then of course yet another PC-5 map would have to be created in addition to the maps he has for what is it now 5 + re-flashes with enough dates to fill up the calendar, and then different maps (for the corresponding re-flash dates of course) for SLP piped sleds, maps for Bikeman piped sleds, and Dyno-Port piped sleds..........etc.
Just to clarify, Jim offered this "inconsistent exhaust valve opening" as a possible explanation as to why the same PC-5 maps sent out to different customers on identical sleds performed so differently. Some ran great, others had the deto light on 1/2 the time, etc....
Jim went on further to suggest a electronic servo motor to control the exhaust valves for the sake of consistency, similar to the system POLARIS used on the 1997-2000 PRO-785 Jet-Ski where the computer had cables coming out of it that controlled the opening of the valves on a triple piped triple 785 FUJI engine.
Casey Mullins, a DynoTechResearch regular, has the valves plugged on his 800 for quite some time now, that should tell you something.
In summary, for less time than it takes to read this thread, anyone can simply test this idea by bringing a couple of mini-vise grips with them out on the trail. Pinch off the hoses, take it for a ride, if it works, GREAT, if not, and one doesn't want to fiddle with different springs or dialing in the fuel controller, remove the vice grips, and it's cost you nothing.
Don't you wish the same could be said of all the after-market
HI-ZOOT stuff everyone has probably paid a lot of $$$$$$$$$ for and provided no performance benefit what-so-ever?
This fall, I may be taking a road trip and bringing some of my toys to DTR for some dyno-testing, and I'll be sure to post the info. One of the changes will be to test both the plugged and unplugged version of the exhaust valves,
and see how the A/F is affected by doing so.
I know how my 700 and my bud's 700 runs before and after plugging the valves. They'll both stay plugged.
And since I'm not selling a $29.95 exhaust valve plug kit, I have no motivation to B.S. here.
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My theory on the inconsistency between CFI sleds is the 3 different color/flow rate injectors and let's color match it with a different E.C.U. game.
All other brands have one size injector for that set-up and one E.C.U.fuel map.
On the modded engines, they just replace let's say a 38 lb (pounds of fuel per hour) with a 42, 48, etc.
POLARIS must have purchased a Train Car car load of injectors manufactured in a sweat shop in some Third World Country, and after testing them found such a HUGE variance between them, and in a cost savings corporate decision, they had to figure out a way to use them up, hence the 3 different codes and E.C.U. colors. Un-friggin-belivable.
