FireStone
Pro
Anyone did this mod?
stock carbs are 39mm.
can we oversize the carbs at 40mm? and correct the fuel with P.Commander?
We did this mod in the past on 700 triple ski-doo we had good gain.
just to know....
stock carbs are 39mm.
can we oversize the carbs at 40mm? and correct the fuel with P.Commander?
We did this mod in the past on 700 triple ski-doo we had good gain.
just to know....
yamaha1973
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I dont think it will be worth the money to do it... These 4 strokes aren't as easy to get power out of as 2 strokes.
nate007
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The throttle body size is already larger than needed for the horsepower they make, or even on a boosted sled it's more than enough.
It's tough to explain via post, but to understand the flow requirements of the motors and the horsepower per CFM, the throttle bodies on EFI bikes and sleds are already way oversized, even for full throttle operation.
Running a throttle body calculation on a 998cc, 4cyl engine producing 115kw (155hp) with a 10000rpm power peak, 3 intake valves per cylinder, 2 exhaust, yeilds a result of a recommended throttle body size (if it were a single tb) ranging from a 46.6mm for maximum throttle valve authority to a single 73mm as a maximum dia for a race application, with an optimal "normal" range from 54.6mm to 58.2mm, on a naturally aspirated engine. Having 4 individual tb's gives it more than enough airflow, and by using a 4 tb setup with no intake manifold, they maintain throttle response and compact packaging. (4) 39mm throttle bodies delivers far more than the calculted requirement of approx 240-275cm needed to suply the stock engine, and the 4 39mm's will actually flow in the mid 600cfm range depending on air density and in-hg.
Sorry for the long tech explanation, but there are other gains to be had simply by modding the airbox, and installing a higher flowing exhaust header. That would gain more than the hassle of re-engineering the tb's, which would be hard to tune to an acceptable "trailable" manner. These motors run pretty strong out of the box, and actual engine mods aren't quite as easy just as yamaha1793 posted. Clutching, airbox, exhaust, gear swaps, piggyback tuners and even just tuning suspensions can yeild quite an increase, but if you're wanting larger, more noticeable gains, nitrous, turbo or a supercharger is the way to go...
It's tough to explain via post, but to understand the flow requirements of the motors and the horsepower per CFM, the throttle bodies on EFI bikes and sleds are already way oversized, even for full throttle operation.
Running a throttle body calculation on a 998cc, 4cyl engine producing 115kw (155hp) with a 10000rpm power peak, 3 intake valves per cylinder, 2 exhaust, yeilds a result of a recommended throttle body size (if it were a single tb) ranging from a 46.6mm for maximum throttle valve authority to a single 73mm as a maximum dia for a race application, with an optimal "normal" range from 54.6mm to 58.2mm, on a naturally aspirated engine. Having 4 individual tb's gives it more than enough airflow, and by using a 4 tb setup with no intake manifold, they maintain throttle response and compact packaging. (4) 39mm throttle bodies delivers far more than the calculted requirement of approx 240-275cm needed to suply the stock engine, and the 4 39mm's will actually flow in the mid 600cfm range depending on air density and in-hg.
Sorry for the long tech explanation, but there are other gains to be had simply by modding the airbox, and installing a higher flowing exhaust header. That would gain more than the hassle of re-engineering the tb's, which would be hard to tune to an acceptable "trailable" manner. These motors run pretty strong out of the box, and actual engine mods aren't quite as easy just as yamaha1793 posted. Clutching, airbox, exhaust, gear swaps, piggyback tuners and even just tuning suspensions can yeild quite an increase, but if you're wanting larger, more noticeable gains, nitrous, turbo or a supercharger is the way to go...
