You guys are forgetting the other benefit to underdrive pulleys. Stock pulleys are very heavy. Underdrive pulleys are very light and smaller diameter. The effect is like installing a lighter flywheel or wheel/tire combo. Less mass to wind up on acceleration = quicker accel or increased MPG. I love my pulley. Way easier to install than a flywheel.
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Only the Civic CX and VX lack a weighted crank pulley. This is due to the fact that the redline is quite low so you never reach the RPM where the damaging harmonic resonance occurs. An alternative to underdrive pulleys is an electric water pump. You install it inline with your coolant system, drill some small holes in your thermostat housing, and cut the fins off your mechanical water pump. You wire it to a relay that is controlled by ignition power and ideally an aftermarket coolant switch that supplies ground somewhere around 120 degrees F. The EWP removes the mechanical drag on the engine and puts a smaller electrical drag in it's place. The reason this works is because the EWP is optimized to flow at one particular speed vs the mechanical pump's speed which is governed by RPM. The problem with mechanical pumps is that they don't make enough pressure at low RPMs and at high RPM's, they produce too much pressure and your coolant cavitates. The low end of this problem causes your engine to run hot at idle increasing engine wear and requiring the radiator fan. The high end of this scale produces increased drag on the timing belt costing you power as well as not providing optimal cooling when you need it most. Like most any engine modification, cost/benefit doesn't make sense from a purely economical standpoint. EWP's will set you back a few hundred dollars assuming you can install it yourself, and the mpg increase is small so it will take many years for it to pay for itself. I recommend this mod only to people like myself who are striving for the combined goal of increasing economy, performance, and engine life. |
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"There is an average of 2.7 HP gained from every pound lost off the crank shaft." -(Unorthodox Racing). btw, I've not verified this claim. Keep in mind that with DSMs they usually were removing the balance shaft pulley (replacing it with a very small spacer) and thereby stopping the balance shafts from rotating which actually weigh about 12-15lbs and spin at twice the crankshaft speed. The underdrive pulley would generally have a similar but much smaller impact and it would need to be lighter weight than the factory original (most aftermarket ones are lightweight aluminum and such). PS The less rotating mass thing can apply to everything from the crank to flywheel (aluminum ones are available), to driveshaft(if you have one), to rotors, wheels, and tires. |
Daveedo,
So was the effect of disabling the DSM balance shafts noticeable at higher rpm? i.e. Was there noticeably more engine vibration? Might this reduce bearing life? I'm just curious since I have a Honda Accord with balance shafts... |
ok this is comming from someone who has bought and installed underdrive pullies and keeps mpg logs:
i bought them because others who have on the 2.2L s-10's have said theyve seen a slight increase on mpg and performace, i said what they hay and treid em. performace wise they made a noticeable increase in the amount of torque i had. i could go up a certian hill using less throttle than before. my mpg increased maybe 1-2mpg. to compensate for the alternater you can get an underdrive pulley for it too keepting the same ratio between it and the crank pulley. i left the water pump and power steering pullies alone. i haven't overheated yet. i even have an efan installed and while driving it doesnt turn on. i made a HOWTO on the truck forum i belong to: https://www.s10forum.com/forum/f105/h...ulleys-304284/ |
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Sorry, I know nothing about removing balance shafts on a honda. vette, thanks for the info. edit: for my '97 civic unorthadox has the pulley for $251 or 381 depending on which if you want just the crank pulley or the whole set. that's alot of $... I was thinking they'd be 75-100. |
ya mine was $100
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I'm surprised this hasn't come up more often. With everyone wanting to disconnect alternators and such.
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as long as you're ok with underpowering the accessories a bit underdrive pulleys are just fine - as long as you leave the main crank pulley where it is. not sure about your hondas, but most are harmonic balancers. they're large pulleys with quite a bit of rubber cast into them. their function is to reduce/eliminate crank vibration so that the bearings dont kill themselves.
even though its steel as the crank turns under such high speeds and loads it will bend slightly - think of the power stroke pushing down on a flexible material. as it does this stress is put on the main crank bearings. the job of the harmonic balancer is to absorb these forces so that the crank doesn't kill itself and its bearings. underdrive pulleys are often used on race engines because they're rebuilt constantly anyways so what does it matter? your car isn't however. just something to think about before you guys toss on a full pulley set. if you're interested, i believe a company called ATI (not the video card company) makes lightweight harmonic balancers - they actually do the job with less weight. cost more however, you get what you pay for. |
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