Underdrive Pullies
 

This seems to be a very common thing for tuners/ race oriented people to do, but I really haven't heard of anyone metioning it for fuel economy. Of couse they cost $100 or more and gains must be minimal. You would have to drive 1,000,000 miles to get your money back.

i can get one for my car for
 

i can get one for my car for about $50 US. it's on my list for testing out next spring when my tools warm up again.

i'd be very surprised if it made any more than a 1 or 2 percent difference. still worth trying though.

hmmm... for the amount i drive, a 2% improvement will save me about 12 L a year, or $9 CDN at 75 cents/L. i'd have to drive about 60,000 km (37k miles) to break even on a $50 expense.

Here is another
 

Here is another gadget:
https://www.gassavers.org/forum_topic/alterpower_shutting_off_alternator.html

interesting - thanks.
 

interesting - thanks.

Re: Underdrive Pullies
 

Then you have to start getting value some other way.
Less drag on engine equals more power and better economy (even if the amounts are small to minute)

Less load on the engine could help in longevity of the engine.

Less load could make quiter engine at all speeds.

(hey it's the little things that count sometimes :))

Quote:(hey it's the little
 

Yeah ****, people who are in it for gas mileage complain a lot about it, but I don't care so much. Something like this I might do just for the power, people drop a grand on some fancy custom exhaust to get ten hp, hell, it's all in the sport, :-)

update (propaganda ) on the
 

update (propaganda :) ) on the underdrive question...

found this on the teamswift site, from one of the 2 guys who makes and sells them.

completely unsubstantiated, likely not tested under controlled conditions, and i'm still skeptical because it seems excessive. but here you go:

50 bucks eh, for 8% that's
 

50 bucks eh, for 8% that's worth the risk, I will go to look about them for my car and report back!

Re: 50 bucks eh, for 8% that's
 

i still think it's going to be much lower than 8%.

ooo! surfing around, just found this... some serious underdrive debunking:

so the argument there is the only gains to be had in underdriving are the water pump and the reduced air drag from the alt pulley "fan".

water pumps... the quote above is talking about racing engines (v8's i gather). obviously the size of the gains to be had depend on engine size.

let's do some rough math for my car:

on the teamswift site, one guy replaced his water pump with an electric one that is rated at 1/2 hp, and is stronger than stock. so let's say the stock one costs 1/3 hp. underdriving it by 25% would save me 1/12th of one hp. let's be generous and round it to 1/10th to accound for reduced aero drag on the alt.

1/10th of 1 hp = 75 watts. that won't even power my headlights. yes, it will save fuel, but looks like the savings will be negligible.

continuing further down my very rough calculation road, another figure you see quoted often is road horsepower at highway speed. i.e. i've read several estimates that it takes a modern car between 10-15 hp to cruise at highway speeds on level ground.

assume my car gets 50 mpg (US) at 60 mph and needs 12 hp. if i save 0.1 hp with the underdrive calculations, my highway load drops by 0.83% (0.1 / 12 hp). if the fuel consumption drop is linear, i have just gained 0.42 MPG (50 mpg * 0.83).

suddenly the investment "risk" doesn't look so good (from a strictly fuel saving perspective)...

Someone tested a saturn
 

Someone tested a saturn stock and a saturn with no crank pully at all and said they only gained 3 hp. They implied that underdrive pullies would provide little if any hp gains.

https://www.teamscr.com/pulleys.htm

I belive this test is totally wrong because the crank pully acts as a blancer for the engine. and a engine with no crank pully would be out of balance.

cubic law
 

Radiator fans and cooling pumps drag power from the engine according to the CUBE of their speed. Halving their speed means 1/8 of the drag. Doubling the speed means 8 times as much drag on a race engine, so high RPMs fans and pumps hurt power for racers and hurt our economy.

Underdrive pulleys saves substantial HP for racers, but the effect is a lot less for us gas pinchers that keep engine RPMs down anyway. Even so, underdrive pulleys WILL help gas economy though.

The biggest problems with underdrive pulleys are:
1) The car may overheat in hot weather and under hard work. like climbing hills.
2) The alternator needs a minimum RPM to produce enough volts to charge the battery at idle. It could run out of electricity when we're stuck in traffic. Underdrive pulley with a couple of deep cycle batteries could cope with that.

Re: Someone tested a saturn
 

A very interesting quote from that article, which I think is summed up in a lot of after market gadgets:

Re: Someone tested a saturn
 

you often hear that statement made about cars in general (if they could make them more efficient, they would have already). seems reasonable. but it's not always true.

cooling systems in particular are designed for "worst case" conditions (e.g. idling in traffic for extended periods in 110 degree heat trying to escape an approaching hurricane). they're not even designed for "average" conditions. the result is that average and "best-case" owners experience lost efficiency through "worst-case" designs that they rarely or never need.

[edit - removed my off-topic rant about aerodynamics being another area where car companies aren't offering efficient choices. will save that for another day.]

I was looking around. Underdrivepullies are avalible for the protege for $60, but it looks like I won't be getting one because of this post.

It's good to check on the old threads from time to time.

Not always so.....Honda engines are internally balanced. Infact the weight difference between all 4 cylinders are less than 1 gram for Hondas.

Unorthodox racing offers a crank only underdrive kit for Honda engines for this very reason. No need for harmonic balancing.

I susbect this to be true with the Saturn that was tested as well?

I would think you could be better off finding a more efficent battery, making sure all of your electrical connections are clean, and reducing your electrical loads.
gold electroplated electric contacts? (gold is not a great concuctor in wire form, but doesn't correde to cause resistance)

Underdrive pulleys do help a lot in some situations, my Camaro can eaily pick up .07 seconds at the track with one. I really don't think you could measure the increase on a Metro though. The Camaro has power steering and a/c driven off the belt and is shifting at 6500rpm. An a/c compressor and ps pump do not need to spin that fast so they are just wasting power. Metros and most of the cars here do not have more than the water pump and alternator on their belts so there is not much gain to be had by slowing down the water pump. The alternator gets less efficient as it goes slower so there is no gain to be had there.

If I get around to it I plan on putting an electric water pump on my Metro. It will at best save 1-2hp at over 4000rpm where the water pump is spinning faster than it needs. At idle and under 2000rpm I don't expect a gain other than the faster warmup times and better acceleration not having to spin up the water pump with the motor.

Either way it will be a small gain and more expensive than it is worth money wise, but that has never stopped me from doing stuff before :) I have already spent more for all the mods total than I will ever get back from saving gas. It is all in the fun of pushing a car to it's limits.

part of the reason for underdrive pullys on race cars is when you have an engine that normal runs at 3,000 rpm 99% of the time the water pump is running at one speed, now if you are racing, your engine is going to be running much faster 99% of the time (to get more power out of it) so you gear the pully drive system down to run everything else at a speed closer to what they are designed to run at.

Grounding Cables
 

So, I expect better grounding cables would help as well? (I installed a set on a peformance car in the past).

RH77

Underdrive pulley
 

The use of an underdrive pulley along with LED lights and I found a pair of driving lights that use only 35 watts each bulb for a total of 70 watts compared to 110 watts for the car lights. These driving lights give off 100 watts of light. So with my LEDs and these driving lights I figure I have reduced my overall wattage by about 106 watts total.This alone will help in the underdrive pulley hands down....Now the cooling issue????

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.

Me thinks they forgot the decimal point. I could be wrong. Under drive pulley takes less power for the accessories. I would imagine that this would have a greater effect at higher RPMS. This may work well with my short ratio tranny.

Not so. Hondas are internally balanced, but the harmonic balancing is in the crank pulley. W/out it, at a certain high RPM there is a damaging vibration to the engine. This is why underdrive crank pulleys are only recommend on race engines and show cars. If you run an aftermarket crank pulley your first indication comes when you blow out your crank seal. People that understand engines very well know that the crank seal goes bad because the crank is out of balance and the engine is nearing it's end. In fact, if you're ever shopping for a used Honda and you see oil leaking from the crank seal, pass on it!

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.

Very good point. When I used to own a DSM (eagle talon) one of the common modifications was to remove as much rotating mass as possible from the crank. A company that sells stuff to help do this has a quote on their website,

"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/

I never had the vehicle motor running until I did the mod (got car with bad motor). However, most people said they feel a little more vibration at an idle (some say they don't feel any difference). At higher rpms I felt no vibrations. As for bearing life I haven't seen where people had a problem they could directly attribute to it. I think more people had the balance shaft belt (behind the timing belt) break and take out their timing belt and bend valves than had an issue with the bearing life. The former was another reason some people did the removal...along with more power and POSSIBLY more fuel mileage.It was an amazing car being turbo allwheel drive, however I sold it and got a honda hx for the fuel mileage even though I was getting 24mpg consistently.

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

I'm surprised this hasn't come up more often. With everyone wanting to disconnect alternators and such.

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.

It is true that you shouldn't change the crank pulley on many engines. My Subaru flat four is an exception. If you are worried about changing the crank pulley some companies make larger, underdrive accessory pulleys. You can get them for just the accessories you want underdriven, they are lighter than stock, and it won't affect the crank. Ideal setup may be one of these on the alternator and electric water and steering pumps.

whole point of underdrive pullies is to make the crank smaller and lighter(hence why i went from large steel to small aluminum), less mass to keep spinning/spin up.(hence why race engines typically have lightweight flywheels too and idle at 2k rpm lol)

AFAIK Honda did not start using harmonic balancers until the 1996 model year. My 1993 del sol D16z6 does not have the rubber in the crank pulley. Neither did my 86 crx EW4, 87 civic D15A3, 88 civic D15B2, 89 civic D16A6.

In any case, if you were building an engine you could have the rotating assembly balanced with combination of pulley and flywheel you want.

Sorry to bring this thread back from so long, but I am planning to install a crank pulley and a lightweight flywheel, and I didn't want others misinformed.

My 94 Honda Accord (2.2L) does have a harmonic balancer built into the crank pulley- as well as rotating internal balance shafts.

perhaps my statement only aplies to the d-series engines then.

I put an aluminum flywheel and crank pulley on a 1990 Z I had and I noticed a big difference and the idle didn't seem any rougher.

it has nothing to do with a rougher idle. it has to do with crankshaft flex chewing up the crank bearings.

I would underdrive my water pupmp but the ecotec uses the timing chain for that so....

yea the accessories are fine, but unless theres some sort of internal dampener the crank pulley is just asking for trouble. they use them on race engines because they're going to rebuild them every race anyhow so who cares?

Let's be careful not to confuse harmonic balancers with dampeners. The difference is that a harmonic balancer is actually keyed to counteract internal forces, whereas a dampener only reduces the shock to and from accessory loads. An undampened underdrive pulley however just by virtue of underdriving reduces the amount of shock and vibration to deal with however. I.e., a larger pulley can both transmit and receive larger shocks by the difference in mechanical advantage.