Underdrive Pullies - Page 3 - Fuelly Forums

Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

Reply
 
Thread Tools Display Modes
 
Old 12-13-2008, 02:14 PM   #21
Registered Member
 
Join Date: Jun 2008
Posts: 19
Country: United States
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.
__________________

Lelandjt is offline   Reply With Quote
Old 12-14-2008, 06:23 AM   #22
Registered Member
 
Join Date: May 2007
Posts: 447
Country: United States
Quote:
Originally Posted by MetroMPG View Post
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:
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.
__________________

__________________
slurp812 is offline   Reply With Quote
Old 12-14-2008, 09:29 AM   #23
Registered Member
 
suspendedhatch's Avatar
 
Join Date: Apr 2008
Posts: 445
Country: United States
Send a message via AIM to suspendedhatch
Quote:
Originally Posted by brelandt View Post
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?
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.
__________________

Civic VX, D15Z7, 5 Speed LSD, AEM EMS, AEM UEGO, AEM Twin Fire, Distributor-less, Waste Spark
suspendedhatch is offline   Reply With Quote
Old 12-14-2008, 10:53 AM   #24
Registered Member
 
Join Date: Dec 2008
Posts: 25
Country: United States
Quote:
Originally Posted by Lelandjt View Post
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.
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 is offline   Reply With Quote
Old 12-14-2008, 12:21 PM   #25
Registered Member
 
GasSavers_Erik's Avatar
 
Join Date: Nov 2006
Posts: 1,027
Country: United States
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...
GasSavers_Erik is offline   Reply With Quote
Old 12-14-2008, 03:13 PM   #26
Registered Member
 
VetteOwner's Avatar
 
Join Date: Mar 2007
Posts: 1,546
Country: United States
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:
http://www.s10forum.com/forum/f105/h...ulleys-304284/
VetteOwner is offline   Reply With Quote
Old 12-14-2008, 03:48 PM   #27
Registered Member
 
Join Date: Dec 2008
Posts: 25
Country: United States
Quote:
Originally Posted by Erik View Post
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...
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.
Daveedo is offline   Reply With Quote
Old 12-15-2008, 01:27 PM   #28
Registered Member
 
VetteOwner's Avatar
 
Join Date: Mar 2007
Posts: 1,546
Country: United States
ya mine was $100
VetteOwner is offline   Reply With Quote
Old 12-15-2008, 01:42 PM   #29
Registered Member
 
Join Date: Nov 2007
Posts: 1,111
Country: United States
Send a message via AIM to dkjones96
I'm surprised this hasn't come up more often. With everyone wanting to disconnect alternators and such.
__________________
- Kyle
dkjones96 is offline   Reply With Quote
Old 12-16-2008, 06:34 AM   #30
Registered Member
 
Join Date: Sep 2008
Posts: 113
Country: United States
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.
__________________

__________________
zero_gravity is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 04:46 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.