Underdrive Pulley Question

[California98Civic]

Originally Posted by Daox

Haha, yeah I got em reversed. You're right.

Thanks Daox. I thought it had to be so... a question? About how much larger would you guys estimate I could/should seek in a custom-made or aftermarket aluminum pulley? I know this is a slightly costly mod, but I am willing given my long-term plans for running this car many years to come, whatever repairs it needs (short of a major smash-up, knock-on-wood).

[Daox]

Most underdrive pulleys are a 15% reduction in speed from what I've seen. Some go as high as 20%.

[EdKiefer]

Originally Posted by California98Civic

Thanks Daox. I thought it had to be so... a question? About how much larger would you guys estimate I could/should seek in a custom-made or aftermarket aluminum pulley? I know this is a slightly costly mod, but I am willing given my long-term plans for running this car many years to come, whatever repairs it needs (short of a major smash-up, knock-on-wood).

I don't think this is good idea if you can get UD over the counter . I used to be machinist along with later being mechanic .
Here few issues that needs to be addressed .

1) you need to make sure tolerances are kept tight as balance can be affected .
2) tolerance at crank shaft nose needs to be tight or all harmonics will not be addressed (you will have less dampering as it is as aluminum is lighter, less dense)
3) you need to key crank pulley and add a steel insert where the oil seal rides (or it will wear an leak) .
last many crank pulleys also engage the oil pump making manufacturing more complex .

[t vago]

And if you don't pay attention to the vibration dampening needs of your particular engine, this could happen.



That was an crankshaft-driven oil pump rotor.

[California98Civic]

EdKiefer, t_vago, thanks for your input. It will be useful. I have seen some cautions about balancing and such on Honda Tech, but those guys too often talk in comic book style Vin Diesel quips without explaining anything. Maybe it is worth saying that until now my interest has been simply in accessory pulleys, not the crank pulley, because of the concerns and greater complexity. But I read something that might change my mind: it seems the stock Honda crank pulley might weigh a little over 4lbs, while some UD crank pulleys, such as the AEM Tru Power weigh as little as 3/4 of a pound. Question I had after reading that was whether rotational mass on the crank pulley is more significant for FE than rotational mass generally. I doubt it, but I wonder what you guys might say.

[t vago]

Crank pulley rotational mass only really matters during acceleration. It is only during times when rotational velocity changes that mass plays any part. Even so, unless you're constantly accelerating or decelerating (and why would you? you're trying to maximize your FE), this will not gain you any noticeable benefit.

Steady-state improvements in FE will come from underdriving the power steering pump, the A/C compressor, and (for me, anyway) the water pump. Electrical draw from the alternator aside (which is the subject of another thread here at Ecomodder.com), mechanical pumps rated to perform at idle using a stock crank pulley will draw less power with a UDP.

[t vago]

I installed my UDP before going in to work today. Apart from noting a slight decrease in fuel consumption (which may or may not be noise), and apart from noting that the truck actually went into DFCO a couple of times, I did not notice any obvious improvements.

EDIT: It is an ASP underdrive pulley, with a harmonic damper, and a steel pulley wheel bolted to the damper. The damper is pressed onto the crankshaft, and the assembly is then held in place with the crank pulley bolt. There does not appear to be any weight savings from this UDP. The pulley wheel is sized 25% under stock.

I will have a log set ready on my return leg tonight, when I can have better control of steady-state speed on the drive.

[hamsterpower]

Originally Posted by California98Civic

Even though 1% is a marginal gain, it is intriguing and thanks for adding your thoughts. Question: how would I research UDPs for my 98 Civic? The racing sites would all be giving me the opposite of what I need. There must be measurement specs for my stock pulley. Could I use them to search for just any like-sized, mountable and lighter pulley? I imagine I could. Do you know good sites or suppliers where I might start? I'm still looking... EDIT: here's an installation of larger pulleys: DIY: AEM Tru-Power under drive pulley kit install - Honda Civic Forum EDIT 2: since I only have the alternator still connected, here is a $60 option: Honda Civic Megan Racing Lightweight Pulleys

Regarding Civic pulleys: Archive from TheOldOne.com
pay attention to the long post near the bottom. TOO (The Old One) is THE Honda engine guru. The Civic pulley is a harmonic dampener and should NOT be messed with. I expect other cars are similar. There is lots of other good info on that site too. The Old One - Energy Dynamics

[t vago]

7/12 - normal crank pulley
59.2 miles / 2.85 gallons = 20.8 MPG

7/28 - UDP
59.2 miles / 2.80 gallons = 21.1 MPG (+1.7%)

I got a slight increase over fuel consumption data collected over 2 weeks ago, but again I must stress that this improvement is barely above what could be considered noise.

I had to slow down to 55 MPH over a 2 mile stretch of I-77 south, due to road construction, where I would normally do about 72 MPH. That slowdown doubtlessly skewed my fuel consumption upward a little bit. It is likely that, had I not had to slow down, the improvement in fuel economy would be even less than what I saw tonight.

Hopefully, there will be no construction work on my return commute leg this weekend, and I'll be able to get a better reading.