Gas mileage is abysmal and I have a big fat battery. I've read opinions on the cheap aftermarket U/D pulleys damaging the crankshaft on K24 engines. Saw a post about using stock RSX Type S pulleys since they have a dampener. He had been riding on the A3 pulley in his element with no issue and getting some improvements for at least a year.

Original pulley:

Part #: 13810-RRA-A02
Found in:
2002-2006 Base RSX (k20a3)
2002-2005 Civic Si (k20a3)
2004-2008 TSX (k24a2)
2002-2006 CR-V (k24a1)
2003-2005 Accord (k24a4)
Diameter: 6.125"

Z1 Pulley

Part#: 13810-PRC-003
Found in: 2005-2006 RSX Type-S (k20z1)
Diameter: 5.40"

A2
Diameter: 5.80"

The Z3 is pretty close too.

Diameter: 5.75"


So to according to this I would need:

Honda Pulley tool - $20-30
K20z1 Pulley - new its $130 but I'm sure having all winter to look I could find one cheaper.
New Serpentine belt ????

That's kind of where I fall off. How can I find a compatible belt. The users of this idea never provided a part number or length.


All in all I hope to gain some HP but mainly a few MPG. In the summer I would get 23-25, when my drive shaft was out even 27. But now 21 is the best I get even driving under 60 on the freeway. Advice or help would be appreciated.

 

What other mods have you done to lessen the MPG?

I don't think UD pulleys will bring up your MPG, not enough to be noticeable....

 

I upped the tires to 32psi, changed the oil to 0w20, made sure the maintenance was up. Short of ECU reprogramming what other kind of mods could I do? I can make it 2wd again, seems like a bad idea in the winter.

I was going to start logging o2s and fuel trim on drives this week just to 100% rule out anything being wrong. I already log every trip via OBD.

 

Honestly you're inline with what the MPG rating is...only way you can change it is to start to remove things like roof racks, and drive slower...

 

V8 where I installed a U/D, only the crankshaft, gave 2mpg more, other people had same experience w/ B series hondas and china underdrives... but those don't have a balancer. The pully is old an rusty sucker, there is some wobble there. I already have a new water pump and tensioner pulley. A/C didn't wobble when the belt was off.

I have no roof rack, I already drive slow.

 

I did some investigation on the belts looking at the dayco site.

Standard:
Top Width (in) 0.96
Thickness 0.17
No. of Ribs 7

Different:
2003 Acura RSX S 5070675 lenght: 67.52"
2003 Acura RSX 5070680 lenght: 68

2005 Acura RSX 5070680 lenght: 68"
2005 Acura RSX S 5070670 length: 67.01"

2003 CRV 5070683 lenght: 68.25"

Stock Circumference: 19.24226"
05 RSX S Circumference: 16.9646"

2.27766 /2 = 1.13883

1/2 the difference of pulley circumference is 67.11117


?? 2003 Acura RSX S 5070675 length: 67.52" would be the belt?

 

So just to update: I finally got the pulley installed. The RSX-S 2003 belt fit perfectly. On the K-series you can remove the crank bolt with the starter unlike other Honda engines. I tried the jack method and 2 breaker bars and it wouldn't budge. It's been on there for like 18 years. 1 blip of the starter took it right off. I think I got it back on to the correct torque, my wrench tops out at 160 but I gave it some breaker bar. So far everything seems normal. No unusual stats in torque, no noises, etc. A few weeks worth of driving with the mileage logger will tell if the effort and $70 was worth it.

 

From testing the pulley gives 3-5mpg bonus. I've seen over 30 on the highway for the first time. 32 was the highest so far. So I think this winter I'll be getting summer mileage.