Thinking about an under drive crank pulley for my 305, good idea?

[1998_K1500_Sub]

Thanks for the feedback, am looking to get a better MPG and willing to do this experiment to see where it may lead. If you are seroiuses about selling me an underdrive kit , I am interested in buying that from you. Thanks

If you can wait until early March, then it's yours. Put a note on your calendar to get in touch with me then, if you want it.

I'll have to dig it out when I return home. I know there's a crank pulley and I think an (smaller than OEM) alternator pulley that comprises the "kit". The pulleys are black and of course are used.

You would have to determine the serpentine belt size for your application. I've got a belt for it, which I'm happy to provide, but it may not fit.

Shipped to you, $100.

Here's another post on the topic:

Underdrive pulley kit

Hello all, I wanted to know what options are out there for an underdrive pulley kit for my 94 Silverado 350 TBI. Any gains? Any recommendations? Thanks in advance

www.gmt400.com

 

[1998_K1500_Sub]

I found some notes on my underdrive pulleys. If my notes are correct:

- Crank pulley 6" diameter (in the kit)
- Water pump pulley 6" diameter (in the kit)

My notes indicate the stock crank pulley is 8". Check this number by measuring yours.

I also have listed TWO different alternator pulleys and I'm not sure why. Perhaps my notes are jumbled, but here's what I noted:

- 3” diameter alternator pulley
- 2-3/8” diameter alternator pulley

I think what I was trying to capture in my notes, as regurgitated above, is the size of the stock pulley and the size of the kit's pulley. You should measure yours for comparison.

I checked March's site, this kit seems akin, in terms of pulley sizes, to what I've got. My kit is for reverse-rotation; this March kit appears to be for standard rotation.

Chevy Small Block : Long Water Pump Performance Ratio Single 6-rib Serpentine Pulley Kit

Single 6-rib aluminum serpentine performance ratio pulley kit for Chevy small blocks with long water pumps. Designed to replace factory V-belt or steel serpentine pulleys.

marchperformance.com

 

[cubandeathgrip]

I found some notes on my underdrive pulleys. If my notes are correct:

- Crank pulley 6" diameter (in the kit)
- Water pump pulley 6" diameter (in the kit)

My notes indicate the stock crank pulley is 8". Check this number by measuring yours.

I also have listed TWO different alternator pulleys and I'm not sure why. Perhaps my notes are jumbled, but here's what I noted:

- 3” diameter alternator pulley
- 2-3/8” diameter alternator pulley

I think what I was trying to capture in my notes, as regurgitated above, is the size of the stock pulley and the size of the kit's pulley. You should measure yours for comparison.

I checked March's site, this kit seems akin, in terms of pulley sizes, to what I've got. My kit is for reverse-rotation; this March kit appears to be for standard rotation.

Chevy Small Block : Long Water Pump Performance Ratio Single 6-rib Serpentine Pulley Kit

Single 6-rib aluminum serpentine performance ratio pulley kit for Chevy small blocks with long water pumps. Designed to replace factory V-belt or steel serpentine pulleys.

marchperformance.com

Thanks, will check my pulley size today, i do appreciate your time for helping me out, I have learned quite a bit on this site from knowledgeable folks such as yourself.

 

[Silverado1994]

Looks like you may be on to something with the fuel economy C&DG. I found some additional stuff on this page (although some of the suggestions are a little over the top) that can be used in addition to the pulleys.

Do underdrive pulleys increase MPG? - Car Forums and Automotive Chat

Do underdrive pulleys increase MPG? Engineering/Technical Car Forums

www.automotiveforums.com

 

[Supercharged111]

I ran one, didn't notice a diff.

 

[wb292]

My 454SS had a March underdrive on it when I bought it. At a red light in the summer the AC would struggle to cool. I went back to the stock pulley. Couldn't tell any difference in power output or mileage. Not that anything could change mileage on it. You can get some good results in mileage with helping the engine breath better. Shorten the exhaust to reduce back pressure has worked on my K1500. Since it is a 305 it most likely does not have the bigger rad in it. Install the bigger rad and the fan clutch will engage a lot less.

 

[1998_K1500_Sub]

@cubandeathgrip, I think underdrive pulleys have their place. Like @L31MaxExpress (who posted in this thread earlier), I have an engine in my Camaro that idles around 1200RPM and shifts WOT at 6500; running an underdrive crank pulley makes sense because the accessories will still run near their designed speed on account of the atypically higher (than stock) engine RPM.

For a stock vehicle, there's a much more limited opportunity for benefit and, as @wb292 noted, downside potential.

However, if you want to give them a try then "more power to you", I admire those that try things and learn from them.

 

[cubandeathgrip]

@cubandeathgrip, I think underdrive pulleys have their place. Like @L31MaxExpress (who posted in this thread earlier), I have an engine in my Camaro that idles around 1200RPM and shifts WOT at 6500; running an underdrive crank pulley makes sense because the accessories will still run near their designed speed on account of the atypically higher (than stock) engine RPM.

For a stock vehicle, there's a much more limited opportunity for benefit and, as @wb292 noted, downside potential.

However, if you want to give them a try then "more power to you", I admire those that try things and learn from them.

what do they mean by

"Long Water Pump"?​

 

[1998_K1500_Sub]

what do they mean by

"Long Water Pump"?​

You have the "long water pump".

The small block "short" water pump was used on Corvettes and perhaps others which had tight engine / radiator clearances. It positions the fan closer to the engine, thus allowing the radiator to be closer as well.

See this for more detail on the matter, from Summit Racing:

What's the difference between short and long water pumps?

help.summitracing.com

These "short pump / long pump" dimensions impact the selection of pulleys.

 

[cubandeathgrip]

what do they mean by

"Long Water Pump"?​

thanks, measured my crank pulley, I have it at 7 3/4 inch.