water pump pulley ratio
Oct 10, 2011 4:36:21 GMT -5
Post by sigmfsk on Oct 10, 2011 4:36:21 GMT -5
I checked the stock pulleys on my
'74 440
crank: 7 5/16"
water pump: 6 3/8"
overdrive: 15%
'76 400
crank: 7 5/16"
water pump: 5 5 15/16"
overdrive: 23%
These fit with the stock ratio usually being about 20% overdrive:
www.moparmagazine.com/2008/may_june-2008/keep_your_cool.html
> The typical production engine uses an overdrive pulley ratio, which means that the
> water pump runs faster than the engine. This is good for low-speed cooling but not
> good for horsepower at high speeds. Generally the amount of overdrive is about 20
> percent.
books.google.com/books?id=MMwGX4-jnxYC&pg=PT211&lpg=PT211&dq=the+approximate+ratio+between+the+crank+pulley+and+the+water+pump+pulley&source=bl&ots=vU0gZf0GhJ&sig=6xSLMhhFlgSXxcnZvRwTmZZYmW0&hl=en&ei=x__GTIaAI8Kclgen7-X0AQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBMQ6AEwAA#v=onepage&q=the%20approximate%20ratio%20between%20the%20crank%20pulley%20and%20the%20water%20pump%20pulley&f=false
> On production 6-bbl engines, the approximate ratio between the crank pulley and the
> water pump pulley is 20% overdrive. This means that the water pump turns faster than
> the crank. In a typical aftermarket billet-aluminum pulley set, this ratio is about 20%
> underdrive.
although it looks like stock could be up to 45% overdrive.
www.moparmusclemagazine.com/techarticles/engine/mopp_0109_440_head_buildup_dyno_test/index.html
> On this engine, we bolted on a set of stock C-Body pulleys, which overdrive the water
> pump to 145 percent of crank speed.
In the original posts, I talked about how I plan on using a March 40550 pulley set
as shown on these cars:
At the time I ordered the kit, March's documentation said that their pulley sizes were:
crank: 6"
water pump: 6 1/8"
for a slight UNDERDRIVE
but I wasn't sure that was what I wanted, so I called them, and they said that their documentation was wrong, and the actual sizes were:
crank: 6"
water pump: 4 7/8"
for an overdrive ratio of 23%
and that sounded fine, but a little high for my tastes. I ordered the kit and found that the actual sizes were:
crank: 5 7/8"
water pump: 5 1/2"
for an overdrive ratio of 7%
When I spoke with them on the phone, they said they just call the crank pulley 6", even though its closer to 5 7/8". And what about water pump of 5 1/2" vs. 4 7/8" ? The new tech guy (current guy on the phone) said the old tech guy (guy I spoke with earlier) was in error. The old tech guy said that the old water pump size was 6 1/8" and the new tech guy said that the old water pump size was 6 1/2". Both tech guys said they switched to a smaller water pump pulley because of cooling issues.
The 1974 440 stock overdrive ratio was 15% and I'm reducing that slightly to 7% overdrive.
Around town (low RPM): cooling should be fine. I'll be using electric fans vs. the manual fan from the water pump, the largest radiator I can fit, and if other March customers don't have cooling issues, I presume I won't either.
Around town (low RPM): alternator. If I had the stock alternator I might have some concern, but I expect the 105 amp AD230 will produce a generous charge at idle.
High RPM: this is where I like the 7% vs. 15%. At 6000PM, the water pump will be spinning at 6400 RPM vs the stock 6900 RPM. Not that this is a huge difference, but I'm certainly glad it's in this direction instead of the 23% overdrive that I was expecting which would be 7400 RPM.
March says that they seem to have hit the sweet spot with this ratio; they haven't had any complaints about cooling, and it's also holding up well at high RPM such for drag racing, as reported to March by Mancini Racing.
Mostly from archived info here:
www.bluesbrotherscentral.com/forum/topic/8327-theres-a-new-marin-county-sheriff-in-town/page__view__findpost__p__113073
'74 440
crank: 7 5/16"
water pump: 6 3/8"
overdrive: 15%
'76 400
crank: 7 5/16"
water pump: 5 5 15/16"
overdrive: 23%
These fit with the stock ratio usually being about 20% overdrive:
www.moparmagazine.com/2008/may_june-2008/keep_your_cool.html
> The typical production engine uses an overdrive pulley ratio, which means that the
> water pump runs faster than the engine. This is good for low-speed cooling but not
> good for horsepower at high speeds. Generally the amount of overdrive is about 20
> percent.
books.google.com/books?id=MMwGX4-jnxYC&pg=PT211&lpg=PT211&dq=the+approximate+ratio+between+the+crank+pulley+and+the+water+pump+pulley&source=bl&ots=vU0gZf0GhJ&sig=6xSLMhhFlgSXxcnZvRwTmZZYmW0&hl=en&ei=x__GTIaAI8Kclgen7-X0AQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBMQ6AEwAA#v=onepage&q=the%20approximate%20ratio%20between%20the%20crank%20pulley%20and%20the%20water%20pump%20pulley&f=false
> On production 6-bbl engines, the approximate ratio between the crank pulley and the
> water pump pulley is 20% overdrive. This means that the water pump turns faster than
> the crank. In a typical aftermarket billet-aluminum pulley set, this ratio is about 20%
> underdrive.
although it looks like stock could be up to 45% overdrive.
www.moparmusclemagazine.com/techarticles/engine/mopp_0109_440_head_buildup_dyno_test/index.html
> On this engine, we bolted on a set of stock C-Body pulleys, which overdrive the water
> pump to 145 percent of crank speed.
In the original posts, I talked about how I plan on using a March 40550 pulley set
as shown on these cars:
At the time I ordered the kit, March's documentation said that their pulley sizes were:
crank: 6"
water pump: 6 1/8"
for a slight UNDERDRIVE
but I wasn't sure that was what I wanted, so I called them, and they said that their documentation was wrong, and the actual sizes were:
crank: 6"
water pump: 4 7/8"
for an overdrive ratio of 23%
and that sounded fine, but a little high for my tastes. I ordered the kit and found that the actual sizes were:
crank: 5 7/8"
water pump: 5 1/2"
for an overdrive ratio of 7%
When I spoke with them on the phone, they said they just call the crank pulley 6", even though its closer to 5 7/8". And what about water pump of 5 1/2" vs. 4 7/8" ? The new tech guy (current guy on the phone) said the old tech guy (guy I spoke with earlier) was in error. The old tech guy said that the old water pump size was 6 1/8" and the new tech guy said that the old water pump size was 6 1/2". Both tech guys said they switched to a smaller water pump pulley because of cooling issues.
The 1974 440 stock overdrive ratio was 15% and I'm reducing that slightly to 7% overdrive.
Around town (low RPM): cooling should be fine. I'll be using electric fans vs. the manual fan from the water pump, the largest radiator I can fit, and if other March customers don't have cooling issues, I presume I won't either.
Around town (low RPM): alternator. If I had the stock alternator I might have some concern, but I expect the 105 amp AD230 will produce a generous charge at idle.
High RPM: this is where I like the 7% vs. 15%. At 6000PM, the water pump will be spinning at 6400 RPM vs the stock 6900 RPM. Not that this is a huge difference, but I'm certainly glad it's in this direction instead of the 23% overdrive that I was expecting which would be 7400 RPM.
March says that they seem to have hit the sweet spot with this ratio; they haven't had any complaints about cooling, and it's also holding up well at high RPM such for drag racing, as reported to March by Mancini Racing.
Mostly from archived info here:
www.bluesbrotherscentral.com/forum/topic/8327-theres-a-new-marin-county-sheriff-in-town/page__view__findpost__p__113073