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Old 02-09-2008, 07:42 AM
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Small Block Chevy cooling

I'm fairly new to the hobby and get my information from books, sites such as this and knowledgeable friends. One of my books, "1001 More High Performance Tech Tips", mentions that for proper cooling, the Small Block Chevy water pump needs to be driven at 30-35% higher rpm than the crank. I've searched my other books, this Bulletin Board and have asked my knowledgeable friends about this, but nobody seems to be familiar with this SBC water pump overdrive concept. Has anybody on this Bulletin Board heard about this overdrive deal or have any experience with it?

Regards,
Grog

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Old 02-09-2008, 07:49 AM
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I would think that Chevy engineers went through all this. Measure the diameter of your crank pulley and water pump pulley see what the ratio is..........that is a start anyways..........
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Old 02-09-2008, 09:19 AM
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Small Block Chevy Cooling

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Originally Posted by poncho62
I would think that Chevy engineers went through all this. Measure the diameter of your crank pulley and water pump pulley see what the ratio is..........that is a start anyways..........
Unfortunately the Chevy Engineers had little to do with the set up I have. I'm the third owner of a '47 Chev Sedan Delivery with a 350 turning a 350 auto trans. The original build was done in '97 and was well done ('74 Camaro stub frame, body work etc.). The second owner installed (I use the term loosely) a brand new Hampton 671 blower and kinda cobbled together the front end accessory drives. It even has a 2 groove ( 1 groove is 5.5 in. dia. and the other is 6 in. dia.) water pump pulley which, in my limited experience, I have never seen before. The accessories are driven by two 6 in. dia. Hampton pulleys on the crank, both trying to turn the two different sized water pump pulley grooves at the same rpm. Well, I fixed that and now have only the 5.5 in. dia. waterpump groove being driven by the crank, giving me an overdrive on the waterpump of approximately 9%. The blower is driven at 80% of crank speed and is making very little boost; however, I'm sure it's adding some heat to the engine (which was not built for a blower). I've been slowly eliminating problems which were causing the engine to overheat severely (it now only overheats a little (210 F.) under certain conditions) and was just wondering about the water pump overdrive situation. I'm going to a car show tomorrow and should be able to see some older v-belt drive systems on some SBCs, and if the owners will let me, I'll measure some pulley/groove diameters. Thanks.
Regards,
Grog
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Old 02-09-2008, 09:58 AM
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I just went out and measured mine.........I have a 62 engine with the short pump setup and a 76 engine with the long pump setup........Both pulleys (crank and water pump) on each vehicle are 7" which tells me my setup is running 1:1..........no overheating problems. I am measuring outside of the pulley........

I know that there are after market crank pulleys so that the water pump is under driven on drag cars....saves HP..........You want to go the other way.

What size rad are you running?

BTW, 210 degrees isn't that bad, if it just at certain times.
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Old 02-09-2008, 10:42 AM
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In some cases overdriving the water pump can cause cooling problems...theory being that the water flows though the radiator faster and does not have time to cool down as much. My 99 Chevy Silverado's normal operating temp is 200-205. That is what a lot of the newer stuff runs...they claim the hotter temps make them burn the fuel more effciently .
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Old 02-09-2008, 11:30 AM
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Small Block Chevy Cooling

Thanks for the responses.

I'm running a recently professionally cleaned Brassworks 4 row radiator which feeds a brand new Edelbrock short nose water pump which pumps into a recently reverse-flushed engine block, returning to the radiator through a 160 F. thermostat. I installed an electric (not top of the line) 2300 cfm "puller" fan behind the radiator which replaced a modified (mutilated ?) water pump-driven fixed speed fan. The fixed speed fan was assisted by an electric "pusher" fan mounted in front of the A/C evaporator which was mounted about 1/2 inch in front of the radiator, and this set up was not very efficient/effective. Right now, I'm only running the electric "puller" but may re-install the electric "pusher" when it comes time to run the airconditioning. Since the "puller" fan seems to be working so well, I plan to eventually install a more efficient unit which has a built in shroud.
Poncho, thanks for checking your pulley size for me. I also measured to the outside diameter of my pulleys.
Regards,
Grog
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Old 02-09-2008, 11:46 AM
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If I were you...I would run a 195 thermostat. Use the puller fan with a proper fitting shrould. Pusher fans tend to block the airflow in my opinion.
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Old 02-09-2008, 02:37 PM
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Here's an article I wrote for the wiki and which has been edited by others. Maybe it will be some help.
http://www.crankshaftcoalition.com/w...cooling_system
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Old 02-09-2008, 04:58 PM
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ALSO ... jetting and timing are very important on supercharged engines. I might try to enrich the carbs a step or two. Richer carbs tend to make the engine run a little cooler.
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Old 02-09-2008, 06:01 PM
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Is the fan you are using mounted on a shroud which covers your entire rad core? That would help pull air thru the entire core not just in front of the fan. I run a smallish 85 vette rad with a dual 11 inch spal fan/shroud setup which fits the core like a glove and pulls 2750 cfm. It cools my 500 hp small block very well. 160 stat with fans set on at 180--off at 170. Did not get over 185 last summer on a 100 plus deg day.
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Old 02-11-2008, 04:29 PM
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Small Block Chevy Cooling

Thanks for the help guys.
My blower is fed by a single Edelbrock 4 bbl and definitely is running rich, although I don't know what jets are installed. As previously mentioned, I installed a relatively inexpensive non-shrouded 16 in. dia. (radiator core is 18.5 in. X 18.5 in.) "puller" fan just to see if I was moving in the right direction. I've been looking at the SPAL shrouded units, which is probably the way I'll wind up going. I think the induced draft "puller" fans are definitely the way to go.
Now back to the original question of over driving the SBC water pump. I went to the car show yesterday, and took a close look at 4 SBCs, both modified and stock. Although I wasn't able to take actual measurements of diameter, it was visually clear that 3 of the 4 water pumps were significantly over driven, and the 4th appeared to be 1:1. A buddy of mine has a 350 in his '49 Packard resto-rod (beautiful car), and his water pump appears to be significantly over-driven. I looked at a beautiful stock '69 Z-28 with the 302, and again, that water pump appeared to be significantly over-driven. Sorry I didn't get to make actual measurements this time but will do so in the future and will report my findings. By the way, talking to the SBC guys at the show revealed that they were all unaware of the water pump over drive issue (if there is, in fact, an issue). It'll be a couple of weeks until the next show.
Regards, Grog
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Old 02-11-2008, 07:24 PM
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I run my waterpump 13% overdriven , The more you overdrive your pump the more HP it is sucking from the engine . if your car will run in a normal temp with the water pump underdriven you will gain a few hp .
I am running a small block chevy , I also plumbed a line from the outlet on the water pump to the the back of the engine block to feed cool water into the back of the block
I also run water wetter , seems to help also.
When I got the car it would overheat just idling , it would run cool at a 50mph cruise but would overheat quick if i started lead footing it . Seems much better now !!
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Old 02-13-2008, 07:08 PM
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Just wondering, but why don't you just do away with belt driven pump and go with electric? You can even get a pulley kit that mounts on side of it to keep your belt system the same. I'm sure you don't drive it every day. Just an idea.
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Old 02-17-2008, 10:35 AM
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Small Block Chevy Cooling

I've looked at the electric water pumps that are presently available and have also talked about them to a lot of small block Chevy guys. The consensus is that the electric water pumps are meant for racing applications and are not rated for the thousands of hours that extensive street use would put on them. If I was just going to cruise a little bit back and forth to shows, the electric water pump might be the answer; however, I plan to make my '47 Chev into a reliable and relatively economical long distance traveler. To achieve this I have lots of mods to do, but among the first will be to replace the blower with a 3-2 barrel set up. I'd also like to replace my 350 trans with the 700 R-4 overdrive unit. Ah well, that's hotroddin' ... it's never finished!
Grog
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Old 02-18-2008, 08:06 AM
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grog,
try simple first with the pulley you have to get a "indication" if more overdrive/more GPM will-can help

clamp a heater hose closed.....
that 5/8" hose is bypassing alot of gpm only thru the pump back into the motor, (not thru the rad)
(the blocked hose routes alot more GPM thru the radiator same as a more overdrive pulley will when stopped/creeping in a I-95 traffic jam!!!)

my mild motor temp in traffic with the AC full blast on our 95* "balmy" summer days with a 20x24 rad.....would creep up.....added a $6 on/off valve to the heater hose....no creep with the heater valve closed (and less heat in the car)

with only a 18x18 rad...I'd strongly suggest you add a good oil cooler
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