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underdrive pulleys on the cheap
https://slantsix.org/forum/viewtopic.php?t=59447
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Author:  Badvert65 [ Tue Apr 12, 2016 8:34 am ]
Post subject:  underdrive pulleys on the cheap

OK, this is for racing only, drag racing in particular. There was a Hot Rod magazine article about the aluminum slant 6. When they drag tested it, they discovered that if you remove the belt on the water pump, you will gain about 20 HP. With that in mind, I figure that under drive pulleys should be of some benefit. since they are not readily available, I looked at some items I had lying around. This is what I came up with for practically zero cost.
Image
The crank pulley is the pulley off of the AIR pump from my 79 Volare super six. I just had to drill the holes so it would bolt to the balancer. This will yield approximately 25% reduction. This was zero cost, but you can buy the small crank pulley for a Chevy V8 that will bolt up and do the same.
The water pump pulley is actually a slant six accessory crank pulley. I used a steel washer (9/16 I think) in the center and reamed the hole out to 5/8 for the water pump snout. then I just drilled the holes for the water pump bolts. This pulley is too large to be powered directly by the balancer, but the offset clears the balancer with room to spare. I did use spacers on the modified AIR pump pulley to align things. The larger pulley on the water pump will give an additional 10% reduction to the water pump.
My alternator has a double pulley on it and the front most groove will line up with the modified pulleys. Total cost was one flat washer.
It isn't for everyone, but for the drag racer out there, every little bit helps.

Author:  Joshie225 [ Tue Apr 12, 2016 9:47 am ]
Post subject: 

Looks good. How did you get everything concentric?

Author:  Badvert65 [ Tue Apr 12, 2016 10:05 am ]
Post subject: 

I used a water pump to center everything. The AIR pump pulley had a pilot hole in it that I used to center that pulley. The pulley on the water pump was easy as the flat washer was a near perfect fit. Using a water pump snout to center everything, use the accessory pulley to mark holes in the AIR pump pulley (for the balancer pattern) and use a water pump pulley to mark the holes on the accessory pulley. The hardest part was cobbling up spacers for the new crank pulley to line up with the new water pump pulley.
The balancer on my race motor is different than the one in the picture (spare engine). The only difference might be to the spacing on the new crank pulley.
These pics show the mod to the accessory pulley so it would mount on the water pump. The washer was a very snug fit and would probably have stayed in place with glue or by staking it.
Image
Image

Author:  Badvert65 [ Tue Apr 12, 2016 10:11 am ]
Post subject: 

After drilling the mounting holes in the new crank pulley, I cut the center hole extra large to clear a socket for the crank bolt.

Author:  slantzilla [ Tue Apr 12, 2016 10:34 am ]
Post subject: 

Very nice! :D

Author:  Joshie225 [ Tue Apr 12, 2016 10:46 am ]
Post subject: 

That's cool. I'm waiting on a cutter to help me transform a 3-groove truck damper into a 6-groove poly v-belt drive pulley.

Author:  Badvert65 [ Tue Apr 12, 2016 10:49 am ]
Post subject: 

Just another shot to show the alignment.
Image
Image

Author:  Badvert65 [ Tue Apr 12, 2016 10:50 am ]
Post subject: 

Quote:
That's cool. I'm waiting on a cutter to help me transform a 3-groove truck damper into a 6-groove poly v-belt drive pulley.
Now that, I'd like to see.

Author:  Joshie225 [ Tue Apr 12, 2016 11:23 am ]
Post subject: 

I'll take pictures.

The poly-v-belt cutter was ordered yesterday and is coming from Texas. I really hope Western Tool Supply doesn't call back to say I need to buy 10. If so I'm likely to grind my own cutter from a parting tool. The big (wide) truck damper is on hand. There is a water pump pulley at Summit Racing, Auto Specialties ASP-820021, that looks good. I will get it on the way. My blower pulley is 8-rib, but I think that I can make it work with 6 ribs and use that water pump pulley. I'll cut 8 grooves in the crank pulley in case the extra belt area is needed in which case I will almost certainly end up fabricating/cobbling together a water pump pulley.

Author:  Badvert65 [ Tue Apr 12, 2016 2:22 pm ]
Post subject: 

For those of you wondering...
Factory balancer is 7inch dia, water pump pulley is 6.5 inch dia and alternator is around 2 inch dia
This means at 1000RPM (crank), the water pump is going 1077RPM, the alternator is going 3500RPM
If you put a large diameter 'hemi' pulley on the alternator (3 inch dia) the alternator RPM drops to 2335.
Changing only the small crank pulley (5.25 inch) the water pump RPM drops to 800 and the 2 inch alternator drops to 2625 RPM while the 3 inch alternator drops to 1750 RPM.
With the small crank pulley and the extra large water pump pulley (7.125 inch) the water pump RPM will drop to 740 at 1000RPM crank speed.
Make what you will of it, these are just the numbers.

Author:  Joshie225 [ Wed Apr 13, 2016 7:30 pm ]
Post subject: 

It looks like the Auto Specialties pulley will work perfectly! (Can you believe I ordered it yesterday?) As you can see by the alignment with the single groove damper and power steering pulley the front 2 V grooves will disappear from the big truck damper when I machine it for the 6-rib drive. I may go ahead and put a 3 or 4-rib poly-V on the rear side of the truck damper to drive the alternator and hang the alternator off the power steering pump mount.

https://drive.google.com/file/d/0B8Nx2X ... cslist_api

Author:  SlantSixDan [ Wed Apr 13, 2016 8:19 pm ]
Post subject: 

This is nifty work, and I have no intent to dismiss it or anything, but it's been about 36 hours and my eyebrow is still in the fully upright and locked position over that 20-horsepower-from-unbelting-the-water-pump figure. Which is to say, I doubt it a lot. Maybe if I had more details—was that belt driving anything else, like an alternator and/or a radiator fan (and if so, which type of each)—it would be easier for me to swallow and/or explain, but for now, nope.

Author:  slantzilla [ Wed Apr 13, 2016 8:42 pm ]
Post subject: 

Dan, they took the belt completely off. No water pump or alternator being driven. I thought at the time the big gain was more from the car being run dead cold than losing the accessory drive.

Author:  DusterIdiot [ Thu Apr 14, 2016 5:37 am ]
Post subject:  x2

Quote:
No water pump or alternator being driven. I thought at the time the big gain was more from the car being run dead cold than losing the accessory drive.
That's what I gathered from the article and experience...

I know one of our racers on this coast, in a race only car has removed the alternator completely and charges the battery between rounds with a portable setup...and so the motor doesn't overheat he has mounted and wired a motor he took from the stock heater box to drive the water pump pulley...

Author:  Badvert65 [ Thu Apr 14, 2016 7:20 am ]
Post subject: 

Quote:
This is nifty work, and I have no intent to dismiss it or anything, but it's been about 36 hours and my eyebrow is still in the fully upright and locked position over that 20-horsepower-from-unbelting-the-water-pump figure. Which is to say, I doubt it a lot. Maybe if I had more details—was that belt driving anything else, like an alternator and/or a radiator fan (and if so, which type of each)—it would be easier for me to swallow and/or explain, but for now, nope.
Dan, I truely value you opinion as you will tell it like it is (sometimes bluntly). This is the sort of feedback I post for.
The biggest caveat to this mod is no cost and is easily reversible. I agree with your skepticism and I plan to try things both ways just to get some numbers.

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