Supercharger recommendation for 575SCI
10-01-2015, 09:14 AM
#41
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I myself, wouldnt be that worried about it. A stock forged bbc crank is a stout piece from the snout standpoint, much stronger in that area then a small block snout. The cog belt, and 871 underdriven, isnt really taking gobs of power to turn. Its not like we are talking a 71 series blower making 35lbs of boost on alcohol being grossly overdriven, and engine turning 8000rpm at the dragstrip. In that scenerio, for sure i would want a dual keyed crank.
I know many many friends with offshore boats, running 871s with single keyed cranks, and mild boost for years without issue. Also, those little blowers, when spinning at 10000 plus rotor rpm, do take quite a bit of power to turn when you start spinning them fast.
The big problem is when running cog belts, with no pop off valve. In the event of a big backfire in the manifold, you have a good chance at hurting the blower itself , or shearing the keyway. With a serpentine setup, the belt will simply slip. Blower shop and other places sell 16 rib setups for 71 series blowers as well.
I know many many friends with offshore boats, running 871s with single keyed cranks, and mild boost for years without issue. Also, those little blowers, when spinning at 10000 plus rotor rpm, do take quite a bit of power to turn when you start spinning them fast.
The big problem is when running cog belts, with no pop off valve. In the event of a big backfire in the manifold, you have a good chance at hurting the blower itself , or shearing the keyway. With a serpentine setup, the belt will simply slip. Blower shop and other places sell 16 rib setups for 71 series blowers as well.
I think the backfire starts the death of a 250 series blower. Mine backfired a few time due to bad fuel, shortly after that the rotors touched and eventually seized together. With the bevel cut gears and the way they are shimmed to time them, I can see how they can easily be knocked out of time. The bearing plate casting can and will shatter in this process of destruction as well.
What do the old 900 SCs use for ballancers?
10-01-2015, 07:02 PM
#43
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I'm calling Dyers tomorrow. Last time I called they would not sell me the thermostat adapter for my old 525sc. Guy said you have to buy the whole kit. I have a collection of blower parts from past projects and do not need all the 575 kit. I need a blower and the adapters and pulleys. I wonder if they will sell me just those parts. If not, moving on to a shop that wants my money.
Last edited by Old Navy; 10-02-2015 at 05:35 AM.
10-01-2015, 09:34 PM
#44
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I still get the heevy jeevys spooling a big roots way off the front of a stock gm single key out of the crate set up.
Its not as much about the power to run the rotors its more about the inertia of the 2 items spinning at speed linked by a unforgiving cog .running a stout key or double key in a good crank and deleting the balancer and using one of those roots specific adapters helps , i was just throwin it out there that if your not gonna show it off a screw compressor will get you into the drive breaking danger zone without all theextra trouble .
The good 8-71s and such will deliver the goods for sure and has 10 times the wow factor but absolutely loads thecrank more
Its not as much about the power to run the rotors its more about the inertia of the 2 items spinning at speed linked by a unforgiving cog .running a stout key or double key in a good crank and deleting the balancer and using one of those roots specific adapters helps , i was just throwin it out there that if your not gonna show it off a screw compressor will get you into the drive breaking danger zone without all theextra trouble .
The good 8-71s and such will deliver the goods for sure and has 10 times the wow factor but absolutely loads thecrank more
10-02-2015, 08:41 AM
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That looks like a great upgrade. Did they ever make the 525sc with a 502 bottom end or just 454's. What kind of numbers did you get with that setup?
10-02-2015, 08:43 AM
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10-02-2015, 09:07 AM
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10-03-2015, 07:18 AM
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575sci 250/256 to 871 parts list:
One of the 2 below (cant remember diameter)
http://www.theblowershop.com/store/6...dia-p-458.html
http://www.theblowershop.com/store/6...dia-p-459.html
http://www.cpperformance.com/p-13315...regulator.aspx
Thermostat adapter from whipple on my setup
To plumb the fuel line to the Tbodies I just re-bent the stainless tubing or you can switch to AN fittings with flexible lines.
If you look at the pic my fuel pressure sender is plumbed inbetween the throttle bodies and sealed with loctite
There are a few guys that can get you close on a map...to be honest the stock map sucks so bad (pig rich at idle) a canned map will be better no matter what. EB marine, Tyler Crocket, Ben of Precision Power can get ya close, AF meter definitely recommended.
You can Send your throttle bodies to CFM (screen name SB) for mods as I did.
Cant remember my pulley sizes but a boost gauge is definitely recommended.
Before any of this, change your head gaskets to an MLS type gasket.
One of the 2 below (cant remember diameter)
http://www.theblowershop.com/store/6...dia-p-458.html
http://www.theblowershop.com/store/6...dia-p-459.html
http://www.cpperformance.com/p-13315...regulator.aspx
Thermostat adapter from whipple on my setup
To plumb the fuel line to the Tbodies I just re-bent the stainless tubing or you can switch to AN fittings with flexible lines.
If you look at the pic my fuel pressure sender is plumbed inbetween the throttle bodies and sealed with loctite
There are a few guys that can get you close on a map...to be honest the stock map sucks so bad (pig rich at idle) a canned map will be better no matter what. EB marine, Tyler Crocket, Ben of Precision Power can get ya close, AF meter definitely recommended.
You can Send your throttle bodies to CFM (screen name SB) for mods as I did.
Cant remember my pulley sizes but a boost gauge is definitely recommended.
Before any of this, change your head gaskets to an MLS type gasket.
Last edited by JRider; 10-03-2015 at 07:20 AM.
