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Old 10-11-2009, 06:04 PM
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Forged or cast crank?

I recently got a great deal on a Weiand 6-71 blower set-up for my 31 coupe project. The guy I bought it from threw in a set of JE forged blower pistons for a 383 sbc stroker. The problem is that I was building a tunnel rammed sbc and have a 10/10 forged 350 crank. Given that this a for a street rod that will see only very occasional time trials at the strip and won't go much beyond 6000 rpm, would a cast aftermarket stroker crank be OK? I have asked around can't find much consensus. I realize that a forged crank is the preferred option, but I have a pretty tight budget, so the prices are pretty attractive if it would work.

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Old 10-11-2009, 06:56 PM
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David Vizard has stated that he has taken 550+ hp out of 383's on the dyno for the past several years without one failure on Scat 9000 cast STEEL cranks.
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Old 10-11-2009, 07:04 PM
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Cast cranks?

You may get away with the cast crank for a while, just as you may get away with a 2 bolt block. Hell the engine don't know how many bolts hold the crank in. What it does know is how much pressure is exerted against the main caps. My guess is that with a small amount of boost and low compression you will double you horsepower the crank will take 400 HP but if you turn up the boost ( you could get 1000HP or 2000 HP ) to high you will spit the crank right out the bottom of the block. Not only you but anyone trying No2 will do the same. Many years ago I put a 4-53 Jimmy blower on a stock 265 Chevy and boy did it wake that thing up. We had to make our own manifold then with pop off valves, You can buy all that stuff now. If your looking for performance for a drag car , You will brake the crank If you are looking for show on the street just turn down the boost, under drive it its got a lot of power with out the blower and a little more wont hurt, A lot will! Now let me understand something this 383 you are building ? a 350 crank into a 400 block? or the 400 crank into the 350 block? Id go with the 350 crank and use a big bore and order a set of Eagle rods because its the rods that will brake first. You can get them what ever length you need.
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Old 10-11-2009, 07:18 PM
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Thanks for this! I am going with a stroker crank in a 350 block as that is what my pistons are designed for. I am running a tight LSA cam (110) with low boost (6-7lbs) to keep things reasonable with pump gas. The car is not meant to be a drag car but I would like to jump into time trials now and again. My horsepower shouldn't be that high, but I don't know the effects that a blower has on a crank. I've heard of cranks breaking in a blower motor under less than huge boost. Really what I am looking to find out is whether or not the crank needs to be forged based on the fact that it is blown (strain on the snout, etc) or on the amount of horsepower that it is putting out.
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Old 10-11-2009, 07:28 PM
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Quote:
Originally Posted by 31oldschool
Thanks for this! I am going with a stroker crank in a 350 block as that is what my pistons are designed for. I am running a tight LSA cam (110) with low boost (6-7lbs) to keep things reasonable with pump gas. The car is not meant to be a drag car but I would like to jump into time trials now and again. My horsepower shouldn't be that high, but I don't know the effects that a blower has on a crank. I've heard of cranks breaking in a blower motor under less than huge boost. Really what I am looking to find out is whether or not the crank needs to be forged based on the fact that it is blown (strain on the snout, etc) or on the amount of horsepower that it is putting out.
Sounds like you're always gonna be worried about it and that will make driving the car a chore. Is that what you want? I wouldn't want to have to worry about the crank everytime I leaned on the loud pedal. Put the project on hold until you can buy a forged crank and rods from Ohio Crankshaft or whomever you like and some 4-bolt caps from Milodon. See part #43503750 here....
http://www.ohiocrank.com/chevysb_cranks.html
and pick your rods here, depending on piston compression height....
http://www.ohiocrank.com/hbeam_rods.html
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Old 10-11-2009, 08:16 PM
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From DR

Lots of Power only breaks parts when the tires hook up-
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Old 10-12-2009, 11:57 AM
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I agree with techinspector. You don't want to be worrying every time you get on it if the crank is gonna snap this time, or maybe next time, or the time after that. Plus who knows maybe you are gonna want to sway pulleys for more power down the road and if you got the forged crank in the bottom end that won't be a problem. Its a lot easier to put the better crank in now, than down the road pull it all apart again. just my .02
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Old 10-12-2009, 01:10 PM
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Much appreciated!

Keith
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Old 10-12-2009, 02:06 PM
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Use a good crank to begin with.
Have the snout cut for 2 keys.
Build the motor so that there will be ZERO detonation. (reasonable static compression ratio for the boost you will run, tight piston to head squish, proper air/fuel ratio, standard-tip spark plugs...NOT EXTENDED TIPS....starting cold and going a little hotter as you read the plugs, proper ignition timing for the boost you will use. Look into a boost retard unit from MSD or other supplier.
Limit rpm's to that recommended by the crank manufacturer.

Use these guidelines from Blower Drive Service....
http://www.blowerdriveservice.com/recommend.php
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Old 10-12-2009, 03:42 PM
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Great information! I ordered the "Supercharing for the Street" book, but that takes afew weeks to get here. Here is the chassis and the previous engine combo:


Keith
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