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Old 12-23-2012, 06:40 PM
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Demolition derby

What would be some good clearances for a derby motor? And kind of pistons with low expansion. Im building a 383 thanks for any help

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Old 12-23-2012, 06:57 PM
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why waste money on a good engine?
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Old 12-23-2012, 07:26 PM
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Quote:
Originally Posted by Sbc10 View Post
What would be some good clearances for a derby motor? And kind of pistons with low expansion. Im building a 383 thanks for any help
we've built some successful ones using stock cast pistons.
some guys like to spend money on forged but that's up to you.
keep in mind, these things get HOT, and need to keep going, even if it is weakly.
we've done .008" extra clearance on the bores (i.e. 4." bore is honed to 4.008")
and .080" top and second ring gaps. no that's not a typo.
what often happens is these get so hot that the ring gap closes up and seizes in the bore. this huge gap helps that.
whatever engine you're running, find a cylinder head that is not crack prone.
if you have more questions feel free to send me a pm.
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Old 12-23-2012, 08:44 PM
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Sbc 383 derby motor

Thanks alot

Last edited by Sbc10; 12-23-2012 at 08:51 PM. Reason: Wrong
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Old 12-24-2012, 02:17 AM
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Quote:
Originally Posted by Plaintoast View Post
we've built some successful ones using stock cast pistons.
some guys like to spend money on forged but that's up to you.
keep in mind, these things get HOT, and need to keep going, even if it is weakly.
we've done .008" extra clearance on the bores (i.e. 4." bore is honed to 4.008")
and .080" top and second ring gaps. no that's not a typo.
what often happens is these get so hot that the ring gap closes up and seizes in the bore. this huge gap helps that.
whatever engine you're running, find a cylinder head that is not crack prone.
if you have more questions feel free to send me a pm.
Excellent, I had no idea that much thought and preparation went into a DD car.
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Old 12-24-2012, 10:17 AM
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more important is your choice of car
i've run a 70 comet moredoor, 72 fury II, 70 monte, 70 coupe deville and a 74 sedan deville before
the caddies have more frame than an f250 and 3 feet from the front bumper to the radiator
no fan, drilled hole in the radiator cap, radiused wheel openings, no stock wiring and a floor shifter will work magic
wire a start and run circuit direct to a battery mounted on the pass floor
a stock column shifter can be knocked loose, we used a maverick cable floor shifter, adjusted with no park and no locks. push forward to go forward, pull back for reverse
cut your exhaust off so you can hear it running over the noise or reverse the manifolds and run the tips thru the hood. it's quite impressive shooting flames at night.

rule number one: have fun
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Old 12-24-2012, 11:21 AM
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Originally Posted by techinspector1 View Post
Excellent, I had no idea that much thought and preparation went into a DD car.
there seems to be two groups of demo guys. ones that run anything, junkyard motors, original motors, whatever was laying in the corner.
it seems when guys start becoming serious about going out and competing for wins, they join the group of people that spend as much on their motor as they do the chassis.
its actually similar to the way beginning circle track stock classes work, albeit a different build style but the serious guys have engines built to "stock" specs that vastly outperform actual oem pieces.
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Old 12-24-2012, 11:33 AM
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If the pay our makes it worth while to build an engine?
I would think a worn out engine or"clearanced" engine would be good.Instead of buying a stroker crank,I think I would buy a set of gears and weld the spiders.I dont see the advantage of a stroker?
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Old 12-24-2012, 01:23 PM
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Quote:
Originally Posted by vinniekq2 View Post
If the pay our makes it worth while to build an engine?
I would think a worn out engine or"clearanced" engine would be good.Instead of buying a stroker crank,I think I would buy a set of gears and weld the spiders.I dont see the advantage of a stroker?
Yep you will never reach more than 20 mph anyway unless your doing some crazy figure 8 style dirby but i think everybody stopped that back in the 70s.

Might want to use seperate trans cooler and not run the trans thru the rad since its a target. Dont forget to weld a backup linkage to the trans and run a lever up thru the floor. Also make sure she will start in gear.

Aumuseal is great for a sealing leaky radiators. I would toss some in there just in case it might help.
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Old 12-25-2012, 10:57 AM
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Well I guess some people are in a different world on demolition derbing. I know where I derby we are going over 20mph when we are hitting. And stock motors won't get the job done anymore around here are features last 45-60 min of balls out. That's why I'm asking on some pointers because I know what I've been running will run all nite long without water but needing alittle more hp and torque. Are Derbys pay from 1 grand to 10 grand to win. I know the basic I have a 35 spline moser axle rearend slider driveshaft ice and fan cooled tranny coolers and the stock steering column is a thing of the past and we can tear the crap out of the old cars with 98-02 crown vics we so I think me and plaintoast are more on the same page but thanks for the comments derbing not knocking the windows out anymore.
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