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Old 10-29-2003, 04:21 PM
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403 pistons in 455

i have plans on boreing my 455 out enough to fit in 403 pistons (4.351).......i have no idea, however, if 403 connecting rods would work with the 455 crank, or if 455 connecting rods would work with the pistons, or if it makes a difference at all ........any info is appreciated

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Old 10-29-2003, 05:21 PM
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Tons of info here.
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Old 10-29-2003, 05:56 PM
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A 455 has a 4.126" bore a 403 has a 4.350" bore. thats over 200 thousands overbore for the 455......good luck!
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Old 10-29-2003, 10:47 PM
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That is NOT possible on a stock 455 block, on the racing blocks it was possible, you could even move the piston center and I "believe" a maxium overbore of .600 in was allowed, but DONT quote me on that.

EDIT: I dont know if desktop dyno is computing it right, but it says that the HP and torque would be no better than a regular 455.
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Old 10-29-2003, 10:56 PM
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Quote:
Originally posted by 87442lover
EDIT: I dont know if desktop dyno is computing it right, but it says that the HP and torque would be no better than a regular 455.
WOW! I would have figured it would have made a noticeable difference. At what rpm range do they differ?
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Old 10-29-2003, 11:11 PM
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Well.. they both seem to be stuck at 375HP by about 550ft. lbs torque. I dont know why? I started out with a 455 .030 over, a generic cam, 265x275 .500 lift. 110 center.
750 cfm dual plane, 10.0:1 on the 455 it fell by 11 CC's going to the bigger bore. 2.0x1.625 valves. ported.

The torque goes up by 50 pounds, but that it, I guess the bore is too big fo rhtat storke?!?! I dont know?
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Old 10-29-2003, 11:46 PM
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in my desktop dyno, i have these figures - 455 - 407hp/4500 523ft/lbs/2500 505 - 406/4500 582ft/lbs/2000
my HP drops slightly with the bore, but my powerband shifts lower which i like


if curious, my other specs are -
ported, 2.078, 1.68
9.5
660, dual plane (its actually a holley 650DP, but no double pumper option)
large-tube, mufflers
(@.050) .496,.520/224,234/112



also, can somebody explain y i cant bore this block out? physically there is plenty more than .2inches available to machine away

im not really familiar with machine work like this, so i apologize if this is a pretty stupid question
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Old 10-30-2003, 02:18 AM
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Quote:
Originally posted by Rocket455
in my desktop dyno, i have these figures - 455 - 407hp/4500 523ft/lbs/2500 505 - 406/4500 582ft/lbs/2000
my HP drops slightly with the bore, but my powerband shifts lower which i like


if curious, my other specs are -
ported, 2.078, 1.68
9.5
660, dual plane (its actually a holley 650DP, but no double pumper option)
large-tube, mufflers
(@.050) .496,.520/224,234/112



also, can somebody explain y i cant bore this block out? physically there is plenty more than .2inches available to machine away

im not really familiar with machine work like this, so i apologize if this is a pretty stupid question
For one, you need a minium amout of material on the cylinder wall to avoid the wall flexing during ignition. Most normal blocks will allow a .060 overbore, the 403 will only allow .020 overbore safely. Also there are the issuses with cooling and the head gasket ring falling into the cylinder. I'm not sure what the minium wall thickness is, but on my 403 between the cylinders is has at least .20 in(I think) and there are no water jackets between the cylinders.
Thee only olds block that could except such a bore of .20 inches over standard was the racing blocks they use to make. But these can be hard to find. You can even re-center the bores on these blocks because they had so much thickness.
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