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How much can you safely deck a 250 block.

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How much can you safely deck a 250 block.

Post #1 by 65-coupe » Sun Jan 14, 2018 9:36 pm

Just seeing if I can zero deck a 250 block. I have a set of new ol;d stock forged pistons I plan to use.

Thanks Brian
1965 Mustang coupe, SPI Orange with custom TMI interior, 250 DUI, CI alum head ported, 274/274 110 Clay Smith cam, 1.65 roller rockers, Holley 390 4bbl, Lokar pedals and throttle calbe. Street or track front coilovers suspension, CI headers stainless with Jet-Hot ceramic coating, CI Stainless 2" impostor dual exhaust, 17x8 Coys C-67 wheels,

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Re: How much can you safely deck a 250 block.

Post #2 by drag-200stang » Mon Jan 15, 2018 9:08 am

The safest thing is a minimal clean up cut... The deck is your foundation..Ford made these blocks to save money..They may seam solid but it would shock you if use measured the bore after the head is torqued down and that effects ring seal..
Is there not a longer rod that someone here just tried that worked well, 2.5 ???
66 Mustang Coupe
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stock adj. rockers, stock timing set, ARP studs
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Went 9's when 10's was fast.

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achieving better quench

Post #3 by chad » Mon Jan 15, 2018 2:27 pm

65-coupe wrote:Just seeing if I can zero deck a 250 block. I have a set of new ol;d stock forged pistons I plan to use.
Thanks Brian

Can U measure 2C what U have for deck now?
Can U do the math on the current rotating assembly?

The 2 numbers together will answ the Q. correctly.

Then U can C what can get U closer to 0 w/o a machining (including dishes, offset grind, etc).
Make sense?
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
Chad - '70 LUEB on '77 frame (i.e. PS, D44, trapezoidal BB 9", 4.11), '69 250ci, NV 3550 & DSII, "T" D20/PTO, 2" SL, 1" BL, 4 discs, 33"X15", tool boxes, etc. Seeking: Hydraulic gear motor for Koenig pto. (413) 259-1749

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Re: How much can you safely deck a 250 block.

Post #4 by CZLN6 » Mon Jan 15, 2018 3:27 pm

Howdy back Brian:

I can say from experience that .070" is doable. That's what I did to mine. Probably not a good idea. What is your engines deck height? Mine was .150". At some point structural integrity becomes and issue.

If I were to do another 250, I start by using the 255 V8 pistons which are .085" taller than 200/250 pistons. But you said you had a set of forged stock 250 pistons you intend to use. You could also consider offset grinding the crank to raise the pistons up another .010" to .12". Also check out the Tempo rods recently discussed here.

PS- hold off on head work until you have figured out dimensions or your CR will be through the roof.

Keep us posted.

Adios, David
co-author of the Falcon Performance Handbook

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