What is the maximum safe overbore for a SBC 400? Experienced builders only.

 

Most will go 040". I had one that I took there. I would not go 060. But I just saw one on e-bay.

 

Anyone Else? I think I'm going to base the overbore on popular opinion.

 

I kept mine to .30, but if it is bored and honed with a plate you might be able to go more. I like the .030, incase it eats something down and road.

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1992 Pontiac Firebird 350/Six Speed
1987 Toyota Pickup 383/500+ HP

 

Nearly all will go safely to .030". Most will go to .040". Somewhat less than half will go to .060", but nobody likes to do that except as a last resort.

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"So many Mustangs, so little time..."
ICON Motorsports

 

400s have a bad tendency for core shifting. i wouldn't worry about .030 anything more and i'd get it UT tested for thickness. i don't like more than .030 in anything even if it's pretty accepted to go bigger, with that said my 68ss has a +.060 overbore.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

I would agree with no bigger than .040". You may well know that 400 have siamiesed cylinder walls. No coolant can get to certain parts of the wall. If they get to thin, this could create hot spots, and even crack under intense heat.



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Joshua Johnston
1991 Z-28
350, T-5, K&N, Ported Vortec heads, Edelbrock RPM, Holley 750 D.P., HEI, 11.07:1 CR, Comp Cams Roller-.510"/.520"-282*/288* dur., Shorty Headers, Dual 2.5 Exhaust, Dynomax Bullet Mufflers, T&R Motorsports custom air intake, Bald tires

 

I'd vote for a safe maximum of 4.155" to maintain adequate wall thickness. I'd hate to see you have to sleeve a good case.

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Later,
Vader
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If you want to beat the World, it might reach up and pull you down...
Adobe Acrobat Reader

 

I'm going to say you can go .060, but I would never take one past .040.

I took mine .020.

I threw away a core that was already .040 and needed a build.


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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
and 2 POS commuters...

R.I.P. #3
"He can see air"

[This message has been edited by Engineboy (edited October 15, 2001).]

 

it is possible to bore it .060

BUT

you need the block sonic checked to make sure there is adequate material in the walls to sustain the bore

 

I know a guy that always had his 400s bored out .060 becuz he said that it was safe. If you notice I said 400s plural he kept on having them bored .060 over and he went through 5 blocks in 2 years. I wouldn't go anything over .030 just to be safe. Anything over .03 and I think you would be pressing your luck.

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97 formula w/6speed,cags skipshift eleminator, hurst billet pro shifter, 30#injectors,adjustiable fuel presure regulator,Moroso cold air induction,ported mass air sensor,accell300+ ignition box, accell 9000 wires, bosch platnum4 plugs,flomaster crossflow muffler,Lingenfiter 52mm throttle body,TPIS L98 SuperProfile cam,Crane 1:6 full roller rockers,Edelbrock subframe connectors,Edelbrock strut tower brace.

Other car is a 89 GTA w/700r4w/stage 2 shift kit,2800 converter, corvette servo, B&M mega shifter, TPIS bigmouth intake, TPIS large tube runners, TPIS 52mm throttle body,Edelbrock ported centerbolt heads,LT1 24# injectors,holly afpr,GMPP LT4 hotcam,CompCams Pro magnum roller rockers,Edelbrock headers, flowmaster crossflow muffler,MSD 6A, accell coil,150 shot NO2. This car is currently under rebuild and restoration.