GeorgeS

I think the standard bore and stroke on a 400 block is 4.125 and 3.75.
Is this correct?
How far can you SAFELY overbore this block?
Can a 4 inch crank be installed without hitting a water jacket while clearancing?

Objetive is to build a SB427 using a late model 400 roller block and utilize some of the internals instead of buying all new.

bluedawg

4.125" bore, 3.75" stroke. Be cautious using the oem 400 block to build a 427. You might want to think about an after market block, you can still use oem roller that way.

GeorgeS

So it sounds like a 4 inch stroke is possible.
I have looked at Dart and World blocks but the price... If I use a oem block I have rods lifters, bolts and accessories I won't need to purchase.

Will I get too close to a water jacket in clearancing?

Saubrenner

I don't think you can bore a 400 small block .125, that's what it would take to get 427. If you try to get it through stroke, I don't think you can use 400 rods.

Ben Lurkin

I would suggest a 3.875" crank and 0.030 overbore; which will land you in the 420 CI range. With the right rods and a small-base circle cam, you will probably only have to clearance the block in a couple of places. What rods do you have now?

4" in a factory block runs the risk of hitting water jackets and you will have to grind a lot on the main rails; an area that isn't particularly strong in the factory block anyway.

The max I've ever been able to bore a factory 400 SBC is 0.040" without having problems. Get your block sonic tested before going any more than this.

BLOCKMAN

X2

We won't put a 4 inch arm in a 9.000 deck OEM block as your getting to small with the base circle of the cam. Lifter hate small base circle cams!!!!

We have been building quite a few of the 3.875 X 4.155 with the Dart SHP block and with the Callies rotators we have been using a 1.000 base circle cams. On some of the builds we have gone to he .903 lifters with the .810 wheel which a .842 lifter uses a .750 wheel.

Actually Morel is releasing a hyd. roller lifter in the next week or so. That being said with the bigger lifter body, bigger wheel and bigger axel its a win win situation.

GeorgeS

[QUOTE=Ben Lurkin;1576659189]I would suggest a 3.875" crank and 0.030 overbore; which will land you in the 420 CI range. With the right rods and a small-base circle cam, you will probably only have to clearance the block in a couple of places. What rods do you have now?

I planned on using the rods from the oem block. The intent is to make a large CI small block and spend my money on new parts I don't have such as a good set of heads and a crank...

Ben Lurkin

[QUOTE=GeorgeS;1576662561]If that's the case scrap your plan and throw the money you were going to use for this at a decent set of heads then. A 406 with a good set of heads will kill what you're planning to build. A decent set of vortex heads can be had for $700. You will spend that much for the crank alone.

If you mean the 5.565" rods, at least upgrade those to the 5.7" rods. You can do this for just a couple hundred$

Ben Lurkin

Vortex=vortec

bluedawg

You could take that 400 crank & rods, have the crank turned down and put them in a .030'' over 350cid block, you can make almost the same power in a block that's more dependable. It seems just about anybody who builds a 400 out of the original block uses the two bolt main block, has it splayed & fills the block up to the bottom of the freeze plugs with block filler. I bought the shp block for my 400, not to pricey, actually budget minded as far as after market blocks go.

L88Plus

There's no such thing as a late model or roller 400 block. They weren't made past 1980, all are OEM flat tappet, it'll take retro-fit rollers to work.

junkman123

i know they say there is no replacement for displacement but just as much power can be made with less cubes.why not just do a .030 with some good 5.7 rods and the 3.75 stroke for the 406 and make up the cubic inch lose with more hp from good cam selection and head work(thats where were is made anyway).it would also be best to use the early 4 bolt main 400 blocks with the 3951511 casting.it has a little more in the cylinder walls and if you puke it you got meat to rebuild it.if you go big bore/big stroke and then puke its trash cause there is nothing left.and dont think bigger is better with the carb either,i have seen engines make more hp with a 660 center squirt then a 780.

due to the current economy i cant afford the usual 2cents so i just put in my 1cent worth

bashcraft

The 4 bolt blocks are trash. The outer holes for the main caps are drilled into the webbing and severely weaken it. 20 years ago I built a 377 from a 4 bolt 400 block. It was turning about 7500 rpm when the block cracked from the front main up into the cam journal. I later found out that this happens quite often.

You're better off to start with a 2 bolt block and have splayed caps installed.

BLOCKMAN

We have sonic tested alot of 400 blocks and so far the cylinders are no different then any other 400 OEM block that GM made and most of the time the OEM 400 blocks are no that good once sonic tested.

But the time you spend good money putting splayed caps on and all the other machine it takes to build you would be much better of buying a Dart SHP block which would be much more dependable in the end then a 30 year old block that sometimes will crack for no reason.

Check this thread out.
http://www.chevelles.com/forums/showthread.php?t=342418

Ben Lurkin

So because you blew one up at 7500 RPM they're trash? That's a bit overstated. The 400 block actually has a wider bolt spacing on the main bearing caps than the other SBC's making them relatively strong.

At 7500 RPM you simply were beyond the design limits of the block and would have likely fried any oem block. It was, quite simply, never designed for that type of usage in the first place. For any application around 550 hp or less, the 4-bolt 400 is a decent block. The two-bolt block on the other hand, always let the caps walk in my experience which tended to chew the bottom end apart on any high perf. application.

I'm with blockman. Reworking a 2 bolt 400 block is an exercise in futility; especially at the price one can get a sportsman block for.

BLOCKMAN

You have that wrong larger span between the main bolts makes for a weaker main cap caps and webbing.

bashcraft

It sounds like you've been misled.

The engine I was referring to was pushed no farther than many other engines I've had which used 350 blocks. The 350 blocks never broke.

Do some searches and you'll find many instances of 400 blocks breaking the same way mine did.

Ben Lurkin

One time does not a majority make.

No need to look it up either. Unlike some, I'm not an internet racer. I ran them in the late 80's and personally built over 20 of the things, all 4-bolts, for myself and others over a period of about 10 years. I never had one fail in the way you describe. These were all built with the old 'turbo' heads and later on, sportsman II's and were in the 550 hp range, so I can say with some authority that they will hold up.

Now granted, I wasn't taking them to 7500 RPM, but they would routinely see 6800 or so. If yours was cammed correctly with a good set of heads, you would certainly be above 550 and remember, stresses increase exponentially with engine rpm's.

Ben Lurkin

If that's true then splayed caps are the wrong way to go.

BLOCKMAN

I was talking that the 400 block is wider between the main cap bolts over a 350 block and being they are wider on the 400 they are a weaker a set up!!!!!!!!!!!!!!!!!!