GM 400 block bore and stroke?
Thread Starter
Instructor
Joined: May 2008
Posts: 154
Likes: 3
From: Indiana
GM 400 block bore and stroke?
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.
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.
Thread Starter
Instructor
Joined: May 2008
Posts: 154
Likes: 3
From: Indiana
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?
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?
Le Mans Master
Joined: Dec 2006
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From: Oquirrh Mountains
St. Jude Donor '09
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.
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.
Drifting
Joined: Dec 2005
Posts: 1,360
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From: NORTHEAST
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.
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.
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.
Thread Starter
Instructor
Joined: May 2008
Posts: 154
Likes: 3
From: Indiana
[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...
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...
Le Mans Master
Joined: Dec 2006
Posts: 5,557
Likes: 9
From: Oquirrh Mountains
St. Jude Donor '09
[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 $700. You will spend that much for the crank alone.
If you mean the 5.565" rods, at least upgrade those to the 5.7" rods. You can do this for just a couple hundred$
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...
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...
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$
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Safety Car
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From: anchorage ak
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.
Drifting
Joined: Aug 2004
Posts: 1,883
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From: Lubbock TX
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.
Instructor
Joined: Feb 2011
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From: Axton va
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
due to the current economy i cant afford the usual 2cents so i just put in my 1cent worth
Le Mans Master
Joined: Jan 2006
Posts: 6,506
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From: Butler Pa
You're better off to start with a 2 bolt block and have splayed caps installed.
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
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.
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.
You're better off to start with a 2 bolt block and have splayed caps installed.
Check this thread out.
http://www.chevelles.com/forums/showthread.php?t=342418
Le Mans Master
Joined: Dec 2006
Posts: 5,557
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From: Oquirrh Mountains
St. Jude Donor '09
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.
You're better off to start with a 2 bolt block and have splayed caps installed.
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.
Drifting
Joined: Dec 2005
Posts: 1,360
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From: NORTHEAST
You have that wrong larger span between the main bolts makes for a weaker main cap caps and webbing.
Le Mans Master
Joined: Jan 2006
Posts: 6,506
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From: Butler Pa
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.
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.
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.
Le Mans Master
Joined: Dec 2006
Posts: 5,557
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From: Oquirrh Mountains
St. Jude Donor '09
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.
Le Mans Master
Joined: Dec 2006
Posts: 5,557
Likes: 9
From: Oquirrh Mountains
St. Jude Donor '09
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST