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400sb or 396bb

R

ramses

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Im looking for a bigger motor to put in my truck this spring and I have 2 friends that I could get a 400 small block or a 396 big block from. I could get them for about the same price. Since theyre about the same cubic inches, what are the advantages of each motor? Which would be better for a truck? My truck is my daily driver but I use it for work and some play on the weekends, nothing too serious. My built 350 has plenty of power for what I need but I want a fresh motor. The advantage of the 400 would be that I already have a whole lot of brand new parts on my 350 that would fit on it so all I would need to do is get it bored and put together and get a cam for it then use my 350 parts for the rest.
 
ditto with echos, smaller package, more cubes, you might not have the horsepower, but you will definetly get the torque.
 
400 is lighter, the more cubes deal isnt worth the argument, 400's need a larger cooling system than a normal small block just as a 396 will.

here is the good thing about the big block... you can bore it out big time. cooling system is still needed and weight is higher. but its can be bored and stroked way larger.

i vote 396, as it should also have a lot more low end torque in stock form.
Grant
 
ditto...

I had a 74 454 from a Chevelle in my 74 K20--it was a bit tired,and was no powerhouse to start with,being an "emission" motor rated at only 235 hp and 360 ft lbs of torque..

When its piston(s) started getting noisy(2 had broken skirts!)- I decided to replace it with a 400 SB out of a 78 Suburban I'd bought for parts..I found the 400 SB to be every bit as powerful as the 454 was,if not more,due to it being lighter!..I swore it had more torque..

I'd say the 400 SB gets my vote,especially in your case,where you have a 350 already,and all accessories will be a bolt on deal..its a PITA to find big block pulleys and brackets used now,and all the other "trinkets" you need to go from SB to BB ..hard to beat the "bling" factor of the BBC though..

BTW--the 396 isn't the greatest BBC in my opinion in stock form..I've had a few that were real dogs!..the worst one was out of a 69 Impala,and it came stock with a 2 BBL carb!..I had guys with 350's that could suck the doors off my truck with that 396 in it....:blush: --they can be built up to respectable ratings though..:crazy: .
 
I'm a bit bias here, but i say 400 small block also because of torque.. i can deff. feel the torque that my 400 is putting out, and it pushes my blazer around with no problems..
 
The 400 is notorious for having cooling problems, so you will probably have to get a better radiator. Same goes for the 396, so that puts them about even from that perspective. To put the heads from your 350 onto the 400, you will have to drill steam holes in them to work with the 400 block (I don't know what heads are on your 350, but they are probably better than the stock 400 heads). Don't get a 4 bolt 400, they are notorious for cracking main bearing caps. The 396 has much more potential for making power plus it has a much higher coolness factor. My vote goes to the 396.
 
Ok, unless I find a 454 for a good price then im going with the 400. How does a 454 compare to a 400? I have a few questions the 400 now. Will everything off of my work on the 400? By that I mean the water pump, power steering pump, intake, headers, valve covers, dirstributor, ect. My plans for the 400 arent too radical, I dont want it bored any more than needed, ill probably build it like I did my 350, a decent sized dual pattern cam with the gear drive, intake, ignition, and headers from my 350, maybe roller rockers too. Is there anything I should check on it before I buy it? Ive looked it over a few times and ive seen it torn down and I never noticed any problems.
 
I dont think you can bore to much on these because there isn't much to bore.. i will have to check what my grandpa did to mine..
 
305 (or even 283) up to 400 do look the same to 99% of the people (assuming outside clues like intake oil fill don't give it away), much like the built 455 in my old GTO that I told everybody was a stock 389. :whistle: I could spot the differences, but almost nobody else could...

396 tends to like to rev more, stock 400 does not. 400 SB has some cooling issues as noted due to the siamese cylinder block. Cracked heads are also common in the SB 400 around "weep" holes required by the siamese cylinders.

One other thing. 396 will be a pre-smog motor and probably beats most any typical post smog 454 numbers across the board. Though if it still has the old heads, they may need upgrading to modern hardened seats and valves.

Also, a while back one of the mags built a pair of chevy motors, one BBC, the other SBC, both as close to identical as possible. 400 ci displacement, comparable cams, compression, exhaust, everything. As I recall, the BBC came out quite a bit ahead, thought it cost a bit more. Primarily attributed to the head design and bore/stroke/rod ratios. More than enough to offset the weight difference (though that is just considering power, and weight may have more implications for you than just offset in performance).

And as other's said, the 400 SBC already has some known issues (though not deal killers) and is considered on the "ragged edge" in some respects, the 396 has lots of possibilities and a certain BB cache' as well.

Summay, I think I would go 396…
 
I think I'd look at the bore vs. bore, stroke vs. stroke, and con rod length vs. con rod length to start with. For a DD that's going work hard I'd want a smaller bore, longer stroke, and shorter rod. That short rod does some undesirable things to the shape of the torque curve (& therefore it's likely to be an unpopular opinion), but the thing that outweighs that is what it does for the engine's resistance to detonation. A short stroke will want a long rod to get as much near TDC dwell as possible to get the most out of each fuel/air charge. A longer stroke doesn't need that long rod to get the most from the fuel/air charge, and less near TDC dwell reduces the detonation tendency.

Basically, if you don't have stroke then you need dwell time and if you have stroke then you don't need the dwell time. The smaller bore/longer stroke when combined with a cam that takes advantage of them will yield an more efficient engine in the lower RPM ranges.

Some time ago I read about a machine shop that drilled thru the outer wall of the coolant jacket near the deck surface of a 400. Then they used an airframe drill and drilled a small hole btwn the siamesed bores right under the deck surface. The holes in the jacket wall were then plugged with 1/8" NPT plugs. The idea was to allow the steam & water to cross up to the high side of the deck surface to prevent localized boiling which is the start of over-heating. I've always been curious how well that worked.
 
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the 400 small block have a syameise(conjoined) cylinders and the water jackets arent big enough which is why it is prone to overheating and the need of the extra cooling but i am with everyone one who likes them cause i still would like to have one
 
ntsqd said:
Sorry about the run-on, the editor won't retain any 'enters' or more than one space. Time for a Hack?
Click to expand...
Switch to "Standard Editor" in your options. Beats the heck out of that (sorta) WYSIWYG editor...
 
I did alot of research on the 400sbc since I have two in my garage. The overheating is true ONLY if you have a small radiator from a 350. If you have a large enough radiator, the 400 will never overheat.
 
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Shawn said:
If you have a large enough radiator, the 400 will never overheat.
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x2. I've been ragging on my blazer in the middle of summer in a deep mudhole and never had her get even remotely hot. Overevved it many times and never had problems with main caps etc. I love my 400sb.
 
never overheated mine (not bad anyway!)..

I had a 454 radiator in my 74 truck(because it was a 454 before the 400SB came along!)..only time I had cooling issues was when I had my plow on it,and tried driving it over 40 mph any distance over 5 miles..found out it had no thermostat in it!--then I learned by locking the fan clutch spring I could drive to NH and back with the blade on,and it wouldn't go over 1/4 of the way up on the temp gauge..it never heated up once in 90 degree summer heat either..it needed every inch of that radiator though..:crazy:
 
How much money do you have?

Seems simple enough. If money is not an issue, go with the 396 and if that's not enough power/torque you have plenty of room to grow. If money is an issue, go with the 400. It's hard to beat the power/dollar of a Chevy small block. Personally I'd go with a 383 and stay away from the siamesed cylinders, but I put a very high value on reliability.
 
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