Need power, Chevy small block or big block??

the 400ci in my 78 blazer is acting up, idles rough, runs rich; black smoke from exhuast and blackened plugs,  is a simple carb problem?  anywasys i want more power than i have now so i am contmplating an engine build but can't decide wheater to put flat top pistons, cam and heads on existing 400, build a 383, or even go for a big block, 454 or so, for all the engines im thinging about flat top pistons, performance cam, heads, intake, carb, valvetrain and ignition, u know regular hot rod stuff, looking for aroun 400hp and 450 ft lbs of tourque what do you guys think also my 400 is only 2 bolt mains so do you think its safe to build it up??    Also i NEED reliabilty, i want to build this motor and forget about problems  
solid axle chevys cant be beat
78 K5: 350 V8,700r4,np208, 8 lug D44 4:88, 14 bolt 10.5 4:88 with detroit locker and 35 inc parenelli jones dirt grip tires

the two bolts are plenty stout.

messing with 400hp really gets into lower gearing and stall converters in the autos.

check out the dyno specs/componets on the summit racing engines.

the 78 400 has valve relief flat tops in em with large chamber heads, ya can just goto a 260 duration cam along with some 64-68cc heads and gain alot of torque and some horsepower.

I had a 454 in one of my blazers that I paid over $3500 for that couldn't keep up with my 3/4t truck that was powered by a 350 with 291 cast heads, stock gm aluminum "web" intake, CraneCams 260-2nc cam, and the stock pistons that came in the 1971 block. I had about $250 invested in the 350.
both rigs were running on 36" Gateway buckshot mudders, 2200 stall-th400-205 t-cases, and 4.10 gears in the d44 front and 9.5" sf rears.  
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Sounds like a carb problem to me. Also for what it is worth, many wheelers tend to think that they need more power when really they just need a better set of gears in axles as many lift them and install bigger tires and NEVER bother to regear axles. Even in a big SUV a SB can do a fine job with the proper set of gears behind it.  

yes i know gears play a big part in performance of truck also that why im getting 4:88s in about a month, but for sure my 400 came with flat top pistons?? What compression ratio i figure that a bit higher compression around 9:1, a good cam and some nice heads the 400 should haul butt right??  What heads do you recomend are there some factory heads i can use or should i go to aftermarket heads  
solid axle chevys cant be beat
78 K5: 350 V8,700r4,np208, 8 lug D44 4:88, 14 bolt 10.5 4:88 with detroit locker and 35 inc parenelli jones dirt grip tires

If they are stock pistons and a 73 or later 400 they are dished and CR is around 8.5 to 1. On heads, this is where I tend to differ a lot for others on which way to go. I take one route for a heavy SUV and another for a fast car. Big valve's and ports can add HP at upper RPM's but they can destroy lower RPM torque because of reduced mixture velocities. In a SUV you need this lower RPM torque and response. I would stay with stock heads and a bit warmer cam and a better intake (dual plane would be good here) Something else to consider, 400 SB's with stock parts tend to fly apart around 6000 RPM or so because the short rods and long stroke places a lot of strain on rods and pistons (it has to do with the quicker rate of acceleration and deceleration that shorter rods cause as piston changed direction of travel) so you would do best to limit it to about 5000 RPM it you want it to last and high flow heads are going to get you in trouble because you are going to want to take it higher. I used to race SB 350's and 400's with a friend years ago and I can tell you what comes apart in them. If you want to really try to crank a 400SB you want to put a 350 crank in it with its longer rods and make it a 377 because the combo of shorter stroke and longer rods will give you more safe RPM even with stock parts and better torque at higher RPM too.  

when u say dished pistions u mean dished in?  heres a list of current engine mods, edelbrock performer rpm intake, edelbrock 650 carb, headman headers, dual exhuast, roller rockers, accel hei ignition, and of course a big ole K&N air filter, yeah i don't want to blow up motor with over reving so i think that the 5000 rpm limit sounds good but your saying that with higher flowing heads my motor will be able to rev higher? Also will a warmer cam give me the nice wappata wappta sound from the motor? love that sound If im going to take apart 400 to make 377 i might as well make a 383 don't u think?  Ive got an oringinal 78 corvette 350 with only 60,000 miles on that i can use, putting an ls 1 in the vette later so is the vette 350 4 bolt mains or what and what pistions and compression does it have?  I now this year of corvette only made about 180 hp cuz of smog stuff.  
solid axle chevys cant be beat
78 K5: 350 V8,700r4,np208, 8 lug D44 4:88, 14 bolt 10.5 4:88 with detroit locker and 35 inc parenelli jones dirt grip tires

By dished pistons I am they are not flat topped but the are concaved to limit CR for NOx emissions. When I said that hi flow heads would increase RPM potential I meant that engine would pull harder at higher RPMs and tempt you to over rev it and destroy it. On the 377/383 thing. The reason the 377 is better if you plan to wind it out a bit is because the shorter stroke and longer rods in 377 is more efficient at higher RPM's and lets you rev it up a bit higher safely as far as pistons and rods are concerned. Also the 350 crank in the 377 makes it a internally balanced engine so you not longer need a 400 flywheel or damper. (you use stock SB parts) With a 383 you use the longer 400 stroke and shorter rods with 350 pistons. While 350 pistons have less mass than 400 ones you still have the shorter rod and higher stresses mentioned earlier which means I would limit RPM to about 5000 again or a bit more (because of reduced piston mass)if you want it to last. There are expensive after market pistons for both 350 and 400 that allow you to use longer rods with 400 crank to improve higher RPM potential. Getting back to issue here, the "beauty" of the 400 SB is the added displacement lets it make more torque at lower and middle RPM's when properly built were it can be of greater use in a SUV. You just need to figure out where you really want to go before you try to do more mods to engine.  

ya can also use 5.7 and 6."+ rods in the 383 and the 400 with the correct pistons.  
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i thougt i had concaved pistons, so there is room for improvement.  Now i get you with the 377 being a better high rpm runner so what do you think if i keep the 400 just stick in some flat top pistions hotter cam and a little better flowing heads along with all the other mods, will be a pretty healthy motor? im hoping at least 350 hp at crank? What has more power potential the 400 or 377 ?  
solid axle chevys cant be beat
78 K5: 350 V8,700r4,np208, 8 lug D44 4:88, 14 bolt 10.5 4:88 with detroit locker and 35 inc parenelli jones dirt grip tires

As you raise CR you will increase octane needs and the large bore and chamber of 400 will be knock prone so you will need good fuel if you want it to run its best. Many ham string engine build and run them on 87 with compromised timing curves which reduces output. I would strongly suggest that you use a better intake and a Competition Cam 260 grind with stock heads. Your biggest bottle neck right now is intake and cam not heads. On the 377/400 thing. Using stock parts the 377 has more potential because it can be cranked up to a higher RPM and longer rods are more efficient at higher RPM's in transferring piston energy to crank shaft. Unless you want to spend coin for custom pistons to accept longer rods on a 400 SB the 377 is more viable if you plan to crank it up.  

What about boring the 6.6 to a 406, putting the vette heads on there?
400 lbs factory rated in 70 wasnt it? for a stock 400?  

if yer buying pistons anyhow, I wouldn't let a set of rods stand in the way of keeping the 400 crank, it doesn't require massivly oversized main bearings as the 350 crank in the 400 block does.
that leaves more torque potential than the 377 offers, really, it depends on how much rpm ya want to run and how money yer gonna spend.

back then the vettes were running 186 and 041 type cast heads with 2" valves in the high hp rated engines.. 64-68cc closed chamber heads which helps make the high cr ratios.  
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see me at robsoffroad.com

When I recommend builds I like to use stock parts to keep costs down. When you use custom pistons and such your costs can go thru ceiling quickly. While a 400 crank and stock rod can make more torque at lower RPM, a 350 crank and longer rod will overtake it at upper RPM's. Many many years ago I raced 400 SB's with a friend and we blew a few them too and when we went to a 377 they stayed together better and turned fastest times ever too by a good bit with a 377.  

wait you understand i have an edelbrock aluminum intake right?  yeah i know raising compprission will riquire higher grade fuel but im hoping for it to accept mid grade fuel like 89??? Im not going to overrev it so i guess ill stick to 400 for now but your saying just to add flat top pistons and cam and leave stock heads?  
solid axle chevys cant be beat
78 K5: 350 V8,700r4,np208, 8 lug D44 4:88, 14 bolt 10.5 4:88 with detroit locker and 35 inc parenelli jones dirt grip tires

yep, ya can, although the stock heads are likely 882 castings, they are light and aren't worth putting money in.

I'd go with the stock pistons, 260 duration cam with a 112 lobe center and a set of heavy cast 64-68cc 327/350/ 194/150 iron heads with hard seats, steam holes drilled for the 400  
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see me at robsoffroad.com