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Build 400 sbc or 402 bbc?

Discussion in 'The Garage' started by madmike, Jan 14, 2003.

  1. madmike

    madmike 1/2 ton status

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    Looking for opinions again. I'm trying to decide which to rebuild: a 400 sbc or 402 bbc. What are the advantages/disadvantages of each, other than the engine weight, and the fact that the 400 is externally balanced? The 400 and 402 have the same 4.125" bore, the 400 has a 3.75" stroke, while the 402 has a 3.76" stroke. The 400 has a shorter rod length of 5.565", while the 402 has a rod length of 6.135".

    I want this engine to power my '74 K10, 1 ton 4:10 geared axles, 36" tires and SM465/NP205 combo. Other than 9:1 compression, intake, Qjet, cam, and maybe headers, I want the engine to be pretty much stock, with good high torque figures at the bottom end.

    Which one would you build and why? Thanks!
     
  2. Z3PR

    Z3PR Banned

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    Go for the big block if you want torque !!!!!!
     
  3. madmike

    madmike 1/2 ton status

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    Why is the big block making more torque if the bores are equal and there is only 0.01" difference in stroke?
     
  4. BorregoK5

    BorregoK5 1/2 ton status

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    For a daily driver / weekend warrior which doesn't need to be under long durations of heavy load or high rpm, loose the extra weight and go with the 400 small block since the specs are nearly the same. But, if your after something that can stand longer durrations of extreme load, perhaps a little more rpm, then the big block will have a better capability to take you there over the 400 sbc and keep the engine temp down. I run a stroked 400sbc (415ci) and absolutely love it, but long durrations of high rpm under heavy load do make the siamese cylenders become evident in their cooling capacity as the temp will rise. Otherwise, I'd never know the difference as its runs consistently cool with a lot of low rpm torque. I'm trying to loose weight so the 500lb small block was the key to my build. What your building yours to do may or may not make a difference with weight, so I'd use the cooling, load and desired rpm duty to determine which one to go with.
     
  5. HarryH3

    HarryH3 1 ton status Author

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    Another thing to consider is cost. Just about any part for a big block will cost more than for a small block. Cams, heads, intakes, headers, etc. Building the big block will just cost more money.
     
  6. JK5

    JK5 1/2 ton status GMOTM Winner

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    If I had a choice....I'd go sbc.... /forums/images/graemlins/thumb.gif
    Why....parts are cheaper...you can get more BANG for the buck.
    I'd get some Vortec heads and a good comp cam kit....
    and try for 400lbs of torque.

    Check those bores......020 is ALL you have to work with.....you may have no choice, but to go bbc!!!

    Remember....these motors stock.....never made much hp and torque....they were DOGS!!!

    Hey....what is .01.... /forums/images/graemlins/confused.gif
     
  7. bigmack

    bigmack 1/2 ton status

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    I would build the 400 SBC. You are replacing the small block thats allready in your truck right ? If you go BBC you will have to round up all the accessories and brackets which can be a pain. Another reason I would go small block is for the cost, and its easy to find the parts you will need. You will not be disappointed with the 400 SBC, it will surprise you /forums/images/graemlins/cool.gif.
     
  8. Mreetz

    Mreetz 1/2 ton status

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    Yea go with the 400, I'm gettin ready to drop one into my '84 K5. Oh yea!! I've got a 400 builder for sale too! Also have a new crank to go along!
    Marty----
     
  9. ratlover

    ratlover 1/2 ton status

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    I wont say one is better than the other but I will try to list some of thier differences and you can decide.

    First off the stumpy rods in a 400 kinda suck but you can stuff 5.7's in there easy enough and you can buy pistons for a 5.7 rod for not much more.

    The main disadvantage to a rat is the weight(you are running a frigging 4x4 not a 1/4 mile car, a few 100 pounds aint a biggy imo) and the cost. BBC stuff is a bit more expensive but still not bad.

    Rat has a stouter crank and bottom end in general.

    The biggest difference between a BBC and a SBC(besideds displacement) is the fact that compared to a BBC SBC heads suck. Built simmalarly a BBC will produce more power than a SBC with the same CI.

    When building a SBC you quickly start to get into were a BBC has a lower overall cost. Overall meaning how much rpm do you have to turn(this effects service life and longevity) and things like were is the power at and what kind of octane do I need to run and what does it idel like. That is the over all cost not just the inital well a intake is 50$ cheaper so a SBC offers more bang for the buck. Its what you want to do with it, with some stock oval port BBC heads and a mild cam and a intake you can have a really stout low grunt motor that will drive like a pussy cat. If you want to throw something together thats nice and stout for as little cash as possible then maybe the mouse is a better pick. Why not hold out for a 454 instead of a 396?

    Its all in the heads
     
  10. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    I'm gonna differ from the masses and say go with the 402. lol, I am a bit biased though. I run the 402. I love it. Never goin back to the SBC. I got lucky as far as the transplant went, I had a complete parts truck with the 402 installed and running. So I had all the brackets. It had a blown head gasket, so that was fixed, while the heads were off, they were sent to the machine shop for a rebuild. 427 head, closed chamber (yuk) heads. I've also got Harland Sharpe full roller aluminum rockers. The crank was balanced and has forged pistons. I still run the stock exhaust manifolds and heavy ass cast iron intake...(double yuk). I know it has a Comp Cams cam from the part # on the lifters, I just don't know which particular cam it is. I'm obviously not lacking in HP and torque as it is, but when I go to headers, aluminum intake and a Comp Cams Extreme 4x4 cam, I'll be doin even better. I've got probably $400 into the swap....Most of that in the heads and gasket kit. I think that, for the most part, the weight argumnet in a K5 is pretty much a moot point. In a truck that weighs 5000+ lbs...what is 2-300lbs? It's nothing. The cost of parts? Thats a pretty insignifiant thing to I think...A compe cams Extreme 4x4 cam for a big block is $99. The Edelbrock intake manifold for a BB is about $60 more than the same for a SB. Also, once again, many thanks to GM for thier simplicity....Alot of the parts are interchangeable. I've used the same starter on the small block as well as the big block..on 3 different trannys, TH350, TH400, and SM465. I'm also using the same power steering pump on the big block that was on the small block. A manual tranny flywheel for a SB 350 is the same as for a BB 402. (They are different if your SB is a 400 though)
    And last but not least, How cool and unique is it to have a BB in a K5? A 402 BB is that much cooler. I like knowing that there are very few 402's in K5's, and that I am the owner of one. I suppose that is a point to be flamed on....But oh well. I have 402 Big Block and you don't!! <font color="red"> Neener Neener Neener!!!! </font color>
     
  11. Sparky87k5

    Sparky87k5 1/2 ton status

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    Building a BBC WILL cost more then the same package in a SBC. Swapping over to a BBC will cost you the brackets, flex plate or flywheel, exhaust mods, and possibly a different power steering pump, depending on whether you keep A/C or not. Also, if you keep A/C, you may need a different compressor if you go BBC. On my 87, the radial compressor was never available mounted on the driver's side with v-belt drive. In order to keep everything where it was factory, I had to go to an aftermarket bracket setup. BUT, having had a strong running 383 before, I very much like the 427 BBC I now have. Would never go back. Regarding fuel economy, about the same running empty, 12-14 mpg hiway, but consistantly 8-9 mpg towing instead of 6-8 with the 383.

    Plus, there is a lot of raised eye brows at gas stations when they see the BBC sitting there. /forums/images/graemlins/grin.gif Worth it alone just for that feeling. /forums/images/graemlins/wink.gif
     
  12. madmike

    madmike 1/2 ton status

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    Thanks for all the input guys! I believe I will be going 402 bbc, not small block. I feel that the 402 is overall a more stout, heavy duty engine, and will be more durable than the 400 in the long run. I also agree that if the same mods were done to each engine, the 402 would probably make more power, and be more reliable. My truck is a K10, so weight is not an issue. I have all of the big block engine bracketry, including a radiator, so the swap will look factory, and most trucks don't have big blocks either, so there is a coolness factor in running the 402. I've been looking at a Summit catalog to get an idea on prices, and BBC stuff is not much more expensive than SBC.

    Yeah, I think rat power should do it!
     
  13. ratlover

    ratlover 1/2 ton status

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    Actually small "closed" chambered heads are better than open chambers. The overwellming thought used to be that open chambers shrouded the valve less and provided better flow. It isnt really an issue.

    Smaller chambers allow lees of a dome to get deccent/higher compression. Less dome gives a better flame travel and is less resistant to detonation. Look at a high end race head for the big boys like pro stock.

    This is all spliting hairs......you wont feel much difference in a normal motor. Not trying to start anything just a bit of info /forums/images/graemlins/smile.gif
     

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