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View Full Version : 400 Small block

04-05-2002, 09:25 PM
I have a 76 k/5 Blazer. It's got a 400 small block. I'd like opions. I plan to stay small block, but is a 400 better then a 350 for off roading ??? This engine runs fine, no need to replace yet. Just thinking about future possibiltys. I do plan on installinng a COMP CAMS "EXTREAM 4X4" cam. probley the one with 262 duration. A HOLLEY dualplain highrise (tall) intake manifold, and a set of HOOKER headers. Yes, all the crome crap is a must aswell. Probley a gear drive to replace the timing chain, love that sound. This truck had a valve job about 4000 miles ago. I might get a set of COMP CAMS "HIGH TEC" rollor rockers. Oh'well, just thought I'd ask everyone's opion.

04-05-2002, 10:27 PM
Ummmmm... Don't take my word for it, but I think a 400 is a big block...

and I'd take a 400 or 454 over a 350 without thinking twice... of course gas is better for the 350, and you don't get stupid comments from stupid freaking idiots at Autozone (whoops, almost went rant on yo arse)... but you get more power from a 400...

04-05-2002, 10:34 PM
The 400 isn't necessarily any better for offroading than a 350, it just might have more power depending on the build of it. Your setup sounds alright, but I definitely wouldn't use the high-rise intake for an offroad truck unless you only play in the mud, because it favors high RPM horsepower rather than low end torque. This is just my opinion.


04-05-2002, 10:42 PM
Capman2k, he may very well have a small block 400. They were fairly common in the 70s in many applications including cars, such as the Firebirds like in Smokey and the Bandit.


04-05-2002, 11:27 PM
ok, the CHEVY 400 is a smallblack, its the biggest SB you could get from chevy. Its also a little bit dofferent from the rest of the Chevy sb's because of a slightly different block design (as far as collong passages and stuff goes) On the outside the look the same. (basically) these could be had in both cars and trucks in the 70's.

The 400's in pontiacs (ie Smokey and the bandit) were totally different engines, not really a small or big block, sort of a mid-block, ALL of the pontiac v-8's used this midsized block. (from the little pontiac 280 whatever ci to the mighty 455ci)

04-06-2002, 12:45 AM
The 400 is a small block. Lot of people get confuced becouse the smallest big block is a 396. Chevrolet did make a 402 big block, basicly a 396 bored .30 from the factory. But what I have is a 400 cid small block. I've built alot of hot rods, but never had the goal of low end tork. The hot rods was always for higher rpm, and midrange to top end horsepower. I've been told when I rebuild, to use a 5.7 rod ( stock 400 cid small block chevy uses a 6.0 rod ) and bore it .30 over will give me a cid of 406. I don't know if that's true, but that's what a friend told me. With a flat top piston (9.5 to 1) it's suposta be a real torky motor.(9.5 to 1 so ya can run pump gas) And ofcorse advance the cam for lower end tork.

04-06-2002, 12:55 AM
What would you recomend for a intake manifold ??? I want to go square bore instead of spread bore. I am going to try the HOLLEY TRUCK ADVENGER carb. It's been redesigned for off road use. I do like to go mudding, but also will be going on old trails. I don't plan on much rock crawling, very lightly if any. I live in the Black Hills of western South Dakota. I'm really intreated in wheelinng the old trails to find the old goast towns from the gold rush days. That sounds like alot of fun to me. More mud then rocks on the old miner roads.

04-06-2002, 12:57 AM
It's the original motor for the 1976 chevrolet K/5 Blazer.

04-06-2002, 01:18 AM
400 SB's came w/ 5.56" rods. They are good for a low rpm truck motor but do put more side loads on the cylinder wall. 5.7" Rods are stock on 350's and are easy and cheep to put in...but it is harder to find pistons. A high-rise DUAL-PLANE would be a good choice (longer runners make more torque and I don't think hood clearance would be a issue). If you want good low end torque I would go at least one step smaller on the cam! I think you would be more happy w/ the 250 or 256 if low end torque is what you are after. Also look into Vortec heads if you are going to replace the intake anyway.

04-06-2002, 01:46 AM
Just figured out how to add a link so everyone can see my Blazer. It's still bone stock. I just got it a couple off weeks ago. Please tell me what you think.

04-06-2002, 08:07 AM
Will the Vortec head's bolt up, or is there modifacations required ???? Knew the 400 sbc used a different rod lenght then the rest of the sbc's, thought it was 6.0, thank you for correcting me, I'll remember 5.56. I've never had a 400 sbc on the stand. How hard is it to get pistons using the 5.7 rods ??? I usely deal with JEG'S.

04-06-2002, 08:21 AM
No replacement for displacement. 400's rock. /forums/images/icons/laugh.gif

04-06-2002, 10:20 AM
Cheverolet made the 400 small bolock. Pontiac made the 400 big block.

04-06-2002, 10:29 AM
Also... I tend to favor a 383 Stroker, which is sort of a cross between the 400 and the 350. The 383 uses a 400 crank in a 350 (some machining is needed), along with 5.7 rods (I think), and is bored .030 over. The longer stroke and .030 give you the 383ci and one low-end torque monster. Talk to any machine shop and they'll tell you all about it.

04-06-2002, 10:31 AM
lots of misinformation here.

400 is a SBC. It comes with 5.565" rods from the factroy that give it a poor ratio for hi RPM's.

The 402/396 are both big blocks. You can tell by the HUGE heads when compared to a SBC.

The ponitac's are a whole different breed, as is the rest of the BOP line. a 455 would be the way to go if you wanted poncho power, but that is a different thread.

The Vortec heads will not work (as intended) because of the lack of steam holes in the heads. This is the weak link in the 400. These steam holes is where 98% of blown head gaskets start (like mine is right now). The 400 you have is problably a 2 bolt main with 882 "smog" heads (if all is factory).

If the engine is storng, no reason to screw with the bubmpstick. Headers work WONDERS for the SBC, as the factory manifolds are very restrictive, especially those in the "smog years". Good headers, an Air Gap Performer manifold and a well tuned carb and ignition will be fine.

I hope this clears the air...

04-06-2002, 10:42 AM
You are in to the same action as me... I would go with the edelbrock performer series intakes, esspecially if you are going with a bigger cam. Edelbrock's Power Packages are no joke and all the components are designed to work together. (ie. The intake and heads are port matched while the cam is designed to take full advantage of the two, depending on your HP and torque range.) Check out for all the specs. You can do all this and stick with the Holley truck avenger carb, which is aslo what I'd do if you don't opt for fuel injection.

04-06-2002, 02:32 PM
AFAIK you can use Vortec heads (along w/ any other SB head) on a 400. You just have to drill the steam holes. I have a 400 block in my truck and the stock 350 heads. I wish I knew that they were drilled...the P.O. put it in.

With the vortec heads (which are 64cc) and 5.7 rods you will have a hard time finding pistons w/ less than 10:1 compression. With the stock heads it isn't as much of a problem because you don't need such a big dish.

04-06-2002, 03:09 PM
What does everybody think is the best camshaft for low end power in a stock sbc 400 with headers and K&N airfilter?


04-06-2002, 08:15 PM
Man this post is all over the place /forums/images/icons/tongue.gif. Well I will trade you my 350 for your 400 any day /forums/images/icons/wink.gif. If I'm building a 400 for a truck... I would rebuild the lower half and use either 5.7 or 6" rods depending one your preference. I personally like to keep all my rings in the traditional spots beacause IMO it is easier, but the 6" rod works fine. I would look for a good cast iron head for up north here, another opinion. I still feel that the iron is better duarability wise then the alum here in the crazy conditions of the north, but alum heads work for many people. The other plus of staying cast iron is they are cheaper.. for about 5 to 6 bills you can get SR Torquers w/ a 2.02 intake valve or the vortecs. I'd suggest a 3 angle valve job on the vortecs, or a VJ and some pocket porting on the SR's. Bothe heads with a 252-258 cam should net you about 300-325 hp and bset of all 420-450 ft lbs of torque up to 4000 rpm /forums/images/icons/cool.gif Top it with a Holley intake and I would use a tweaked quadrajet so you get enough fuel for this beast or go with a quad off one of the 455 cars, or the 472/500 caddys. They flow about 800cfm and work awsome. Quad is the only carb I would recomend using with the angles you will see out in the Badlands. There is my $.02

04-06-2002, 10:44 PM
The 400 is a great motor for your k5 for two reasons:
1. It's as much stock displacement as you can get in a 'light' 500lb small block.
2. It delivers great bottom end torque to get you moving off the line or crawl slowly over obstacles.

The 400 would not be a good choice for trying to get high rpm hp/tq numbers from unless you want to get really spendy on the rotating assembly with all forged equipment. This is due to the longer stroke.

The 400 is a great platform for making big hp/tq numbers at low rpm though, cast Speed-O-Motive stroker kits can put you in the 500hp/500lbft under 5500 rpm with a focus on RV. I recently built the above with a small Comp Xtreme 4x4 cam, lightly matched/pocket ported 1.95/1.5 cast iron smog heads with stock intake and exhaust and a Q-Jet (in other words - totally corked up!) . With 3.07 gears and 33's the truck leaps off the line, climbs hills relentlessly and gets much better gas mileage than my warmed over 350 that it replaced due to the torque. I'm sure many people will tell you the same with their stock 400's as well.

Due to the fact that a cast 400 rotating assembly doesn't rev high, you really can't take advantage of a big carb and big valves like you can with a 350 which lends well to high rpm. Small valve heads will taper off around 4500 rpm but make tremendous bottom end, good vacuum and great mileage while larger valve heads lose a little on the bottom and vacuum but rev up to 5500 nicely. I used 350 heads and drilled the steam holes (a must) and it wasn't difficult so choose a head you like. I'd agree on the recomendation to get a good air gap high rise dual plane manifold and headers as it will make a big improvement.

If your looking for more, you could spend the money on a forged assembly but it might be cheaper to either build a high rpm 350 or move to a big block. Good luck!

04-07-2002, 08:02 PM
Tell me about the 415 cid small block chevy. I'd be intrested in building one with a forged crankshaft, and forged connecting rods, and approx. 9.5 to 1 compression. I think it's Milodon that makes the 4 bolt mains with splayed outer bolts. I know the block will have to be re-lined bored, but it'll make it much stronger. What I want to use the truck for is mostly exploring on old trails. there is minor rock crawling, but quite a few mud bogs. I really enjoy mudding alot. I also will be useing the Blazer as my daily driver.

04-07-2002, 09:26 PM
Here's a link to
<a target="_blank" href=>Speed-O-Motive 415 Stroker</a>.
There is a forged kit underneath the cast kit. They are very easy to work with and will have no problem substituting parts of your interest. Miloden does make the splayed cap kit and I would highly suggest this route. Machining a two bolt is relatively inexpensive and yes they will have to align hone it. I went with a 9:1 on 76cc heads but will upgrade to 72cc heads here soon. I run mine on regular unleaded but had to curve my distributor to keep the ping away. Before I curved my HEI I needed premium but it was an all out rocket ship (and drivetrain snapper). I had my hyperuetectic pistons ceramic coated to assist in heat/detonation control but I never researched the effects on a forged piston... you'd better ask the experts there. You can't get too aggressive on the cams with these kits because of the close proximity of the rotating assembly, the machine shop I had bore my block had to clearance the rods more than they had already been clearanced with an aggressive schneider cam they mistakenly installed in my block (Long story...) Most everything with the kit goes along the same lines as building any other small block. Just make sure your using heads with the steam holes drilled and get yourself a windage tray and crank scraper. I would recommend a manual transmission for strength and definately one ton gear. My 12 bolt is getting sloppy and I've been through countless U-Joints so far with it all corked up, tends to blow them when I'm climbing and under heavy load but not usually on the street punching it. Let me know which way you decide to go, I'd be interested in following the build up and hearing your success!

04-07-2002, 10:42 PM
I just emailed speed-o-motive about their 415 forged kit. I'll let ya know how it turns out. I don't plan on building it up till next winter. I've only had this truck a few weeks now and want to play with it this summer. I'm still in the planning stage, but the 415 stroker sounds like what I'll need. I'll probley stay with the automadic transmission, I've built a few of them up befor. Speaking of U-joints, I've got to go through this Blazer and replace them all. I think that's a must do when ya buy a used 4x4. Do you know of a good name brand for U-joints ???? I don't mind spending more for the better parts. I want to go all heavy duty. I'd reather do it right the first time then have to do it again.

04-07-2002, 10:58 PM
The Spicer U-Joints I get tend to last the longest!

04-08-2002, 08:50 AM
in reponse to "never had the goal of low end tork. "

haha, it caught on.
my intentions of changing common spellings are paying off, soon everbody will speak "ryan" and say words like "gooder" and "unadvertanly" and spell torque tork


04-08-2002, 08:56 AM
I've been spelling it like that for a long time. I know my spelling sucks, but I try to make it so everyone can understand what I'm saying. I'll try to spell "gooder" next time.

04-08-2002, 09:06 AM
I plan on useing COMP CAMS. They make a EXTREAM 4X4 SERIES camchaft. I've used COMP CAMS in all the prefomance motors I've ever built. A friend of mine used a CRANE camshaft in a 327 for his NOVA and one of the lobes was off by 4 degrees and coused a valve to put a hole in a piston. CRANE was happy to replace the camshaft, but would not pay for the damage to the valve and piston.