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"400 sbc" rebuild it to run

12-16-2003, 09:04 AM
I have a 400 smal block ready to be rebuilt. I want input as to the best way to go. Any and all ideas wanted. Should I go for cubes? Should I go for revs? Please list dyno tests if possible, any and all parts for the rebuild also.

12-16-2003, 12:35 PM
From the two 400's that I've rebuilt, and the other that a friend of mine has done, going for revs might not be the best thing to do. There are engine kits out there that'll give you 406, 408, 412, and I believe a 420 cubic inch also. The first thing to do with these engines are to get rid of those connecting rods. Unless you're on a REALLY tight budget, get rid of them...they're too short (5.65 compared to 5.7 in other small blocks), and cause excessive side loading on the cyl. walls and pistons. Depending on what you're going to do with the engine, will dictate how you should rebuild it. But revs are definitely not the 400's specialty. It's more of a torque motor. You won't have to do much to get neck-snapping torque out of it. I'm on my way to work, but I'll come back on later with a little more info...gonna have to pull my PAW catalog out from the closet :).

12-17-2003, 06:23 PM
Just curious, what year 400 do you have? I ask because mid 70's 2 bolt blocks are the best you can get for a 400 core. Anyways, stick with the stock crank, but, do yourself a favor and have the bottom end set up with splayed main caps and use arp bolts to hold everything together. Then scrap those stock rods in favor of some lighter and stronger 5.7 rods. Do the same with the pistons as well. Lightweight is key because the mass of the 400's rotating assembly is one reason why they dont like rpm's, but trust me if you build it right it will rev just fine and stay together. I know plenty of guys who thrash the crap out of em and use juice as well and no probs to speak of. Look for about 10:1 compression with the piston and combustion chamber combo. Have everything internally balanced. Factory small block 400's are externally balanced but thats not a good idea cause what happens if you bust a flexplate(which is used to balance the motor)? Than you need everything rebalanced just to bolt on a new flexplate. Get the rotating assembly internally balanced and then add good neutral balance flexplate and damper. Have the block decked down to ensure straightness and the use what ever gasket is needed to ensure a piston to head clearance(called quench) of .040 thousands. A lot of guys will zero deck the block and then add a .040 gasket but I dont like that cause if you ever need to rebuild, you cant shave the deck surface any more if needed cause its already at zero deck. As for heads, I wouldnt mess around with too many facotory casting heads. About the only factory cast head that I would consider is a vortec, but aside from that, any other head wont flow well enough(even with portwork) to justify using them and once its all said and done youd have the same invested in aftermarket heads. Get some pro toplin 200cc iron lightning heads and make SURE to have them steam drilled for the 400 block. This is another reason why 400's get a bad rep. Guys sometimes swap the heads and forget to drill those holes and they overheat because of it so get it done. If your really wanting to thrash the motor(like over 6000rpm regularly, Id add a little bit of HardBlock to the water jackets(just about 1/4 full). As for a camshaft, I like solids. Also not as bad as everyone say cause after they are set, I only look at em about twice a year and they only seem to be a little out of adjustment every other time. I like the comp 282 solid magnum cam. It has 236 degrees duration at .050 and .495 lift. Itll make tons of torque and good horsepower with a max prm of 6000 rpm in the big 400. Stap on an rpm airgap intake and a 750 carb and you should be looking at like 420-435 horsepower and about 470-485 torque. Plenty fun in any street car. If you get a solid, order the right valve springs. If you dont want a solid, use an isky 280 mega camshaft and the proper springs. It will run similar and still make tons of power. By the way, I woundnt worry about any sort of stroker setup. Id bore it out .030 over and youll still make more than enough power with just 406 cubes.

12-17-2003, 09:59 PM
The 400 i have is out of a 1984 Blazer i used to have. The mileage is 175000 with only main seals leaking, no major work ever. I dont remember the numbers off the top of my head but i did check them once and it is a good one. I want to get the biggest bang for my buck at a reasonable price. Had considered going to a 327 crank, got the plans look pretty good for pump gas, says it will torque 400 ft lbs from 2800 to 5200 but the ponies are a little small 214 at 2800 and 397 at 5200. Max torque is 435 at 3800 and max horse is 412 at 5700. Does this sound like a good street engine for a 400 ? I do like the torque range but wish it had more horse.

12-24-2003, 07:20 AM
Not getting alot of input here guys! I havent been recieving any dyno tests or build plans for my prodject motor. I need ideas or past proofs to help me decide.

01-04-2004, 09:20 AM
400s have bigger main journals than other small blocks, so you run into a complication if you want to run a different crank. There used to be some shims available to do this, but I don't remember how to get them or if this is the best way to go. If you have an unlimited budget, you can get custom parts and build it any way you want. Otherwise, you may want to consider using a 350 crank with spacers in the mains and 5.7" rods. This way you can use 400 pistons and avoid the expense of custom parts. You would also have an internally balanced engine this way. I can't give you any torque and HP data on this combo - depends on what type of heads and induction system you use. This combo would give you a 365 ci displacement with a .030 overbore.


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