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Old 07-04-2006, 07:25 PM
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400 sbc

I have heard some good things and some bad things about the 400 sbc. could somebody help me sort out the fact and fiction! thnx

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Old 07-04-2006, 07:51 PM
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Tell us what you heard and we will go from there.
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Old 07-04-2006, 09:14 PM
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Lots of people have all sorts of "stories" on the 400. Main one I always hear is "they all overheat!". Personally, i've built 2 so far and have had no problems. Last one went 60 over and runs at 1/4 on the guage here in Phx, street driving in 116 degree weather! Nothing like free cubes!
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Old 07-04-2006, 09:27 PM
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we used one in mildly modified form in mud racing in a full size 4WD. It had 18cc dish forged pistons, camel hump heads with a mild port, a 234/244 duration cam with .488 .500 lift, a weiand intake, holley 750, headers, 3000 stall, front and rear posi traction. From the line it would break loose all 4 of the 38 inch tall mud tires, and we have a few 1st place trophy`s to show the effort. 400`s aren`t like the rest of the small blocks, they don`t like to be tached, so we never went over 5500 rpm, but there torque is what makes them so great. If the proper steps are taken there are no overheating problems. You do have to check for cracks on the decks where the steam holes are.
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Old 07-04-2006, 09:40 PM
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I have no complaints about them. The siamesed cylinders add strength over the other blocks in the small block family.
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Old 07-05-2006, 06:31 AM
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400 SBC's tend to be more crack prone in the deck area, usually around the steam holes. Also in the lifter area, above the lifter bores. Cylinder bores tend to distort a bit more than smaller SBC (use a torque plate). 2-bolt blocks are more desireable than four bolts in many situations. The 2-bolt blocks have thicker main caps and accept aftermkt "Splayed" type main caps better. A special rear seal is required on blocks that have had main bearing bore work.


BUT, "There ain't no substitute for cubic inches". So I like em!!!
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Old 07-05-2006, 06:45 AM
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I've been running a 400 for 3 years now. Its a mild combo, Comp Cams Magnum 280H cam, 1.6 roller rockers, RPM intake, 9.8:1 compression, Sportsman ll heads and good aftermarket guts. It makes a ton of torque, pulls 14" vacuum, sounds like a warmer over 350 and goes like stink. Runs at 180 deg all the time. I would not go with anything other than a 400.
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Old 07-05-2006, 06:26 PM
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sound good to me

Quote:
Originally Posted by Jmark
Lots of people have all sorts of "stories" on the 400. Main one I always hear is "they all overheat!". Personally, i've built 2 so far and have had no problems. Last one went 60 over and runs at 1/4 on the guage here in Phx, street driving in 116 degree weather! Nothing like free cubes!
maybe Ive just been talking to the wrong people! Ive been told you cant find a good block, you cant go more than 30 over, they have no top end, and finally, "THEY ALL OVERHEAT"! I want somethin different than a 350 0r 383 but dont want to pay the weight penalty for a bigblock. I figure a 400 and a muncie would make a pretty cool combo. thanx for your input. just what I wanted to hear!
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Old 07-05-2006, 06:42 PM
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How about one of the 427 small blocks?

The guys on the MonteSS boards all love 400 small blocks. They say a decent 2 bolt main block untouched nets around $300... IF you can find one?

I like the '73 I have. But I did something to it? I was told by a few people DO NOT change both the harmonic balancer and the flywheel on a 400 small block. you can change one OR the other but not both. I changed both. And I used to get some nasty vibration through my V-gate shifter when I'd drive the car.

A local crank place said they'd turn the crank for me for $80 or grind a new one for about $180 (I think?) if I wanted a new crank for the engine.

But when I ran the engine (with a 2x4 set up) I never had any overheating problems with it?
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Old 07-05-2006, 06:54 PM
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Quote:
Originally Posted by rj57
How about one of the 427 small blocks?

The guys on the MonteSS boards all love 400 small blocks. They say a decent 2 bolt main block untouched nets around $300... IF you can find one?

I like the '73 I have. But I did something to it? I was told by a few people DO NOT change both the harmonic balancer and the flywheel on a 400 small block. you can change one OR the other but not both. I changed both. And I used to get some nasty vibration through my V-gate shifter when I'd drive the car.

A local crank place said they'd turn the crank for me for $80 or grind a new one for about $180 (I think?) if I wanted a new crank for the engine.

But when I ran the engine (with a 2x4 set up) I never had any overheating problems with it?
would love a 427 small block, but sadly I dont have that kind of coin. One of these days....... I think my mind is officially made up, I will start looking for a 400 2morrow. Maybe i will get lucky and score a good block. The bad part is there really isnt a good machine shop for 150 miles as far as prepping the block. If it comes down to it it will be worth the drive. and i wont be changing the balancer AND the flywheel!
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Old 07-05-2006, 06:57 PM
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rj57 = the vibration thing does not make sense. If it was balanced like a 400 all 400 parts should fit it. Most all 350s are internally balanced, 400s are not. Don't mix flex plates or dampers.

I'd not poke a 400 more than .030 for myself. Some get pretty thin.

Always acid dip a block to remove the rust inside the water jackets, a good idea on a 400. Use a high volume water pump like a Stewart. www.stewartcomponents.com It won't overheat.

Some people have cooling system problems, but a 400 won't overheat if done correctly.
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Old 07-09-2006, 12:13 PM
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I've got a factory 400sbc in my 1974 SS El Camino. Its still stock with points, 2 barrell, etc.

As is I can still spin the rear wheels even with posi.

I just picked up a set of worked over 98 vortec heads at a great price that should find their way on to my 400 at some point.

One of the mags did an article called the impersonator and used a 400sbc, vortec heads, air gap intake, 750 carb, mild cam, headers, etc and were able to make around 425hp 525tq on pump gas.

I'm planning to go along those lines for a nice little street motor that can still make some passes down a track.
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Old 07-09-2006, 12:18 PM
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rj57

Another thing popped into my head.

Sometimes people balance a crankshaft at neutral at the front and external at the rear. 350 damper and 400 flexplate.... so yes, it does make sense..... I stand corrected...

just a thought.


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Old 07-09-2006, 02:59 PM
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Quote:
Originally Posted by Devin 427
maybe Ive just been talking to the wrong people! Ive been told you cant find a good block, you cant go more than 30 over, they have no top end, and finally, "THEY ALL OVERHEAT"! I want somethin different than a 350 0r 383 but dont want to pay the weight penalty for a bigblock. I figure a 400 and a muncie would make a pretty cool combo. thanx for your input. just what I wanted to hear!
Overheat hahahhahha, no they don't.

Like xntrik stated
Quote:Some people have cooling system problems, but a 400 won't overheat if done correctly.

You have some replys from some of the best on this site or any other site.
They do NOT overheat if built correctly.
434 sb w/twin 700's, no problem.
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Old 09-09-2006, 01:32 PM
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400 FAQ - "There's no replacement for displacement!"

Everything you need to know about 400 small block chevies!

Do 400's run typically run too hot?
The myth about 400's overheating is true.... If you know nothing about 400's or siamesed blocks, you will just grab any old head gasket with the bore you need, and slap it on there. (detect sarcasm) Then what happens? You have forgotten a very important part of a street 400 build - the steam holes that are in the head gasket! Or else since they were pretty much all smoggers, you change the heads out to say, a double hump or vortec head (or any other non-400 sbc head), and put on a set of 400 head gaskets. What happens? No steam holes in the new heads! You have to use the head gasket with the steam holes as a template and drill them!
The cylinders are siamesed, as in they all touch each other in the middle, instead of smaller bores in 350's and smaller that have space between the bores for water to circulate. without a steam hole opening into the head's water jacket, water gets up to a trapped spot at the corner in the siamesed bores just under the deck, and boils to steam. Steam does not cool a block off, nor circulate with the water, therefore they run hot spots there. This can also lead to blown head gaskets and warped heads. With the stock 400 rods (a little on the short side @ 5.565"), they exert more force on the outside cylinder walls, and when the thing is running a serious hot spot there under loads, there comes the other myth about 400's - they crack a lot on the outside cylinder walls...

Unless it's a high rpm race engine, steam holes are a must! High rpm's cause so much turbulence and excessive water flow in the block that it purges out all the steam no problem.


4 bolt 400's are definitely weaker than the 2 bolts due to a poor GM design. they are casting # 3951511 1970-72. Good for maybe 425hp. Good street engines for drivers, no problems with daily driver power levels. It's really the monster camed engines' higher rpm's that will break these blocks more than the street cammed engines' hp and tq figures.
GM also made some warranty blocks due to this problem that have the 3951511 casting, but are actually a 2 bolt warranty replacement fix due to the problem on the 400-equipped truck blocks that were flogged pretty darn hard. The outer bolts on these 4 bolts are not splayed, they go straight up into the block and the bolt hole threads go into the webbing area between the cylinders, which is a big weak spot, and can cause some cracks up in there. If you take a 2 bolt block and install splayed 4 bolt aftermarket caps, this will be 10 times stronger than the non-splayed (straight). I think the 4 bolts were the only blocks drilled and tapped for a manual trans clutch linkage (belcrank/z-bar) ball stud pivot. Others just have blanks. Most 70-72 400's were found in trucks with manual or auto, 73+ were mostly full size family car engines and mostly all auto. You can drill and tap them however.

The 3951509 block is the most sought after 2 bolt 400 block. Some have the better metallurgy with 1% added tin and 2% added nickel, which increase the strength of the cast iron block A LOT. The added nickel is used in a lot of newer blocks, GM and ford among others. I have heard of guys taking 5.0 'stang engines apart at 100,000 miles and not even needing to bore them to rebuild with the cylinder bores checking out like new still, as the added nickel blocks wear so much better than the older cast alloy formula. 010 and 020 numbers will both be stamped usually under the timing cover area. Strange thing on mine, they are stamped on the side of the block, smaller, near the deck. Never seen that. These I believe are also the "cheater" blocks, as you can pass them off as 350's because they have the same amount of freeze plugs on the sides - 2. 8" balancers also are a giveaway that it's a 400, but you can buy externally balanced 6" harmonic dampners. Then the only clue that it is not a smaller sbc would be the casting numbers.

the 330817 block is also a 2 bolt, but not likely to have the 010 020 designation. Some of these blocks have been known to have a lot more coreshift than the other castings of 400's. Mine appears to have an immense amount of coreshift, but when I used bow calipers to measure the cylinder walls, they suprisingly turned out pretty even and actually really thick- would easily go .040" over.

My 4 bolt has some coreshift, but both my old 509 and the new one I got (bought a "checked out" block on ebay with a crack in the lifter valley...) were really straight. Like I said, the 330817 looked like it had a lot of shift, but wall thickness was excellent still.

I will add that due to all the overheating rumors, most guys who know about 400's do tend to take more care of the cooling system. I have never heard any real legitimate complaints of guys aware of steam holes and proper 400 building techniques that have had any problem with running a stock cooling system (just a myth, or mismatched parts).
I personally don't agree with high flow water pumps 100%. The faster the water flows through the radiator, the less heat is transferred into the air to cool the water. The high flow will definitely purge any steam out of the siamesed block for you if that is at all an issue (if you opt not to drill the upper steam holes, it's a negligible argument), but high flow does use more power from the engine and will return hotter water back to the block. I suppose this will shock the block less, but I think the cooler water temps are well within GM engineering specs for the metallurgy of the block. What I would recommend most is an aluminum radiator, possibly in conjunction with a high flow water pump. Hotter running engines with big cams I would definitely recommend those in conjunction with the modification of dual electric fans for those stuck in traffic moments, as well as the power gains from ditching a mechanical fan. In 2nd gen 70-81 Camaros, the popular thing is the LT1/LS1 dual electric fans, and the addition of a DCC motor controller (or else you will have electrical problems). Lincoln Mk VIII electric fans are the biggest monsters of all, but the shroud is smaller, requires some mods and harder to get to look right on our radiators unless you order one that is the same size as that fan. the LS1 flows around 2600 cfm's I believe, and the Lincoln Mk VIII fans flow something close to a massive 5000 cfm! The Ford Taurus fans are good for at least 3000, and look like the Mk VIII fans. The Summit fans are around 2000 cfm if I remember right. The LT1/LS1 are great for my 71 Camaro size-wise (fits right on my 4 row SS396 radiator), and also it is great to get the aluminum LS1/LT1 radiator with them. They do have plastic tanks, but it's a weight savings game on those high tech masterpieces of 4th gen camaros... The best choice I think I will run is an aluminum radiator (maybe 4th gen LS1) and LS1/LT1 dual electric cooling fans with a DCC motor controller for speed controls and temp sensors (you will have voltage problems unless you run this type of system, these fans are hooked to the factory computers on the oem application). Then if you run a high flow water pump, you at least have freed up more power from the lack of mechanical fan than what the high flow water pump will use. I think a high flow pump WITH an aluminum radiator is a good choice.

Last edited by Chuck78; 09-09-2006 at 02:23 PM.
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