400 small block motor

[teamharvey]

Give me your thoughts. I just ran across a 71 with a 400 in it.

[Ron 586]

I think I would need a little more information to give you an answer. But I like 400 sb chevy engines and have had good luck with them.

[teamharvey]

It is a 71 custom longbed, but the glovebox sheet indicates a 350 so I asked what was up. He bought it 11 years ago so it had to be swapped out at some point prior.

[wolfthing2000]

Make dang sure the block is not cracked on the 400. They are notorious for overheat sensitivity and will not generally survive being overheated. Reasearch the fact and you will see what I mean.

[wolfthing2000]

Not trying to ryle up anyone here, just that you need to know that the 400 is a whole different breed of small block in the structure of the cooling jackets. Once you are aware they are different than say a 350 0r 327, then it is your choice to go the 400 route or not.

[Bad71chev406sbc]

I'm telling you guys from experience......I have had no problems with my '71 w/ a 400sb. I have a friend who drag races his 450hp 406sb(bored 400).....with no problems....of course he's running dual electric fans, and running a high 11 sec. '67 nova. He built his motor, and he's helping me build my first motor, a 406sb.

But make sure, that the block is good. If it 's not, you're SOL. there are cooling differences than the 350, but still do share a good amount of parts.

[hardline_42]

Ahh the mighty 400. Pay no attention to the overheating rumors. You just need to understand how these engines work. The biggest cause of overheating in these engines is swapping 350 heads onto it WITHOUT drilling the STEAM HOLES! There are six 1/8" holes between the bores on the block that need to be drilled in corresponding locations between the chambers. This keeps steam from getting trapped under the deck.

The blocks come in three casting numbers: 817, 511 and 509 with the 817 being the softest/weakest casting and the 509 being the strongest. Check the casting number to see what you've got (stout, long-lasting engines have been made from each casting so don't be discouraged if it's not a 509).

Unlike the 350, the 2-bolt version of the 400 block is stronger. It has more web material than the 4-bolt which makes it perfect for adding splayed 4-bolt mains (read: indestructable).

The 400 came from the factory with an externally balanced rotating assembly which is great for low RPM torque but not too easy on the crank for higher RPM applications. If you are swapping out the internals, definitely get an internally balanced crank. Also, stock 400's suffer from incredibly short rods (5.65" IIRC). A 5.7" or 6" rod will decrease side loading on the cylinder walls and prolong TDC piston-dwell.

These engines need cam, and lots of it for serious performance. They are stump pullers from the factory but they can swallow huge amounts of lift and duration without getting too "cammy." The 406 in my camaro sports a sizeable comp cams XE284. In short, these engines are the perfect compromise between big block power and small block size and parts availability and I don't think I would ever go with any other chevy engine.

[Kager67]

My only experience with a 400 was in my 78 blazer. It only lasted six months before it scored 3 cylinders. Maybe it was a fluke, but in my opinion, the only good part of a 400 is the crank.

[wolfthing2000]

So , like I said , considering all of the facts, it's your call. One of the big reasons the cylinders will score is that with uneven cooling around the cylinders,,,, they will run egg shaped. Some race engine builders run hot coolant through the block so the 400 will duplicat the running temperature and then they bore the cylinders.







Too much trouble if you ask me.+

[hardline_42]

The 400 block is a siamesed block just like any number of performance 350 blocks (read: bowtie blocks). It shouldn't run any hotter or any different. Granted the factory applications of this engine was not for high performance or high RPM use. The extreme side loading at high RPM caused by the short stock rods is probably more of a culprit in egging out the bores than anything else.

[Bad71chev406sbc]

Only overheating even remotely shows up, is when I'm idleing in 80+ degree weather, and am running a flex fan. Crept up to 220 in 20 min of just sitting in traffic.

[wolfthing2000]

A built 400 = gobs of torque and power( good idea if done right!!! I agree with that, I tried to do it ubtil mine was found to be CRACKED!!!)

General good old boy run and maintained 400 with miles and plugged/sludged cooling passages and steam vents ( an 1/8 of an inch hole that if plugged spells disaster!!) is a catastrophe waiting to happen!!

Steer clear!!!!!!

[gmcman7202]

ok guys, i got a 72' 400 sbc now at 406, longer rods, air gap intake, 99' gm vortech heads, drilled for teh holes, new springs, a step above a stock lt1 cam, edelbrock 650 carb, 1 5/8 headders, with estimated 9.5:1 compression on pump gas, with hei ignition,, mated up to a sm465/np205 all situated into my 72' gmc jimmy.... my main problem now is keeping u joints, and yokes on the truck, and i have yet to take it off road, the 33" tires, 3.73 posi rear, with a slight clutch dump, will break anythign on the driveshaft super fast

[wibilly]

no other small block for me when it comes to a truck!

[stllookn]

My budget sb400 rebuild. Just had to try out the new camera. I am going for the retro look...no paint yet.

[Bad71chev406sbc]

Originally Posted by stllookn

My budget sb400 rebuild. Just had to try out the new camera. I am going for the retro look...no paint yet.

WOAH! I'm doing the same look to my 400/now 406. i've got a set of those valve covers. How are you planning to put in the oil??? I'm going for the old school, sleeper look. Orange covers w/ white lettering, orange block, orange heads, orange timing cover, orange oil pan, orange air cleaner topper or black.

[wolfthing2000]

A good point. The old valve covers look cool but what about the cranckcase vent???? and like you say, what about the oil fill?????

[hardline_42]

Originally Posted by gmcman7202

ok guys, i got a 72' 400 sbc now at 406, longer rods, air gap intake, 99' gm vortech heads, drilled for teh holes, new springs, a step above a stock lt1 cam, edelbrock 650 carb, 1 5/8 headders, with estimated 9.5:1 compression on pump gas, with hei ignition,, mated up to a sm465/np205 all situated into my 72' gmc jimmy.... my main problem now is keeping u joints, and yokes on the truck, and i have yet to take it off road, the 33" tires, 3.73 posi rear, with a slight clutch dump, will break anythign on the driveshaft super fast

I've got a similar setup for my camaro. It's a 509 casting 2-bolt 406 with a forged, internally balanced rotating assembly, 6" rods, severely worked-over Vortec heads (machined for studs/springs/lift, ported out the wazoo and fitted with 2.02"/1.6" valves), a Comp Cams XE284 cam kit and a Stealth Ram EFI intake with a '92 Z28 computer. For what it's worth, EA dynoed it at 511 peak HP and 509 peak TQ.

[gmcman7202]

what r's were thoes at?

[hardline_42]

Originally Posted by gmcman7202

what r's were thoes at?

I'm assuming you're asking me and I'm assuming you're referring to RPMs

IIRC they were both at about 5.5 - 6k

[gmcman7202]

Originally Posted by hardline_42

I'm assuming you're asking me and I'm assuming you're referring to RPMs

IIRC they were both at about 5.5 - 6k

thats higher than i was thinking, but hats off to you

[Rake]

My '72 has a sb400...it came with a 402bb, but it was traded somewhere along the way. The sb400 is a '73 model which was used in vans/buses, and only rated at 175hp.

[Longhorn Man]

Originally Posted by Rake

...only rated at 175hp.

You can't just go by that number alone... if that was the case, my 500 big block wouldn't be worthy of anything being rated at 190 horses.

[hardline_42]

Originally Posted by Rake

My '72 has a sb400...it came with a 402bb, but it was traded somewhere along the way. The sb400 is a '73 model which was used in vans/buses, and only rated at 175hp.

Those are basically factory underrated numbers. Plus, the 400 was never used in a performance application from the factory. It was either in trucks/vans or land yachts that needed massive amounts of torque at low RPMS. That's why they came with low power smog heads and RV cams. The draw of these engines is the potential they have to make big block torque and power and still fit everywhere a small block fits.

[stllookn]

Bad71...Great minds! I am going to look at boring a hole in the manifold for the old-school "hat and tube" filler. I have access to a Bridgeport so can do that. If I can't find easy access through the intake I may have to weld a filler onto the valve cover toward the back where it will not obscure the script lettering.

I am now toying with a new paint scheme that would include the Anniversay Gold and Ivory but would cover the entire block. Just a thought!

As a last resort I can always cut an old school fill pipe and weld to the back of the cover. I will just use a patch panel on the other side for the vent or just go into one of those tree fittings behind the carb. for the rest of the vac lines.