I'm right off exit 33 on 78 in Martinsville. It's nice to see so many jersey guys hanging out
I lean towards edelbrock heads if money isn't tight. With the stock Pistons you'll want the smaller chamber 62-64cc to push you close to 10to 1 compression.
The other very important part that make a sb400 special is the flywheel and horminic balancer. They must be installed or the motor will rattle your teeth out. Summit racing has them at a reasonable price if yours are missing or beat up. I'm retired law enforcement so I'm around all the time if you ever need any help. Just PM me and I'll send you my info. I have met up with a few guys on here out on rt22 and they're all good guys. You tell us what you want out of you car and we can help. Everything from a burnout machine to a screamer. I lean towards burnout machine!

 

A friend of mine ran 400 SBs bored out to 410 on alcohol in his open wheel cars in Wisconsin. He picked up seasoned 2 bolt main blocks and had them drilled out to 4 bolt. Aluminum heads (DART I think) and mechanical fuel injection. They were rock solid. There's a lot you can do with the 400's. You can de-stroke them with a 350 crank if you want also.

 

Great points and things to be aware of, thanks!

I'm exit 20 in Lebanon Borough - 22 is a great spot. I appreciate the offer and will definitely shoot you a PM

 

Running a Muncie M20 behind it, with a 3.73 rear...

 

Another 406 owner checking in, if you can afford it have it checked out, in stock form the 400 had the short 5.5 in rods which led to alot of side loading of the cylinder walls and caused alot of problems which gave the engine a bad rap in stock form. Switching to the 5.7 in rod helps reduce the issue and you will hear arguments of that the 5.7 is still placing to much side load on the cylinder and a 6 in rod is best for longevity of the block.

 

I did this to a 400SBC just took a pile of "Benjamins" and threw them in the direction of the machine shop.....if they were good enough for early Sprint Car Racers to use in their builds its good enough for one of mine.

 

the real advantage of the 400 is you get larger bore. Destroke it with a 350 crank and you have a large-bore 372. In a Corvette, it's like a match made in heaven because you get torque AND HP.
The biggest advantage is from deshrouding the valves. Put good heads on a destroked 400 and you will surprise yourself with just how awesome of a motor it is. Just keep in mind 500 hp, don't go above that level - and it will last a long time.

I'd never race one because of the siamesed cylinders (though if you run alcohol, that would change that opinion). It's just too much of a temperature difference on the walls. I also wouldn't boost it - I did this and have this really cool 1/4" hole that runs front to back on the motor (again, heat)

With those said, people overheated a lot of 400s. I'm not making a judgment call on it, but I will point out that it's never their fault when the motor blows up - so the negative press may simply be that. In that era of motors, GM was running vehicles as lean as possible to pass emissions, and that means heat - in a motor that already could have issues with heat due to the siamesed cylinders.

I also wouldn't bore it any more than I needed to clean up the bore. The more metal you keep in the walls, the happier the motor will be. If you really want to make it even better run an oil cooler as well. But built right, you'd have a 500 hp motor that starts making power at 1500 rpm and pulls all the way to 6500 rpm - and it's a blast to drive, and gets decent economy.

don't be afraid of them.

 

All these replies have me pretty excited to look at modding the 400 down the road. Now...I suppose the question comes down to what kind of cost can I expect for some moderate enhancements? Roughly how much should I expect to have someone inspect the block?

My goals: I don't need anything with like 500HP but something in the mid-to-upper 200s/300HP would be my target.

Thanks!

 

I would guess it makes 300 at the crank now.

 

What did you spend on the block and prep if you don't mind. Did you have it sonic tested?

 

Here's a machine and parts list of what I put into mine--I already had the heads on another motor, so those were just machine work, so you'd have to consider what heads you are planning to use. All in all, i was about $$2600 into my motor, minus assembly (which I did on my own, and the heads--as mentioned)...

406 build
Machine work:
Block: cook and Magnaflux $60.00
Block: Bore and hone $110.00
bearings/freezeplugs $93.03
Heads: disassemble and clean $40.00
Heads: comp valve job $85.00
Heads: setup spring presure and assemble $50.00
Balance assembly $125.00
Drill steam holes $0.00
Resurface flywheel $25.00
Comp Cams 7609 pushrods $90.42
Machine work total $678.45
Parts:
Cam Kit: K12-432-8 $983.27
cam kit discount ($49.16)
Roller rockers--CCA-17004-16 $165.95
Rods--Scat--SCA-25700 $283.97
Pistons--SLP-H615CP30 $168.39
Harmonic balancer PFS-80001 $60.00
water pump-SUM-311006 $67.95
Timing tab SPE-4237 $4.95
Head bolts NAL-12495499 $33.97
oil pan bolts SUM-G1570HS $4.95
Timing cover bolts SUM-G1574HS $2.95
Head gaskets-FEL-1014 $77.50
oil pump MEL-M155 $31.95
oil pump screen assembly MEL-55-S1 $7.95
oil pump pushrod MOR-22070 $14.95
Parts total: $1,859.54
Total: $2,537.99

 

I spent a fair lump building my Shp 400", I know I could have done it cheaper, but didn't want to build it and it not last. I've got about 15k miles on it so far.

 

When I was young, we use to have stupid fun with super chargers. Take a stock smog motor with low compression and slap a 144 Holley supercharger on it! It will eventually blow up but I've gotten 2 to 3 years of burning tires off the rims with junkyard motors. The only problem when it comes our C3s is the hood must be modified but a lot of fun for under $2500

 

If you have a good running 400 now then do the basic mods first.Intake,carb(if needed),headers,good exhaust,good tuneup and better advance curve in the distributor.Maybe a cam as stock 400 cams were on the small side.
If you are happy with how it runs then leave it alone and drive it.If it blows up I would much rather lose a stock motor than a built one.
If you decide to rebuild/upgrade down the road then you have lots of options.
It wouldn't hurt to verify you have a 400 motor rather than taking someone's word.

 

I am currently building a 406 ci small block for my 72'
It will have KB 125 pistons, 5.700 Eagle SIR rods, Eagle Cast Steel Crank, Comp 292H Magnum cam, Dart 200 Iron Eagle heads, and a Weiand Team G intake with a HP750 Holley on it......
This combo should make close to or 500 horsepower on the nut and about as much torque....

The 400 block is susceptible to uneven deck surfaces between the cylinders.....make sure you check before replacing heads.

The main bearings and main seal are bigger.....and it takes a different freeze plug, and we all know about the "steam holes". Other than that.....it is pretty interchangeable....

I think they are a great way to make budget power.....
Mine should put my 72' in the 11's easy.....

Have Fun!

Jebby

 

Have few bucks to spend? Here's my 400 bored over 30 in action. PM me for specs.

 

The block? I bought it back in the 80's for $125......spent $300 on steel splayed caps which I did machine work myself on a Bridgeport mill....align bore/hone new caps.....$180.....square decks using BHJ Blocktrue system, bore/hone with BHJ deck plate.....well no money out of pocket but 10HRS labor installing/programming/wiring an aftermarket VVVF motor drive on my buddies Sunnen VGS20 when the factory drive took a crap on it. So.....less than a SHP block would cost but, for the normal guy.....they would be ahead buying a Dart SHP block. Sonic check showed good wall thickness but, I have lost the sheet.....bore is 0.030 over 4.155" stroke 3.50"....NOT...3.48"....3.50"!

The complete engine....someone here says they built theirs for around $2500......I spent multiples of that amount.....**** canned all the foreign made crap AFR puts in their heads for Manley Severe Duty valves, Exceldyne ultralight tool steel spring retainers (more $$$ than titanium retainers but weigh about the same and I shouldn't see the TI flakes in the oil filter anymore), CV products Super7 valve locks (they are damned proud of that stuff.....$96 for 32 itty bitty parts!) T&D shaft rockers with steel exhaust rockers....if you have to ask....can't afford them! Isky Tool Room springs......another IF......, Manley USA billet connecting rods (not their sourced in China machined in USA Hbeam rods), 42LB low mass 5140 steel crank....., Mahle pistons (substitute Napier 2nd rings for packaged stuff), Ported Super Victor intake, Holley HP Ultra carb, TCI dampener, Exceldyne belt cam drive, Isky EZ Roll bushed roller lifters, Bullet Cams solid roller, programmable MSD with crank trigger pick-up.....MULTIPLES of that $2500 build, I even bought ARP stainless outer head bolts so they don't get rusty

Speed costs money.....RELIABLE Speed costs even more! How fast do you want to go? How long do you want to go fast for?

 

The above poster is building a hell of a motor....I use to build high end stuff like that all of the time....
But I would like to give you another angle.
I bought my Vette with the 406 in it...when they dropped it off 8 weeks ago....one spin around the block confirmed that it vibrated over 3500 rpm.
Undaunted I jerked the motor and disassembled it.
The motor had KB 125 Pistons that were 60 grams lighter than stock. (About 550 grams)
Further inspection revealed the crank bolt was snapped off and the balancer tack welded on!
So I sat down with a $2000 budget and decided....on the Eagle cast steel crank and SIR rods which are plenty strong. These will be balanced with the KB Pistons as this thing maybe had 600-800 miles on it. A 400 balance plate is utilized with the stock flywheel. A Professional Products 6.75 inch balancer is spec....King Crank/Rod bearings, Durabond cam bearings installed by me. Speed Pro file fit moly rings will seal against a touch honed block as the piston to wall was .0015...it can take a little more....
The 6qt Corvette pan hides a Melling M55 with the spring stretched and the correct 6qt pickup with a steel driveshaft.
At this point I decided to shop for heads....after a lengthy search on the net (e-bay, Craigslist) I scored a complete set of Dart 200 Iron Eagle's for $500. The 265/175 cents these provide are a big factor.
I am going flat tappet as $600 for a hyd. Roller was not in the budget. I chose a cam that I have much experience with....the Comp 292h Magnum.
This specs at 244/244@.050 .501/.501 lift 110lsa. This cam is an old school grind that is easy on springs...revs well...makes great power and sounds better than any other flat tappet abc cam I have ever heard.
Speaking of springs, I am replacing the ones in the Darts with Isky Z28 copies...120 seat/320 over the nose....these are resilient and inexpensive. Rounding this off is a set of Magnum roller tip rockers, 1.52 ratio....this is to run the stock LT-1 valve covers.
Capping this will be a massaged by me 7530 TeamG to run under the stock hood and a 750HP Holley I scored on e-bay for $225. This should fit under the stock hood.
The block is being decked .010 as well. .010 in the hole w/72cc heads=10.5 to 1. This will work excellent with the cam on pump gas.
The block is a four bolt....at this power level....it is fine.
Max redline is 6200. Estimated power is 480-485. 500-510 ft-lbs. torque. I guessed this and the Engine Analyzer program said the same thing (479).
There is nothing radical at all about this motor.....it has a few of my tricks but as posted previously....it is more or less a Saturday Night Special modified motor.
Just another angle.....
Oh BTW....every bolt is stainless ARP....and the WP is a Weiand aluminum....
This is a meat and potatoes motor that anyone can duplicate.

Have Fun!
Jebby

 

I'm completely with you their. Love my 400'', not as radical as some but makes my vette move.