Advice on 400 sbc engine
 

I've got a chance to pick up a .040 over 400 short block. Casting # says it's a 70's 2 bolt. Owner drove it for just over 1000 miles when while tuning dropped a nut down the intake which cracked #5 piston when said nut was driven into the head. #s on the engine tab are almost illegible (due to decking) I suppose. Anyway the short block is intact and turns. No tin, no balancers, just the short block for $200. I think .040 makes it a 406 right? My goal is 400+ torque and 425+ hp. Is the 400 CI noticeably (sp) torquier than a 350? Don't wanna do this if it's not much different. Any things I need to know i.e. differences from a 350 such as engine height and the such. Thanks:cheers:

the 400 blocks tend to run warmer and have steam hole between the cylinders. the heads will always need hole dilled but 350 heads will work.
read this.

http://www.chevyhiperformance.com/te..._block_torque/

It will give you an idea what you can do

They've got a lot more grunt than a 350. I don't know what to tell you about your goals. The only issue I see here may be the condition of the cylinder wall in that cylinder. It may be cracked from side thrust of the piston when it crunched the nut. A sleeve isn't a problem but adds to the cost.

You can not bore it any more (and live on the street).

$200 is a good buy. I would buy it. Getting 425hp out of a 406 is easier than a 355.

Are the rods stock? 400 rods are shorter than 350 rods.

You will need to start pricing parts for a 400 vs a 350. :D

You will need to keep in mind that all the rotating parts are 400 cid only as they are externally balanced, whereas the other small blocks are internally balanced, they also have been known to have cooling problems, however they can be delt with.

AFR offers the needed steam hole drilling as an add on machine service
for their heads... A good set of AFR's or some Big Power for little money
Dart Platinums with the proper cam will have you blasting past the
500 hp mark... as mentioned the 400 block is not as overbore friendly
as other SBC's... the torque increase should be healthy when compared
to a 350. I'd proceed with some caution... I believe you're saying it's
still in short block form where you can't tell if the bores have been hurt
... if they are ok you've scored a good power maker for $200...

A possible plan B if the situation doesn't work out would be a
395 stroker built on a 350 block... this is becoming a more popular
choice all the time.... and if you chose a 87 or newer roller cam 350
block to build the motor on.... then you have a 395 roller vs. a 406..
A 3.875 crank is dropped into .030 over 350 block...

the 406 has a few more cubic inches
the 395 has a little longer stroke, a roller cam built in, no
special machining for the heads, off the shelf aftermarket rods.

.040 over =397.38
.060 over =401.33

Either choice is a good building block for big power.:thumbs:

*mickey thompson offered a 4.00 stoke crank for SBC's back in
the 60's

The 400 blocks are hard to cool with midyear smallblock radiators particularly if you get them to make any power. Also recognize that the 400 blocks are prone to cracking the decks.

Hi Dave,
The 400 SBC is a great platform to build on I have one in my 55 Chevy and it pulls like a Big block. Everyones going to tell you that they run hot but that's just a myth that was created in the 70s early 80s when people first stated using 400s in performance applications they would install 327/350 perfomance heads with out the steam holes and trap air in the block, making the engine run very hot! There is no differance externally all 327/350 componates will work with the exception of some after market oil pans and the above mentioned Damper Flywheel/Flexplate that are 400 specific. The Engine that your looking at may have a cracked block due to the bolt consumption so be aware of that. The .040 over will make it a 408 and that's as far as you can safely go with the stock block with out adding block fill. $200 a good deal. 425 HP is easily attainable with decent after market heads and a mild cam. Don't forget the steam holes and good luck. :cheers:

Thank you all for the timely info. :thumbs: My 355 sbc has Sportsman II 64cc chambers and I believe the steam holes were already there so this wouldn't be an issue. I am suspicious though, as to why after a 1000 miles on a rebuild he didn't just install a new piston in place of the damaged one and drive on....:toetap:

The sportsmans will work great! I have 210 sportsmans on my engine but I had to run a 22cc dish in the piston to get the compression down to 10:1. but I have a 3.832 stoke. Mine is setup with a Solid roller, Victor jr ,Demon 750DP and makes 450H/P at the tires. You can just compare the gasket to your heads to see if you have the steam holes if not it's not that hard to do just a little scary. I would try to get a promise of return just in case of a crack. You will see about 30-40 FTLB of torque over a comparable 350.

Dave:

I'd also carefully check the crank and rods if you are planning to reuse them. Dropping a bolt into a running engine is a violent mess. My brother went through that nightmare. After resleeving a cylinder and fixing the bent crank, he was back on the road.....and broke.

Properly built, starting with a good, solid block, SB400s are outstanding engines. Contrary to what a lot of people are told, they do not have heating problems any worse than any other engine-----------------SO LONG AS THE CAR HAS A GOOD, FREE FLOWING, UNCLOGGED cooling system. PERIOD!
in the past 30+yrs, I've built about 25 SB400s, the biggest is a 420 right here.
http://s65.photobucket.com/albums/h2...t=100_0232.flv

Another is here. This one has a stock, copper, 3 row radiator core. Stock type water pump.
http://i65.photobucket.com/albums/h2...O/Chevelle.jpg

And another is here, with a stock, but re-cored copper radiator. Stock type water pump.
http://i65.photobucket.com/albums/h2...O/100_0134.jpg

All the SB400s that I've built used a stock block, cast crank and either stock 400 heads with 2.02/1.6 stainless valves, guide plates and screw in studs, or, aftermarket heads such as Dart Iron Eagles on the boat engine.
It is true that SB400s have siamesed cylinders and for street use, steam holes in the heads are required, but as long as the cooling system is in good condition, there just should not be any cooling problems.

Dz,
Thats the best looking 400 I've ever seen. :smiliedrool:

Well, I was able to talk him down to $150 due to the 'unknown' factor. Engine has surface rust only on the cylinders and #5 piston is cracked across the top with an obvious couple of hits by a nut. Other than that it's clean and has obviously had a recent rebuild. Nothing on the piston crowns at all. Does anyone know if the rotating assy can be installed in a .040 over 350 just in case the 400 block is no good? This makes a 383+ right? I do have an extra 350 short block. Oh, it also looks like the rod caps have been ground to take the lips off at the fwd and aft edges (does that make sense)? The caps are smooth and do not have the I beam look like I'm used to seeing on 327/350's. I'll take pics tonight for your thoughts. :cheers:

.040 over 400 pistons are too large for a 350 block. You'll be in the water jackets. If you use the 350 block, you'll have to buy new pistons/rings plus the price of the bore, swapping pistons and rebalance. If you buy new pistons, do yourself a favor and get rid of the short 400 rods if that's what's in it. The crank will fit in the 350 block if you turn the mains down. I don't know about rod clearance. Plus, if you swap blocks, I wouldn't re-use the cam lifter out of the 400 engine. There're already run in to that wear pattern in the 400. Now you have spent a small fortune.

If you change blocks, you have just ruined your reasonably priced purchase. See if you can get by with a little scothbrite rubbing on the surface rust, put in a new piston of the same kind and weight and you're in business for only a few bucks. That is assuming there a no cracks. $100 for a cylinder sleeve.

Others may see it differently but that's the way I see it.

Hi Dave ,
The rotating assembly will not work in a 350 block and it's not worth spending the money to turn the mains down when you can buy a new crank already done for $250. The rods have been balanced( grinding on the end) and the beams have been polished to relieve stress risers(smooth on the sides) both good things. Check the depth of the piston at top dead center on the hurt cylinder and the one next to it to make sure the crank is ok.When you pull the piston pull the one next to it and disassemble both when you get the new one weigh both and make sure there the same or ask the owner if he has the balance card with the weight of the piston. Waiting for pics.:cheers:

Thanks Mike. I will disassemble and get it crack checked first of course. I believe the cyl's will clean up or I wouldn't have bought it at all. If all's well I was going to do just as you suggested. I'm not familiar with the 400's but can assemble a 350 with my eyes closed. I'll be asking questions, please bear with me. I'm assuming you measure rod length center line to center line right? :thumbs:

[. I'm assuming you measure rod length center line to center line right? :thumbs:[/QUOTE]



Yes, and you measure the compression height of the replacement piston from the pin centerline to the top of the piston. It should be the same as your others. And before you tear it down do like Injected Stingray suggested, measure you deck height on all the pistons. They should be very close to the same on all eight. If one or more is off, I'd be looking for a bent rod or something.

That's one mean sounding boat engine!!! Cool! Wanna share the specs on that engine?

Tapio,
Its a stock block 400 with a stock crank, bored .030, stroked .100. The stroke was accomplished by offset grinding the rod journals down to small journal 327 rod size. Pistons are Speed Pro hypereutectic with a small dish and a pin located for a 5.7 rod. The added stroke places the top of the piston ABOVE the block surface, thus, each piston top had to be slightly milled. I chose to have the piston clearance milled to .010 deck clearance.
Heads are out of the box DART iron Eagle with 215 intake runners, 2.05/1.6 valves and 1.47in springs
Cam is .510/.533 lift flat tappet hyd and duration is 244/254 @ .050 lift (cheap in-house generic cam from Summit).
Flywheel and balancer are stock 400 pieces.
Max power will be somewhere in the range of 5500-5700.
As you see, its nothing terribly exotic. Should make a heck of a street engine!