chuckaroo

Hi guys
Please straighten me out here...I always thought the 327 and 350 were completely two different blocks and that the 350 was not a punched out 327. They both have a 4" bore, right?? Next I find out a 383 is a 350 with a stroker kit. Where I'm I screwed up?? Inquiring minds.
Thanks.

Faslane

all same block, 327,350 4 inch bore, different stroke, 383 is .30 over and different stroke

Randy G.

327 has a 4.00" bore x 3.250" stroke.

350 has a 4.00" bore x 3.480" stroke.

383 has a 4.030 bore (.030 over 350 block) x 3.750" stroke which is the from the crank used in the 400 CID small blocks, but the main journals are smaller on the 350 block. The 350 has 2.450" mains while the 400 cranks and blocks were set up for 2.650" mains.

383 stroker crank kits use the 2.450" stroke so they can be used in a thicker cylinder wall 350 block without modifying the mains. People don't like using the 400" larger bore blocks because they feel they are prone to overheating due to thinner cylinder walls. Steam holes were added on the deck and heads to offset this.

.

JohnZ

Short answer - There was a whole family of small-block displacements that grew out of the "4-inch bore blocks", depending on crankshaft stroke chosen (302, 327, and 350). Several blocks were used for both 327 and 350 applications in '67-'68 with machining changes (notably the 657 and 678), but blocks used for 350 applications were unique to that usage, with "large" (2.45") main journals, longer main cap bolts, 4-bolt mains on many applications, and many other improvements.

DZAUTO

I am here to EMPHATICALLY verify that MANY of the so called problems with SB400 engines are unfounded and are somewhat "old wives tales"!!!!
I do not know exactly how many SB400 derivatives I have built in the past 40yrs (maybe around 25 engines), but I have NO KNOWLEDGE of a single problem with any of those I've built, NOR, did any of the cores I used have a problem. At this time, in my family, there are four SB400 engines that are still kicking butt with zero issues. One of them is a 420 in my jet boat.
Of course, it goes without saying, when a SB400 is used to build an engine, a machinist needs to THOROUGHLY clean, inspect and magnaflux it. And if your machine shop has the equipment to do sonic testing of the cylinder walls for thickness, to determine overbore limits, it's a good idea to also have that done.
WITH THE EXCEPTION OF A SERIOUS RACE ENGINE, I strongly feel that heads used on a 400 block should have matching steam holes drilled.
A clean, good flowing, efficient cooling system is absolutely essential.
With all of that said, I have zero hesitation using a SB400 block for building a strong performance, or even a nice street/driver engine.
Both my 70 Chevelle and the 56 Vette have .030 over SB400 engines.
I built the engine in the 56 almost 20yrs ago and the one in the Chevelle 18yrs ago.
The 420 in the boat was originally built .030 over about 25yrs ago. About 9yrs ago, I pulled it out, rebuilt it and stroked it to 420 (went to a 3.85 stroke). Oh ya, and instead of buying a 3.85 stroke crank, I had the rod journals OFFSET ground down to SMALL JOURNAL size and used 66-67 style (small journal style) rods with ARP Wavlock bolts. Again, ZERO problems.

Soooooooooooooooo, it's my position that if a SB400 should become available to anyone, do not back away from it!

Westlotorn

I think the bad Karma on the 400SB came from its beginnings. It was used in trucks and Heavy impala's. It was also used when the 1st gen smog laws were taking effect and the manufacturers had some poor tuning ideas on how to meet the new smog laws.
The engines were low compression boat anchors with good torque.
In a Corvette or lighter performance car I think the 400 is a gem. More torque and HP for not much more expense. I am building one with no qualms about heat issues.

mashinter

Steam holes were added because the bores are siamesed; there is no coolant passage between the bores on the 400.

DZAUTO

Now, back to the original issue----------327-350-383.
There is no question that a 327 (with its shorter stroke) can easily be built to turn very high rpm's. Thus, it develops its horsepower in the very upper rpm ranges-----------------add a retro roller cam, and it's really killer (of course, anything is with the addition of a roller cam).
The 350 provides more torque at a lower rpm range (a little more practical street engine which works well with higher gear ratios). The ideal choice of course is a 383. Stroke = torque. Simple. For an ideal street/performance engine that will work at lower rpm's, thus, even a higher rearend ratio, the 383 is hard to beat. And, with today's availability of aftermarket parts/kits to convert any 350 into a 383, the economics of building a 383 are excellent.
It's true, when building an early, traditional 350 (or even a 327) into a 383, there is some VERY, VERY minor clearancing required------------TOOOOOOOOOOOOOOO EASY. You can have the required clearancing at the bottom of the cylinders done by your machinist, or, do it at home using a die grinder and a carbide rotary file, as shown below.



And while we're on the subject, SB400 blocks are cast with this clearance notch already at the bottom of the cylinders.



This little bit of clearancing at the bottom of 350 (or 327) cylinders is all that has to be done (top picture) to drop a 3.75in stroke crank into a 350 block. The remainder of the build is just the same as would be done when building a 350. Since 350 blocks DO NOT have siamesed cylinders, then there is no need to add the steam holes in the heads.
BUT, if a 400 is built with 350 heads that do not have the steam holes, again, they are TOO EASY to add. Simply place a 400 head gasket on the head, use a few head bolts to hold it in position, center punch for the 6 holes, and drill them. VOILA, you now have a set of 400 heads.

Tampa Jerry

This months edition of the NCRS Driveline has a great article on how to stretch a 327 into a 383. The author also changed the mains to four bolt. When finished, the 327 is a powerhouse sleeper. Jerry

bcwaller

Getting off topic, but since the 400SB has come into the discussion...

If you are thinking about a non stock engine with more power, any experienced builder can get you a great engine based on the 400. The blocks are still available, and as DZ said, you can set the heads up for them specifically.

Want the same RPM performance as a 327 but with 352 cubic inches? 327 crank in a 400.

Want more bottom end, but still rev pretty well with lower priced parts? 350 crank in a 400.

Want the bottom end grunt of the 383 that everyone loves? Build a stock 400!

Want to pull stumps? Get a 400 stroker kit (418?) and don't expect to rev much over 500 rpm.

If you can't tell, I'm a fan of the block, and have a 352 in my Corvette and it keeps as cool as can be.

DZAUTO

Correct.
What he outlined in the latest NCRS issue, is basically what I did to a 327 block over 20yrs ago. The end result of this kind of mod to a 327 block is that you can retain a 100% original appearance using NO HOLE valve covers, and have a killer SB!!!
This is a GREAT mod of a 327 for a 57 Chevy that you want to look like a stock 57 283.-----------------Oh, but then there are going to be the comments that you cannot make it look like a 57 283 because 55-59 heads had a staggered bolt pattern. WRONG! Again, simple solution. Have additional bosses welded to later model heads (2.02 versions if you prefer), drilled and tapped for the early staggered bolt pattern valve covers. Then VERY CAREFULLY grind off the double humps and shape a pyramid symbol on the ends of the heads to look like 57 power pack heads (or FI heads). DANG, what a (cheater) concept!




This is the 400 in my 56, disguised to appear as an early FI 57 283.

DZAUTO

True, 5-6000rpm is pretty much max for a SB400-----------------but trust me, 2nd and 3rd shifts are real whammys! And with something like a 3.08 rear, you are long gone when wound out in 2nd gear.

tuxnharley

And that's NCRS approved? How would that judge?

toddalin

While you don't see many, the 377 ci is the hot ticket (aka fun)!

This uses the 400 overbore and 350 stroke and can be made to rev with the best of them.

Dave Alciatore runs a 377 with a modified '65 FI unit and dynos at >400 RWHP in his L'il Red Engine.

JohnZ

Judges fine. NCRS doesn't tear engines down - they just observe them.

tuxnharley

IIRC 377 was the displacement the original Grand Sport engines ran. Did they get there by this same type of engine architecture (bore and stroke), or isit just a coincidence?

MikeM

The 377 if yesteryear was because they used virgin 4" blocks. No need to bore them .030 due to wear.

Back then, 377's were considered commonly the biggest SB.

DZAUTO

That is EXACTLY correct!!! If it can't be seen, it can't be judged.
The next easiest displacement increase for a small journal 327, is to just turn down the mains on a 350 crank and drop it into a small journal 327 block (oh ya, the flange between the rear main bearing journal and the rear main seal journal of the 350 crank also needs to be slightly cut down). Bore it .030 and you got a 355 from your 327.

Randy G.

Exactly.

Randy G.

327 .030"over = 331 ci.

Ran pretty good.