brianfiske

I am going to do a rebuild next year, my best friend who has been building cars his entire life suggested I do a 377 vs a 383 on my 86. His reasoning was that the 377 is more efficient and reliable than the 383. Im curios about the feedback from the corvette community...

Benny42

Tom400CFI

^Totally.

cv67

Destroking any street car is kind of going backwards. That longer stroke is what pushes you back in the seat.

pologreen1

take the 400 and go 421.

More=better
Bigger= better
Better= more bigger fun

KyleF

The 383 as must know is taking a 350 and putting a 400 crank. Both of the above replies are correct, since both the 350 and the 400 are on the same archetecture, once you take a 350 and put a 400 crank in it, it is just a bore difference form being a 400. There are difference in the blocks overall, so you can't just bore your 350 .120" over.

You end up with a 377 because the block isn't bored. A 350 with a 400 crank is a 377 (376.8)... .030 over bore = 383 (382.47).

a .030 is pretty standard and common. When a 350 is rebuilt, this is a common re-bore size and net a 355. Shouldn't be cause for concern.

Typically as the bore to stroke ratio goes up, you make more HP. Longer stroke is more torque.... this is for motors with relatively the same displacement as shorter stroke motors tend to like to rev higher since the piston doesn't have to accelerate as much per stroke.

All things being equal, the 383 should make more average torque and HP across the RPM range due to the added displacement. What is his reasoning to say it is more "efficient". More fuel efficient, or makes more power?

I don't want to insult your best friend, but there is a difference between an opinion from someone putting things together for a long time that work... even those that work well, and a well researched, tested, and documented fact.

C409

…… A Wise Old Man (the wise part rules me out) once said " There is NO Replacement for Displacement" … I believe him ! …..


<<<<< 421 <<<<<

383vett

MatthewMiller

That is definitely one way to end up with a 377, but typically when people reference a 377 they mean a 400 block with a 350 crank. I'm assuming this is what the OP meant. They tend to get used in racing series where there is a displacement limit. Otherwise, I can see zero reason to intentionally reduce the displacement of a 400 SBC. There's no practical rpm limitations imposed by the longer stroke (the valvetrain is always the limiting factor); and as C409 noted, displacement is always king when it comes to making power. There's simply never a case where less displacement makes more power, all else being equal. In general, the 1/8" extra bore of the 400 block should give room for bigger valves and/or allow less shrouding of the valves, and both of those are good for flow through the engine. I don't know if there's much actual difference in real life, though.

To the OP, there's no difference between the two engines in reliability or efficiency. There's been talk over the years that the 400 could suffer cooling issues due to its siamesed bores. It appears that this is not really true, however, based on the many people who have used it successfully.

PS - C409, is your engine a 400 bored 0.040 over?

Vette5311

Zip Corvettes

It all depends on what RPM he wants to run. If you are wanting to go RPM then big piston short stroke is the way to go. There is a limit to the piston speed so there are physics at play in engine building, you can't just go huge bore and stroke and then decided you want to be able to rev it to the moon. For the street, you can't beat a 383 or 406.

MatthewMiller

It's true that there are differences in piston speeds at a given rpm between the two builds, due to their strokes of 3.5" (377) and 3.75" (383). But that doesn't cause any practical limitation on rpm. The limitations to engine speed are always going to be found in the valvetrain first, for any decent build. 13 years ago Chevy mass-produced the LS7 with a 4" stroke and redline of 7000rpm, with a full warranty. Now we live in a day and age when massively stroked LS engines with 468cid and strokes of 4.25" and more are easily being built to be reliable at 8000rpm and more. There's no reason that a 383 or even 396 SBC (strokes of 3.75" and 3.8125" respectively) can't be built to survive any rpm that any street driver would ever want to see. IOW, the desired rpm should never be a factor in determining whether one wants to build a 383 or 377. There's just no good reason to destroke a 400 SBC unless one's racing class limits displacement to 377cid.

383vett

Not necessarily. A long stroke smaller bore motor such as a 383 is rpm limited because the piston speed is increased causing increase loads on connecting rods, friction and ring wear, not so much valvetrain limited. A 383 is great for a street motor or tow vehicle. It isn't ideal for the racetrack. It just can't be revved high enough to make good horsepower which is important at the track.

Izzy Dizzy

"That's what she said when the bed broke!"

Tom400CFI

Doesn't a 383 have the same stroke as a 400? Aren't there 400's out there that rev decent/make good power/have a usable RPM range?

MatthewMiller

Right, a 383 and a stock 400 both use the same crank with a 3.75" stroke. All I can say is that the empirical evidence suggests that in the year 2019, there are plenty of engines with much longer strokes than 3.75" that are revving to the moon. As Tom mentioned, plenty of 3.75" SBCs rev safely way above 8000rpm. Chevy's own LS7 had a 4" stroke and came in mass-produced vehicles with a 7000rpm redline and a warranty. And companies like HPR routinely sell LS engines with 4.25" strokes (and more!) that can safely go past 8000rpm.

There's simply no good reason for a 3.75"-stroke engine to be rpm-limited by its rotating assembly. This obviously depends on the parts one specifies: a stock 400 rotating assembly isn't good for 8000rpm, but then neither is a stock 350 rotating assembly. I'm going out on a limb to suggest that any build the OP is considering would not entail rpms that a stock 400 rotating assembly couldn't handle. It's probably going to be kept to a 6000rpm redline, and that is uber-safe for any of these assemblies.

KyleF

You are glossing over why. You are also glossing over the fact that a lot cars have long term issues that do not show up when they are fairly new. The 3000GT/Dodge Stealth come to mind. The output shafts from the transmission to the transfer case almost always eventually fail. Same with opti sparks, the ash tray lid on Fox Body 'Stangs, Spark Plugs breaking in Triton heads, dash pads cracking, electronic dashes going out...this list goes on. With enough age and miles weak links show up that may never be an issue in the first 5-10 years of ownership.

Physics dictates that it is easier on a block and rotating assembly to have a shorter stroke if you want to rev high. This also has less inertial losses as with the pistons moving and accelerating less, less power is consumed to move them. GM did not start with a blank slate. They started with their LS architecture. All products of mass production are a result of a series of compromises. I suggest you read the book "Car guys vs. Bean Counters" by Bob Lutz. Just because it is built, doesn't mean it is the best way to do it.

I didn't see anywhere in the thread that anyone said a SBC couldn't spin to 8000RPMs either. You are making your own issue to debate. A properly built and balanced SBC should be able to rev to 8000RPMs and not spontaneously explode. Doesn't mean it will be as reliable over years of service as one that stops at 6500RPMs.

Tom400CFI

I'm wondering what the point is here? How does this relate to this thread? You are totally right; With enough age and miles weak links show up that may never be an issue in the first 5-10 years. Ayuh. But....(?)


Dtto here. What's this got to do with a 377 (destroked 400) vs. a 400 crank in a 350?


Who disputed that...or even brought it up? Talk about making your own issue to debate!

MatthewMiller

I don't know what any of that has to do with anything we're talking about. The LS7 is a 13-year-old engine, and plenty of them have well over 100k miles on them with zero problems in the short block. My own 396 (3.875" stroke in my original LT4 block) is about 11 years old now, and has seen many hours of road track and autocross usage at high rpms. Zero problems with the short block, ever. And it wasn't even built with super-high-end rotating assembly parts.

This is true, of course. OTOH, we know enough in this day and age to build engines with much longer strokes than a 383 that can survive at 8000rpm or above: we are talking about 4.25" strokes and up (how much up I'm not allowed to say, but more than you can imagine). So while a 3.75" stroke does obviously put higher loads on the reciprocating mass than 3.5" stroke, it just isn't a problem for a competently built engine. It's child's play these days, and it would be stupid to limit the displacement of one's engine due to a concern about longevity with a 3.75" crank throw. There's just no other way to say it.

Again, the best info we have is the many OEM engines that have been mass-produced over the last 10-15 years with 7000rpm redlines and full warranties and strokes at or over 3.75". They all last. The LS7 has been mentioned. Even the Voodo engine has a stroke of 3.66" with a redline of 8250rpm, with the regular Coyote not far behind at 3.65" and a 7000rpm redline. It's not hard to make a reliable short block with 3.75" stroke and a high redline these days.

ChumpVette

There is a replacement.


Boost.

But I do love a good NA engine.