Why does the 4.3 not rev higher if it's oversquare?

[Jimwhall]

So I'm just doing some off season research into the 4.3 for fun; I think I have a good mechanic who is going to do my yearly maintenance and all is good, but I'm just curious.

In some of the reading it said that the 4.3 is oversquare. I wasn't sure what that was so I looked it up and it said it was an engine with the bore of the cylinders larger than the stroke. It further said that oversquare engines tend to rev higher and develop power and torque higher in the RPM range.

Was this correct? It just seems odd. It seems like for marine purposes I'd like to have more torque down low; and this 4.3 certainly is *not* a rev monster with a redline between 4400-4800rpm.

 

[achris]

While you are correct that the 4.3 is over square (like the SBC, 101.6mm x 88.4mm), and this does allow an engine to spin faster, there is a few more things that come into play.
The camshaft profile has a lot to do with it, as does things like the compression ratio. There's also the fact that once you get up in the 6,000rpm range you need to look at the ability of the drive to cope. Much more than 6K and they need a proper force-feed internal oiling system, and that adds $$$. Also spinning the engine fast (with the appropriate hardware to achieve that), while making more HP at the high end, it reduces the low and mid-range power, the exact opposite for what you want in a boat engine.

Chris...........

 

[Lou C]

It’s a pushrod OHV Chevrolet whose basic design dates back to 1955 with the 265 cu in V8. They were not designed to be high rpm engines; with a few exceptions like the 302 and 350 cu in Z28 versions.

 

[Scott Danforth]

factory GM balancing is +/- 29 grams - lots of shaking going on

the 4.3 also has a really bad firing imbalance (look at the crank throws and you get the picture. this is tied to the cam comment above

while you can get more RPM out of a 4.3 with a fat wallet, by the time you are done, you spent more than a SBC that will spin 11,000 rpm or big block that will spin 10,000 RPM

case in point:
a forged crank for a SBC or BBC is about $400
a forged crank for a 4.3 is $4000 https://www.crower.com/crankshafts/crankshaft-4340-billet-chevy-v6-specify-stroke.html

 

[achris]

..the 4.3 also has a really bad firing imbalance (look at the crank throws and you get the picture...

Yeah, not pretty at all!

 

[Bondo]

Ayuh,..... Kinda a fragile crank,.....

The boss hit a shoal in '06, 'n broke the crank in two,.....

 

[Lou C]

That was the solution GM came up with for the shaky Buick 231V6 with the 90* angle between the cyl banks in about 1975/6 when they bought back the tooling from AMC. They used it for a few years sold it to AMC who used it in the CJs then bought it back after the 1st oil embargo. So when Chevrolet created their 4.3 V6 from the 5.7 they did the same thing. My wife had a ‘78 Pontiac LeMans with that 231 V6.

 

[Scott Danforth]

That was the solution GM came up with for the shaky Buick 231V6 with the 90* angle between the cyl banks in about 1975/6 when they bought back the tooling from AMC. They used it for a few years sold it to AMC who used it in the CJs then bought it back after the 1st oil embargo. So when Chevrolet created their 4.3 V6 from the 5.7 they did the same thing. My wife had a ‘78 Pontiac LeMans with that 231 V6.

I have broken buick cranks in a few motors I built over the years...... if you dont break parts racing, your not trying