Why Do Buick BBs Have So Much Torque?

I'm not an engineer or engine builder, but I understand the basic physics of torque. What I don't understand is why Buick big blocks have more torque than other engines of equivalent displacement and horsepower. Is it a matter of the bore/stroke ratio? The combustion chamber design? Or???

 

GOD told Noah and Noah told Denny Manner " Denny, I need something strong to power the ack" !
And thats the rest of the story !

 

It's a matter of a looonngggeerrr stroke. Think of it in terms of a torque wrench.....the longer the handle the more torque applied

 

All of the GM 450+ cid engines had a longer stroke than the Buick 455.

 

Big bore, short stroke, and rather small port cross section, for the bore size.

This equals high charge velocity and good cylinder filling at mid range rpm.

Even big cube fully ported STG 2 heads are small for what we are doing with them, compared to other makes.

All of this makes good mid range torque, but limits higher rpm HP.

Even the most radical BBB still has a torque peak far lower than similarly built motors of the 60's and 70's.

JW

 

Not sure why, but it seems that the 90 degree blocks produce more torque than a similar displaced 60 degree block. Possibly due to increased runner length?

 

That's a possibility, the intake manifold on the 2nd gen Dodge magnum truck engines have very long runners and the intake is shaped like a keg, great for low end but really runs out of steam at high RPM, the runners almost wrap around the entire intake. Many doge guys will cut the runners down a bit, and fill in some space to create a stock style manifold that breathes better at high RPM, but looses some low end.

Then on the Dodge 3.5L Charger engine the manifold has a valve that switches between long runners for low end, and short runners for high end, very neat idea.


the chrysler slant-6 also had extremely long and even radius/length on the intake and helped it along with being underquare to create more torque, the popular trend at the time was over-squared engines or squared engines (ex: Chev 350 if I recall correctly) you can see the difference between this and the "log" style you'll see on many Ford and GM applications.

And now some of you know more about MOPAR intakes than you ever wanted to know. :grin:

 

I'm no engine builder, but I've had my hands on a few over the years. Buick did an excellent job in the 50s and later in the 60s with their V8 designs...and the 67 new generation V8s with their over-square bores, heavy-duty cranks, balancing and induction/flow characteristics kicked the hell out of everybody.

90-degree V-engines theoretically produce the best low-end power delivery. This is the principle for motorcycles as well...that's why the Honda V4s and the Ducati V-twins have great pickup off the line.

I look at my 430, big cast-iron brick sh*thouse of an engine...and feel confident this thing can move mountains.

 

Long stroke...short stroke...makes almost no difference.

Long stroke vs. short stroke, but with equal displacement:
Long stroke engine has more crankshaft leverage, but less piston surface area.
Short stroke engine has less leverage, but greater force pushing piston down (pressure X piston head area)

Overall, hardly any functional difference.

The difference between long stroke vs. big bore is in the potential for breathing.

Long stroke engine has small bore, therefore small valves, valve shrouding. CANNOT make high-rpm power, therefore always biased to low-rpm power...which equals high torque at low speed. Put another way: Long stroke/small bore engines don't excel at making torque--they SUCK at making high-rpm horsepower.

Short stroke/big bore engine has POTENTIAL for larger valves, larger ports, less valve shrouding. Can make high rpm power if ported, valved, and cammed for high RPM; and if the basic engine design will accept the high loading. Otherwise, with small valves, small ports, mild cam makes torque just like a similarly valved-and-cammed long stroke engine.

Designing a high-torque engine is easier than designing a high-horsepower engine. The engineering is easier and more forgiving--Lots of displacement, small-ish valves and ports, and a mild cam gets that job done.

 

Three more ways Buick increased torque (using thermal efficency).

1. ANGLED PLUGS - Remember the rage about angled spark plugs. Buick had them in the new 400 and 430 engines for 1967. Improved combustion.
2. DISH PISTONS - Are more cumbustion efficient than domes and flattops. Dyno test have backed this up.
3. CLOSED CHAMBER HEADS - Good squish and turbulence for efficient combustion. Open chammbers are dead and detonation prone. We avoid using the 1975-76 Buick open chamber heads for performance.

 

Buick engines don't produce any more torque than other engines of the same or similar displacment.

That being said, low speed torque is what they were designed to produce and that they do as good as any other engine. The largest single factor in torque peak RPM is the intake valve event timing.

 

I can't answer the question except to say the BBB is a more efficient than the rest ( Don't ask me why ) which explains the better fuel mileage. Probably explains the performance also. It seems it has to be in the head and intake design.

Bob H

 

I've heard so many people say Buicks make more torque that I was believing it. But I looked at those Car Craft articles from a few years ago where they did basically identical builds on the GM 455's and what they got was Olds at 565, Buick at 576, and Pontiac at 579. I would say for practical purposes that's equal. But a friend of mine with a '75 Grand Prix will claim bragging rights if I tell him those figures. :grin:

 

I was going to say, Ponchos arent too bad in the torque department either.

But this aint a Poncho board, so I wont say it.:laugh:

 

The thing about the Pontiac, is the torque curve was already on the down slope at the lowest point their dyno could pull from! The 440 Mopar had a couple pounds more torque than the Pontiac, but they don't actually know how much torque that engine was making at peak torque. Pontiac's make a crap ton of torque down low every time. Buick's from the factory just had cam grinds that made a lot of torque down low because of the cars they went in and GM wanted a pretty smooth idle.

 

I always found that Buicks Pontiacs and Olds all made pretty comparable numbers when it comes to torque. The Chevies usually make a bit less in exchange for a higher power band. The Caddies make billions of ft-lbs at around 0 rpms, but they die at 3k rpms which is why most people don't go for them in their muscle cars.

 

ALL horsepower is torque x rpm....
It was torque x rpm that hung in there for the higher rpm and got the 555 HP to win the challenge. That,s what Buick engineering accomplished with a good ballance of all the features mentioned above.
The torque doesn't just fade away.