MonnieH

If I have any of this wrong please let me know. But what I understand is the new 427 7.0L engine is a bored out ls2. What is the difference between a block cast to be a "big block" motor and a reguler block bored out for big displacment? The only thing I can think of is for increased structural rigidity. But GM would not use the "small Block" 427 if it was not bullet proof.

My snake has a huge block in it, but what is the advantage, if any, of that?

jvp

With Chevy engines, one of the key indicators of small block vs. big block is the bore center spacing. All SBCs (that I know of) have a 4.4 inch bore center spacing. Anything bigger than that, and I think it's automatically considered "big block" territory.

That said, the main difference to the customer is, plain and simple: mass. Big block motors are, by their nature, BIG. With all that extra metal comes extra mass. Since they are, in fact, larger, they also have packaging contraints that come along with them. You just can't drop a big block into the snout of any car. It might not physically fit.

There have been reasonably successful attempts at cutting down the mass of the big block. Look to the all-aluminum rat motor as an example. The probem is, it's still physically large.

The LS7 is a bored and stroked all-aluminum SBC displacing the same cubes as big blocks have in the past. The reason the SBC was used, mainly, is mass and size.

jas

John Wiz

Also the LS7 was developed in conjunction with those that developed the 7.0L engine for the C5R... and I don't think that they have ever lost an engine during a race....

MitchAlsup

There is also the issue of rod/stroke ratio. A longer rod is slightly more efficient at transfering the piston forces tot he crank. A Big Block can allow for longer rods. A high deck height can also enable a longer rod.

But, it is the advances in materials, castings, and other parts, that now allow a big block sized dispalcement to be available in a small block sized motors. Just witness the size of racing engines (CART, F1) over the past 25 years. Every year they get physically smaller, and smaller, and lighter and lighter; while producing more power--and now lasting longer and longer.

bernrex

No advantage to you. A disadvantage in fact. More, unnecessary weight. Retains heat longer ... keeps your snake den hot enough to fry a Texas chickenhouse egg.

TCU-Z06

Big blocks allow for a larger bore and a shorter stroke to achieve the same displacement. Correct me if I'm wrong but I thought the following is true of big blocks....

Shorter stroke = less internal friction = higher potential HP
Shorter stroke = higher max "safe-operating" RPM limit
Bigger bore = larger max valve size
Bigger bore = flatter torque curve

Overall, I don't believe that the above is enough to offset the increased weight and Rod/Stroke ratio of a big versus small block at the same displacement.

bernrex

A longer stroke helps build more TQ .... and a shorter more RPM.

Since HP = RPM X TQ , its probably a tradeoff. Some like TQ , some RPM. Personally ... I like the down low TQ.

Hope Duke gives us his take ... for he explains this from the engineer's perspective.

GOLD72

Your snake still has a "small block" design in it. It looks big only because it has two more cylinders (hence longer block) than the LS1/2/6/7. Add two more cyls to the LS7 7.0L and it would have more displacement than the Viper.

GOLD72

EuG

Big block has bigger bore spacing and higher deck height.
In simple terms big block can be bored and stroked FAR beyond 427ci.
That means you could have, let’s say, a 540ci motor, something that can NEVER be accomplished with small block.

There are also factors like bigger valves etc, but it’s not that important.
The conclusion: if all you need is 427ci there’s no point adding more weight for big block.

However small block can’t even dream of competing with big block if you modify both (427ci vs 540+ci – yeah right )

LTC Z06

As other threads have stated the reason the big block was made was because the tech of the time could only get so much HP out of small blocks because of valve size. So a big piston allowed for more flow, etc. Now we don't need the big piston to get the flow. 1.17 HP per cube that is emissions legal and noise legal is awesome!

AU N EGL

Isn't the BIG BLOCK physicaly larger and weights much more then the small block?? and putting the big block into the C5 or C6 take some space alterations in the engine bay?

The C5R & C6R Ketech 7 liter engine puts out some where north 900 BHP unresticted. Even with the quarter size restritor plates in each of the two thottle bodies it is 650 BHP in race prep mode.

With power like that who needs a big block??

LS WON

Torque is what you want as there is no replacement for displacement.

EuG

I do.
I would love to be able to get 700-750rwHP NA in a street motor.
I don't see small block doing it

AU N EGL

Well the street virson of the C5R Ketech 7.0 liter LS6 has 585 bph.




http://www.katechengines.com/index.htm

Rkreigh

I have a 605 BB drag engine that struggles to get 915 hp so that kind of power out of a small block is pretty cool

at least the bb is cheap!!

EuG

I know. I got this much in my car right now.
I could use A LOOOOT more

EuG

You must’ve misunderstood.
I’m saying I’m sure LS7 style 540+ci BB would make 700-750rwHP NA in street form.
There no way a street 427ci will make that much NA

LS WON

The older version from the early 60's to the 454 from 1970-1974?
Or The 427 based on the LS-2 motor? Just the facts..which one is better?

JJMalone

The LS motor, hands down.

1985 Corvette

Heh, well for the throwback feel of the "good old days" of cruising, many would say the old 427s but compared to the new rendition of the LS7 which won't overheat itself or be plagued with other problems that needed maintainence, I'd say technological advances win out on this one.