If you had a choice between building a 6.0L LS or a 396ci big block Chevy, what would you choose and why?
I have a 1969 Nova. The car has the 396 in it currently but it’s not a matching numbers car. I’m also running Sniper throttle body EFI induction. The 6.0L is out of a late model truck while my 396 is already bored 0.030″ over and needs a rebuild.
G.D.
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This is a bit of a theoretical question since there are pluses and minuses to each application—but it’s an intriguing question nonetheless, so let’s dive in.
I’ve built LS engines and big block engines so I have experience with both. Let’s take the big block first.
Understanding the 396 Big Block Chevy
The main issue with a big block is its size and weight. Assuming we’re talking about an iron-headed 396 compared to an iron block 6.0L with aluminum heads, the big block is going to weigh in at around 650 to as much as 700 pounds. These engines are big and heavy. The iron heads alone are massive and the pair weigh close to 140 pounds by themselves.
Compare that with an iron block 6.0L truck engine with aluminum heads that comes in around 540 pounds depending upon its accessory package. Right away, we’re talking about a difference of 100 to 150 pounds. That’s substantial. If you can tell the difference in a normal street car in acceleration between the driver alone and the additional weight of a passenger, imagine carrying an additional 150 pounds all the time.
Big blocks do make more torque due to their greater displacement. But if you are going to rebuild a 396 to around 402ci, there is only a minimal displacement advantage compared to an iron block 6.0L (364ci) LS engine with aluminum heads. The Rat motor enjoys a minor 38 cubic inch advantage. The 396 would have a 3.75 inch stroke while the 6.0L LS stock enjoys a 3.62 inch stroke which is 0.130 inch shorter.
Low end torque is often attributed to longer stroke engines.
In terms of big block Chevy parts, my feeling is that it will probably cost more to rebuild the 396 than it will to perform a similar rebuild on the 6.0L LS. If you stick with the less expensive flat tappet camshaft and lifters for the big block to save money, you need to be concerned with making sure the flat tappet cam is properly broken in.
Of course, you could go with a retrofit roller cam but that adds big dollars to the rebuild cost. What doesn’t help is the big block you are dealing is limited by 1960s technology.
A stock 396 uses a 4.094 x 3.75 inch bore and stroke. The problem is the very small 4.094 inch bore. This really limits breathing potential on even stock oval port heads. The 396 engine came with a relief cut into the top of the cylinder bore to help breathing—which is a big clue that the bore is way too small to make serious power.
An Option Beyond the 396?
Frankly if you are leaning toward a big block you’d be much better off starting with a 454ci. With one of these larger bore engines, you will be up 50-plus cubic inches over the 396 and 90 cubic inches over the LS 6.0L.
Then if you wanted to pull out the stops, you could stuff a 4.250 inch stroke crank and have a 489 or 496 while saving money with a cast crank and aftermarket 6.135 inch connecting rods. Scat offers a 489ci rotating assembly with a cast crank, 6.135 inch forged rods, and forged pistons for a pretty good price. Eagle also offers similar packages.
Many years ago at Car Craft, I bought a used cast crank 496 short block from a friend, carefully set bearing clearances and re-used the hypereutectic pistons and made really good power with this engine even with some rather cheap parts. We never revved it more than 6,500 rpm and it made over 600 lb.-ft. of torque and well over 600 hp with a set of oval port aftermarket aluminum heads.
But now we’re talking some serious coin with a set of aftermarket aluminum heads.
The Case for the 6.0L LS
Now let’s look at the advantages of the LS engine. We’ve already covered its reduced weight—plus this engine is significantly smaller compared to the 396. The LS already comes configured for a hydraulic roller cam using stock cathedral port heads if you use a Gen. III or Gen. IV engine.
Yes, the LS hydraulic roller cams are more expensive but add a 230 degree at 0.050 duration camshaft to a stock 6.0L with a carbureted intake and you have the makings of a 500 hp engine.
Add a carbureted single plane intake, Holley 750 cfm carburetor, and an MSD ignition box and you have the basic ingredients for a 500 hp LS engine. This engine won’t make as much torque as a 496ci big block because of its smaller displacement, but you could assemble one of these LS engine probably for less money than a Rat motor.
Most Cost Considerations
One thing to keep in mind is that with a big block already in the car, you won’t need to purchase any exterior components if you stick with the big block. Headers, water pump, accessory drive and the like are already in place on your 396.
If you go with the LS, you will need to purchase all of these pieces plus adapt the cooling system slightly for the LS engine. None of this is difficult, but all these little things do add up in terms of overall cost of the LS conversion.
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We’ve tried to look at this question from simply a logical viewpoint. The issue is that we’ll get tons of responses to this answer with passionate views on both sides that will mostly come from an emotional attachment to one engine or the other. It may come down to which engine has a more emotional lure for you. That’s the one you will have more fun with because you will want to work on it.
Ultimately you don’t need input from anybody else…
Do what you want and have fun!
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