Is it possible to make modern power with a gen 1 small block chevy?

The small block chevy is the iconic hotrodders engine. Its been around since 1955 and is even still made new today for the aftermarket. Without too much trouble, 400hp out of one of these engines isn’t hard to achieve. But in this modern age where we see 350hp out of NA V6’s and now turbo 4 cylinders with that level of output, 400hp doesn’t really sound or feel all that special. Is it possible for the hotrodders mainstay to compete with modern engines?

My current state of affairs

 

Throughout the 80’s and 90’s, having 400hp on the street was considered a pretty big deal. In those days, even exotic cars didn’t tip much more than that. With a decent set of heads and a good cam, it was easy get to this power level while still maintaining easy driving characteristics – this is what earned the small blocks place in history.

But now with many cars coming from the factory with this level of power, is it possible to get, say, 500hp out of these old engines to stay ahead in performance?

The answer is more of a mixed bag than anything. There are a few issues that need to be addressed before building an engine capable of putting this kind of power out. One of the first things is addressing the block itself. GM never designed these blocks to withstand much more than 400hp, and because of this, you will find things like 2 bolt main caps and weak castings. In the hotrod forums, people seem to be all over the place in estimating how much power a 2 bolt main engine can hold, but the general consensus seems to be 400-500hp. It is also worth noting that many in these hotrodding forums only do drag racing, which is a very short race and does not stress the engine the same as road racing. While a high HP small block might last years drag racing, the life could be quite short on a road course. Another way to make power is to turn more RPM’s, and again, there is a debate on how many RPM’s can be turned with a basic 2 bolt block. But, it is true that how well the engine is balanced, and how much stroke the crank has, has an impact on the stresses encountered at the main caps. Furthermore, some of the factory cast GM blocks were just better than others, and if a serious engine is going to be built with a GM block, then it is a good idea to have it sonic tested to ensure its free from any defects.

The next issue is having a set of heads that can flow 500hp worth of air. This is the major problem with the classic small block. The common heads for these engines use a 23° valve angle which is extremely inefficient. While there are plenty of heads that can support 500hp and well beyond, they require opening the valves very far to get big flow numbers. While this might not be a problem for a drag race engine, high amounts of valve lift really puts a beating on the valve springs and valve guides. Opening the valve much more than .600″ really effects how long the valve springs last, and going as wide as .700″ means you will be replacing valve springs even if you don’t drive the car. This is due to the fatigue they take simply sitting with the valves open.

There are exotic head options that have narrower valve angles, and these heads flow substantially more than a 23° head at lower lifts. The problem with these heads is that they are expensive and require special pistons and valve train components that cost a fortune; not to mention a limited selection of intake manifolds that are specialized and are also expensive. In many cases these exotic heads, their valve train, and the intake can cost more than a running 23° engine.

Finally there is the cam choice. Because 23° heads are so inefficient, a large cam is required to extract ever ounce of power. This means that the cams are going to be optimized for higher RPM, have long durations, and poor low rpm performance. These cams make driving around town a challenge due to their choppy nature at cruising rpm’s.

So while its possible to build a 500HP classic small block and even one far beyond this, the engines start to have questionable durability at this point. This is why the LS based engines were such a leap forward. LS heads, being designed with modern technology, are much more efficient than the old 23° head, not to mention, the main cap design of the LS is vastly superior. Because the LS heads flow so much better at low lift, lower lift cams can be used and the engine can sustain higher RPM’s because the valvetrain takes less of a thrashing.

The main issue with the old small block is the 23 degree head. These heads just don’t have the flow characteristics that a modern engine does, and this is the big limiter in overall power, driveability and durability.

 

 

 

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5 Comments to "Is it possible to make modern power with a gen 1 small block chevy?"

  1. Adam's Gravatar Adam
    May 18, 2018 - 2:30 pm | Permalink

    I agree there’s plenty of reasons to go LS vs. SBC, and I agree when you compare GM OEM 23 degree SBC heads to GM OEM LS heads, BUT the advantage of the lower valve angle in LS heads and the idea that SBC heads can’t be made to flow like LS heads, and therefore able to produce similar power numbers with the same duration cams seems to be incorrect when tested. You’re comparing ancient SBC head designs to modern LS head design; an apples to apples comparison is modern SBC 23 deg heads vs modern LS heads.

    The LS 706 and LS 241 heads are kinda “meh”, so let’s compare the best 317 6.0 LS truck head to a modern, inexpensive SBC 23 degree head.

    317 Head: 2.00″ intake valve size, 1.55″ Exhaust (212cc intake, 76cc exhaust)

    317 LS Head (212cc) Flow Data:
    Lift In. Ex.
    0.050 33.3 24.5
    0.100 63.4 54.2
    0.200 144.1 103.8
    0.300 200.2 142.5
    0.400 234.6 167.9
    0.500 241.7 183.1
    0.600 243.3 193.7
    0.650 244.8 195.1
    0.700 242.4 197.2

    Profiler 210cc 23 deg SBC head Flow Data:
    Lift Intake CFM Exh CFM % Exh/Int
    0.200 145 110 76%
    0.300 207 145 70%
    0.400 258 180 70%
    0.500 283 206 73%
    0.600 285 213 75%
    0.700 291 216 74%
    0.800 297 218 73%

    Results:
    0.200 flow – Near TIE
    0.300 flow – 7 more CFM for 23 deg SBC head
    0.400 flow -24 more CFM for 23 deg SBC head
    0.500 flow -41 more CFM for 23 deg SBC head (estimate: 82 HP MORE than the LS head with the same cam duration)
    0.600 flow -42 more CFM for 23 deg SBC head
    0.700 flow -40 more CFM for 23 deg SBC head

    Note1: The LS head will have more torque with the same intake port volume vs the SBC because the min and average CSA is smaller due to the port being longer to accomodate the shoter valve angle.

    Note2: Even the 195cc Profiler 23 deg SBC head’s flow tops the 221cc LS 317 head’s flow #s and will have way better low-end torque.

    The LS engines have huge benefits in terms of maximum power the block can sustain, longevity, oil leaks, fuel economy (port EFI with a high resolution crank trigger, coil-on-plug ignition, and thin ring packs will do that), and if you compare all-out aftermarket heads, for sure, but for someone trying to make a decision on whether to rebuild the top-end of their 23 deg SBC vs. do an LS Swap with an affordable LS1, LS2, or LS3 with stock heads the power production ability isn’t that different naturally aspirated -the 23deg can win out with a roller cam with LS-like intensity in many circumstances.

    The SBC heads’ who’s air flow profile I posted can be obtained for $559 / head or $499 each when on sale, too: $998 for a pair fully assembled with taxes and shipping so they’re not freakishly expensive race heads that represent an unreasonable comparison, either. https://www.jegs.com/i/JEGS-Performance-Products/555/514022/10002/-1

    Adam

  2. Greg's Gravatar Greg
    August 1, 2018 - 9:45 pm | Permalink

    He was comparing the highest flowing cathedral port heads from the factory. The words
    As Cast and Race head never belong in the same sentence as Profiler garbage. The low lift flow numbers show how well a head will work at low rpm. It’s just that most people put 240 plus duration cams to make 600 horse and beyond. Profiler heads are junk. Can buy used for a few hundred bucks and usually crack and break. An AFR sbc 195 eliminator head flows around 308-310 and has the highest low lift flow numbers of any aftermarket head. Go any bigger, the low lift goes down, but a afr 210 will work on a mild
    11-11.5 compression 350-355 sbc and make 500-580 horses and live in a real street car for years.

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