I had posted a video of my new best a few days ago..and in that thread someone mention small blocks are always faster than Big Blocks.. that comment has had me thinking for a few days. We no that small block wedge.. has tons of R&D because of NASCAR and Pro Stock truck.. I don't know that much about the big block Max effort wedge heads.. what is the real answer . The most power per cubic inch..

I do believe that there is no replacement for displacement , and big makes a lot of sense for a lot of reasons.
If you have an artificial ceiling.......make 800 h.p with each and the big block will be easier on parts , maintenance and maybe even the wallet.
But taking each platform to the top of the heap , big block would have an advantage on the time slip and maybe on the bank account too because there are more " shelf " products available.

The big block always wins...if you can get it to hook. Bigger bores, wider bore spacing, taller decks all make more power.

Let's say you build two engines, both 400ish CID. The BEST you can hope for on the small block is a 4.250 bore. On a BB platform you can easily go 4.500 with a much shorter stroke. Now you can shorten the decks (saves weight amongst other issues) and you'll have bigger valves and room for bigger ports. Plus, you can RPM the piss out of it and RPM makes horsepower.

All one needs to do is look at Pro Stock (or what's left of it) and see they run the biggest bores with the shortest stroke and RPM (until NHRA killed that).

It's simple physics really. The BB wins every time. Unless you want to talk Modified or Comp eliminator stuff. Even then, small displacement BB architecture has advantages unless you can get the car light enough to benefit from the SB architecture.

cubic dollars vs cubic inches.

cubic inches wins in both the wallet and on the track.

When I see what these small block guys spend on just convertors it makes my hair fall out.

I was looking at the rule package 4 nmca.n/a 10.5.. they call out big block Chrysler gets a weight break but yet they do not give the small block Chrysler a weight break.. so is there a cylinder head deficiency for the big block. I think at the highest level Australian Pro Stock small blocks make the most horsepower per cubic inch they are at 3 or maybe even slightly above.

N/A 10.5 RULES.. these rules are somewhat to help keep the field level..

Big,,,,small,,10k rpm...Never made much a difference to me.I caught HEMI-ITIS on the starting line @ National Speedway back when there were at least 3 legal dragstrips on Long Island.All the real fast cars had spark plug wires coming outta the valve covers!!I knew at age 12/13 what I had to have one day.Took almost 30 years but............

If you go by HP per cubic inch, historically, smaller displacement engines have had the advantage (up to a point). It is easier to make smaller engines more efficient.

It was done in the early Pro stock days when they started destroking the 426 Hemi to make it more competitive with NHRAs cubic inch to weight formulas. There were even some 383 blocks modified to accept Hemi heads so they could achieve smaller displacements, better bore/stroke ratios and overall lighter weight.

Old Modified Production and some newer sportsman classes also follow that pattern. i.e.: At the same level of execution, using 10 lbs per cubic inch, a 300 ci engine in a 3,000 lb car would tend to be faster than a 350 ci engine in a 3,500 lb car.

As pointed out, when there are no specific rules, max displacement will provide the best results.

EDIT/ADD: Interesting NMCA rules to help make a variety of combos competitive. Just gotta figure out what will work best for you.

Head flow and RPM, add lots of cubic inches

If you go by HP per cubic inch, historically, smaller displacement engines have had the advantage (up to a point). It is easier to make smaller engines more efficient.




If you go horsepower per cubic inch then you aren't truly answering the question which is faster.

Well....technically he did. As I pointed out and Myron added to (very well I might add) when class racing on a pounds per CID the smaller engine in a lighter car is almost always faster. It's easier to make a 3000 pound car with a 300 CID engine out run a 3500 pound car at 350 CID.

The smaller engine will RPM more, be able to use more gear and effectively move the car quicker. It's all about the levers.

I should have been my dad. Modified Eliminator was the SHIIIIIIIIIIIIIIIIT.

I was just trying to point out that finding the optimum combo gets more complicated than just getting, as he mentioned in his original post: "The most power per cubic inch."

NMCA is obviously trying to even the field by actually helping the bigger inch engines with their formula to allow more diversity and help racers with existing combos.

This (big vs. small) was transformed from rumor/gossip/opinion over 100 years ago. Dr. Lanchester's formula to predict outcome of a 4-stroke engine is still accurate, where:
B = bore diameter
S = stroke length
N = number of cylinders
C = a constant representing quality of materials and fuel energy value.

HP = B^1.65 × S^.5 × N × C

As you can see, displacement is far less valuable than large bore and more cylinders. Note that there is no factor for valve mechanism or number of valves. A significant flaw: no correction for mandatory parasitic loads which are disproportionately high for small engines: water pump, oil pump, cam drive, ignition.

In the LB/HP classes, they usually make the car as light as allowed and build the engine accordingly.

Which makes more power, more power per CI, which is faster, etc., are all very different questions with different answers. Is this a max effort project, budget, reliability, index, rules, ???.

A bigger engine needs to make enough power/CI to make it worth carrying the extra couple hundred pounds (unless you are in the aluminum block club) on the nose of the car.

Mostly it comes down to personal preference. If it was all about the "best option", we'd all be running Big Chief 632s or some such thing.

Clinton Cranston best machine built big block, NA wedge style head, over 1200 hp. Enuff said ! Lol

My nitrous cammed combo with a 1050 carb and C23 ( not very conducive to make NA hp, should make over 1000 with a 1200 carb and c14) only made 915 NA...lol , but can take 600 or more of nitrous....lol

If you had a race class which was NA, 2800 lbs, door slammer and no cubic inches what do you think guys would build? I bet there wouldn't be a single SB car in the lanes. People would show up with mountain motors. It would basically be IHRA Pro Stock.

SB engines win if there is a weight break or a cubic inch limit or something along those lines. If there aren't any size limits then guys are going to show up with big engines.

Have a car weight? Figure out what cubic in small or big block you can run.

Have a certain cubic inch engine available/planned? Figure out how much the car has to weigh. Don't know if that includes driver or not.

10.5" slicks "might" be a hindrance under some conditions/situations.
Big blocks do put more weight on the nose.

NMCA 10.5 rules

These are answers to the simple question of "most HP". If the question is "most HP per CI" or "most HP per lb of engine weight", then it gets more complicated.

Original post was basically comparing a wedge small block to a wedge big block. Horsepower per cubic inch I understand that an 800 cid Mountain Motor hands down is going to make more power and potentially go faster than any small block.. that's not what I was referring to I'm curious to know about Max effort big block Chrysler wedge heads not predator can valve or hemispherical headed Motors... so if someone was going to do a Max effort big block wedge semi conventional what would be the cylinder head of choice and how much power per cubic inch would it make

N/A hp/cube is easy. The smaller the motor, lighter rotator, more rpm, the more the HP. Bracket race maybe a different story. Big block, lower rpm, lower maintenance. My bet is a 900HP small block will not go 300 passes with nothing but lash and oil changes. Not to mention it would probably have less torque. Lets face it, the wedge big block head development is light years behind the small block stuff. That being said, they can run pretty decent. I'd love to have a 9000 rpm stick car. It's more work and $ than I can keep up with. Anybody that's a real power junkie uses boost. Variety is what makes all this stuff interesting.
Doug