How does cid make power?

[273]

Then spin the 632 to 15k, now who's winning again? This is why this argument is circular. The 'common wisdom' is correct - bigger wins every time, but you keep throwing imaginary crutches at the 'bigger' motor.

Yes obviously if we take things to the limit max piston speed same level of bottom end parts a 273 can't turn enough to make more than even a 318 since both would have the same rpm capability. Ultimately piston size limiting factor so with stock blocks 400/440 have max bore capability, If you bored a 400/440 to 4.375" and no matter what crank you use 3.38" 3.75" 3.915" 4.15" 4.25" etc.. Taking it to max piston speed they all dispace the same amount of air, same theoretical capability of hp, so my question that I was trying to get at and finally figured out why can't the 3.38 spin up to make same hp as the 4.25, what's hindering it ?

 

[Phreakish]

Yes obviously if we take things to the limit max piston speed same level of bottom end parts a 273 can't turn enough to make more than even a 318 since both would have the same rpm capability. Ultimately piston size limiting factor so with stock blocks 400/440 have max bore capability, If you bored a 400/440 to 4.375" and no matter what crank you use 3.38" 3.75" 3.915" 4.15" 4.25" etc.. Taking it to max piston speed they all dispace the same amount of air, same theoretical capability of hp, so my question that I was trying to get at and finally figured out why can't the 3.38 spin up to make same hp as the 4.25, what's hindering it ?

OK, so we agree that in 'never never land' where we're not constrained by the realities of availability and OEM-designed engine architecture, bigger is always better.

So if we approach the question with some measure of reality the reality is that RPM is HARD and EXPENSIVE and all the things which let a 3.38 'spin up' will let a 4.25 spin up too. The only thing 'harder' about the bigger motor is getting bigger heads, and only because these aren't chevvies and so we can't just go buy a 400cfm head off-the-shelf from Summit tomorrow...

Getting an engine to 7k is relatively easy. 8k takes work. 9k+ is a whole other world, and 10k is not for the casual tinkerer. That's why the 273 "can't" be spun up to make the same hp, because cubic inches no longer cost cubic dollars - but RPM does! If you've got the time and budget to make that 273 rev that high, doing the same to a 408 is kinderspiel. There is nothing intrinsic about stroke or piston size which limits RPM. With strength-optimized pistons, pro-stock cars run 4.7"+ pistons at well over 10k! So why do strokers tend to disappoint? "it's the heads, stupid"

Not only that, but the development has already been done for ~4" stroke motors to run that high, and the parts can be had, and a 273 bore is too small for those valves/heads. So physically you're time and money ahead going for greater displacement in that regard - imagine that, smaller somehow costing more. 900hp 410's are not mythical, just atypical - mostly because people are cheap and would rather not source and fabricate a w2/5/8/9 top end.

Here's the thing from an engineering perspective. The benefit to smaller displacement is lower weight. If I wanted to get high revving HP from a smaller displacement, I push the bores closer together. If I can't push the bores closer together I'll shrink the stroke to get the block deck lower to shorten the intake tract. Can't do that with a stock block - at least not to an appreciable degree, and the parts to do so will become custom and thus $$$$ in a hurry. If I'm a dedicated race team, I don't care - but if I'm a hot rodder, I do! That's why it's common wisdom - because commoners aren't race team members.

I keep this link bookmarked because there's a post in there which shows the math to develop a race engine. Lots of the smaller details and constraints get brought up and you can imagine the impact when each variable is altered. Give it a read, you may find it illuminating.

 

[PRH]

The big problem with many of these arguments is trying to compare extremes.

Take a bread n butter SBM hot street build:
4.00” bore x 4.00” stroke(402ci), exactly 10.5cr, rpm heads to flow 275cfm, port matched Victor, 850 carb, 1-3/4” headers, small solid roller cam, and the motor ends up making exactly 450hp.
This is a combo that has plenty of everything to make the power it does, and more....... except a somewhat limited camshaft.

If you built a duplicate short block, maintained the exact 10.5cr, only bore the cylinders to 4.040”, you’d have a 410”(1 more ci per cylinder).
If you took the entire top end/headers/cam out of the 402 and installed them on the 410, the HP/ci would barely change at all, and the motor would make nearly the exact same 1.119hp/ci it did as a 402..... and make another 8-9hp.

In the real world....... that’s how it works out.

 

[rumblefish360]

Sometimes you follow the herd off a cliff.

And sometimes you lead a man, dying of thirst to the water fountain and he refuses to drink any water to save his own life because he thinks the water is tainted. Even though everyone else drinks from it and continues to be happy. After a week the man passes on convinced he did the right thing.

 

[92b]

Then spin the 632 to 15k, now who's winning again? This is why this argument is circular. The 'common wisdom' is correct - bigger wins every time, but you keep throwing imaginary crutches at the 'bigger' motor. Apples to apples, displacement wins. HP is just torque times rpm, and torque is just force at a distance. Increase the force (bore), the distance (throw) and you increase torque. Displacement ups both of those. Whether an engine can continue to make HP above the torque peak all depends on the heads and the valvetrain. Using 'similar' build arguments is meaningless with such a rhetorical question.

I petty much agree with what you are saying. I think it would be more accurate if conventional wisdom was this "Bigger wins every time in theory, in practice it depends."
In real life many times and I would argue most times there are "crutches " that are thrown at a bigger engine. I know you know this already. Sometimes it's the cylinder head. Sometimes the carburetor or the exhaust. This list could go on for a mile and it's likely that you have encountered some of these limitations or crutches in your own builds. In theory if you have a carb that is not a crutch for a "big" engine and you make the engine bigger eventually it will become a crutch.
Some reasons why you might encounter a crutch.
1. Budget. I list this first but because for most of us this is a crutch at some point.
2. Rules. For those who race, santioning organizations impose all kinds of limits that dictate the type and or size of builds. Naturally aspirated, carb size, restrictor plates, limits on heads and intakes, spec parts, exhaust limits, RPM limits, compression limits, even cubic inch limits just to name a few.
3. Technology. In the past limitations were overcome by new technology. Lighter, stronger materials were developed to eliminate previous crutches. Technology will likely eliminate crutches in the future.
4. knowledge. Good old fashion trial and error can lead to a better understanding of how things work. Testing with new equipment can lead to a better understanding of how things work. Studing others work can add to your own Ideas and lead to that eureka moment that eliminates a crutch and takes you to the next level. Even participating in this discussion might inadvertently cause me to learn something.
5. This is ridiculous. I've wasted too much time typing this out. I need to get back to work. Sorry if you wasted your time reading it.

 

[Dale Davies]

I keep hearing displacement makes power but don't see how so my question Is how?

But let me clarify what I mean, I understand if you raise torque at any
Rpm at that rpm hp will also raise. Torque is obviously heavily related to displacement
If I was to say I'm gonna build a 440 without any other info you could ballpark guess how much Torque will be made. Because torque happens in a narrow range for an naturally aspirated engine 1-1.5:1 lbs-ft per cid and for most engines we deal with would be narrower, your not gonna get 550 lbs-ft NA out of a 100 cid engine but could get 550hp since there about 0.5-5.5:1 hp per cid range.

Torque is basically one powerstroke and hp is the sum of all the powerstrokes added up over time.
So obviously displacement has a huge impact on one powerstroke and only has one powerstroke to do it.
The limit on hp is mechanical limitations and ve% limits of rpm so as long you can keep spinning it higher while filling the cylinders you'll make more hp.


So question is how does displacement makes horsepower?

What it boils down to in reality is chemistry. An engine runs on oxygen from air and hydrogen in a hydrocarbon fuel. Combustion is a chemical reation that generates heat. To burn all the fuel requires a set quantity of air (oxygen) so that all the hydrogen is oxygenated. For our gasoline engines this is about 14.7 pounds of air mixed with 1 pound of fuel. Now this is for theoretical complete combustion. Fuel quality and any additives can/will modify this. For maximum power and considering all the liquid fuel is not likely fully vapourized, a richer mixture is required of about 12.5 to 1.
1 pound of fuel contains the capability to produce a value of power or more like pressure. A typical street engine has about 80%VE. So a 400 CID engine pumps 80% of its displacement in air, or 320 cibic inches in two revolutions. The combustion in the cylinders produce torque at the flywheel. This is what an engine dynomometer weasures. It does not measure power. Horsepower is a calculated value using the measured torque and RPM. A larger displacement engine pumps more air and fuel to make more torque. Camshaft design and head port efficiency will determine at what RPM that torque will be developed. With compression ratio (both static and dynamic) about equal, more displacement will develop more torque.
The old musclecar engines of 427 and 450 CID produced up to 450HP, as advertized. Most were in the 450 to 480lb/ft of torque range. Maximum power was about 5500RPM.
F1 engines have normally been regulated to 122 to 181 CID. The turbo cars were limited to 90CID. The Renault engines were essentially from a joint passenger car V6 jointly developed between Renault, Peugot and Volvo. In North America we saw this engine in Volvo 240 series cars at 2.6L or 158CID. These were destroked to reduce the displacement to 1.5L. Then a bunch of expense parts were used internally so they would last at 15,000RPM while turbocharged. These engines made phenominal power at high RPM but as a street engine are useless, especially in a 3,500 pound family car.
To get more street useable torque out of a 225CID engine similar to a 450CID engine, use a supercharger to push the same air and fuel volume through it as what the 450CID engine pumps. Boost with strong enough components will not wear an engine out or cause early failure as much as raising the RPM. Boost loads the crank, pistons and rods more, but not like RPM. Stress on the reciprocating assembly is squared as RPM is doubled. This reduces engine life expectancy quickly.
Big industrial engines have block castings with cast iron 1" thick to withstand the vibration loads inflicted on it. These engines will produce 1,200HP at 1,200RPM 24/7 for years. Head swaps to replace worn valves and sometimes a cracked head and occasionally an inframe overhaul, but the block and crankshaft may be intalled without removal for 20 or 30 years. You can get a big block to make that power, ricers make that power. But they sure do not make the torque and last that long. Do the math to calculate the torque produced by a Sulzer marine engine that produces 10,000+HP at 100RPM. These engines idle at 10RPM. Pistons are 1 meter+ in diameter with a stroke of 6 feet or so. Head studs that hold the heads and cylinders in place are like telephone poles.

 

[Dale Davies]

Goes back to what I said, and many others. Engines are air pumps, they need to breathe, yes cubic inches is factor. But you can do anything you want as far as cubic inches goes, any manifold or header. Any intake, or power adder. If you ignore your cylinder heads, you’re not using your full potential, and frankly wasting your time.

The old way of thinking was bigger is better. Now through research, all it takes is a good set of heads, a good intake, a good cam, and a good set of headers, and you can have a pretty potent engine.

Weather you like him or not, Freiberger really saved the car hobby.

As you stated, a good set of heads is a key part of the combination. Good heads does not necessarily mean huge port volume. Air velocity and the resulting port energy are values to be desired when looking for heads. A head with 10 to 15cc smaller volume and higher velocity and port energy will probably make more torque and provide a more useable engine. This still pertains to a race head where volume is likely going to aid at high RPM, but even there port energy rules.

 

[Dale Davies]

You missed one Rob. Horsepower is NOT the result of torque. It never is. It is the result of torque and RPM. You can have all the torque in the world and without RPM you have zero horsepower.

A quick look at a dyno graph shows this clearly. As torque starts to fall after its peak, the horsepower keeps going up. If you had to have torque to gain horsepower, once torque peaks and starts heading down (or even if it just went flat) you’d lose horsepower.

You absolutely can not ignore RPM in figuring horsepower. And without horsepower a car won’t move.

Steam engines and electric motors make their highest torque at 0RPM. That gives zero HP as no motion involved. An ICE requires some RPM to create the airflow for the engine to run for combustion. In steam and electric, the chemical reaction known as combustion occurs outside the engine or motor. They use an independent energy source.
An ICE dyno graph of a well thought out set of components will start with a fairly high torque for the displacement at 3,000RPM and remain fairly flat until intake flow is restricting cylinder filling. As long as the torque does not drop like a rock the power curve will continue to climb for another 1,500 to 2,000RPM.

 

[Rat Bastid]

Steam engines and electric motors make their highest torque at 0RPM. That gives zero HP as no motion involved. An ICE requires some RPM to create the airflow for the engine to run for combustion. In steam and electric, the chemical reaction known as combustion occurs outside the engine or motor. They use an independent energy source.
An ICE dyno graph of a well thought out set of components will start with a fairly high torque for the displacement at 3,000RPM and remain fairly flat until intake flow is restricting cylinder filling. As long as the torque does not drop like a rock the power curve will continue to climb for another 1,500 to 2,000RPM.

First paragraph. I couldn’t care less about steam engines. I haven’t seen a steam powered race car of any type in my lifetime. I don’t expect to see one. So who cares?

Second paragraph. You evidently haven’t seen a well thought out Comp Eliminator or Pro Stock or any other well thought out race engine dyno graph.

What happens at 3k on most race engines is so insignificant that the dyno pull doesn’t start until far above 3k.

 

[273]

What it boils down to in reality is chemistry. An engine runs on oxygen from air and hydrogen in a hydrocarbon fuel. Combustion is a chemical reation that generates heat. To burn all the fuel requires a set quantity of air (oxygen) so that all the hydrogen is oxygenated. For our gasoline engines this is about 14.7 pounds of air mixed with 1 pound of fuel. Now this is for theoretical complete combustion. Fuel quality and any additives can/will modify this. For maximum power and considering all the liquid fuel is not likely fully vapourized, a richer mixture is required of about 12.5 to 1.
1 pound of fuel contains the capability to produce a value of power or more like pressure. A typical street engine has about 80%VE. So a 400 CID engine pumps 80% of its displacement in air, or 320 cibic inches in two revolutions. The combustion in the cylinders produce torque at the flywheel. This is what an engine dynomometer weasures. It does not measure power. Horsepower is a calculated value using the measured torque and RPM. A larger displacement engine pumps more air and fuel to make more torque. Camshaft design and head port efficiency will determine at what RPM that torque will be developed. With compression ratio (both static and dynamic) about equal, more displacement will develop more torque.
The old musclecar engines of 427 and 450 CID produced up to 450HP, as advertized. Most were in the 450 to 480lb/ft of torque range. Maximum power was about 5500RPM.
F1 engines have normally been regulated to 122 to 181 CID. The turbo cars were limited to 90CID. The Renault engines were essentially from a joint passenger car V6 jointly developed between Renault, Peugot and Volvo. In North America we saw this engine in Volvo 240 series cars at 2.6L or 158CID. These were destroked to reduce the displacement to 1.5L. Then a bunch of expense parts were used internally so they would last at 15,000RPM while turbocharged. These engines made phenominal power at high RPM but as a street engine are useless, especially in a 3,500 pound family car.
To get more street useable torque out of a 225CID engine similar to a 450CID engine, use a supercharger to push the same air and fuel volume through it as what the 450CID engine pumps. Boost with strong enough components will not wear an engine out or cause early failure as much as raising the RPM. Boost loads the crank, pistons and rods more, but not like RPM. Stress on the reciprocating assembly is squared as RPM is doubled. This reduces engine life expectancy quickly.
Big industrial engines have block castings with cast iron 1" thick to withstand the vibration loads inflicted on it. These engines will produce 1,200HP at 1,200RPM 24/7 for years. Head swaps to replace worn valves and sometimes a cracked head and occasionally an inframe overhaul, but the block and crankshaft may be intalled without removal for 20 or 30 years. You can get a big block to make that power, ricers make that power. But they sure do not make the torque and last that long. Do the math to calculate the torque produced by a Sulzer marine engine that produces 10,000+HP at 100RPM. These engines idle at 10RPM. Pistons are 1 meter+ in diameter with a stroke of 6 feet or so. Head studs that hold the heads and cylinders in place are like telephone poles.

I get and agree with what you stated here, My original question was very ambiguous, what I was getting at most say added cid equals added hp 100% of the time, My question is what's stopping the lesser cid from spinning up displacing similar air to make similar hp with same/similar top end parts. Like eg.. 318 vs 360 360 vs 408 400 vs 500 even 289 vs 396 etc..

 

[Dale Davies]

First paragraph. I couldn’t care less about steam engines. I haven’t seen a steam powered race car of any type in my lifetime. I don’t expect to see one. So who cares?

Second paragraph. You evidently haven’t seen a well thought out Comp Eliminator or Pro Stock or any other well thought out race engine dyno graph.

What happens at 3k on most race engines is so insignificant that the dyno pull doesn’t start until far above 3k.

Yup, Confirmed. Your head is stuck in race engines only.
Steam and electric only mentioned as comparing/illustrate the difference between torque and horse pressure.
I saw no indication in the OP post on what engine may be under consideration. I highly doubt a highly developed race engine for a class was the consideration.
Concerning 3k on the dyno is more in reference to the majority of high performance street and street/strip engines.
You want to devote your thinking to race only, then maybe a race only site is a better place for you to be.

 

[Dale Davies]

I get and agree with what you stated here, My original question was very ambiguous, what I was getting at most say added cid equals added hp 100% of the time, My question is what's stopping the lesser cid from spinning up displacing similar air to make similar hp with same/similar top end parts. Like eg.. 318 vs 360 360 vs 408 400 vs 500 even 289 vs 396 etc..

Boils down to how much do you want to spend. A F1 engine develops, depending on the period rules, 750 to 1,000HP but torque is not that much. You have say a 3.0L engine reving to 12,000+ RPM. These engines cost $100,000+. Nascar engines are running 900+HP at 9500RPM but cost $50,000. RPM is expensive due to the high precission parts required and fairly regular maintenance required. A larger displacement engine turning slower will be lower cost and generally more reliable.
Larger displacement is no guarantee of more HP. The engine combination is to be considered. The cam and possibly the valve sizes may need to be changed as well. There is an aweful lot to consider, especially your ambiguous post. With engine building there is no simple answer to coming up with a workable combination. What works for me may not be right for you, and probably not in the same ball park for Rat.

 

[273]

Yup, Confirmed. Your head is stuck in race engines only.

Problem with most of these convo's what's the frame of reference to compare to, since most of these build's are just street only with vague goals. Guess street only cars zero 60 and or 100 mph would be a good reference but that's basically is just part of a drag race.

 

[Rat Bastid]

Yup, Confirmed. Your head is stuck in race engines only.

No it isn’t. That’s what you want to believe. And you make a bad assumption.

My point was exactly what I said. “Race” engines need to be defined. I expect you are a guy who thinks anything over 6k is a “race” engine. Maybe in your world, but not in reality.

Today 7k is NOTHING. So why pull an engine all they way down to 3k? All you are doing is putting a load on the engine is should never see. What kind of asshat is driving around at 20 MPH in high gear and then goes to WOT??? That’s about as idiotic as it gets.

All that gets you is detonation and broken parts. Or you have to lower the compression (lose power) or use a higher octane fuel than you really need (lose power).

Yup, confirmed. You have horse and buggy thinking. Time to move forward.

 

[273]

Boils down to how much do you want to spend. A F1 engine develops, depending on the period rules, 750 to 1,000HP but torque is not that much. You have say a 3.0L engine reving to 12,000+ RPM. These engines cost $100,000+. Nascar engines are running 900+HP at 9500RPM but cost $50,000. RPM is expensive due to the high precission parts required and fairly regular maintenance required. A larger displacement engine turning slower will be lower cost and generally more reliable.

Ya but generally were talking 20-100 cid maybe up to 150 cid differences in some cases. And guess under 50-100 hp if true.

 

[Rat Bastid]

Problem with most of these convo's what's the frame of reference to compare to, since most of these build's are just street only with vague goals. Guess street only cars zero 60 and or 100 mph would be a good reference but that's basically is just part of a drag race.

That’s exactly the issue. You get guys here who think anything that isn’t OE is a “race” part. Or any modification that is used on a “race” engine can’t translate to anything else.

 

[Dale Davies]

Problem with most of these convo's what's the frame of reference to compare to, since most of these build's are just street only with vague goals. Guess street only cars zero 60 and or 100 mph would be a good reference but that's basically is just part of a drag race.

A stroked 318 or 340 with moderate cam and heads can provide snappy street performance, reasonable fuel economy and fun to drive.

 

[Dale Davies]

Ya but generally were talking 20-100 cid maybe up to 150 cid differences in some cases. And guess under 50-100 hp if true.

Yup, I get that. Stroking a 318 or 340 brings 50 to 60 CID extra. Just dropping the crank kit in will maybe bring an extra 50HP but should definately give 50lb/ft. Generally if you spend that money, cam and head work or replacement heads are on the table. This is where the extra displacement really begins to shine.

 

[Dale Davies]

No it isn’t. That’s what you want to believe. And you make a bad assumption.

My point was exactly what I said. “Race” engines need to be defined. I expect you are a guy who thinks anything over 6k is a “race” engine. Maybe in your world, but not in reality.

Today 7k is NOTHING. So why pull an engine all they way down to 3k? All you are doing is putting a load on the engine is should never see. What kind of asshat is driving around at 20 MPH in high gear and then goes to WOT??? That’s about as idiotic as it gets.

All that gets you is detonation and broken parts. Or you have to lower the compression (lose power) or use a higher octane fuel than you really need (lose power).

Yup, confirmed. You have horse and buggy thinking. Time to move forward.

So who brought up the Comp Eliminator and Pro Stock engines. Yes I brought up F1 engines only to illustrate the difference in displacement, torque and HP. I also mentioned large industrial and marine engines to illustrate the other side of the coin.
No worries about the horse and buggy comment, even if they do have their place. Actually still used a lot in eastern European countries. I am fully aware you can go out and unload a pocket full of cash and come home with an American built supercharged car off the showroom floor that develops 700+HP and revs to 7500 or more RPM.
You also chewed out another poster for not understanding your viewpoint and thinking over 6k RPM must be a race engine. Possibly it is time you consider it is you who does not understand.
3,000RPM for most engines built for street use as a start of a dyno run is not lugging the engine. For a race engine designed to run to 9500+ RPM, maybe so.

 

[Rat Bastid]

So who brought up the Comp Eliminator and Pro Stock engines. Yes I brought up F1 engines only to illustrate the difference in displacement, torque and HP. I also mentioned large industrial and marine engines to illustrate the other side of the coin.
No worries about the horse and buggy comment, even if they do have their place. Actually still used a lot in eastern European countries. I am fully aware you can go out and unload a pocket full of cash and come home with an American built supercharged car off the showroom floor that develops 700+HP and revs to 7500 or more RPM.
You also chewed out another poster for not understanding your viewpoint and thinking over 6k RPM must be a race engine. Possibly it is time you consider it is you who does not understand.
3,000RPM for most engines built for street use as a start of a dyno run is not lugging the engine. For a race engine designed to run to 9500+ RPM, maybe so.

Ok. Pull as low as you want. The curves end up the same. Which was my point, or part of it anyway.

Now I have to go back and look and see what you said to make sure I’m not wrong.

 

[Rat Bastid]

Ok, post 258. Lots of torque curves drop quite rapidly and it does not matter. IMO, dragging the torque curve flatter, longer means you are out of induction. That’s not a good way to make power.

Part of my point was you can’t just manipulate torque (especially above peak) and not hurt horsepower.

Which, BTW may be calculated but again, you can have all the torque you want and have zero horsepower. That’s not good is it?

No matter what, you have to have RPM. Otherwise no work gets done.

Show me any performance calculator that uses torque and I will renounce every word I’ve ever said about horsepower.

 

[Phreakish]

I get and agree with what you stated here, My original question was very ambiguous, what I was getting at most say added cid equals added hp 100% of the time, My question is what's stopping the lesser cid from spinning up displacing similar air to make similar hp with same/similar top end parts. Like eg.. 318 vs 360 360 vs 408 400 vs 500 even 289 vs 396 etc..

This is a better question, and comparing 318 vs 360 and 360 vs 408 is the right approach because the engines are all limited by what can be put on top, either by budget or availability. It's not like we can go out and buy aluminum W2 heads ready to bolt on. The only good offset heads out there require someone well steeped in the knowledge of those heads and what-works-with-what, and comes at a hefty price tag too.

The original question of 'does CID always make more power' is far more open ended and impossible to state 'no' to.

So, with that in mind, and the better question from above the answer is absolutely nothing. The only reason I opted for a 408 over a 360 is that the cost difference in the shortblock was trivial - so bigger is better, right? If I did it over again, the only thing I'd probably do different is A) not kill my original shortblock with stupidity and B) re-apply the money from the dummy-induced-rebuild into a monster top-end to let this sucker breathe, because every 408 with non-offset heads has asthma.

The rpm difference required of a 360 vs a 408 to make 'the same' (and I mean this relatively since the curves will be entirely different) power wouldn't be unreachable (408@5500 rpm is 1300 cfm, or a 360 at 6,233 rpm - a 360 at say 7500 would be 'equal' to a 408 at 6,600). Obviously this comes with some major caveats because the engines are going to shape their curves and change peaks due to other differences. But that said, it wouldn't be money wasted to put even better heads on the 408 short block. That way you can reduce the compression height of the piston vs trying to make heads and intakes fit a lowered deck. What heads? I couldn't even guess - which ones are the right ones for a big-inch small block seems to be a question best left to those who specialize in building them since most solutions require the right combination of parts, and it's not a magazine-build type of deal at that point.

But look how many guys on this very site are running in the 9's with stock stroke small blocks and many with stock (albeit modified in some ways) blocks. I wouldn't want to drive one on the highway, but they get it done and then some. With an overdrive swap, there's no reason the cars couldn't be street driven though - or close enough to street drivable for me!

The key to making the smaller engine compete with the bigger one is ensuring it's operation stays in the right rpm range - which is a matter of gearing. The same gearing that could make a street car less fun to take down the highway (anything 60mph and below though is still cake).

 

[273]

Show me any performance calculator that uses torque and I will renounce every word I’ve ever said about horsepower.

I think the problem is most see torque as a dyno number not when you apply optimal gearing, which is mostly cancelled out if were talking similar hp and power curve.

Larger engines trades rpm for torque and higher gear needed trades torque for rpm and a smaller engine will do the opposite.

 

[273]

This is a better question, and comparing 318 vs 360 and 360 vs 408 is the right approach because the engines are all limited by what can be put on top, either by budget or availability. It's not like we can go out and buy aluminum W2 heads ready to bolt on. The only good offset heads out there require someone well steeped in the knowledge of those heads and what-works-with-what, and comes at a hefty price tag too.

The original question of 'does CID always make more power' is far more open ended and impossible to state 'no' to.

So, with that in mind, and the better question from above the answer is absolutely nothing. The only reason I opted for a 408 over a 360 is that the cost difference in the shortblock was trivial - so bigger is better, right? If I did it over again, the only thing I'd probably do different is A) not kill my original shortblock with stupidity and B) re-apply the money from the dummy-induced-rebuild into a monster top-end to let this sucker breathe, because every 408 with non-offset heads has asthma.

The rpm difference required of a 360 vs a 408 to make 'the same' (and I mean this relatively since the curves will be entirely different) power wouldn't be unreachable (408@5500 rpm is 1300 cfm, or a 360 at 6,233 rpm - a 360 at say 7500 would be 'equal' to a 408 at 6,600). Obviously this comes with some major caveats because the engines are going to shape their curves and change peaks due to other differences. But that said, it wouldn't be money wasted to put even better heads on the 408 short block. That way you can reduce the compression height of the piston vs trying to make heads and intakes fit a lowered deck. What heads? I couldn't even guess - which ones are the right ones for a big-inch small block seems to be a question best left to those who specialize in building them since most solutions require the right combination of parts, and it's not a magazine-build type of deal at that point.

But look how many guys on this very site are running in the 9's with stock stroke small blocks and many with stock (albeit modified in some ways) blocks. I wouldn't want to drive one on the highway, but they get it done and then some. With an overdrive swap, there's no reason the cars couldn't be street driven though - or close enough to street drivable for me!

The key to making the smaller engine compete with the bigger one is ensuring it's operation stays in the right rpm range - which is a matter of gearing. The same gearing that could make a street car less fun to take down the highway (anything 60mph and below though is still cake).

I agree for a NA street engine you want to keep hp:cid ratio high.

 

[Phreakish]

I think the problem is most see torque as a dyno number not when you apply optimal gearing, which is mostly cancelled out if were talking similar hp and power curve.

Larger engines trades rpm for torque and higher gear needed trades torque for rpm and a smaller engine will do the opposite.

But also, torque is meaningless. It's a force. It's measured instantaneously. It doesn't have anything to do with how well the engine can accelerate - that's why the HP measure exists. Without it, we cannot relate to what happens 'per unit time', meaning we can't figure out how the engine will accelerate, how it will propel, or how much weight it can move in a given amount of time.

It's why tractors are rated by horsepower and not torque, despite needing torque to 'pull stumps' and such. Only having a 105 ft-lbs measure wouldn't tell me much about what I can do with an engine. But tell me 5, 10, 40 horse and I know how much it can 'do' in a unit of time.