Some interesting aspects of engine design are being brought up, but the bottom line is that for a street or street/strip motor the stroker is the way to go. If you don't want invest in a forged crank, the 383 is the best option. If you are going to a forged crank anyway, go for the 396. All the other parts will cost ~ the same for a given quality between the three combos and the larger motors will simply make more hp. But exceeding 396 gets expensive quick.

Rich Krause

 

if everything in motor is right, a smaller motor will make as much power as a bigger motor you will just have to turn it more RPMs...for example i know a guy who ran competition eliminator in NHRA and IHRA and me and my dad were talkin to him one day and he said when his motor was 49X C.I. it made 1050 horsepower, he de-stroked it and made it a 477 and it made 1050 horsepower...he just had to turn more RPM's...a smaller motor will be more efficient you just have to be willing to turn it more RPM's, if 6000 RPM's is gonna be peak RPM then goin w/a 396 would prob be the smartest choice, but if you could turn it up to say 8k the 355 will prob run faster than the 396 using the same cylinder heads...

 

Don't want to start an argument, but it's patently untrue that "if everything in motor is right, a smaller motor will make as much power as a bigger motor". If it were, why would every engine in a displacement limited racing class be built right up to the limit?

Now, if we are talking about an NA 355 v. 383 v. 396, the differences in hp are not proportional to displacement. If the heads are identical, there will be a less than proportional increase in airflow (and hence power) as the stroke gets longer. But there's no question the stroker will be faster, even if the peak power is only marginally greater, due to greater area under the torque curve. Acceleration is a function of power applied over time, not just peak hp.

For a SC setup, the stroker's advantage is even more pronounced.

Rich Krause

 

Me and A buddy have two 1971 nova's 308 gear's a3 same heads; cam; intake;headers;carb; My nova has A 406 his has 355. In 1320' he smokes me buy 6 car's.smaller moter on same air and gas I gess. You tail Me.

 

the reason is because with a bigger motor, you can put the bigger head to turn the bigger motor the same RPMs as the smaller motor, a motor with high horsepower that turns RPMs will run faster than a torque motor that turns less RPMs...Look at NHRA Pro Stock, why would they turn their 500 c.i. motors 10,000 RPMs??? also compare that to the IHRA Pro Stock cars, they run 815 cubic inch motors and turn them 8000 RPMs! thats 314 more inches and they only run two tenths faster? explain??? what im sayin is to a certain extent a smaller motor that turns RPMs will run as fast or faster than a bigger torque motor with same heads/cam setup because its a more efficient motor cuz there is more head flow for a smaller motor, believe me, ive seen it too many times...

 

2 tenths is a buttload of power dude!

and at their power levels- their speeds are tire limited

they can spin their tires through most if not all of the 1320.
They make more power than they can put down.

its like having a 60 ft race on street tires with a 900 hp and 1200 hp car.
who cares?
both are traction limited

 

true it is but with 314 more inches and heads that flow 80-120 cfm more you'd expect them to run faster...


they prob could on a typical local unprepped track but on the tracks they run on they will spin off the line a little bit but the rest of the ways down the track they dont...they have computers on the cars with sensors that show RPM's of the motor during a pass, if the graph shows the motor peaking more than its supposed to on a shift, they will take clutch out of it so that it will not spin...

also, i think NHRA Pro Stock cars make around 1300 hp and the IHRA pro stocks make around 1500-1600 hp and when you do the calculations, the formula will show that it takes more power than they have to run what they run due to the efficiency of the tranny's...

 

1500hp? LMAO

1500 hp is like 7 sec range.

 

NHRA Pro stock cars are 500ci because thats the limit according to the rules. If they were allowed to build a bigger motor I assure you they would. They spin them to 10k rpm because thats what it takes to make power they need to be competative.

Also as someone else mentioned when you're running in the mid 6's two tenths is a huge difference in power.

None of that really matters since a Pro Street motor is not even remotely similar to the type of buildup we're discussing here.



If you've seen it "too many times" then prove it. Show us an example of a smaller motor running faster than a larger one all other things equal.

 

isn't it physically impossible for a smaller to make more power "all things being equal?"
I'm fairly confident it is

if power= work/s
and you do more work in the same second- isn't your power higher

and 1/2 sec tenths is 250ft at their speeds
winning by 250ft in a 4 sec race is pretty good IMHO

 

Yes, but what is work?

Work = Force x Distance

But thats for linear motion. For rotational stuff (like motors) we use torque to represent force and revolutions for distance.

Now we have Power = (Torque x Revolutions)/Time

Now its easy to see if we want more power then we need to increase torque, or increase the number of revolutons the motor performs for a given period of time.

Granted thats a pretty simplified explination but it gets the general idea across.

So in the end, yes, it is possible for a smaller motor to make more power than a larger one. It just needs to apply more force (torque) than the larger motor or it needs to apply its force at a higher RPM. However since torque is relatively proportional to engine displacement (generally speaking) if you want to make a smaller motor match a bigger one you're going to have to spin it faster to make up for its torque deficit.

 

This is getting pretty unfocused, but there really should be no doubt that if we are talking about a 355, 383, or 396ci LT1 with LTx head castings and otherwise comparable parts the 396 witll be fastest, the 383 next, and the 355 slowest. The 355 will be more "efficient" in the sense of more hp/ci. It will not be more efficient in terms of performance/$, as there is very little cost difference when comparable parts are used.

Rich Krause

 

Agreed, I'm not even sure I was awake when I wrote my last post, lol...

 

Maybe I missed the boat, but what's this big stink about efficiency anyhow? Power is power, or else we'd all drive 1.95HP/CI Honda S200's based on efficiency alone

 

I think this was a good discussion as it has brough tto light alot of questions i woul have eventually posted on.