Just out of curiosity to see what my build would make I downloaded Desktop Dyno 2003. I already bought my bottom end for a 355 but just out of curiosity I had changed the desktop dyno displacement to a 383. Using the same heads, cam, intake and exhaust why would I make more hp out of the 355?

The only thing I have left to do is buy my heads, I'm looking into Speier ECONO 195's. I'm sitting at 10.3:1 compression if I run 64 cc chambers, desktop dyno seems to think it will make 470ish horses on a .549" lift/249 duration cam... I was expecting around 420 horses.

I understand this program isn't 100% accurate but why does it think the 355 will make a descent amount of hp over a 383? (It did say the 383 would have around 30 ft lbs more throughout the rpm range though).

 

No way of knowing without seeing what you've done in the model.

 

All factors were left the same between the two motors, same heads, cam, everything. The only thing touched was displacement.

Would their actually be a possibility where a smaller motor (using the same parts) can make more HP throughout the RPMs?

 

Ok they're the same, but what were they? And what were the numbers that came out of it?

 

Software dyno programs are only good for playing "what if". They assume the best possible situation from the input data. There are many factors the software dyno can't calculate for. With the 2 real world engines both sitting on dynos, the bigger engine may require things like different jetting or ignition timing which the software dyno can't change.

Then there are actual components. A camshaft that may be aggressive in a small engine becomes mild in a bigger engine. Heads that provide enough flow for a smaller engine may choke a bigger engine. There are too many factors to say yes or no to the results but the software dyno can show you areas that need improvement to compliment the larger displacement.

In general, such a swap as you've tried should produce better results with just a displacement increase but there's more than just total numbers. The area under the curve is probably different. The peak rpm numbers are probably different etc. The 383 probably makes a lot more torque through the lower rpm range than the 355 does. You'll feel that in the butt dyno.