Desk Top Dyno

One thing to understand about the DD program is…….. it Loves big air flow numbers……… and does a poor job of predicting output on larger cube builds using small-ish heads that have modest flow.

As an example, I built 2 BB’s during the same time period several years ago…… a 446 and a 493.
The top ends were nearly identical(heads were done at the same time), same intakes(Holley SD), same carb(Holley 850), compression ratio within 1/2 point, very similar cams from the same lobe family, same dyno, same dyno operator(me).

The DD predicted the 446 would make more power than the 493.
The actual dyno showed what I expected the outcome would be……. Which was that the 493 was better than the 446 everywhere.
Peak was about 40hp better.

The only way to get the DD to show the 493 hp the same as what the actual dyno showed was to artificially inflate the head flow numbers……. By a fair amount.

I ran multiple actual builds, that had been tested on the real dyno, thru DD…….. and frankly, the predictions were often not very close to real world results.

If you plug in numbers for something like 355 SBC with a decent pair of heads and a typical bracket race cam…….. the numbers are pretty close.

BBM stroker with cleaned up RPM heads? Not close.