I know of the picture you are talking about and it is very deceiving. It wasn't a cut thru the center and that has a dramatic affect when trying to view 2 different diameters. Here is a better cut picture that shows the 1" difference in sizes. Click on picture for a larger view.

Wow, youīre absolutely right. There is quite a difference in diameter! I missed that!
It didnīt make a difference to the performance, though. However, if a 496 is already running at a max around 5000 revs, maybe it needs more than a little extra gas flow to free up more horses at the top end. 496īs tend to produce their best speed figures a tad below 5000 revs.

The only way to be sure is to remove them after a trial run ON THE SAME day. otherwise it's not an accurate comparison. We all know how different our boats can and will run from day to day. Temp, humidity, water conditions etc.. all play a factor. So a same day comparison is the only true way to tell. The few that I know that did it that way all seen a min of 100 rpm.. I will be trying the same water test in a few weeks.