Hi

If so we still have not more than aprox 50-60 hp difference all together.

So it must be the hull construcion and rigging who gives this speed difference. Wich ofcourse is logical, my reaction was
that we are talking about 25 mph. Unbeliveable *S*

The research I've done on the 353 shows weight at 9,500lbs dry (Formula website). Speed with 500 EFI should be around 78-79 GPS (trustworthy friends who have them). These are fresh water speeds, aprox 105 degrees, elevation 500'? Phoenix, AZ. The weight you underestimated on the 353 and the 40HP difference from 500EFI/525 account for the difference in speed you're talking about.

The speed of 74.4mph for a 353 Fastech is not correct. I have known 2 people with them. Both had 500efi's. one has factory stellings boxes. Top speed is 80-81mph w/o boxes and 82-84mph with boxes.

We have several 353 owners with 525's/Stellings boxes. Gps speeds vary,as with most boats.The fastest one we ever ran was 89,most are 85,86,87.The 89 GPS boat is a 2004,will still run that today.Took a lot of prop testing to get it there,never gotten one quite that fast since.

that is exactly how i understand it, the 500 efi as well as the 525 are very underestimated motors. in 2005 we ran a 353 525/ITS boat in the windy city poker run along side a 2003 500efi boat with stellings boxes, boats were almost identical with us in the 525 boat managing maybe 1-2 mph faster.

I not 100% sure on this but fountains also run a higher drive height. I think that the high drive heights also account for the fact that fountains blow drives as often as they do.