Speaking of speculating, I do think that the improvements between the 500 and 525 are worth more than 20 HP - try about 65 HP...

If you put all the changes Mercury made to the 525 efi over the 500 efi into a computor program to determine hp, the new 525efi is closer to 575 than 525! I tried it.
JB

Okay then, let's talk about sound...John B. , are you talking about the quality of the idle? If so, I've never thought the idle of the HP500EFI was quite up to par, although, I think that motor is very nice.

It's not, but the 525 is HAIRY, from idle on up.

Then my vote is for the header theory....although the new Motorola & MAP setup probably improves the idle somewhat. Just asking, what is the compression of the new motor? Thanks, Berg

Advertised compression ratio of the 525 is 8.75:1 - a whopping increase of....0 over the HP500EFI

Wow, hardly seems worthwhile from a MFG.'s standpoint to upgrade to aluminun heads and not take advantage of a higher cr.

Adivanman- not doubting you, but where are you getting a 65hp increase? Seems like that kind of oomph puts this motor is too close to the 575efi sc!! This could be a marketing snafu that could upset some 575 owners!!!! How 'bout it Von Bongo?
Take Care, Berg

Estimated gain over 500 efi

Heads 40 hp

Headers 15 hp

Throttle body 10 hp

Cam "what is it?" + something

Anyone else??

lounge - it is closer to 570HP and yes, that is encroaching on the 575SCi's numbers. Shouldn't upset the 575 owners much though - their engines say 575 right on them...

575's make more power than 575. Probably closer to 650.