how picky are these engines on fuel? I was offered on trade a twin 575 boat. was told they melt piston when using regular fuel, like 89 octane. they apparently need at least 91. True or false?

that make a long trip almost not possible, since I guess there is only or mostly 89 in different marina, right?

What about adding octane booster? would this solve the problem if any problem there is?

You can run about anything in a STOCK 575!!! Hell, stock merc throws so much fuel at it it could possibly run E85.

7.5 CR and only 4psi boost...very safe

575s stock need at least 91 octane and if they are tweaked need 93.

When I first got my boat, the 575s were stock and I was told by multiple people to run at least 91 octane.
A year later I had Ron Potter build them up to 700's and got 6 seasons out of them before I got bad fuel this spring in Louisiana and blew them both up. I detonated both motors blowing out the head gaskets in multiple cylinders because of it.
That said, I have KNOWINGLY got 89 - 91 octane fuel and put in legit octane booster with no problem. I always have enough octane booster on board to cover my 240 gallons if need be. Ron Potter has told me on numerous occasions that it is ok using a good octane booster if lesser grade fuel is the only thing available.

It sucks that no matter how diligent you are, all it takes is one gas station to screw up (or intentionally cheat) and have regular gas in the super tank.

Here is a pic from the other day, already to go back in! Hope I get another 6 seasons!

Manual says 92. That being said I run my 575 with 871 at 10psi innercooled on 92.

here is the ad.

how much would you think it's worth in today's market with those '' less popular'' engines?

http://www.kijiji.ca/v-bateau/laval-...ationFlag=true

I can't answer your Q because I can't read French!

question for TOM A
I called a ''local'' distributor for TORCO octane booster.

I explained the case, he told me 32 onzes treats 5 gallons of fuel. each 32 onzes of torco cost 24.95$
if you multiply 24.95 x 40 (200 gallons gas tank in boat divided by 5 gallons = 40 times needed of 32 onzes) that's roughly 1000$ of cost of octane booster per gas tank !!!!

Does not make sense to me!!! is this really what you do when you need to add booster?

long story short: 2001 formula 353 with 575's !

Numbers are usually both in french and english!

What if you dropped the boost a pound or two? Maybe you could get away with lower octane fuel if that is your main concern.

I agree 100 percent. I ran mine stock for 1 year, pulled them down to bump them up and the builder noticed dangerous piston wash from the stock rich tune.