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View Full Version : 18 Classic, 350 MAG MPI/Bravo 1 - Speed?



Patrik Sweden
06-11-2007, 11:14 AM
Hey guys,

maybe I will buy a new 18 Classic with a 350 MAG MPI/Bravo 1.

Can someone tell me what speed I can except.. I had the same set-up on my -98 22 Classic, and it almost hit 60 MPH.. The ad says 70 MPH, is it possible?

Pics (http://www.bilauktioner.com/obj/fil/712nn/90/pic.lasso?chopic=1)

BGH18
06-11-2007, 02:12 PM
Hi Patrik, I have a 1999 18 but with an Alpha 1 and I'm getting about 64 mph
gps with 3 people and full fuel. 1.62 drive ratio & 23 pitch prop 350 mag mpi
Brad

TheFees
06-11-2007, 02:50 PM
I have a 1987 18 classic Mercruiser 350Mag 270hp Alpha SS. I called Donzi back when I bought my boat, at least a few years later, during the OMC years, and Donzi tech rep told me that if I had the OMC set up, that the 18's top speed out of the box was 64.1 for the OMC, add 3 mph for the Mercruiser, and add 3mph for the speed prop, which is what I have. That adds up to 70.1
I ran this guy in a 19 foot baja outboard, and we stayed in it, and the whole 5 minutes, you could have tied a string between our bows. Neither of us gained an inch on the other. We slowed down and talked for a while, and he mentioned that his buddy is a state trooper so he had him shoot the boat with a radar gun, and it registered 70. So to the best of my knowledge is the boat does 70. (It sure feels like it)
Their are contributing factors, such as chop, wind, how many people are onboard, fuel levels, to mention a few.
I'm impressed with those who have a GPS, they can tell exactly how fast they are going based on a global positioning satellite. Way Cool. That is a toy that I definitely will be buying in the future.
One more note, is that in 1989, they offered a 300hp option. I found out it had a slightly hotter cam, larger exhaust manifold, and a jet change in the quadrajet carb. He also mentioned to me, not to change anything. You already have the magnum motor, so the whole boat is engineered to a T already. He said at Donzi, "Everything you do to increase the HP, will result in increased internal temperature, and that is where the problems arrive." Combine that with a hull that chime or chine walks at 72, you realize that 70 is right where you want to be. I go through heavy chop, moderate rollers and the like, and just stay in the throttle, and let the natural hull without trim planes do the job, and all I can say is it give me an adrenalin rush that nothing else can touch. :eek!:

DonCig
06-11-2007, 03:23 PM
Hey guys,
maybe I will buy a new 18 Classic with a 350 MAG MPI/Bravo 1.
Can someone tell me what speed I can except.. I had the same set-up on my -98 22 Classic, and it almost hit 60 MPH.. The ad says 70 MPH, is it possible?
Pics (http://www.bilauktioner.com/obj/fil/712nn/90/pic.lasso?chopic=1)

When I first purchased my 1997 Classic 18 it had a 350 Mag MPI Gen +, Bravo 1 with a 1:65 ratio and a Mirage Plus prop and I could hit 67 mph on a regular basis. With a -2" shorty I could hit 69.4 mph. With a 427c.i. SBC and a Bravo XR drive I can now break 70 on a regular basis.

Don

Ranman
06-11-2007, 09:10 PM
I have the same Engine and drive combo as Don (1997 350 MAG MPI Gen+ / Bravo One 1.65, 25P Mirage+) and run about the same speed. I got 68.5MPH all day long at Lake Cumberland a few weeks back...

DonCig
06-13-2007, 01:59 PM
The following sheet may help you. I put it together for my boat and it appears to be very accurate. I have checked other Classic 18's against it and they are usually with 1 mph of the table if they are running modern and accurate equipment.
Also, as a gereral rule of thumb, each 70 pounds that you remove from the boat can gain you 1 mph in top speed, provided that the rest of the package is still within the safe operating zone. So if you dump the cooler (40#), dump the beer belly (30#), dump the second battery (40#), pitch the iron exhaust manifolds and replace them with something lighter (30#); you have eliminated 140 pounds and gained 2 mph. Or you can go the lazy route and spend $2,800 for a -2" shorty and gain the same 2 mph. We sell a lot of shortys on this site. What does that tell you? LOL

Don