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Magnum Ralph
09-07-2015, 11:28 AM
My 94 classic 18 had stock 350 with alpha gen2 ran 58 2 adults 4600 rpm. Over winter installed mild 383 dart steel heads imco thunder exhaust and alpha ss outside I think 1.5 or 1.6 gear . Also installed imco dual ram hydraulic steering . Boat handles very but to same top speed at 5200 rpm. Prop is mirage 3 blade 15 inch 19 pitch. I did not buy prop new but assume not altered. Any suggestions are welcome. I will try and verify gearing.

f_inscreenname
09-07-2015, 11:47 AM
Oh the pain. Went from a 360 Chrysler to a 454 in my boat. Picked up 4mph. Talk about being bummed.

murfman
09-07-2015, 01:22 PM
Did the same on my old Nova 250XL went from stock 260 HP Mercruisers (Old style with the rear riser log manifolds) to 383s with Stainless marine manifolds and risers that dyno'd at 375HP each and went from 57 to 61 MPH that cost me about 2000$ per MPH.

And F_ingscreenname, being a Mopar guy, Id say I'm surprised you gained anything at all LOL.

OP can you borrow a bigger wheel from someone to try? if noting else change the extra 400 RPM is all prop slip.

Ghost
09-07-2015, 02:51 PM
A Nova doing 61 would be fun to see though--not many of them ever got up that far,kudos even if it was disappointing. I'd like to see a Nova with a single 525 in it...

f_inscreenname
09-07-2015, 10:57 PM
A Nova doing 61 would be fun to see though--not many of them ever got up that far,kudos even if it was disappointing. I'd like to see a Nova with a single 525 in it...

I've got a Nova that will do 60mph :shades:

Ghost
09-07-2015, 11:12 PM
I've got a Nova that will do 60mph :shades:

NOW you tell me! ;)

osur866
09-07-2015, 11:26 PM
My 94 classic 18 had stock 350 with alpha gen2 ran 58 2 adults 4600 rpm. Over winter installed mild 383 dart steel heads imco thunder exhaust and alpha ss outside I think 1.5 or 1.6 gear . Also installed imco dual ram hydraulic steering . Boat handles very but to same top speed at 5200 rpm. Prop is mirage 3 blade 15 inch 19 pitch. I did not buy prop new but assume not altered. Any suggestions are welcome. I will try and verify gearing.

19 pitch for a decent 350 is to small unless your running 1.36 gears, I'm gonna go out on a limb and say your all over the rev limiter , try a 23 or 25" prop, are you running this at altitude or close to sea level, you prolly raised your prop slip % going from the standard Alpha to the SS, try a larger pitch prop and see if your RPM's don't come down a little and your speed up, unless the cam changed and ECM has been remapped I'd prop that for around 4,900-5,000 that's prolly where your gonna see the best top end.

chip w
09-08-2015, 09:02 AM
try a 23 or 25" prop.

I agree. I'm running a stock 350 with the Alpha One Gen 2 outdrive and a Mirage 21 pitch prop and getting to around 62/63 MPH on GPS at sea level. Try the 23 or 25" prop.

Pat McPherson
09-09-2015, 02:57 PM
The shorter drive will likely cause the same 3 blade prop to slip a lot more.
May I suggest you try a 4 blade prop; the Rev 4 works great for a number of us.

woobs
09-09-2015, 07:04 PM
plug your numbers in here... might get some insight.
http://www.mercuryracing.com/prop-slip-calculator/