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350 meg not performing up to par ?

Old 04-30-2018, 09:53 PM
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She little dirt but cleans up nicely
Originally Posted by Ryan00TJ View Post
yep, this will give you an idea of how much power you have gained. With that setup you want to spin at minimum 5000 rpms.
iíll try that over the weekend.......but what I think it is exhaust is cutting it back. Going to put through transom exhausted this week. and also if I could find some used headers try to0

trying to get the thing to at least 450hp 450tq

what do you guys think about port matching the stock exhaust manifold to the AFR heads ? Exhaust ports are about a 1 3/8 and the stock exhaust manifolds are about 11/4inch

Last edited by hotshot537; 04-30-2018 at 10:31 PM.
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Old 05-01-2018, 12:18 AM
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Originally Posted by hotshot537 View Post


She little dirt but cleans up nicely

iíll try that over the weekend.......but what I think it is exhaust is cutting it back. Going to put through transom exhausted this week. and also if I could find some used headers try to0

trying to get the thing to at least 450hp 450tq

what do you guys think about port matching the stock exhaust manifold to the AFR heads ? Exhaust ports are about a 1 3/8 and the stock exhaust manifolds are about 11/4inch
As others have stated you are currently overpropped. With SBC head/cam/intake upgrades you are better off keeping the same prop and simply spinning it faster. You might go up a little in pitch but not a lot.

Your thru prop exhaust is not limiting the motor to 4300 rpm. Your prop is. Thru hull will allow your motor to breath better above 5000 rpm.

Don't waste your money on exhaust manifolds over what your have. Ryan, myself and others have spun strokers well north of 5000 rpm with GLM style manifolds.

Don't waste your time port matching. There will be zero difference.

A prop is a simplest fix. Go back to your original prop see how things go. You may not need a new prop.
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Old 05-01-2018, 07:15 AM
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23 pitch prop / 350 5.7 mercruiser / port matched / turns close 6000 rpm / velocity stack w K&N / 220 intake w a heavy port , all the internet experts say it will never run , right
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Old 05-01-2018, 10:28 AM
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To small of carb
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Old 05-01-2018, 10:44 AM
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have the valves been lashed properly, where is the timing set
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Old 05-01-2018, 01:43 PM
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some edelbrock carbs have a small orifice on the end of the emulsion tube on the secondary boosters....when running larger secondary jets the end of the tube becomes the restriction...not the jet...this can contribute to lean WOT operation.

something to look into


Last edited by SS496; 05-01-2018 at 01:45 PM.
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Old 07-02-2019, 03:43 PM
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How did you ever make out with this build? I was looking at the exact same top end and cam for my small block merc.
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Old 07-02-2019, 08:09 PM
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Originally Posted by Trash View Post
As others have stated you are currently overpropped. With SBC head/cam/intake upgrades you are better off keeping the same prop and simply spinning it faster. You might go up a little in pitch but not a lot.

Your thru prop exhaust is not limiting the motor to 4300 rpm. Your prop is. Thru hull will allow your motor to breath better above 5000 rpm.

Don't waste your money on exhaust manifolds over what your have. Ryan, myself and others have spun strokers well north of 5000 rpm with GLM style manifolds.

Don't waste your time port matching. There will be zero difference.

A prop is a simplest fix. Go back to your original prop see how things go. You may not need a new prop.
Try the prop and get a baseline before you do more work and spend more money!
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Old 07-09-2019, 04:59 PM
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Originally Posted by hotshot537 View Post


She little dirt but cleans up nicely

iíll try that over the weekend.......but what I think it is exhaust is cutting it back. Going to put through transom exhausted this week. and also if I could find some used headers try to0

trying to get the thing to at least 450hp 450tq

what do you guys think about port matching the stock exhaust manifold to the AFR heads ? Exhaust ports are about a 1 3/8 and the stock exhaust manifolds are about 11/4inch
nice boat. That set up is probably around 300 hp at the prop. To get that to 450 hp you would probably be better off supercharging it.
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Old 07-09-2019, 05:08 PM
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Originally Posted by RBeyer View Post
Try the prop and get a baseline before you do more work and spend more money!
For sure. Had a small block boat lose almost 20 mph last week. (50mph vs 70mph) Motor was lugging. Not sure what happened to prop as it looked fine. Put another 'same' prop on and BAMM ! Mph was back...boat and engine where happy again.
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