1971 Donzi Classic 18 power....

**FUJIMO** · 01-18-2017, 06:57 AM

You are up way too early Xstream. Yes, big difference in motors. To build a durable marine 450 yourself, you will have comparable dollars into the build(or more) that a marine engine supplier has already tested & warrantied. A turnkey engine is bolted in and running, in a couple hours. All of this is value. Value in the ease & quality of the engine install, but also to the entire boats final value. Imagine NEVER having to wrench & repair your new engine, just enjoy it, EVERY TIME you hit the key?! Priceless.

**XstreamVking** · 01-18-2017, 07:17 AM

Fugimo, I do not think that many builders can out engineer the guys at mercury when it comes to making reliable power that still performs at a higher level. Same reason I got a GMPP crate motor for my old hot rod, performance, but still reliable. I've had my ZZ 383 motor for 5 yrs and run it hard. No problems at all. But it was built to do what I use it for. In a performance boat like the capt says, it wouldn't live that long. Up early? Being a fish guide for 25 yrs, I can't sleep past 5am, even on my days off. Dammit!

**Classic18** · 01-18-2017, 08:18 AM

Originally Posted by FUJIMO

You are up way too early Xstream. Yes, big difference in motors. To build a durable marine 450 yourself, you will have comparable dollars into the build(or more) that a marine engine supplier has already tested & warrantied. A turnkey engine is bolted in and running, in a couple hours. All of this is value. Value in the ease & quality of the engine install, but also to the entire boats final value. Imagine NEVER having to wrench & repair your new engine, just enjoy it, EVERY TIME you hit the key?! Priceless.

I understand your points and agree. I was originally planning on building up my 1991 donor, but due to yours and others feedback, I think my best road home is a marinized SP383. It's a known entity (well, the 383 base is). Forged components, fast-burn heads, 4-bolt main (my 91 Mercruiser has 2-bolt), rollers, warranty, etc. I expect the marinization will take care of the marine touch points - its done routinely. I just don't see a down side to going that route over a one-off engine.

Any idea what the 91 Mercruiser motor is worth? Its got about 400 hours and is complete.

**Capt.Insane-o** · 01-18-2017, 08:38 AM

Complete 2-2500. Keep the sea water pump and bracket/pulleys.

**XstreamVking** · 01-18-2017, 12:02 PM

The 383's are torque monsters. IIRC Make around 400 ft #' at 4000 r's. 400hp at 4500 r's. So don'r need a lot of r's to make power. Keep it below 5500 and it should live... I do believe the SP motors still have hyper pistons and not forged....

**Classic18** · 01-18-2017, 01:19 PM

Originally Posted by XstreamVking

The 383's are torque monsters. IIRC Make around 400 ft #' at 4000 r's. 400hp at 4500 r's. So don'r need a lot of r's to make power. Keep it below 5500 and it should live... I do believe the SP motors still have hyper pistons and not forged....

That's correct, the SP383 has hypereutectic aluminum pistons....should be good for this app.

**FUJIMO** · 01-21-2017, 03:42 PM

If you are using a good remote pickup, you can install the standard Bravo any height you want. Keep in mind also that above 17" you will need a four blade. You might barely be able to use a good 3-blade, but it won't be as practical as the 4. Those hulls also don't do well with a surfacing drive, higher X. Are you familiar with the 50 "presold", special edition small Donzi's that were advertised ahead of time, to attain a given speed, with the then new Black Hawk drive, but could not deliver, due to poor performance? Partially due to incorrect rigging, but also hull design.

**Classic18** · 01-21-2017, 04:58 PM

Thank you for the information. It should be helpful as I begin to install the outdrive. Is there a remote pick up that seems to perform well and one that you're from famaliar with?

**Greg G** · 01-22-2017, 06:08 AM

I'd be careful with raising the X dimension too much, perhaps go 1/2" from stock. You are not setting it up for top speed, you want the best "all around" and gain some speed. Unless I missed something earlier in the thread. At 1/2" higher, the 18 Classic will respond very well to a Merc Rev4 prop btw. What top speed are you looking to achieve btw?

**Classic18** · 01-22-2017, 07:59 AM

I'm targeting to be able to hit 75, but probably never run there.

**Greg G** · 01-22-2017, 09:56 AM

Originally Posted by Classic18

I'm targeting to be able to hit 75, but probably never run there.

Oh yes you will! I've never seen an owner yet who does not chase the GPS over time. 75 is achievable in the later 18 Classics. The fastest one in the US is doing 91mph. Life vest and a plugged in safety tether is a must. You might also consider a very slight modification to the 24 degree round bottom as well to help. Btw, the very early 18's had a full V bottom.

**Capt.Insane-o** · 01-22-2017, 10:59 AM

Your not going to need the remote pick up.

**Classic18** · 01-22-2017, 12:56 PM

Originally Posted by Greg G

I'd be careful with raising the X dimension too much, perhaps go 1/2" from stock. You are not setting it up for top speed, you want the best "all around" and gain some speed. Unless I missed something earlier in the thread. At 1/2" higher, the 18 Classic will respond very well to a Merc Rev4 prop btw. What top speed are you looking to achieve btw?

are you talking about a half inch higher than the nominal 16 inch setting?