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View Full Version : Possible Mercruiser 383 MPI swap out Z21



bigalups
06-15-2007, 07:06 PM
Hey Guys,
Al out here in California. The weather is great and Lake Tahoe is just beautiful. Yesterday was a great outing on the Z21.

I have been thinking about swapping out the 1987 320 EFI Alpha because she is a little thirsty and I think I can do better on speed. I am running a 17 pitch @5200 rpm at Tahoe and a 19 pitch at sea level running around 52 mph at sea level.

What do you guys think of the Mercruiser 383 MPI Bravo I package. I know the X dimensions are different but I don't think it would be a problem.

Let me hear what you guys think, Thanks!:dolphin:

MOP
06-15-2007, 07:46 PM
That is a nice package worth considering, the X is no different from Bravo to Alpha what is different is the Bravo steals about 2 MPH but will last a long time.

Phil

bigalups
06-15-2007, 09:41 PM
My other question is will my Alpha take the 383? No use gettng rid of a perfectly good drive if I dont have to.

Rodger
06-15-2007, 10:00 PM
I ran a 406 with an Alpha (1.50 gears) for a number of years but in a 16'. The Z21 does weigh a considerable amount more. 454's were offered with Alphas in the mid 80's but with 1.33 gears.

chappy
06-15-2007, 10:01 PM
The Alpha will take the 383, I've seen guys push over 400 hp through theirs, I've read guys have pushed up to 500 hp through theirs. They won't last as long as a Bravo, but they're easy to get if they go.

Good luck,

Rich

mrfixxall
06-15-2007, 10:07 PM
A friend of mine has a1980 30' scarab panther with 425 hp 454's with alphas,just as lons as you east into it and not can it out of the hole it should last..

LKSD
06-16-2007, 12:07 AM
The 383 is a nice engine.. The alpha can tolerate power in the 300 hp range, but for how long is usually up to the driver.. :) Jamie / Lakeside

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Formula Jr
06-16-2007, 12:33 AM
Z21's need 1: Weight in the back. 2: A ton of torque just so you know what the zero force controls are doing.

The gas price stuff is messing this up, but the perfect engine for a Z21 would be a 454.

A light, High output engine will do you no good as to handling on this boat.

The sweet spot, even with a 350 mag is razor thin.

bigalups
06-16-2007, 12:57 AM
With that said my next question is will a 454 fit on the current stringers and engine mounts?

Cuda
06-16-2007, 01:08 AM
Congrats on having a 320 EFI that's still running. I doubt the 383 swap will make a lot of difference other than in your wallet, unless you feel the 320 is tire. If it's tired, I think you'd be ahead of the game to either do a bore job, top end, and maybe a cam. You may think about switching to a carb too. I heard there was design flaw in the 320's that caused the injectors to put the gas against the clylinder walls, washing off the oil, and causing their early demise. The 320 is the exact same engine as the 300 Tempest put out at the same time. They have all the real good parts in them, forged pistons (so maybe just rings without boring the cylinders), four bolt mains, forged crank, pink rods, and I think they had the 2.02 intake heads with the screw in studs.

I bought one with my Minx that was truly a basket case. I honed the cylinders, turned the crank, new bearings, and new (rebuilt) 2.02 heads. I also put a cast iron (salt water for me) high rise GM intake and a Qjet carb on it. It ran great for a short while, then I had a problem that I couldn't figure out, so like a dumbazz, I took it to a shop to have them look at it. They told me the valve guides weren't right, and the pushrods would sometimes hit the lifter, and sometimes miss it. I had them fix that (another set of heads), and when they got it running, they told me it had a knock in it. I told them it never knocked before. The said I had water in the oil, which I didn't have before. I figured they must have put either the head gasket, or the intake gasket on wrong, and allowed water to get in the oil, and wiped out some bearings.

I mean this engine was in bad shape when I bought it. I had been sitting dissasembled for some time before I got it, and I didn't think I was ever going to beat the pistons back out of it. That's what I get for just bolting on a set of rebuilt heads without checking them.

Here's what it looked like when I bought it, and after I had it done and in the boat. The cause of this engine's failure wasn't a design flaw, it was the aluminum intake. It was originally a tender on a yacht, and they don't get the best flushings.

Cuda
06-16-2007, 01:11 AM
With that said my next question is will a 454 fit on the current stringers and engine mounts?
Yes it will.

bigalups
06-17-2007, 12:53 AM
Since the Z21 was one of the heavier hulls produced would putting in a 454 defeat the physics of lightening up the boat to produce more speed?
I love the way it handles so wouldn't adding more weight to the boat bogg it down?

Formula Jr
06-17-2007, 01:41 AM
Since the Z21 was one of the heavier hulls produced would putting in a 454 defeat the physics of lightening up the boat to produce more speed?
I love the way it handles so wouldn't adding more weight to the boat bogg it down?

I'm all wrong..
Put that expensive 383 in there. Lighten up the back as best you can..
z21's after all, handle just great as are.....

Enjoy... :)

The Hedgehog
06-17-2007, 07:54 AM
We put the 383 Bravo packahge for the X-18. It is a good deal. Should have it on the water in a couple of weeks

MOP
06-17-2007, 08:10 AM
A lot of your decision on what engine needs to be based on just how fast you need/want to go. There are both BB & SB fans on the board, some need to go as fast as possible for the depth of their respective pockets (but there is always some body faster). Some like myself are content with reasonable speeds, I have a 383 in my 22C it will break 65 on a good day and cruise low to mid 40's with a boat load of people. With the SB I get over 4 miles to the gallon which is real decent.

Phil

gero1
06-17-2007, 05:38 PM
4 mpg????? how do you even figure mpg on a lake? i wonder if don a ever worried about fuel economy?

MOP
06-17-2007, 08:16 PM
4 mpg????? how do you even figure mpg on a lake? i wonder if don a ever worried about fuel economy?

At cruise on a long runs many of which are over 30 miles, 3500 gives 42-43 with four people aboard, I built my setup for "work & play" I cart customers around to various marinas that are had to reach on weekend due to traffic.
Example from Mattituck where my office is to Montauk by car round trip is over 5 hours including showing the boat, I launch out east a 25 minute ride the the run to Montauk is about 25 Minutes dock to dock 15-30 minutes showing the boat and back usually about 2-1/2 hours total and the customers love the ride. I bet I burn less gas in the boat then I do stuck in traffic for 4+ hours to me it is a no brainer.

Phil

Formula Jr
06-18-2007, 01:13 AM
The Z21 is an odd boat. I watched Eric get his to fly with a 350 mag. But he knew exactly what he was doing to get it to plane correctly. I saw him run from a bluff and saw how he maxed it. It was quite beautful to see.

When you get into waves, there is a problem with this boat. It will not sing and dance. It wants to dive or flip. There is no middle where you launch and Land. It never lands right for the next wave. You can fix a Z21 by taking stuff out of the cabin: make the Bow lighter. OR you can put a big and heavy engine in it.


For this boat. The lighter engine is better idea doesn't work. The bow is too Heavy.

If I won a lotto, I'd buy a Z21 and gut, then rebuild the interior so it was 400 lbs lighter, then 502 and Bravo. Then you have the ultimate offshore go fast pocket boat.

fegettes
06-18-2007, 05:04 AM
I have always heard good things about 383's.

Actually, at this very moment, my Donzi Sport is in the shop to change out a perfectly good 350 SBC to a 383/450 HP and upgrade the Alpha drive to a Bravo I. I am anxious to get it back. About 10 plus years ago, I changed my 350/350 HP to a 383/400 HP in my Stingray, and it is just plain HEALTHY, I really like it. The 350/350 HP is a 11.0/1 Compression, and does not like the pump gas octane, and the stroker is about 10.0/1 and does okay with the premium fuels.

My humble opinion, for what it is worth, go for it.

Steve

VetteLT193
06-18-2007, 02:41 PM
The 383 and Bravo 1 package is a great deal (I think about 12k buys you everything).

But, if your boat is still running it would probably be more cost effective to sell it and upgrade to a newer model or a boat that has already been re-powered.

bigalups
06-19-2007, 12:27 PM
AAHH, decisions, decisions! I totally agree that the Z21 is bow heavy. Once I am on plane I retract the trim to keep the bow up and she flys. After reading all the suggestions and consulting with the resident boat mechanic extrodanaire I am bending towrds the 383 bravo package.

The one thing about the Z21 is she handle crappy when going through no wake zones. One of you smart gentlemen advised to keep the trim all the way down while going very slow and that seems to work to a certain extent.