How can I get more speed?

[rulost2]

I have just purchased my first Donzi 1988 Z21Mercruiser 7.4l(Boat of any kind for that matter). I went out to Lake Martin last weekend and I maxed out at 58 on the GPS. I was wondering if anyone had any tips on how to get more speed out of the boat. It has a Quadrajet carb on it now and I was wondering if maybe a better Carb would help out. Also I need a new pump for my trim tabs and I thought that might help as well. Anyway, thanks in advance for any answers. Check out my boat and tell me what you think here is the link for the pictures: http://albums.photopoint.com/j/AlbumIndex?u=1715909&a=13187155&f=0
The pictures are in the recreation folder and the email is scott36079@yahoo.com

I paid 10k for it what is it worth?

[EricG]

Congrats on the new boat!! It's beautiful (of course, given the fact that mine is IDENTICAL - I may be slightly biased!!) http://www.donzi.net/ubb/biggrin.gif

Anyway, What RPM are you running at 58, and with what pitch prop?

Mine is a smallblock and I'm getting about 54, so realistically, that may be in the correct ball park for your boat? I know another Z21 owner here has a modified 350 in his (around 330 HP) and he was getting something like 58.5MPH with his...

Overall, although the early Z boats may not be the fastest boats on the water, the ride, build quality, and styling are all first class (just like the rest of the Donzi's!). Good luck with the new boat - and welcome to the board!!

EG

Oh yeah, as far as the price, most of the Z21's seem to be in the mid teens asking price (depending on where they are), so 10k for a big block sounds like a good deal to me!!

[This message has been edited by EricG (edited 06-06-2001).]

[RedDog]

Don't have help on speed, but that is a pretty boat! Congradulations
http://albums.photopoint.com/j/View?u=1715909&a=13187160&p=49944759&Sequence=0&res=high

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Reddog
mailto:tsfloyd@bigfoot.comtsfloyd@bigfoot.com</A>

[rulost2]

I am running about 3800 at 58mph. How would I check the pitch of the prop It is a 3 blade stainless.
The Numbers on my prop are Quicksilver 48 13706 A40 25P


MSM



[This message has been edited by rulost2 (edited 06-06-2001).]

[marcdups]

Rulost, I believe your tach must be on the wrong setting or on it&lt;s way out, check the settings first, sweet looking boat, speed sound,s resonable, good luck

Marc

north of the equator!!

[Donzitester]

do you know the ratio or your drive,
I dont think your speed is bad, short of major modifactions your pretty close to
Max speed for that set up, nice boat by the way

[wintersux]

You are over propped. I have the same setup in a 88 Z and I have a 23 mirage+ which will turn 4500 or a 22Bravo 1 which will turn 4600 loaded normally. I am running just over 60 with the Bravo1 and 63 or so with the mirage+. This is with 1/2tank fuel and no extra baggage in the boat. The Bravo 1 really is great thru the whole range of RPM's but you loose some top end. The cruise is efficient with the Bravo1 prop. How slow are you to plane? You need to try a new prop. I have been hearing great things about the new revolution 4 prop. Try to get a trial on a 22 or 23 pitch. Good Luck. This is a good looker with storage.

[BigGrizzly]

Prop is too big, use a 23,ot less.

Randy

[rulost2]

Thanks for the great response. I was thinking about a new prop. After looking and reading about them I like the Bravo, Mirage, and Revolution 4 (thanks wintersux). How the heck do you really know what to buy can a shop let me test a prop(kind of like home stereo equipment). Personally I like what I read about the Revolution 4. Does anyone know what the redline on my motor is?

BTW: I wanted to change to black or yellow rubrail. Were is the best place to get some replacement that looks decent and functions well?

[This message has been edited by rulost2 (edited 06-07-2001).]

[marcdups]

Rulost, I am not, I have a revolution 4, 21 pitch, only used once, makes the little 16 squirmy, but great hole shot and acceleration,would let you have it for 250$, no nicks or dings, basically brand new. You could have some cup added to it.
Marc

north of the equator, wishing it was south!

[rulost2]

Originally posted by marcdups:
Rulost, I am not, I have a revolution 4, 21 pitch, only used once, makes the little 16 squirmy, but great hole shot and acceleration,would let you have it for 250$, no nicks or dings, basically brand new. You could have some cup added to it.
Marc

north of the equator, wishing it was south!

I am very intrested. What does adding cup to it mean. Is that increaseing the pitch?

[marcdups]

what I would do is run the boat with it on and get specs, RPM's and speed and talk to a decent prop shop, I would recommend DAH pro pellers ,phone# 262 534 4440, they are excellent and warranty their work.
Let me know if you want the prop.
Marc

[wintersux]

Your top rpm should not exceed 4600rpm if you have the stock 454/330hp engine. The 21 will spin too many r's. The 22 bravo 1 prop on mine will turn 4600 with a light load. The 23 Mirage+ will turn 44 to 4500 with light load. If you are looking for top speed the Mirage+ will be the best all around prop. Have fun.

[BigGrizzly]

I had better luck with the Revolution 4 than the Marage pluss. Another great prop and the fastest on my boat now ( big engine hp) is the turbo. It is faster the the Marage pluss at the same rpms on my boat. My Criterion origionally had a 454/330 hp. Oh yea the bravo 1 was the worst on my boat, the plus and thr rev4 were both better.

Randy

[marcdups]

mirage + lab tested from merc over a grand, I bet your engine will turn it but you can get a std mirage+ for a lot less, the rev 4 is a great prop, if it didn't do what it does to the 16 I sure would keep it, tooo much lift.

Marc

[mikev]

There is a Donzi that looks exactly like yours in the boat storage place I keep mine nice looking lines.

[jdsdonzi]

Hey I think thats my old Donzi. I sold it to a guy in Al about three years ago I reconginized the trailer. Is the engine hatch one solid piece and the stripes our painted. Also does the flush system have a ball valve in place. I would know my old Z any where I have done some engine mods to it when I owned it. A Crane cam, forged pistons, trw timing chain however the bottom is still a two bolt. The best I ever got it was 65 on the speedo.