View Full Version : zx 28 383s??

01-09-2013, 04:19 PM
i have a 03 zx 28 with 350 mags ,and i am wanting to do twin 383s and would like some help with props,and has anyone done this and what speeds did they get?? i would like to get 90 if possible

01-09-2013, 04:21 PM
any help would be nice!

01-09-2013, 04:37 PM
Can I ask what you're getting now out of your 350 mags? (<scratching head> Trying to recall what some others have gotten and 71-74 comes to mind. If so, 90 feels like it's a good bit away without doing some mods to the typical 383s. But I don't claim to know, just figured I'd offer up my best SWAG until the folks who know show up... :) )

01-09-2013, 04:55 PM
about 68-70 with stock 300hp each, iam talking to a builder that said he can build a motor that would have about 500-540hp that all being said is 1100hp but i dont know if this will get me to high 80s? also the lost wight with alum heads and exhaust ,i hope to reach some what of that but i havnt been in the boating performance world

01-09-2013, 04:59 PM
Well, THAT sounds fun. :) Nothing like spending other people's money, I expect you'll hear a whole list of ideas shortly...

01-09-2013, 08:32 PM
1100 hp would get you into the 80s. 1100 reliable hp out of 383s is a different story.:popcorn:

01-09-2013, 09:25 PM
High compression a real aggressive cam shaft and dry exhaust. I dont think they will hold up long. Why not go the whipple route? Little less horsepower lot more reliability.

01-09-2013, 10:40 PM
i would have to beef up the bottom end to support a chager and then come up with 14k more,this build will cost me 19-20k .i have a marage 23 on there now builder said i can use the same prop and get aroound 84 at 5600rpm but i think ill have to change prop buthas anyone done this to a 03 donzi 28zx twin small b?is anyone out there ,i hate to do this and get to a big 75mph that would suck

01-09-2013, 11:28 PM
Mr X had a scorpion 28 and was running 80 with mirage plus props i think. There is a 28 on lake Winnie running over 100 but not sure of his set up. You will get the speed just expect a short life out of the engines. Cheap fast reliable. Pick two. It will be cheaper and more reliable to super charge. To ge that kind of horsepower out of a small block you are gonna have to run a dry exhaust so add that into the price. Not to mention you won't be running pump gas on that kind of set up. What about Ls motors ?

01-10-2013, 02:57 AM
Andre did exactly what your looking to do

boat runs real real well

maybe he'll chime in at some point

01-10-2013, 08:47 AM
this build will cost abt 20 k at the end , two chargers alone is 14k in the box then build the motors will be 5 k each thats 24k not installed are no extras so i think that would be total 30 to 35k .the builder said i can run pump gas in this app .i would like to talk to the guy that has done this if anyone knows him?

01-10-2013, 09:20 AM
There was one guy that had whipples on his scorpion that claimed 100+ @ 650hp.

My opinion is going naturally aspirated 383 in the 500+ range you might have issues with exhaust / reversion. You'll need a pretty good cam and the exhaust is really close to the water and somewhat different in clearance/height than most other boats. At least keep it in mind. What exhaust did you go with?

Also, the Bravo 1's are probably going to need beefing up or replacing with XR units.

The hull has proven to take power well so getting to 90 is very doable.

01-10-2013, 09:35 AM
i havent got the exhaust yet looking into that also i have bravo 1zx? i thought these where the good ones that is good for 500 hp ? i am new in the boating preformance , what upgrades will i need to do to the bravos?

01-10-2013, 10:25 AM
If it is stock you should have Bravo 1 drives.

Merc also made Bravo 1 XZ for a while, but they are pretty rare. IIRC the XZ had an XR lower with stock Bravo 1 upper.

Merc also makes:

Bravo X, which is a slightly beefed up Bravo 1. (not worth the upgrade to Bravo X)
Bravo XR, which is a Bravo 1 with straight cut gears.

You can get just the XR gears and go for a rebuild with them on your drives. Another option is to stick with the Bravo 1's, baby them for a while, then rebuild when they let go but you run the risk of destroying a case.

another option is an aftermarket setup like imco.

The drive is also a major consideration in the engine build because higher RPM seems to kill Bravos.

01-10-2013, 10:35 AM
Oh... and for exhaust:

The 28 ZX uses the tallest Merc riser. This is not "standard", it's a 6 inch taller version.

So if you are internet shopping manifolds and risers you have to keep that in mind. The 6" taller risers from imco are over $1100 for the pair. http://www.imcomarine.com/cal_store/exhaust-systems/merc-replacement-risers/mercruiser-replacement-riser-6-taller-a.html

Stainless marine, CMI, etc can all do the same thing. So far I have not found an aluminum riser that is 6" tall on any of the cheaper systems like GLM.

01-10-2013, 10:35 AM
As long as we're spending other people's money, what about re-rigging the boat for a single monster BBC? Obviously a lot of cost and time involved with filling the transom, mounting a new drive, getting the engine compartment reconfigured, new controls, etc. Not outside the realm of possible though.

The old motors & drives & rigging could certainly be sold to recoup some of the cost. And a single blown big-inch 900+hp BBC would arguably be more cost effective and reliable than small blocks running right on the ragged edge of disaster. Only one outdrive, maybe an XR or something more exotic, and one prop to figure out. Plus whatever x-dimension you want to run. Less drag in the water for sure... Lots of BBC parts (exhaust, blowers, etc) and even complete engines on OSO and other websites, and lots of engine builders out there capable of building something with the power you need. There are way less small block marine performance parts available because most folks aren't using SBCs for high-hp marine applications. There is probably a reason for that...

LastRealTexan is running big numbers with his 27 with a single blown BBC so it is certainly possible. Plus it's cool as hell to be able to run that fast on a single mill.

At the end of the day I think that is more realistic for $25k than building two small blocks that will be living on borrowed time.

Just for fun I figured out the cost of converting my 21 SBC / Alpha to 450hp BBC / Bravo using new parts. Once I hit $20k I put the crack pipe away and resigned myself to having a slow boat for now. I am definitely not the voice of experience here, but there are other guys that are and will hopefully steer you in the right direction.

01-10-2013, 10:39 AM
+1 on that. In addition to the reduced drag and increased efficiency of a single, I bet that saving 800-900 lbs would change a lot.

01-10-2013, 10:54 AM
dollar for dollar / speed to speed the single vs. twins tends to be a wash.

When they were new you could get a 27/28 ZX with either twins or a single HP500 for the same price. Stock they go the same speed but the HP is harder on its drive than the stock small blocks are in theirs. The maintenance on twins is higher per year on twins but after a few seasons you have to pull the 500 for a top end rebuild as well as a possible drive refresh.

To do a big power single and compare it in a fair way to a twin engine setup you really have to add in the cost of a drive better than an XR (either NXT or #6), along with the transom assembly, etc. Comparing a big single with an XR is like comparing the built small blocks with stock Bravo 1's in reliability.

There is a reason why the guys running big power singles have seen the wrong end of the tow rope.

01-10-2013, 09:34 PM
Andre did exactly what your looking to do

boat runs real real well

maybe he'll chime in at some point

I'm pretty confident Andre wont share! He likes to be in sleeper mode. But he sho is fast and solid wit the 80's, 90's are in reach if he hasnt already been in that range yet.

While the speed is kool, I really enjoy turnin the keys and hittin the sticks and be dependable and peak out in the low 70's. wow, that sounded old.


01-10-2013, 10:07 PM
thats one good thing abougt stock. but i want to go faster !and prob next year ill want that 100mph but for now i hope this works,i have told the builder to go ahead so if anyone has any good info to pass on please fill free

01-10-2013, 10:19 PM
Good deal, making a decision is half the battle. Start hanging some pictures on here!

I would bet a case of beer that the only way to get that hull to 100mph with SBC/Bravos is to drop it out of a plane, so build that sucker and take my beer!

01-10-2013, 10:20 PM
Oh and don't get me wrong, I hope u hit the century mark, I'm all about supportin my Donzi Brethren! Good luck and keep us posted.


01-10-2013, 10:29 PM
yea i wouldnt put any more money in this boat than what iam doing this year ,but someone said a guy is getting 100mph out of his same as me but charged so i do have a chance with this boat but ill sale befor i go that far,i really like the sound of the guy on the video on here i think he has 2000 28 zx and his gf is starting the boat sounds really good

01-10-2013, 10:40 PM
this i whati hope it sounds like its not always about speed,,, http://www.youtube.com/watch?v=4yK_o7GSd-8 (http://www.youtube.com/watch?v=4yK_o7GSd-8)

01-10-2013, 11:13 PM
hmmm, dont know that video. There was a 28ZX (red faded to pink w/High Roller graphics) out east that was on ebay for a while that claimed he was over a hundred on GPS. not sure if he put BBC's in it or if they were beefy SBC's. Where do you boat at? would love to see her run when she's done

01-11-2013, 10:02 AM
hmmm, dont know that video. There was a 28ZX (red faded to pink w/High Roller graphics) out east that was on ebay for a while that claimed he was over a hundred on GPS. not sure if he put BBC's in it or if they were beefy SBC's. Where do you boat at? would love to see her run when she's done

The red fade one is the one I mentioned earlier. 377 Scorpions running Whipples in double overdrive.

Here's the link: http://www.donzi.net/forums/showthread.php?67653-Donzi-2001-28ZX-Supercharged

01-11-2013, 10:36 AM
Didn't Trueser have a similar setup? I thought he was close to 80 stock.

01-11-2013, 10:49 AM
Yep, thats the red one i was thinking of, thanx.

Trueser I think was peakin out at like 81.8 or 82, somethin like that. and yes, he's a stock Scorpion boat (377hp each side).

01-11-2013, 12:48 PM
I was poking around old posts and found where Dr. Dan referenced the whippled scorp boat as being 105 MPH so I think it's safe to call the speed confirmed.

It also leads to a number. 100+ with twins in a 28 means you are looking at 650 HP small blocks. There might be more speed in there with props / shorties though.

01-11-2013, 03:10 PM
is there any difference on a twin 28 zx350 mag and a scorpion zx28 other than motors? the twin 350 mags are 300 hp each and scorp s is 377 each right?the 300 hp is abt 70 mph,and the 377hp is abt 81mph ,so 11mph for 77hp?? thats pretty good if thats how the numbers are so i think by my math ever 10 hp you get 1mph so if i add 225 hp that should add 22.5 mph . - slip 3% so add 15.75mph to my total now70mph = 85.75 ..?

01-12-2013, 12:35 AM
dang my math scared everone ?hahah

01-12-2013, 08:24 AM
so 11mph for 77hp?? ..?

154hp...gotta times it times 2, twins remember?!?!?!?!?

The Scorpion boats sometimes got a McLoed interior and also got the Scorpion script on the interior,deck and sides. the hull is still the same. also, not sure what the torque difference is between the 350mags and the Scorpions. One other thing that Trueser did to his Scorp is he gutted out the exhaust. Don't know if it helped much, but it definitely is louder:cool::biggrin:


01-12-2013, 01:36 PM
Agree with Tom on going with total HP, though I followed it (you can do the math per motor or with both added together) until it got up to the "slip" and "3%" and such? What sort of slip? Why 3%? There's prop slip built into the 70 you get now and the 80 that others have gotten. And were you talking about adding 225 per side, or 112.5 x 2 in this example?

Last, bigger picture, I don't think it's linear...as you climb, each new MPH should take more HP than the last. How far from linear it is I don't know, but I'd think you'd be more likely to make a goal by interpolating down from an existing setup than extrapolating up.


01-13-2013, 09:07 PM
yep 200 to 225 per side putting me at 500 to 525 per side tolal 1000 to 1050 total ,now the project has began .next will be props. 23 marage now

01-14-2013, 11:43 AM
The 377 scorps are 350 HP at the prop. They sold them in towsports edition too which are rated at 377 HP because they go by crankshaft power (inboard).

So they are 50HP more than the 350's and 30 more than the standard 377 / 6.2's.

The other difference on the scorp boats is they got labbed props. 1.5 drives spinning labbed 25" Mirage +. The labbed props should be worth a good 3-5 mph so that's where some of it comes from.