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toddturowski
10-09-2000, 08:35 PM
Has Anyone Experienced trying an extension plate on a 18 classic for more perormance???
Once again, I have a 1999 18 classic 350 Mag Efi 300hp, I run a 23 pitch Mirage plus. Or should I just try to adjust pitch or a maybe a four blade prop revolution prop, which someone amongst the registry suggested. Also, has anyone tried to put a chip in the 350 EFI. What afe the opinions, any at all whether on these particular options or any that will produce more speed. I am running consistantly 67-69 mph give or take on the Gaffrig II gauges at 54 rpm before the rev. liminator kicks in. It seems to that there is plenty more speed there when the liminator hits. thanks. -Todd

GeneD
10-10-2000, 08:33 AM
From what I am told by the Merc dudes, you are there with the chip. Don't screw with the chip!
Your revs seem a bit high, but not that bad. You gotta lose about 200 RPM's WOT.
You should start playing with props. There is a Bravo 4 blade that is pretty nice at 24 pitch. And there are plenty of others. Mirage has another at 25, that is what I am running.
But man, you are running very fast for a 350, EFI or no.
Be happy!
Now, what are you talking about in an extention plate? Do you mean an extention BOX? That is a racing item and it's going to cost you big dollars. It works, that's for sure. Most of the guys on the circuit use them, on Bravos of course.
And if your rev limiter is kicking in, you got to know that you are running too high an RPM. Got to cut it down. Not that it's going to get hurt mind you, but I can't see it doing any good.

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GeneD
007
Melbourne, Florida

[This message has been edited by GeneD (edited 10-10-2000).]

PaulO
10-10-2000, 09:11 AM
Todd,
You need more pitch or you need to change the ratio on that drive. That setup should have the 1:50 ratio. As is Gene, I am curious as to what extension plate you are referring to. Land and Sea makes a "stern jack" that (at least in my mind) the jury is still out on. Also, run that thing with a GPS. Although Gaffrig makes a good speedo, you are setting some kind of record at 69 mph with 300HP and if that's the case, I want to know how!!
PaulO

Forrest
10-10-2000, 09:13 AM
Is anyone running a four-blade prop on a Classic Donzi (except GEOO) with good results?

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Forrest

GeneD
10-10-2000, 10:00 AM
Well, Forrest, you can't really even include GEOO in on this since his 4 blade-er is a racing cleaver for surface drives only.
I had a 4 blade that I think I got from GEOO, and it had GREAT bow lift. But that was before my re-gearing so I don't know what it's full potential was. Fantastic mid-throttle acceleration.

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GeneD
007
Melbourne, Florida

RickSE
10-10-2000, 10:55 AM
I ran two Revolution-4 props on my boat this summer, a 21P and 19P. Going from a 19P Tempest to a 21P Revolution-4 I lost 800 RPM, and picked up about 2-3 MPH. The Revolution-4 has a lot of bite and minimal slip, my slip numbers were below 10%. It's a great prop but I think it's meant to run at a higher X dimension. I've been told that the 4-blade Bravo is also a great prop, and the advantage as Gene mentioned is that it comes in even pitch sizes. The 4-blade Bravo works really well on the newer hulls, but I'm not sure about the Classic hull, and unfortunately Donzi has no data irt. using 4-blade props on the Classic hull. The difficult part of the 4-blade is figuring out your RPM change. I expected the 4-blade to drop my RPM’s by 400 (19 to 21) and was surprised to see an 800-RPM drop. Mercury does state though that 1” of pitch can change engine speed anywhere from 200-400 RPM’s, depending on the prop family. I guess I found the extreme case!

I'd think you might want to try a 25P Mirage+ or a 24P Bravo. Either one would probably drop your engine speed by 400 RPM's and maybe? give you more speed.

Also I agree with Gene, 4-blades have great mid-range and acceleration. I'd also like to add that they hold better in turns than a 3-blade. Revolution-4 adds stern lift though instead of bow lift.

[This message has been edited by RickS (edited 10-10-2000).]

Craig
10-10-2000, 06:45 PM
To Paul O (a few replies back),
Why is 69 mph with 300hp setting a speed record? I understand questioning the speedos compared to a GPS, but the Donzi 18 Classic test drive video shows, I think a 97 or 98, with that same set up, going 73 to 75 at WOT. Is that questionable? I figured with fuel injection and the Bravo, etc. it probably did go that fast. I'm sure it said it had a 300hp 350. Should check.
Craig

CDMA
10-10-2000, 07:37 PM
Would somone who says they are going 68 or 69 in a new 18 please take their x dimension and compare it to Paul O's. Just for my peace of mind. Oh and preferably somone who has confidence in their numbers and can give an accurate speed.

Chris

GEOO
10-10-2000, 08:42 PM
Paul, Chris, I drove in Barry's 1998 or 99 18' with a 250hp Bravo package; with two of us in the boat it radared around 65mph; 68 to 70 seams possible with a 300hp. The 300hp is at the prop, shaft hp is closer to 320-330hp. GEOO

CDMA
10-10-2000, 08:58 PM
It has to be the x dimension

Chris

Emmo
10-10-2000, 09:42 PM
I think the MadPoodle uses a 4 blade Ultra on the Tin Cup. Is that correct Mr. Poodle?

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Emmo mailto:emmette@emmette.comemmette@emmette.com</A>

RickSE
10-10-2000, 10:28 PM
I have three things to add.

1) Chris, "X" dimension on a new 18 Classic is 14 1/2 inches.

2) toddturowski, Looks like Donzi delivers most new 300 MAG MPI 18's with a 25P Mirage+ prop. Alpha-1 comes with 1.62 ratio and Bravo-1 with 1.65 ratio. Both are rated at 4600-5000 RPM's. You may not gain much speed from a 25P but you'll be helping your motor survive by lowering the WOT RPM's.

3)The following data is directly from Donzi.

300 HP 350 MAG MPI
Bravo-1 Drive w/1.65 ratio
25P Mirage Prop
Full fuel tank
Probably one occupant

68.4 MPH @ 5040 RPM and drive 90% up.

BigGrizzly
10-10-2000, 11:30 PM
The tolorance on merc props is 1/2i ch in either direction. This means that it is possible ti get two of the same props (ie. mirage plus) at 23pitch one willbe 22.5 and the other a t 23.5. If a boat uses one or the other could be the difference. tom has a 23 marage plus on tomahawk, and I have one on my Criterion. On my gps his prop is faster on my boat, by 3 MPH then mine is. This is true that his prop pulls 200 rpms more than mine. Lab finish eliminates part of this problem, but is expensive.
Maybe this is the difference in speed, or is there a hook in one boat and not the other. The x dimention isn't the only factor. Better look closer.
Todd if you are bouncing off the revlimiter, better put on a bigger pitch prop. This is not a soft touch limiter and will eventually cause some large problems. You can't change the chip for two reasions 1) you don't which ecu you have(Merc says there are several) 2) where are you going to find the chip. the ecu on the merc is really low level no O2 sensor etc just a knock sensor.
unless my nath is wrong--a 1.65 with a 25 inch prop is about the same as a 1.5 with a 23 pitch .
Also the new Bravo has a low water pickup- look at Mark's new 18 clasic.

[This message has been edited by BigGrizzly (edited 10-10-2000).]

Barry Phillips
10-11-2000, 07:47 AM
I saw that Classic 18 test on Power
Boat TV, it was 97 MPI Bravo setup.
They did not GPS or radar the boat, it ran
a speedo indicated 75mph. I think this is
optimistic, but I do believe 70 is possible
I test drove the same boat before I
purchased mine and recall seeing 67
on the speedo the lake was bumpy, could
not trim the boat out. I spoke with a guy
on this site, Bill who was wondering
about my gear ratio. He has a 97 18
running a 350mag Brovo 1 setup he
told me he was getting 70.5 mph on
GPS with a 21" Vengeance, I run a
a 23" Vengeance, and Geoo radared
my boat at 65 MPH with 2 of us aboard
with about 30gallons of fuel. In optimal
cool conditons with the right water I
have seen 67 in my boat. A guy I ran in
a 454 Checkmate told me I running 68
on his speedo. I called the factory when
I purchased the boat in 97 they had no
test results on a Bravo 250 but thier
test on the 350 Mag yielded 68.5 mph.
I agree that 5400rpm is to high, your boat
should tack out between 5000 &
5200 rpm. Before you go buying new a
prop have the tack checked, try to barrow
a shop tack and compare them. My tack
was off by 400 rpm. The VDOs have a
calebration set screw on the back, a
pain to ajust, very sensitive. I think your
performace is quite good , need to find
true RPM

Good Luck
SO-SLO

PaulO
10-11-2000, 09:44 AM
When I repowered my '73 with the Merc/Alpha setup, I got the location of the drive (x-dimension) by measuring Alex Seefried's 18. Although I am certain I got a match, I am not sure where that 14 1/2" that RickS quotes is measured from. Does anyone know?
I think we need a Donzi Classic radar shootout. Let's put this stuff to rest.
PaulO

RickSE
10-11-2000, 11:57 AM
I believe the 14 1/2" is from the low point on the hull to the centerline of the drive input shaft. I did a quick measurement on my 96 and it seemed correct. I got the number from a process engineer at Donzi. I wrote it down on a peice of paper though and haven't been able to find it again but I'm pretty sure it was 14 1/2". I'll look again for the paper tonight.

RickR
10-11-2000, 07:32 PM
The true X Dimension is measured from the driveshaft centerline to a horizantal line above the keel that is the width of the anti-cavitation plate.

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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

GEOO
10-11-2000, 07:41 PM
Paul, Spring 2001,(with FastEddie's approval) I'll bring a radar gun to Lake George's Spring outing. Hopefully our boats will be running. Every one can safely check their speed against the gun. We can write down the results with; boat size, drive, gear, hp, prop etc. for Scot to have in the tech section. That gives us 8 months!!! GEoo

RickSE
10-11-2000, 09:07 PM
I found the paper. The number I was given for the "X" dimension is 14 1/2".

PaulO
10-12-2000, 09:51 AM
Geoo,
Excellent idea. Barring any unforeseen difficulties, I will be there with a running boat.

Rick,
Thanks for checking on the x-dimension. I will see if I can measure mine accurately somehow.
PaulO

GeneD
10-12-2000, 10:06 AM
Rick,
Draw a picture.
I'm having a rough time following that.


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GeneD
007
Melbourne, Florida

GEOO
10-12-2000, 02:03 PM
I believe the X dim is measured from the center of the output shaft to the bottom of the boat,(where the transom and the bottom meet). GEOO

RickR
10-13-2000, 02:17 PM
GeneD
I got this from a Merc rep,

Engineering Bulliten No 146
6/23/92
To: All Plants
Subject: "X" Dimension-Merc Outdrives

Instructions:
Starting immediately the "X" Dimension will be determined when installing Merc Outdrives as follows:
1. Determine the width of the anti-ventilation plate (7" width current Alpha and Bravo Models)
2. Scribe a line on the transom perpendicular to the line as follows:

[Diagram shows True Bottom above the actual bottom.]

3. This point is the true bottom of boat and is the point from which that measurement will be taken for an "X" Dimension refered to on the Mercruiser installation manual 's "X" Dimension chart as even with the boat's bottom.
4. This point is the intersection of the center line and the line equal to the width of the Mercruiser AV plate as it coinsides with the boats bottom.

[Example; on my 18 Classic the true bottom is a horizontal line 5/8" above the keel. The width of the line equals the width of my OMC King Cobra AV plate (6")

A picture is worth a thousand words. If anyone still wants a diagram email me.



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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

GEOO
10-13-2000, 02:35 PM
Rick, HUH!!!! You lost me??? GEoo

RickR
10-13-2000, 07:36 PM
Sorry, kind of hard to describe
Does this help?
http://albums.photopoint.com/j/View?u=1261326&a=9330578&p=30606380&Sequence=0&res=high


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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>



[This message has been edited by RickR (edited 10-13-2000).]

GEOO
10-13-2000, 07:56 PM
The light went on!!! Thanks. GEoo

Craig
10-14-2000, 03:21 AM
I needed that diagram for my light to come on too....but then I'm only burning a 40 watt bulb.

GeneD
10-15-2000, 09:27 AM
I'm limiting myself to one post this weekend. This is it...HA! Yeah right!
Anyway, yesterday I measured my "X" dimension from the prop shaft, to the bottom of the keel.
6.5 inches.
I knew that was wrong.
The pic clears up a little bit of confusion. But for me, some still remains.
Why bother even measuring the width of the cavitation plate, when you don't use it.
Unless, you are saying to take the width of the cavitation plate, and transfer that width to the transom, and measure a distance say 7" across the keel area there. That determines the "True Bottom"?
I'll try it and get back to you all.
But...what if the width of the CP, transfered over to the hull, is not at the same height of the CP? Will it be at the same height? Higher or lower?
This is a good excercise, and we need to figure it out exactly. The sketch was good, but the whole explaination left me with questions.


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GeneD
007
Melbourne, Florida

[This message has been edited by GeneD (edited 10-15-2000).]

RickR
10-17-2000, 07:10 PM
AV Plate 101

After you find the true bottom scribe a line on the transom from the bottom of the anti-ventilation plate (at neutral trim)
The distance between the two is + or - the standard X Dimension.

The standard mounting for a medium performance sterndrive is for the bottom of the AV plate (at neutral trim) to be on a horizontal plane with the TRUE BOTTOM. Increased X-Dimension on Hi-Perf Stern Drives (V Bottoms) is usually 1" to 3"

An AV plate is used to prevent prop ventilation at slow speeds especially when planing off.

If it is mounted too low you'll have too much drag and handeling problems when using positive trim.

If mounted too high you ventilate the prop and cause cavitation.

A good way to check real world application is to bring your boat up to cruising speed and neutral trim. Work your way to the back of the boat being very careful you don't fall off and become hamburger http://www.donzi.net/ubb/eek.gif. The top of your AV plate should not have any water running over it.

A greater X Dimension will give you less gearcase drag and with the correct prop better performance. Some Hi-Perf Bass boats have a transom jack to raise and lower the outboard so they can change the X-Dimension while under way (same unit is used on Flats Boats to lessen draft). Many perform best with 2/3 or less prop in the water, similar to the way the Black Hawk and Arneson runs.

Sometimes a high X Dimension will cause tremendous steering torque because the prop acts as a "paddle wheel" pulling the drive laterally. A Cleaver type prop will alleviate some of the torque from a surfacing prop.




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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>



[This message has been edited by RickR (edited 10-17-2000).]

GeneD
10-24-2000, 10:42 AM
Okay,
Would you believe my X dimension is:
Ready?
8 inches.
Now this number is from the line between the true bottom, and the direct translation of the cavitation plate to the transom - to the prop shaft.
This still doesn't sound right.
But I will double check the dimensions again.


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GeneD
007
Melbourne, Florida

boxy
10-24-2000, 12:09 PM
GeneD, that makes sense, given the shape of your hull at the stern. You must have to travel a fair way up till your hull is 8 inches across, where as a newer, rounded hull would be 8 inches wide closer to the keel bottom, therefore giving a greater X dimension number.

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boxy
mailto:sboxma@sprint.casboxma@sprint.ca</A>
Smuggler's Cove
Ontario

RickR
10-24-2000, 01:47 PM
GeneD
NOT the prop shaft!
The DRIVESHAFT (center of the gimball bearing!)

But that X Dimension # is only used to drill the transom holes to mount the gimball bracket.

To check to see if your X Dimension variance is high or low, check the distance between the true bottom and where your AV plate lines up with the hull (when in neutral trim)


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RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

GeneD
10-25-2000, 09:38 AM
Okay,
From the "true bottom", to the driveshaft?
Not a problem.
See how confused I was?
X dimension has always had me scratching me head.
But wait...
What difference does that make?
That would mean that my X dimension would be the same for the Alpha One, and the Alpha SS since the gimble/transom plate/motor height remained the same. All I did was replace the drive and supposedly reduced my X-dimension that way!
What do you call it when your prop shaft has been raised? Does it matter how high the motor is? The motor could be a foot higher, and the drive a foot lower, did the X-dimension change?
Isn't the X-dimension a function of where the propeller is in relation to the true bottom of the boat?
Now I'm REALLY confused!

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GeneD
007
Melbourne, Florida

Len
10-25-2000, 11:01 AM
Gene, I think you have a point here. The SS drive would place the cav plate in the same spot but the depth of the prop would change. Thus the positive change in the X-dimension without actually raising the eingine on mounts, gimbal housing etc, etc. Then there is the IMCO Bravo drives. They have the cav plate in same place I believe but have VERY little of the rest below. Again, this is raising the X-dimension but not the plate. I thought I understood this relationship until your last post. Now I'm confused as well. Oh well, who cares, I still don't have a Donzi to worry about that measurement on... http://www.donzi.net/ubb/frown.gif

PaulO
10-26-2000, 11:13 AM
How can a drive like the SS have the anti-ventilation plate in the same location but have the prop higher? The prop diameter would not allow it?
PaulO

GeneD
10-26-2000, 11:31 AM
Ahhhhhhh,
Very good question!
YOu may not know it, but you can not put a torque tab on the SS. There is no room for it. There is a place for it, but it is just a flat zinc plate. The tab would hit the prop.
Now, the cav plate 'might' be a bit higher, I am not going to say this is a certainty. From what I remember when I placed the two drive together, they were practically the same. Because I thought we could replace the upper with an Alpha One upper, but the two were very different, or let me say that another way, they were slightly different. And I don't really remember how. I think I have some pics somewhere, let me consult them and get back to you.

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GeneD
007
Melbourne, Florida