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Selecting an engine, transmission with the proper gear ratio and sizing the propeller for your custom built inboard can be a
daunting task if this is your first inboard installation. To help you sort it all out, we've listed specs and pricing
for inline, down angle and v-drive marine transmissions as well as base marine engine and turnkey engine packages from several
suppliers. We've also included a gearing and propeller calculator and links to articles describing how to drill the
propeller shaft hole.
Sections
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Marine Transmissions
- Co-axial (inline), Down-Angle and V-Drive models suitable for light pleasure craft use are listed.
- In the Installation Drawing column, we've included links to Installation Drawings to help
visualize the various engine/transmission combinations. 10°, 12° and 15° propshaft angles are shown.
- HP and RPM are Max Input ratings. (G)=Gasoline & (D)=Diesel. Click the hyperlinks to see the
transmission specifications.
- Pricing is for informational puposes only. Prices highlighted in red indicate lowest cost supplier.
- We've recently added Velvet Drive and Cyborg Performance transmissions.
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| Performance Transmissions |
| Manufacturer | Model | Mount
Type |
Angle | Ratio
Weight |
Input HP @ RPM
G=Gas D=Diesel |
Price | Specs |
Installation
Drawing |
| Velvet Drive |
72L
Liberty Series
High Performance
Model 3007
Aluminum Case | Direct |
Inline | 1:1
76 lbs. |
700 ft.lb (G)
600 ft.lb(D)
Max RPM 6000 |
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Specs |
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72L-X
Liberty Series
High Performance
Model 3011
Aluminum Case | Direct |
Inline | 1:1
76 lbs. |
860 ft.lb (G)
700 ft.lb(D)
Max RPM 6000 |
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Specs |
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72L-H
Liberty Series
High Performance
Model 3010
Aluminum Case
Dry Sump | Direct |
Inline | 1:1
82 lbs. |
Max 2500 ft.lb
Max RPM 6500 |
|
Specs |
Drawing
Slow or fails to load |
72L-HP
Liberty Series
High Performance
Model 3009
Aluminum Case
Dry Sump | Direct |
Inline | 1:1
86 lbs. |
Max 2500 ft.lb
Max RPM 6500 |
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Specs |
Drawing
Slow or fails to load |
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| Performance Transmissions |
| Manufacturer |
Model |
Mount
Type |
Ratio |
Specs |
Price |
Supplier |
| Cyborg |
900 |
Direct |
1:1 |
|
$3399 |
BAM Cyborg Marine Transmissions |
| 1350 Dry Sump |
Direct |
1:1 |
1350 HP, 1600 ft.lb |
$3995 |
BAM Cyborg Mrine Transmissions |
| 1500 Dry Sump |
Direct |
1:1 |
1500 HP, 1770 ft.lb |
$4175 |
BAM Cyborg Marine Transmissions |
| Super Cyborg Dry Sump |
Direct |
1:1 |
2000 ft.lb |
$5299 |
BAM Cyborg Marine Transmissions |
| Velvet Drive |
Mercury Quicksilver Stock and NEW Terminator series
modified Velvet Drive Transmissions.
Customer must supply 71 & 72 Series Transmission.
Stock 71C & 72C
Terminator 750
Terminator 950
Terminator 1200
Terminator 1350
Terminator 1500 |
500 ft.lb
750 ft.lb
950 ft.lb
1200 ft.lb
1350 ft.lb
1500 ft.lb |
$1050
$1300
$1700
$2300
$2900
CALL |
sterndriveconnections.com Orillia, Ontario, Canada
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| Cyborg, ZF & Velvet Drive performance transmissions |
BAM Cyborg Transmissions |
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Supplier Links
See the links below for more models, details and pricing :
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Installation heights
Installation heights from top of engine stringer
Dimensions taken from Installation Drawings @ 15° propeller shaft angle |
| | Velvet Drive |
|---|
| Riser Height | ZF 63A
Down Angle |
Liberty Series
Down Angle |
71C
Inline | 72C
Inline |
|---|
| Standard | 25-3/16 | 24-1/8 | 25-5/16 | 24-9/16 |
|---|
| 3" | 26-15/16 | 25-3/4 | 26-3/16 | 25-7/16 |
|---|
| 6" | 29-15/16 | 28-3/4 | 27-3/4 | 28-5/16 |
|---|
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Overall Keel to Riser heights (Standard Riser)
Dimensions taken from Installation Drawings @ 15° propeller shaft angle |
| Model | Riser to Stringer Top | Keel to Stringer Top |
Overall Height | Overall Length | Notes |
| ZF 63 A |
25-3/16 | 6-9/16 |
31-3/4 | 42-1/16 | |
| Liberty A |
24-1/8 | 7-3/4 |
31-7/8 | 40-1/2 | |
| 71C |
25-5/16 | 7-5/8 |
32-15/16 | 42-1/2 | |
| 72C |
24-9/16 | 8-3/8 |
32-15/16 | 43-7/16 | |
350 MAG MPI with 71C |
| | | |
Drawing |
| 350 MAG MPI with 72C |
| | | |
Drawing |
| 350 MAG MPI with 5000A |
| | | |
Drawing |
| 350 MAG MPI with ZF63A |
| | | |
Drawing |
| 350 MAG Tow Sports with 71C |
26-1/2 | 7-1/4 |
33-3/4 | 42-11/16 |
Drawing |
-->
Specs based on MerCruiser MIE 5.7 carbed version unless noted otherwise.
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Turnkey engines and packages
In the following tables, we've selected several Turknkey and Partial engines from several manufacturers for comparison
purposes. Pricing is for informational puposes only.
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| Partial Engines |
| Description | Induction | Specs | Model # | Price | Supplier
Link |
Remarks |
4.3L Vortec Marine Engine
SILVER Package
(1967-2011 Replacement) |
Carb |
225 HP @ 4800 |
4300-SS |
$3599 |
michiganmotorz |
Requires exhaust manifolds and related parts. |
| 5.7 LH GM VORTEC POWER PAC |
Carb |
300 HP @ 5000 |
Item # 1671 |
$4060 |
skidim |
Base engine, fuel and ignition systems, 8" harmonic balancer. |
5.7L Vortec Power Pack Special
with Merc Exhaust |
Carb |
325 HP |
PPS350E |
$4295 |
dougrussell |
Includes exhaust manifolds and risers for Mercruiser application. |
| GM 355 Dressed Marine Engine |
Carb |
365 HP / 390 FT LBS |
mbp3550ctc-marine |
$4995 |
blueprintengines |
Requires exhaust manifolds and related parts.
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5.7L Vortec Marine Engine
GOLD Package
(1967-2011 Replacement) |
Carb |
315 HP @ 5000 |
5700-IGOLD |
$5099 |
michiganmotorz |
Includes exhaust manifolds, risers, gaskets and bolts. |
5.7L MPI Vortec
CRUSADER Power-Pack SD |
MPFI |
330 HP @ 5000 |
5700-CrusaderSD |
$7499 |
michiganmotorz |
Plus shipping and taxes |
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GM Base Engines
May require intake manifold, thermostat, carburetor, flame arrester, fuel pump, ignition system,
raw water pump, exhaust manifolds |
| Description | Specs | Model # |
Price | Supplier
Link | Remarks |
| 3.0L POWER PACK SPECIAL |
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$3599 |
dougrussell |
Includes carb, flywheel and distributor. |
4.3L Vortec Base Marine Engine
(1996-2011 Replacement) |
225 hp @ 4800
268 LB*FT @ 4000 |
4300-BaseV |
$2449 |
michiganmotorz |
Engine block, 4.3L Vortec cylinder heads, valve covers, marine oil pan, circulation pump, harmonic balancer, roller cam & roller lifters, roller rockers. |
5.7L (350ci) Vortec Base Marine Engine
(1996-2011 Replacement) |
295 hp @ 5000
355 LB*FT @ 3600 |
5700-BaseV |
$2699 |
michiganmotorz |
Engine block, 5.7L Vortec cylinder heads, center-bolt valve covers, 5-quart marine oil pan, circulation pump, harmonic balancer, roller cam & roller lifters. |
| Vortec 5700 (5.7L) Base Marine Engine |
295 hp @ 5000
355 LB*FT @ 3600 |
Item # 1730 |
$3440 |
skidim.com |
Engine block, cylinder heads, valve covers, aluminum 4V intake manifold with brass water jackets, circulation pump, oil pan, flywheel, harmonic balancer |
| Hardin Marine New GM Marine Base Engines |
hardin-marine.com
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H&H Marine Engine Service Ltd.
Vancouver, BC, Canada
manifoldwarehouse.com |
Quest 3.0L GM Base $2,545.00 US
Quest 4.3L GM Base $3,672.00 US
Quest 5.7L GM Base $3951.00 USD $
CAD
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| BluePrint Engines (Marine Performance engines) Kearney, NE |
blueprintengines.com |
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| Marine Conversion Parts |
| Part Description |
Part # |
Price |
Supplier |
| 5.7L (350 ci) GM Delco Voyager EST Marine Electronic Distributor Kit (U.S Coast Guard Approved) |
GM Marine # 107-C |
$349.00 |
michiganmotorz.com
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| Mounting Kit - Velvet Drive 71C & 72C transmission (mounts, oil cooler, hoses and plumbing fittings) |
Barr Marine # 494101 |
$346.00 |
michiganmotorz.com
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Calculators
Shaft HP VS Speed : Gearing and propeller sizing calculator
Revised 07-FEB-2015
The SHP VS Speed Calculator determines optimum propeller diameter from HP and RPM using Crouch's Diameter-HP-RPM Formula.
It will calculate attainable speed and propeller sizing for up to two engines with four transmission ratios per engine.
We've included an algorithm to calculate and plot minimum, average and maximum pitch ratio curves. If the pitch ratio falls outside
these curves, the shaft speed is unsuited to the boat and must be changed using either a different reduction gear and/or an
engine of a different rated RPM.
We've run our calculator with the following data :
- Engine Option 1 : 185 HP @ 4000 RPM, Engine Option 2 : 325 HP @ 5200 RPM
- Displacement : 3200 lbs
- Transmission Ratio : 0.88:1, 1:1, 1.25:1, 1.5:1
- Required speed : 45 MPH
The spreadsheet is still under development, so if you find any glitches or have any questions about the spreadsheet, please send us an
email.
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PropCalcPlus : Gearing and propeller sizing calculator
Revised 15-APR-2013
Your transmission vendor should be able to suggest appropriate gearing and propeller sizing for your application. You can also
do the calculations yourself with one of the many online propeller calculators.
Here's a quick explanation on how to select the correct propeller for your boat :
"The propeller is selected to load the engine and still permit full power to be developed. The propeller must allow the engine to come up to rated speed. It is incorrect to use a propeller so large that the engine will be overloaded, because this will not only reduce the power delivered to the propeller shaft, but more importantly it will cause abnormally high loading within the engine. This can result in destructive pressures and temperatures which cause premature bearing and valve failure. For ski towing, it is best to select a propeller which will permit the engine to maintain rated RPM when under load."
Source : Velvet Drive Installation Manual
Our downloadable Excel spreadsheet can help you select the proper gear ratio and propeller for your application. We've
expanded Surfbaud's Freeware Propeller Calculator for Excel to include a Theoretical Speed Table and
Diameter-HP-RPM calculations.
You'll need to input several parameters into the spreadsheet, namely engine horsepower, Max RPM, gearbox ratio, displacement of
vessel, waterline length and required maximum speed in knots :
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Diameter-HP-RPM Formula
This Excel spreadsheet uses the Diameter-HP-RPM Formula from Dave Gerr's Propeller Handbook to
find optimum propeller diameter from HP and RPM.
Click the image to the right for a PDF preview, or download the spreadsheet to do your calculations :
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Calculate shaft angle from strut drop and transmission output flange location
Revised 12-APR-2013
Our latest calculator obviates the need to make a detailed shaft layout diagram to determine the shaft angle and shaft entry point for a
given strut drop.
| Definitions : Strut Drop and Shaft Angle |
Photo courtesy of Glen-L Marine Designs |
Drop is the distance from the strut base to the centerline of the shaft bore at
the aft end of the strut.
Angle is the degree of the slope between the strut
base and the shaft bore centerline. |
Inputs required are limited to the distance from the transmission's output flange to the transom, keel to transmission
output flange centerline and strut drop. If you're stretching the hull, values may also be input to determine
the shaft angle and shaft entry points for the stretched hull.
The sample calculator output depicted in the right hand side of this page was run with the following data :
- Aft face of strut barrel to transom = 16"
- Keel to trans output flange centerline = 4"
- Strut drop = 7.5"
- Alternate strut drop = 9"
- Hull stretch factor = 10%
The computed shaft angle can be verified by using our
Shaft Angle Table :
- Take the length dimension from the shaft entry point to the aft end of strut e.g. 28",
- Scroll down to 7.50" in the Drop column,
- Locate a value that is close to 28" in the Length column,
- The shaft angle for that length is listed in the Angle column. Angle is between 14.5° and
15°.
The spreadsheet is still under development, so if you find any glitches in the spreadsheet, send us an
email with the particulars and
we'll look into it.
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Shaft Angle Table
Revised 05-SEP-2017
Table computes the distance between the aft end of the strut bore and the shaft entry point for strut
drops between 6 to 10 inches and shaft angles between 6 to 16 degrees.
Shaft Angle Table
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Propeller Slip Calculator
Revised 20-APR-2013
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Theoretical Speed Table
We have devloped a Theoretical Speed Table which calculates theoretical speed for various RPM, propeller pitch, reduction and overdrive ratios.
- Given the desired engine RPM, the table presents multiple gear ratios, propeller pitches and
resultant speeds.
- Given the desired speed, engine RPM for multiple ratios and pitches can be determined.
Theoretical Speed Table
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Shaft Angles & Layouts - Drilling the Shaft Hole
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Calculate shaft angle from strut drop and transmission output flange location
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Shaft Angle Table
Table computes the distance between the aft end of the strut bore and the shaft entry point for strut
drops between 6 to 10 inches and shaft angles between 6 to 16 degrees.
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Shaft Layout for Flywheel Forward Installation
Sample shaft layout for installing a flywheel forward V8 and Velvet Drive C71 transmission.
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Inboard Motor Installations Chapter 6 : V-drives (www.glen-l.com) WebLetter 59
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Inboard Motor Installation Chapter 11 : Shaft Angles & Layouts (www.glen-l.com) WebLetter 12
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Inboard Motor Installation Chapter 12 : Making the Shaft Hole (www.glen-l.com) WebLetter 44
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Designer's Notebook: Drilling the Shaft Hole for an Inboard (www.glen-l.com) WebLetter 119
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Riviera Shaft Hole Boring by Dave Lott, Glen-L Riviera builder (MS Word document)
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MerCruiser Inboards Installation Drawings (www.mercurymarine.com)
These drawings may help you to visualize the various engine/transmission combinations.
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Technical Articles
We've developed articles on the following topics :
- Selecting the engine, gearing and propeller for your boat
- Propeller Diameter Notes
- Propeller Page
- Inboard Installation Notes
- Stretching the hull
- Chevy LS1 Engine Conversion Notes
- Parts required for inline installations
- Frame Templates
Technical Articles
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Flywheel Forward Engine Notes
We've developed a web page with some notes about Chris-Craft Flywheel Forward engines.
Flywheel Forward Page
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LS1 Marine Conversion Notes
Links to marine conversion parts for Chevrolet's LS1 engine.
LS1 Marine Conversion Notes
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Bellhousing and Adapters
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Marine Engine Torque Vs. Marine Engine Horsepower
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GENERAL
When it comes to engine horsepower versus engine torque in marine engine applications, most people make the common mistake of focusing on the marine engine horsepower rather than the marine engine torque. When it comes to both gas marine engines as well as marine diesel engines, in most cases focus should be directed to the torque more so than the horsepower. There is a common saying with in the OEM industry that "Horsepower sells a boat however Torque is what actually moves it". This could not be closer to the truth! One should realize that horsepower is really a measure of the torque over a given period of time. This taken into account by the rpm variable in the specification. The following equation may help to shed some light as well.
Torque = Hp x 5252 / Rpm (5252 is a constant)
It is interesting to note that the formula also verifies the typical torque bell curve when the torque trails off as rpm increases at the top end. One may consider that engines making torque at a lower rpm tend to work better in marine applications due to the fact that "most" boats tend to plane in the range of 2,000 - 3,000 rpm. It's not by chance that most marine engine manufacturers continue using the larger displacement - lower rpm, cast iron marine engines because of this fact. Many people wonder why these manufacturers haven't changed over to the high rpm engines the automotive industry has been converting to over the past 10 years; for the same reason the LT-5 Corvette engine and Lexus V8 engines didn't work very well in these marine applications --- nice Hp but at higher rpm's and therefore poorer low rpm torque characteristics.
Another interesting item to note is that since the proper method for propping a boat is to select the size prop that allows the engine to turn at it's maximum allowable rpm. It is required that a similar level of torque be produced at the top rpm condition as well as the proper planing rpm for a given boat hull (draw a straight line across the torque bell curve and see at what "lower rpm" this takes place. If this is not the case the selected prop will over-load the engine at the boats planing rpm and therefore yield very sluggish low rpm performance characteristics. For example a high revving engine that makes 400 hp at 5500 rpm would be making about 382 Lb-Ft torque (using the above formula) at 5500 rpm, since it would have a maximum torque output at probably 4,000 rpm it would be likely not to produce enough torque at 2500 rpm to make the boat plane very well since the prop was selected based on the 382 Lb-Ft value. Notice the higher the rpm an engine makes it's torque the worse this situation becomes.
In contrast to this; large engines that make significant horsepower at "very" low rpm's will therefore make a tremendous amount of torque, but at extremely low rpm. For example a diesel marine engine that makes 300 Hp at 2,000 is making 788 Lb-Ft at this same rpm. Noting that the torque curve is generated in "bell form", and therefore the maximum torque could be as high as 900 Lb-ft on this 300 Hp engine. Comparing this against a 300 Hp GM small V8 engine that makes 300 Hp at 5,000 and 375 Lb-Ft torque at 3200 rpm, this is a considerable difference. Very low rpm diesel engines typically make tremendous low rpm torque and therefore require specific gear ratios not supported by sterndrives, as well as requiring much larger diameter prop shaft's.
Source : Marine Engine Torque Vs. Marine Engine Horsepower (perfprotech.com)
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References
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Catalogs
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Hydrasearch Recreational Marine Hardware Catalog (www.hydrasearchrecreational.com)
Formerly Buck Algonquin Marine Hardware Catalog.
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Stright-Mackay Catalog (stright-mackay.com) New Glasgow, Nova Scotia
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Mack Boring Marine & Industrial Accessories Catalog (mackboring.com)
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