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Motor ID and information

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Mhorn0817

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Just picked up a new to us boat and learning more about it every day. Hoping I could get some insight on the motor. So we bought a 98 Sea Ray 215 Express Cruiser with a 5.7 carb with thunderbolt v ignition. It has the flame arrestor cover with serial numbers so I thought nothing of it. I needed to replace the oil sender and I always thought the motor looked really clean for the age so then I got to thinking it may have a repower. Which got me wondering if it was even the original motor, if it was really a 5.7 and not a 5.0, etc etc. So I googled as much as possible and from the number on front of the block, the last 3 are 3MD.

From what I read the 3 is the year code but could be 1973, 1983,1993, 2003, etc. And MD did mean 5.7 so I feel a little better knowing it's a 5.7. I wasnt sure if it was vortec or not because it had the 4 bolt through the valve covers but 6 bolt per side Intake manifold bolt. Or it could just be a pre vortec all together which would make it a 1993. Then I was wondering if it was a regular 350 or a 350 magnum. Not sure how to find out the difference yet.

I havnt been able to see the serial code by the starter but I'm going to try to borrow a small camera and see if I can read it. How can I tell if it's a regular 350 or 350 Magnum? The motor does have a Edelbrock performer intake manifold as well as an Edelbrock 1409 carburetor. Not sure how much of an upgrade that is or is not. The motor will spin to 5,200 RPMs which from doing some reading seems like it should be between 4400 to 4800 rpms. So then another question would be what prop should I change to. It currently has a aluminum 3 blade 14x23 on it.

Thank you for all the help and information in advance, I look forward to hearing from everybody.
 
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1. Edelbrock intake and carb is aftermarket Not Mercruiser. So there would be no reference to those two components in any mercruiser parts listing.

2. Center bolt valve covers started in 1987 when GM went to One piece rear main seal so this is the same to present day on standard 350 SBC prior to LS engines.

3. Based on 12 intake bolts this would be a 1988-1995/6 5.7 liter block. (Gen I). I believe Gen II has the 8 intake bolt patter also called Vortec I believe.

Propeller at 23 pitch is 5200
Propeller at 25 pitch would give you ~4900 which would be OK.

One pitch 17-19 or 19-21- or 21-23 or 23 -25 will adjust RPM by ~ 300 RPM up or down based on the pitch direction you go.

Issue is there may not be a 25 pitch as I am not sure of this.
 
1. Does the intake and carb seem like an upgrade? Or basically stock replacement?

2. Ah okay, I thought I read somewhere there was a difference of center bolt valve covers and around the outside bolt valve covers. Good to know there's no difference .

3. So it's more then likely a regular 1993 5.7L.

4. Yeah I think stock prop is 19p so I figured with a 23p prop the rpm wouldn't be as high so I'm not sure what of I need to go with a larger diameter prop or a 4 blade prop.
 
Based on 5200 rpm with a 23 pitch. You would need a 25 pitch to lower RPM.

If you go back to 19 pitch you will increase rpm by ~ 600 rpm.
 
Mhorn0817 said:
1. Does the intake and carb seem like an upgrade? Or basically stock replacement?

2. Ah okay, I thought I read somewhere there was a difference of center bolt valve covers and around the outside bolt valve covers. Good to know there's no difference .

3. So it's more then likely a regular 1993 5.7L.

4. Yeah I think stock prop is 19p so I figured with a 23p prop the rpm wouldn't be as high so I'm not sure what of I need to go with a larger diameter prop or a 4 blade prop.
Click to expand...

When Rochester stopped manufacturing carbs, Mercruiser went to Weber carbs.
They did not change manifolds that I am aware of so the standard would be cast iron and most likely with the spread bore opening.

If someone replaced both the carb and intake (aluminum) then it is simply a replacement. It could be considered an upgrade but a very minimal if any performance increase. More of available plug and play and ease of acquisition and installation.

Many today are going with the Eldelbrock MARINE carbs as they bolt right up (plug and play) as a replacement to the Rochester and Weber. (Weber have many issues)
 
You can't use the aluminum intake in a salt or brackish environment if that makes any difference. Fresh water, no issues.
I always recommend that you have a propeller shop fit and tune the prop to the boat. Just don't go and hit something with it after you spend the money for it ha hah!
 
Edelbrock used to offer 'marine' versions of their intakes, with brass lined water passages....so, might be lucky there...

I'd also check the outdrive's gear ratio before swapping propellers...
 
Okay, I was able to get the serial number off the motor from by the starter. Comes up as a 1993 350 Magnum tournament ski carb. Serial number is D854451 if anyone wants to confirm.

How do I know or confirm my drives gear ratio?

Prop gods said to go with a 15x15 3 blade SS prop. I want to take the advice and check to make sure the tach is accurate first. Is there a way to do so besides replacing the tach?
 
the key to prop selection is max rpm on the water with drive trimmed up. max should be around 4800-4900


To check drive ratio if unable to see it on drive then you have two choices.

remove top cap on drive and count gear teeth on the two gears and post back or remove drive and spin dive shaft one rotation and then mark and count/determine rotation (s) of prop (drive must be in gear).

you could have a couple of issues.

1. most alpha ones, the gear ratio is determined by the upper gears. This means the lower gears are the same ratio for the "most alpha drives".

2. Some, especially in high altitudes or on larger under powered boats run a different lower gear ratio.



most 350/5,7 21 ft pleasure boats would have a 1.5:1 ratio (newer drives have 1.47:1) the difference is to small to matter for what you are doing.

if the issue of high altitude or under powered come into play the lower ratio is changed and the final ration may be 2.0:1.
if one of these drives or lowers was put on your boat then your prop selection will be very different then normal.


This example is from my boat.
21 ft 1987 Cobalt 350 260 hp Alpha one Gen 1. Out drive gear ratio 1.50:1

Before props went to plastic hubs I ran a 19 pitch standard aluminum prop. Boat ran 4800/4900 rpm at 52 mph all day every day.
then with the change to plastic hubs I had to go up to a 21 pitch prop to maintain the same rpm . With a 19 pitch plastic hub prop I was running around 5200 rpm. so the increase in pitch lowered my rpm to the correct range and maintained same speed of 52 mph.

Most small pleasure boats are designed to run a 19 pitch prop to achieve proper rpm at wide open throttle and drive trimmed out.

So to assist in proper propeller selection, final drive ratio must be known.

Based on your earlier post you said you are running a 23 pitch at 5200 rpm. The logical change would be a 25 pitch to achieve ~48-4900 rpm.

If someone recommended a 15 x 15 3 blade, I would try it before purchase. It will launch the boat (great hole shot) but may over rev at top speed.

I am not a prop selection guru at all. I only understand the basics so maybe someone else who really understands may be able to chime in.

Here is a drive chart for Gen 2's

EngineHPLiters/CIDCylindersGear Ratio
Tooth Count
Year
3 Liter1303.0/18142.024-241998-2005
3 Liter1303.0/18141.9420-241991-2005
4.3 Liter1754.3/26261.8117-191991-2005
5.0 Liter2305.0/30581.6124-241991-2005
5.7 Liter2605.7/35081.4720-221991-2005
 
Agrre with jacks comments something seems off here a 21 ft express cruiser with a 23” pitch prop and a 1.5 or 1.62 ratio drive i wouldn’t expect to turn 5200 rpms . So either the tach is way off or the drive ratio has been changed due to mechanical failure or high altitude use.

youncan check the tach vs a shop tach or some newer timing lights have a tach. I got a wireless ignition analyzer that you just hold close to the engine while running, also gives peak voltage output.

https://gtc.ca/product/ta100-smartach-wireless-ignition-analyzer-and-tachometer/
 
Mhorn0817 said:
I was able to find and see the outdrive Information.

81P.
0F709773.
Click to expand...

i think what you saw as 81P. Is actually the drive ratio of 1.81R can be hard to read after a while , which would explain the 23” pitch prop. If someone where to look up the serial number they can probably confirm, but it looks like the drive was replaced.

assuming thats the case i would swap in a correct ratio upper so you can use the ‘normal’ 17” to 21” pitch range.
 
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Yeah from what ive been reading it is the 1.81 ratio and the serial number comes out to be a 1996 drive.

Would I need to change the whole drive? The whole upper? Just gears?
 
Probably the easiest would be to find a good used Upper only with a 1.47:1 ratio (gen II).

As said that would restore you prop size to the correct pitch range.

Also you can sell your upper as that is for a V6 I/O.
I am sure there are many looking for those!!
 
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