upgrade from 3.7 to 4.3; same drive???

[luckyluke]

I'm doing my research for eventually swapping my 3.7 (470) to a freshly rebuilt 4.3 carburated from a local shop.

I thought I would have to change the drive as well because of different gear ratios.

The shop owner tells me no, the 4.3 bolts right up to the same drive (see my signature for s/n if interested).

They have to install/modify the stringers for the mounts, but other than that it should mate up no problem.

The engine comes complete with manifolds, risers, etc...

They're quoting me $6500 installed (please note, Canada) $1000 more if I want closed cooling. Just looking on-line, this seems like a good price.

Anyone have experience with this change (3.7 to 4.3) and know of drive issues or other? Advice would be appreciated......

 

[stonyloam]

Re: upgrade from 3.7 to 4.3; same drive???

The shop owner tells me no, the 4.3 bolts right up to the same drive (see my signature for s/n if interested).

It does. You should have a 1.84, which is correct for a 4.3.

 

[Eric 3.7LX Alpha 1]

Re: upgrade from 3.7 to 4.3; same drive???

Have a look at this chart with the drive ratio for each engine:
(taken from the "Adults Only Sticky at the beginning of this forum)

 

[stonyloam]

Re: upgrade from 3.7 to 4.3; same drive???

Something to think about: You will not gain much with the 4.3, it has more horsepower but also weighs 200 pounds more. Do you really want to invest $6500 in a boat that is worth 1/2 that. You could probably rebuild or put in a really nice 470 for less than 2500. You could probably do an engine change in a weekend easily. Just a slightly different point of view.

 

[Howard Sterndrive]

Re: upgrade from 3.7 to 4.3; same drive???

you'll need a y-pipe and flappers, coupling hoses etc. for the conversion as well, as a bobtail 4.3 would not come with that (I don't think)

 

[Eric 3.7LX Alpha 1]

Re: upgrade from 3.7 to 4.3; same drive???

Something to think about: You will not gain much with the 4.3, it has more horsepower but also weighs 200 pounds more. Do you really want to invest $6500 in a boat that is worth 1/2 that. You could probably rebuild or put in a really nice 470 for less than 2500. You could probably do an engine change in a weekend easily. Just a slightly different point of view.

I didn't even read the post!! :redface: just the title... :facepalm: and with that I'll 2nd this ^^^

 

[thumpar]

Re: upgrade from 3.7 to 4.3; same drive???

For the price you could just buy a boat with a 4.3 in it already.

 

[luckyluke]

Re: upgrade from 3.7 to 4.3; same drive???

Thanks,

All good points. I really like the boat and it's very solid, runs nice. I'm not looking for more power, I would just like something reliable I can depend on.

The 470 has all kinds of power, and works quite well. I'm just having cooling issues and as soon as you mention a 470 (3.7) to someone you get "the look".

There are some rebuilt 470's available, but I was thinking I might be better off buying something newer, with warranty.

I think parts are cheaper for the 4.3 as well. An exhaust manifold for a 470 is around $1600!!!!

As I said, I'm trying to do some research in order to make a good decision.

Thanks for the input....

 

[Eric 3.7LX Alpha 1]

Re: upgrade from 3.7 to 4.3; same drive???

Mine has the 4" heat exchanger with a new impeller kit this year (everything but the lower housing) it stays firm at 160?F all day long.

If yours is running well, do a compression test to see the health of the motor, before making any big $$ decisions. If results look good, just keep that baby going.

Have you done anything yet to fix the temp issue?

Here's a link to a site that has a pretty good assortment of 470 parts, their EM is half of what you found:
http://bpi.ebasicpower.com/p/BPI6219A

 

[dn010]

Re: upgrade from 3.7 to 4.3; same drive???

I'll agree with this - there's nothing wrong with a 470 that has been updated and taken care of. I have the 4" exchanger as well, the cam fix, alternator conversion and mine too will run 155-160 depending on the load - it has never failed me or left me stranded however I do need a new carb since mine is from '78.

Instead of dropping a bunch of money you can fix up what you have for a lot less and still have a good running powerful motor. Don't be turned off by all the people who complain about the 470, there's plenty of us who've had little issues.

Mine has the 4" heat exchanger with a new impeller kit this year (everything but the lower housing) it stays firm at 160?F all day long.

If yours is running well, do a compression test to see the health of the motor, before making any big $$ decisions. If results look good, just keep that baby going.

Have you done anything yet to fix the temp issue?

Here's a link to a site that has a pretty good assortment of 470 parts, their EM is half of what you found:
Manifold | Exhaust | Mercruiser 3.7L 224 cid | Aluminum | 816219A5

 

[stonyloam]

Re: upgrade from 3.7 to 4.3; same drive???

All good points. I really like the boat and it's very solid, runs nice. I'm not looking for more power, I would just like something reliable I can depend on.

One note on reliability, a well maintained 470 is every bit as reliable as any other engine of that vintage. In 22 years mine has never left me stranded, even when I had a blown head gasket. There is one big advantage, especially in colder areas, and that is ease of freeze protection. All you need do is keep the antifreeze at about 50/50 and drain the heat exchanger before cold weather. If you keep the boat on a trailer all you need do is pull the aft plug on the exchanger and let it drain. I do it right on the ramp when I pull the boat for winter, pull transom plug, pull exchanger drain, done in 5 min. So on a nice late fall day, just put in the plug and go, drain it when it comes out and done. Never have to worry about a cracked block.

 

[luckyluke]

Re: upgrade from 3.7 to 4.3; same drive???

Thank-you all for the advice.

I pulled the hose of the exhaust elbow last night and ran water through it and out the leg with a garden hose and there does not appear to be any restriction. I did the same from the hose between the voltage regulator and fore end of the exchanger; running water through the exchanger, and out the elbow and there didn't appear to be any restriction there either. I took the fore end cap of the heat exchanger and everything looked clear in there as well (maybe a little green corrosion).

As I've indicated before, I had the raw water pump replaced at the begining of the season, changed thermostats, changed coolant, changed the temp sending unit and gauge.

I do not appear to be loosing coolant.

I think I've covered the most obvious bases.....

I'll be picking up an IR temp gun ASAP to attempt more diagnosing. Anyone ever use one for this purpose? Aim at block, elbow, exhaust man, ???.

Trailering the boat tomorrow to the coast of New Brunswick (Northumberland Straight) for two weeks vacation. Will definitley have the chance to put her through some "sea trials"....

Thanks again all. Your comments and advice are very much appreciated.

 

[dn010]

Re: upgrade from 3.7 to 4.3; same drive???

Has it had cooling issues since the impeller change? I've posted this before to somewhere else and it might not be your issue but - I once messed up the alignment of the tubes in the outdrive where the copper tube didn't line up with the plastic guide tube, so the impeller was working and pumping water with water exiting my drive but it was never making it up into the exchanger...

I only knew this was my issue because the exhaust sounded loud continuously - normally it starts loud but muffles when the water starts to work its way through the exhaust.

 

[CV16]

Re: upgrade from 3.7 to 4.3; same drive???

I had a cooloing problem after changing the impeller a few years back. I went crazy trying to figure it out. Turns out that the Sierra brand I had was the problem. When I bought the QuickSilver(Mercury) one, my problem went away. This has happened to a few other people I know of as well. Just a thought, might not be your problem, but it sure cured mine!

 

[stonyloam]

Re: upgrade from 3.7 to 4.3; same drive???

After all of that I suspect that your gauge is off a bit. If the temperature is stabilizing (and it looks like it is) at WOT then that is a very good sign. BTW the acceptable range for a 470 is 165 to 200 degrees F, so 185 is not out of line. It can run a little warmer than a raw water cooled engine because of the closed cooling system.

 

[Howard Sterndrive]

Re: upgrade from 3.7 to 4.3; same drive???

For the price you could just buy a boat with a 4.3 in it already.

yep- drive to Ontario and I'll load mine on your trailer for $6500

 

[luckyluke]

Re: upgrade from 3.7 to 4.3; same drive???

I had a cooloing problem after changing the impeller a few years back. I went crazy trying to figure it out. Turns out that the Sierra brand I had was the problem. When I bought the QuickSilver(Mercury) one, my problem went away. This has happened to a few other people I know of as well. Just a thought, might not be your problem, but it sure cured mine!

Thanks. I'm tempted to check/change the impeller (pump kit). Is there a visual way to tell if the impeller is pumping sufficiently; as in how much water is coming back out when you run the engine with muffs?

 

[stonyloam]

Re: upgrade from 3.7 to 4.3; same drive???

An impeller change never hurts. If you are going to do it, change the whole thing, housing and impeller. Use OEM Mercruiser parts. If you had insufficient water flow through the exchanger the temperature would continue to rise when you run at WOT. How hot does the hose going up to the exhaust elbow feel. If there is not enough raw water flowing it would get very hot.

 

[luckyluke]

Re: upgrade from 3.7 to 4.3; same drive???

An impeller change never hurts. If you are going to do it, change the whole thing, housing and impeller. Use OEM Mercruiser parts. If you had insufficient water flow through the exchanger the temperature would continue to rise when you run at WOT. How hot does the hose going up to the exhaust elbow feel. If there is not enough raw water flowing it would get very hot.

Thanks, going to check those things out over the next 2 to 3 days. Stand-by for update.

 

[luckyluke]

Re: upgrade from 3.7 to 4.3; same drive???

Update....

Was on vacation for two weeks and had the boat out quite a bit. Bought a infrared temp gun (laser) to check the temp more accurately on different parts of the motor.

I suspect my gauge is off; ran at cruising speed for a couple of hours and the gauge held steady at what appears to be 185 or 190.

Using the temp gun, the temp at various points (engine water pump, temp sender, hoses, heat exchanger, etc) ranged between 155 and 165.

One thing puzzles me and I'm looking for input here. When I measured the temp on top of the coolant reservoir close to the cap, the temp is 160. When I measure the temp a little further aft on the reservoir/elbow, say centre and further aft, the temp was 211. Why? Exhaust? The temp on the raw water outlet hose of the reservoir is around 160.

Thanks,