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4.3l to 5.0l
https://www.smwebhead.com/phpBB3/viewtopic.php?f=3&t=14067		 Page 1 of 1
Author:  dbergeron [ Sun May 31, 2015 3:00 pm ]
Post subject:  4.3l to 5.0l
hi everyone i just picked up an 88 200 horizon its got the 4.3l but its locked up. It was free and has a spectacular interior and titles for both boat and trailer. it currently has the OMC 4.3 cobra, but I've found its the same price for a re-manufactured 4.3 as it is the 5.0 and even the 5.7. what im wondering is if the gear ratio is different in the outdrives. will i have to change out the outdrive or will changing the prop be enough? also is it worth the motor increase or should i stay with the 4.3.. i like to do a lot of wakeboarding, tubing, etc.. i also plan to take it out to the long island sound for day trips. my last question is on efficiency, how much will my fuel efficiency change whether its + or -.
any info will help, thanks all
Dan
Author:  LouC [ Sun May 31, 2015 3:45 pm ]
Post subject:  Re: 4.3l to 5.0l
The gear ratios are different between the 4.3 and 5.0 engines; I'll pull out my OMC books later and look it up. The 5.0/5.7 are the same width but about 3.5" longer than the 4.3. Other things that are different is the exhaust system. I don't know if the angle of the Y pipe is different between the V6 and V8s. So I'm not sure if the V8 exhaust will work on the V6 Y pipe you may need to get a V8 one.
When I re-power mine I may stick with the 4.3 for these reasons and also I want closed cooling on the new engine and with the V8s the heat exchanger would barely fit.

Here are the gear ratios from my OMC manuals:
4.3: 1.68:1
5.0: 1.50:1
5.7: 1.41:1

So it sounds to me that you'd be giving up some top end if you used the 4.3 drive ratio with either of the V-8s. The drive itself is the same, no difference in the strength of gears etc. And if I was going with a V8 for sure go with the 5.7.
BTW, the 4.3 is a 5.7 with 2 cyls removed. 6/8ths or 3/4ths of a 5.7. Same bore and stroke.
If you stick with the 4.3, consider up grading to a 4 bbl carb, if it came with a 2 bbl, it is worth the performance increase.
Author:  rpengr [ Mon Jun 01, 2015 7:48 am ]
Post subject:  Re: 4.3l to 5.0l
To add to Lou's answer:

I am fairly certain the Y-pipe is the same for the V6 and V8 engines.

Within reason, you can make up for the different gear ratio with a higher pitch prop.

Your fuel usage will be about the same. You are going to get about 3.5mpg with any of those engines. It takes the same amount of power to push the boat through the water, although the extra weight of a V8 would cause a slight increase in fuel use...not really a noticeable amount. If you are concerned about fuel economy, the biggest difference you can get is Fuel Injected vs Carburated because a Fuel Injected engine is typically about 15% better on fuel economy. However, the simplicity of a carbureted engine has it's advantages on purchase and maintenance costs.

Like Lou said, if you are going to change to the V8, go to the 5.7
Author:  Graham R [ Mon Jun 01, 2015 9:13 am ]
Post subject:  Re: 4.3l to 5.0l
rpengr wrote:
Like Lou said, if you are going to go to change to the V8, go to the 5.7


For sure.

As a matter of interest, what is the historical reason for the 5.0 V8 ever being offered in the first place by OMC/ VP/ Mercruiser rather than "just" the 5.7 ( likewise the 5.0 and the 5.8 Ford V8 used for a time) ? Surely GM would sell it to them at the same price as the 5.7, it can't have cost any more for GM to produce the 5.7 ?
Author:  deafwish [ Mon Jun 01, 2015 4:15 pm ]
Post subject:  Re: 4.3l to 5.0l
For ease of replacement, also consider a Vortec roller 4.3 with a 4BBL.
Author:  LouC [ Mon Jun 01, 2015 5:22 pm ]
Post subject:  Re: 4.3l to 5.0l
Graham R wrote:
rpengr wrote:
Like Lou said, if you are going to go to change to the V8, go to the 5.7


For sure.

As a matter of interest, what is the historical reason for the 5.0 V8 ever being offered in the first place by OMC/ VP/ Mercruiser rather than "just" the 5.7 ( likewise the 5.0 and the 5.8 Ford V8 used for a time) ? Surely GM would sell it to them at the same price as the 5.7, it can't have cost any more for GM to produce the 5.7 ?


Good question; maybe GM would only make a certain number of 5.7s so they used the 5.0 to take up the slack. The Chevy small block has historically been offered in many sizes:
265, 283, 327, 350, and 400 cu in. Yes there was a small block bored and stroked as far as it could go, 400 cu in with siamesed cylinder walls. Early 70's. They also made a special 302 for the Z/28 Camaro in 68,69 years because that was part of the Trans Am racing series rules; it was a de stroked 350.
I think they offered the smaller displacement small blocks because at the time fuel economy was a big deal and they were not offering much in the way of higher tech stuff so all they did was reduce engine displacement to make it look as if they were trying to make their cars more economical.
Author:  babbot1 [ Tue Jun 02, 2015 9:10 am ]
Post subject:  Re: 4.3l to 5.0l
In my mind it is a marketing scheme. The upgrade from a 5.0 to 5.7 has benefits for power and it is usually big bucks more but probably pennies more to produce.
Also, I can't seem to find the info online but is the 5.7 a 4 bolt and the 5.0 a 2 bold main or are they identical other than displacement? Not sure which merc or volvo uses.
Author:  rpengr [ Tue Jun 02, 2015 9:25 am ]
Post subject:  Re: 4.3l to 5.0l
A 5.0 would make sense for certain classes of auto racing. Can be built to a very responsive, high RPM engine.

for Marine applications...go for more displacement and lower RPM.
Author:  dbergeron [ Fri Jun 05, 2015 8:19 pm ]
Post subject:  Re: 4.3l to 5.0l
thanks for the info, last question would be what it would take to take a 4.3 from a truck and just switch out the heads, intake, exhaust manifolds, starter, alternater etc.. is it a realistic or is it not at all worth it. if be keeping the carb.. no interested in trying to run fuel injection. let me know guys
thanks
Dan
Author:  deafwish [ Fri Jun 05, 2015 9:45 pm ]
Post subject:  Re: 4.3l to 5.0l
It is possible.
You'll need brass freeze plugs, marine circulating pump and stainless steel head gaskets.
Author:  rpengr [ Sat Jun 06, 2015 6:37 am ]
Post subject:  Re: 4.3l to 5.0l
deafwish wrote:
It is possible.
You'll need brass freeze plugs, marine circulating pump and stainless steel head gaskets.

As you mentioned, you need marine starter and alternator and distributor (ignition protected).
Also Carburetor must be marine version (95% the same as auto, except all vents and overflows are directed into the throat to prevent any fuel drips in the engine compartment)
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