Mercruiser 4 cylinder engines vs. V6s

[joliette]

As I'm restoring a 1960's Levi I'm wondering about the virtues of installing twin 170hp 4 cylinder engines vs. V6s.

On the positive side, my thinking is that the 4 cylinder engines
a) will have better power to weight (as they are considerably lighter than V6s) and be more economical to run
b) are fresh water cooled and therefore less prone to internal corossion than the standard raw water cooled V6
c) will be easier to access for servicing as they have a smaller footprint in the engine bay

On the downside I will not benefit from the additional hp of the V6. However, just how reliable are the 170hp 4 cylinder engines? Are they still supported with spares? Would anyone recommend them?

 

[AndieMac]

When considering the MC 470 as a long term serviceable proposition, afaik, you will not be able to acquire non genuine spare parts anymore, leaving only the costly genuine option. An example recently was a fuel pump retailing locally for GBP270.00.

We still have quite a number of them running here locally in both single and twin installations.
I ran a pair myself for a couple of years in a heavy older Bertram 25 (10 foot beam) and it used 50 litres per hour (total for both engines) at 20 knots. Some well looked after examples (moreso trailer boats) have been running for 30 years now, only suffering normal issues like blocked heat exchanges etc. but generally running quite reliably.
I've seen examples where the owner has grafted an externally mounted alternator to the engine rather the pay the expensive genuine cost for a replacement for the internal stator arrangement, specific to this engine.

They say the iron head is from one side of the old Ford 460 CI V8, as are the lifters, pushrods and rockers sitting on the alloy block.

I would think the V6's would be a smoother, quieter option if you have the space and bouyancy at the stern to facilitate (assume outdrive?), with plenty of cheap spare parts. Why not fresh water cool the V6's?

 

[joliette]

I would think the V6's would be a smoother, quieter option if you have the space and bouyancy at the stern to facilitate (assume outdrive?), with plenty of cheap spare parts. Why not fresh water cool the V6's?

Yes, V6s would be smoother and I guess I could fresh water cool them. However, they weigh in at around 400kg each with drives. I think I'd save around half of that weight if I go for 470s, but would sacrifice the 40 - 80hp extra I'd gain from a pair of V6s. I guess my question is would a 40 - 80hp gain from a V6 set up give me any extra performance (speed and fuel economy) over a the much lighter 470 set up? Or are there other considerations that I should be taking into account?

 

[AndieMac]

What size and weight of boat are you powering?

The set-up that works well for the twin 470's is around 3 tonnes for boat and engine weight (no trailer).

I've just remembered a couple more known issues with the engine (it's been a lot of years now).
If the coolant level drops and you see a leak from the bottom of the front of the engine, its probably due to a groove that wears under two seals on the front of the cam over time. The coolant has escaped through a relief passage (do not block this) designed for this purpose. It's important to fix this asap, before the second one fails resulting in oil contamination and total coolant loss. Speedy sleeves on the cam is the fix.

The water cooled voltage regulator can fail as can the magnets release from the previously mentioned internal stator (alternator alternative).

They run a lot cooler with the 4" heat exchanger, so it is worth changing if you have the earlier 3" version.

Regarding the V6's, I've heard from late 1995 they were made with a balance shaft which greatly improved the smooth running, rather than the previous model's fluid mounts.
I've never owned a V6, but owners speak very highly of them.

 

[Monique]

The v6's would add a lot of extra weight at the stern.

I would think you would get nearly identical performance from the twin 4's... IMO.

GL

 

[scej]

as has previously been said parts for the 470 merc are very hard to find, assuming you plan on second hand units for repower. i would probably look at the 3l mercs as these are still available new so parts wont be a problem although you will still be giving up a little performance.

 

[joliette]

What size and weight of boat are you powering?

The set-up that works well for the twin 470's is around 3 tonnes for boat and engine weight (no trailer).

Now there's a good question! The design weight - loaded with twin V8s and 500 litres of fuel - is 4 tons. The V8s and drives would account for nearly a ton of that and I'll be carrying slightly less fuel at 440 litres, so I think I'd be quite close to 3 tons with 470's fitted.

These boats were originally fitted with 165hp Interceptor engines and some were fitted with Mercruiser 225s, all based on the Ford 302, I think.

I feel that the boat needs around 170hp minimum, so the 3.0L Merc at 135hp is going to be underpowered. I guess I could look at an MPI V6 to get even more hp out of the extra weight or a even just go for the V8 ... I want to look at a pair of Volvo Penta V8s with DPS drives. At 400kg and 210hp this could be a good option if any access issues to service items can be overcome?

 

[ian38_39]

Had Merc 4 cyl 3lt and Volvo 4.3 lt V6's, think the engine is basically the same for merc and Volvo petrols and IMHO I would go for the V6 every time if you have room, so much smoother and don't seem to be working any where near as hard.

 

[AndieMac]

Had Merc 4 cyl 3lt and Volvo 4.3 lt V6's, think the engine is basically the same for merc and Volvo petrols and IMHO I would go for the V6 every time if you have room, so much smoother and don't seem to be working any where near as hard.

Ian, the older (no longer manufactured) 470 Merc, 170 H.P. was a torquey 3.7 litre motor that gave an alternative to the straight six Chev. 165 H.P. in their day.
Afaik Volvo didn't do a version in this big cubed 4 cylinder.