Aluminium heads on a 350 engine

[HorizonblueDK]

Now and then I'm thinking about replacing the Volvo 4.3 V6 in my 18 footer with a smallblock Chevy (350).

There is enough room for it, and I have worked with boats for many years now, so it's no big deal really. But I would like to keep the weight down. A cast iron small block engine is quite heavy for an 18 footer, I think.

So I would like to find a good fresh water cooled smallblock marine engine, and replace the heads (& intake manifold) with aluminium parts instead. Also install a couple of Hi-Tek stainless steel manifolds.

Not for performance gain, only weight saving. A standard 4 barrel 350 makes enough power for me.

Has anyone done this before?

Thoughts?

 

[HT32BSX115]

Re: Aluminium heads on a 350 engine

So I would like to find a good fresh water cooled smallblock marine engine, and replace the heads (& intake manifold) with aluminium parts instead. Also install a couple of Hi-Tek stainless steel manifolds.

Not for performance gain, only weight saving. A standard 4 barrel 350 makes enough power for me.

Has anyone done this before?

Thoughts?

Howdy,


You're talking about installing some things combined) that might cost MORE than an entire engine!

Those Hi-tek manifolds are something like $2000 each and a set of decent loaded aluminum heads might easily $1500-$2000.

You didn't say what drive you're using (SX?) but the ratio will likely not be correct for a much higher HP V-8 and just changing the prop might not cut it....

Aluminum heads have been used. They're ok fresh water. Not so good in salt. If you're planning to operate in salt, you'll need closed cooling. (+$700-900)


Regards,


Rick

 

[HorizonblueDK]

Re: Aluminium heads on a 350 engine

Hmm, yeah it's not going to be a cheap swap, but compared to what we are used to pay for marine parts, where I live, it's not insanely expensive.

Like I said, I'm not striving for performance gain, so I don't need a set of expensive "high performance" heads. But on the other side, I don't want any Chinese crap either.

A set of good used cast iron heads cost 900 USD here, a friend of mine just bought a set for his engine. I mean, add a little(relatively) more and you have new aluminium heads.

A set of HI TEK manifolds cost approx. 2400 USD here, which is 600 USD more than a set of original Volvo cast iron manifolds.

I was going to add fresh water cooling anyway(maybe use the one from the V6 engine, if it has enough capacity). But yes, it all adds up.

My SX sterndrive already has a V8 ratio (1.61 :1) It actually works fine with the V6 and a 15.5x19 prop.

I was interested in knowing if there is any special type of heads/intake manifolds I should be looking for, when just wanting to have normal performance and steady idle from a 350 engine ?

 

[HT32BSX115]

Re: Aluminium heads on a 350 engine

Several years ago I had priced Hi-Tek SS manifolds for my previously installed 460Ford. They would've been approx $2000-2500 EACH side! I bagged that idea real quick! I also considered aluminium heads too. They were roughly $2000-2500 (loaded/ready to go)

It is possible to use slightly higher compression with aluminium heads. I would suggest going to a good automotive machine shop where they've done this before. too much compression and you're risking detonation.

I was interested in knowing if there is any special type of heads/intake manifolds I should be looking for, when just wanting to have normal performance and steady idle from a 350 engine ?

I would look to the Edelbrock performer's The steady idle is more related to the camshaft than the intake system.....and you're not going to get a radical idle from any marine cam

 

[HorizonblueDK]

Re: Aluminium heads on a 350 engine

Ok, thanks

By the way, my SX sterndrive has 1,66:1 ratio. It was the old 290 drive that had 1,61:1 ratio, which also worked fine with the V6.

Parts for the 460 Ford seems to be a lot more expensive than for the 350 GM. Prices starts much lower for the 350 parts, as far as I have found on the web.

Anyway, I will see what parts shows up, at reasonable prices.

 

[HT32BSX115]

Re: Aluminium heads on a 350 engine

Many critical parts for the 460 (OMC King Cobra) are largely non-existent now......

I am not saying you cannot do what you want to do, it will probably be a LOT more expensive than just buying a complete engine and doing a rebuild. I also totally understand the weight savings of the heads, intake, and SS manifolds. I'm just not sure the difference will be worth the additional cost...

The increase in HP/performance between the aluminium head engine will not be much different vs a similarly equipped cast iron engine. (don't forget to add the additional weight of the closed cooling system)

The main performance limit is more related to exhaust than heads, intake etc. You can install VERY free flowing heads and intake system only to have it limited by exhaust flow.

It would presumably improve a little using those Hi-tek manifolds and thru-hull exhaust, but if you plan to use the Y-pipe/thru-prop exhaust, you are right back to original exhaust limitations. Over on Offshoreonly.com they disagree though.....

The only way to greatly improve performance in a sterndrive boat is to increase cu-in (which you're planning to do).
[or supercharge]
And/or switch to thru-hull exhaust ............................

AND (for even more hp) ultimately dry stacks (which would allow you to use a VERY high performance camshaft that wouldn't have reversion problems) .........DRY-stacks of course, do not work in an enclosed engine (sterndrive) application......

Other than having to do a little engine mount and other minor engine compartment work, what you're planning to do will work......

If it were me, I would do the V-8 upgrade without the aluminum heads and spend that money on a DP (Duo-Prop) lower.

Cheers,


Rick