454 400/330 swap
 

Are the heads and intake off a 400 series 454 useable on a 330 hp 454? What do you expect to be the power gain?

Re: 454 400/330 swap
 

maybe 35 hp at best

Re: 454 400/330 swap
 

If both blocks are the old Mark 4 design, then the heads and intakes should fit without any trouble. The problem is that if you are just swapping out the heads (rectangle port) off of a Merc 400hp engine and installing them on an untouched Merc 330hp engine, they just might be some SOGGY running engines I would think.

The GM rectangle port heads are already too large for a 454cid engine for marine use to begin with----and to install them on the 330hp Merc without at least a cam change you will probably end up disappointed in the performance catagory.

And just incase you didn't know, the Merc 330hp 454cid engine has all cast rotating assemblies (crank, rods, pistons) where as the Merc 400hp 454" is all forged parts.

I remember back in 1982 we were going to swap out the heads with some rectangle port heads on one of my friend's 24' Pantera with a Merc 330hp, but I spoke to a Merc High Performance back then and he said that we could do it, but we may not be too happy. So, we never tried it.

Also, the larger rectangle port heads have larger valves....not sure if they would interfere with kissing the pistons on the 330's or not...I know if you installed a larger cam they would...it's the domino effect! If you change one thing then you may end up having to change other things as well so that everything is done correctly and in sync so to speak. Just be careful. It would probably be good to get a few more opinions about this from some of the other guys on here who may have some experience with swapping heads on a stock Merc 330hp bottom end.

Re: 454 400/330 swap
 

To answer yout question, yes, they will fit, assuming the block is a Mk IV.
The 330 has a compression ratio of 7.4:1 whereas the 400 had a c/r of 8.75:1, which means the 330 will be really anemic.
I have to disagree with KAAMA on the point about the rectangle-port heads being too big for the 454. The aftermarket heads that are available typically have better design characteristics (raised exhaust ports for example) than the stock GM heads, even though the intake runner volume can be comparable. Besides, if they were that bad Merc would have picked something else.
KAAMA has been around this sport for a long time and is quite knowledgeable about marine bigblock applications. Doesn't mean I can't disagree with some of his thoughts though.
See Mark? I don't always sound like a pot head from the 70's.
Pink Floyd rules.

Re: 454 400/330 swap
 

Didn't the early 454/330's have something other than the peanut port heads?

Re: 454 400/330 swap
 

I am going to rebuild my 310HP/7.4 this winter and my plan is to use GM rec port heads with a new set of piston that will yield 9:1 compression and the cam from a 500EFI.
My opinion is that a good used set of GM rec port heads is a great upgrade when building on a budget.
Remember, Merc had a lot of 454 cube engines come of their line with the GM rec port heads; they can't be that bad... :drink:

Re: 454 400/330 swap
 

there is some very good advice going here...

the 330 center riser exhaust engine is pretty torquey in it's own right, the log manifold setup was 330, and the center riser was prolly 340... the 330/340 round ports aren't peanut ports like the later 310 has.. they have pretty good port velocity for a torquey engine.. I am pretty sure they weren't 7.xx something comp ratio though.. I am a HUGE fan of round port heads under 5200-5500 rpm, and I just learned a lesson of my own on this... you need 5500-6500 to take advantage of port air movement to make the rect heads work, and the torque band is higher, so actually the round port engine makes better usable/smarter power up to 5400 than the rect port heads do, with the same internals/carb/cam. A well built 8.75 ratio 454-468 round port engine with the right cam is a REAL powerhouse..

JH

Re: 454 400/330 swap
 

I'd agree with most of this, except that it's my opinion that the GM 049 oval-port head rpm limit would be 4800. Again, just my opinion, the rectangle-port heads really come alive above 3000 with an effective compression ratio (8.75 and up) and with a suitable camshaft. Center-rise exhaust is a big improvement over the early log-style exhaust manifolds and is affordable if your budget won't allow an EMI Thunder (or better) setup.

The earlier 330 engines came with 049 oval-port heads which work very well.

It's about time for KAAMA to pop in and kid me about my mis-spent youth and roach-burnt fingertips,,,,,,,,,,wow man, farm out.

Re: 454 400/330 swap
 

I have rebuilt and modified 5 BBC marine engines to date so I'm by no means and expert. However, from my experience rebuilding two 330s/7.4s, marine engines with round intake ports (peanut port) heads, they make good low end torque, but the power dies out after about 4400rpm. I have tried a few different cams and unless you install larger valves and port the hell out of them, peanut port heads suck... :rolleyes:
I also made a cam change on the L-29 engine (large oval head 454) that engine still only made power to about 4600rpm. This time that engine get different heads and intake.
I did have vary good luck rebuilding a Gen V 454Mag that came stock with rectangular intake port heads. We milled the heads to add a little compression and rollerized it. That engine has descent low end torque makes power to 5400rpm.

To the question that started this thread. IMO, the rectangular intake port heads would be a great upgrade for a 330 if the pistons are changed to raise the compression ratio and a the cam is changed to create torque at higher rpm.

Good Luck and Happy Boating! :D

Re: 454 400/330 swap
 

The peanut heads came out about 1986/87 and it's become pretty common to upgrade any 330/340/310 to aftermarket oval-port heads.
Midrange torque is what you're looking for here. Whether it's with aftermarket oval-port or stock/aftermarket rectangle-port heads, it will make tons of midrange torque if the c/r is in the mid-nines. A nice roller cam is a good addition but flat-tappet cams work very well if your budget is a little tight.
As KAAMA said, the GM rectangle-port heads tend to crack between the seats so if you choose these heads make sure they are magnafluxed.