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.

Re: 454 400/330 swap
 

my 330 was a 1980 vintage.. went 66.xx with only a mild cam change and mild porting, stock center riser exhaust and Qjet, went to a 454-425 HO crater, tried 5 different carbs and SSM manifolds, and it still stuck at 66.xx... both turned 4950, same prop, you tell me the 330's potential..

Re: 454 400/330 swap
 

I'd say the 330 was running pretty good when you pulled it out.
Oh yeah, for all you west MI guys lurking out there, I'm putting the superchargers back on for next season.

Re: 454 400/330 swap
 

My 32' A/T had some 454's that were bored to 468" with some ported Merlin oval port cast iron heads and 2.30" intake valves, Dart single plane intakes, 850cfm Holley carbs, Crower mechanical/solid roller cams, 9.5 cr, 36* timing that dyno'd around 600hp @5500-5700rpm with car dyno headers, no accessories and the torque was right around 590lbs @4800 or so. Not too shaby for oval port heads---it pushed my A/T at about 83-86mph or so with Merc TRS dirves and 3-bladed Mirage Plus props. (My A/T has Bravo One drives now, but was originally built with TRS drives.)

With the heads that GM only had available at the time, Merc didn't have much of a choice when it came to heads back in the 1980's when they had their 370hp, 400hp, 420hp, 425hp, 440hp, etc, 454 engines. And as was mentioned, the oval port heads that were available from GM only had the 2.06" intake valves with the 1.72" exhaust valves compared to the 2.19" intakes and 1.88" exhausts on their rectangle port head.

I mean, I don't know....seems to me that an oval port head (ONLY if they had larger valves and some bowl porting) like some Merlins would work better on a 454cid marine engine up to around 5500rpm. If they were my 454's I would not put a GM rectangle port head on them....but hey, what do I know??? I just kill bugs for a living! I am sure someone knows more about this oval port vs rectangle port head stuff on a 454cid engine for a marine hi-perf application up to 5500rpm, but in the mean time this has been a fun thread with all the input---even from my friend Crazy Dave the horse! :D

Re: 454 400/330 swap
 

that's a very good combo of parts...

Re: 454 400/330 swap
 

Yeah, he ain't got JC Whitney stuff in these motors either.
Good talking with you this afternoon, KAAMA. I hope we get to run together up north next summer. Mac Island, Hessel, De Tour.

It ain't the pot that gets you high, it's the papers. Always double-roll.

Re: 454 400/330 swap
 

I'm curious to see what the exhaust swap does to this 1982 454/330. If nothing else, I weighed the old log style and the new Dana, and saved exactly 90 pounds. Once I run it with just the exhaust change to get a baseline, I'm going to change the intake and carb, and run it again.

Re: 454 400/330 swap
 

Cuda, if your Merc 330 is of 1982 vintage, then to answer your question "yes" you probably have the larger, better "049" casting GM oval port heads on it. Which is probably one of the better flowing oval port heads GM ever produced. The problem is that if you ever install stainless valves you should install hardend seats with it as well.

Re: 454 400/330 swap
 

I'm almost positive it is. I don't think there were ever many hours put on this engine. The more I take off of it, the more I'm amazed how good things look after 25 years.

Re: 454 400/330 swap
 

When I change valves, they will be on another set of heads, and block. ;)

Re: 454 400/330 swap
 

And yet again I have to slightly disagree with my esteemed colleague KAAMA. The heads of that vintage have flame-hardened exhaust seats and wouldn't necessarily need to have new seats due to a valve change.
The truth is that the seats will probably get changed because of installing larger exhaust valves, if not also because the seats are sunk so far down you'd need a rope ladder to climb down there.
The intake side can be ground to accept the bigger valves if that is being considered.
Get the heads cut for teflon seals when the guides get replaced.

Re: 454 400/330 swap
 

my 1980 heads had hardened seats..

Re: 454 400/330 swap
 

Man, looks like I'm takin' a beating on this...oh well, good thing that what I have said is not written in stone eh? :crazy: :D :D Well anyway, we had some 049 castings off a pair of Merc 330's from a 1978 30' Scarab and we made the mistake of not installing hardened seats---at least we ignorant about it and weren't told by the shop that we needed to---maybe they didn't know at that time either??? So, we eventaully ended up with sunken seats and had to have them upgraded---live & learn.

So because of our expereince with the 049's we had, I always thought ALL 049's needed to be upgraded with hardened seats when installing stainless valves. I have learned that when the later design "peanut port" oval port heads came out that the hardened seats already came that way as stock from the GM factory----but hey, maybe I am wrong on that one too! :o

:drink: :drink: :drink:

By the way Cuda---lookin' MUCH better on that exhaust!!! :)

Re: 454 400/330 swap
 

Most heads that are out there and available have already had hardened seats installed in them. Most shops doing quality work would want to do it for a couple of reasons;
the seats are junk from being ground or just beat from running long hours,
to get the cc volume consistent and to get the spring installed height correct.
KAAMA, you've been around big-blocks way longer than me and have tried way more stuff than I have. Keep the information coming. We all benefit from it.