your thoughts on these heads!
 

Hi guys

I have just bought a pair of 336781 oval port heads really cheap and wondered if they could be fitted to my engine to give any power gains without changing anything else?

Would they cause any issues?

My engine is a 454 Mk4 peanut port 330hp with an edelbrock performer rpm inlet manifold at the moment.

They will definitely help, but if you really want to wake that motor up you'll have to change the cam and exh. If your performer RPM intake was for peanut port heads (small oval), you should change that too (to a large oval intake).

Adding 781s shouldn't cause any issues, as long as you get later model castings with hardened valve seats, and you use quality valves.

How do I tell what year the castings are? And do I have to change the valves or just regrind the ones that are in it?

Intake was for large oval anyway so will match as far as that is concerned.

There should be a casting date code inside the head that will indicate what factory it was cast at and the year. It will say something like "F 71" under the valve cover. You can take that date code and look up online when and where they were made. Check each head. They may be different.

The heads alone will make no difference. You will need to change the cam and exhaust and spool up to 5000 or so RPM to get any gain. If you decide to use the heads have 2.19/1.88 valves installed, do a little cleanup/port work on them. I use the 820's very similar to those but a smaller chamber.

My budget will not stretch to new exhausts and cam at the moment so is there any harm in fitting these as they are?

Casting date is H11 73 and H13 73 I think. Have had a search online and can not find out exactly what this means.
Would these have hardened seats?

They put these heads on big blocks all the way from 1973 up to the late 80's. I believe unleaded fuel did not become mandatory on new vehicles until the mid 70's. Based on the 1973 date, these probably do not have the hardened seats.

With stock valve sizes and everything else remaining equal, you will probably see little if any gain for the trouble of switching the heads. I found a website that had an exhaustive list of flow numbers for cylinder heads, and the stock 781's flowed about the same at lifts of .500 and below as the peanut port heads. Maybe just a little higher, but these heads do not really "wake up" until you add the larger valves and do some cleanup work in the valve bowl area. Then you would be looking at some healthy gains.

As a side note, you would be surprised at the flow numbers that the peanut port heads can achieve with larger valves and a little port and valve bowl work done to them. A setup like this would run pretty well on a 454.

The old heads have to come off anyway as I suspect they may be cracked as am getting a lot of water in the oil. So I figured as they were off I could simply swap them for the large ovals, bit if I have to spend money on new valve seats this boat might never see the water again!! Living in the UK and loving powerboats is painful!!!

If the old heads have to come off, then i'd say ya, put the larger ovals on. But, before bolting any used head on my motors, i would want to go thru them anyhow.

Water in the oil could be several things. Leaking exhaust manifolds, intake manifold gasket or manifold leaking, oil cooler leaking, camshaft reversion, etc. I wouldnt go pulling heads until you trace down the source.

Wow I didnt know any 211 Libs made it to the UK. They are a real popular boat around here since they were made in Michigan.

If your Liberator has an Alpha drive you have to be very very careful about adding any power whatsoever. A stock 454 maxes an Alpha right out. If you have an OMC King Cobra drive you are a lot better off.

A cam for you engine is a couple of hundred bucks, you will need a new intake for the heads anyways, and the heads will have to be checked for straightness and good valves installed before you use them anyways. If I were you I would pull the motor and do everything now, instead of band aiding the engine together.

A little time and money now could save you a ton down the road

Im in the middle of a build now with same motor its been 3 weeks and ill be lucky if back by next week. Changing the cam isnt as simple as ppl post it to be, you will need all new valve train parts, adjustable rockers, longer lifters, stiffer springs, im also doing it with 781's ill let you know what happens. But my idea is sell it and buy a bigger motor or blower run that ***** till it blows your transom offff.
or be like me blow your bank account out :lolhit:

Heads alone will help a stock 330, even with a stock exhaust. The heads are the weak point of the motor and choke it at 4500 rpm, followed by the cam, followed by the exhaust. In addition, the 781s generally have a 113 cc combustion chamber. The majority of the peanut port heads are the later vintage and generally have 118cc combustion chambers. Lowering the head to 113 helps the compression, and helps to make more power. You may want to run 89 or even 91 octane through the motor with the head change. Run some numbers and calculate the difference in compression ratio. I believe the stock compression ratio of a 330Hp Merc is 8.75 to 1.

With 781 heads the motor will make more power throughout the lower end and add a little upstairs with the larger intake ports. It will also help to match your large oval intake with the large oval heads. I wouldn't expect much (maybe 20hp or so), but they will absolutely help.

In Re hardened valve seats:
You can check around, but the conventional wisdom is that 1971 was the year that Chevy started using hardened seats. Allegedly it was only the Vette and Chevelle heads that got hardened seats in '71, but by 1973 they should all have hardened seats. You can do your own research if you'd like, but I have looked into the subject in depth and that's what I have discovered.

If you don't want to get into swapping your cam for whatever reason, you could do a "poor mans" cam change and add a set of 1.7 roller rockers and likely pick up a little bit. To do anything else you're going to have to upgrade your exh. and cam, and that's a couple thousand dollar investment to boot.

Without looking up I am pretty sure 781's are 118cc. I think the comp on a stock 330 is 8 to 1. The heads alone will get him nothing without the cam and exhaust. But if the old heads need replaced anyway then go for it
I agree with most of what you are saying. I used to have the Gen V 330 engine so that is what I am going by. I also did a ton of research on the old GM heads. Just going by memory.

Pretty certain that stock BBC rockers are 1.7. You will need a set of 1.8's.

Thank you all so much for your help, I would be lost with out you.
I will strip the engine down and fit these heads after a little freshen up as it will make it easier in the future to upgrade. Trying to find decent exhaust manifolds in the UK is a joke but I will keep looking. Once I have those then it's time for a new cam, oh.....and a bravo one!!!!!!

I also say the heads will help...the ports are much better than the oem 330 heads...with a little work you can make some great power with 781's...used them several times...

I can't get a straight answer on compression ratio of the 330. I hear everything from 8.1 - 1, to 8.8 - 1. That said, they generally use a 118 cc combustion chamber in peanut port heads on the motor. The 781s generally have 113 cc combustion chambers:

http://outintheshop.com/faq/casting/castings2.html


That list was taken from Mortech, who for some reason took down the casting number search from their website. They were an online "go-to" authority on GM casting # research.

Great info there, thanks.

The 781's are 118cc

http://web.archive.org/web/200805130...ec.com/bbc.htm

The older 330's were around 8 to 1, they used -3cc flat tops, very low comp. They were made for reliability not HP.

Delete that page from your favorites, that is very incomplete and has a bunch of wrong info. I found the old Mortec page after doing a little research. Hope this helps everyone out.

If you can find them in the UK, the stock exhaust from a Merc 496 are an upgrade over your 330's (better flow, much lighter weight). I bought a set for my 330 for $400. I changed the heads to 781s and intake to a Performer and picked up a little bit of top end and fattened up my mid-range. Not a dramatic change, but certainly noticable. I made the change due to a cracked head that had to be replaced anyway. At the time I was on a tight budget so didn't have cash to put into it.

If I would have had a little more cash in my pocket, I would have upgraded the pistons to forged, ported those heads, put on a Performer RPM Air-Gap intake and a bigger cam. That, I think, would have made a substantial difference.

Hey strega, I have everything you need, I did the same thing a few years ago and have all the parts you need for around 425 hp out of that bottom end....VERY AFFORDABLE. Pm me or call Robby