781 bbc heads from auto?
 

What do i need to do to a fresh set of 781 heads built for automotive application?
Going on stock 454/330 with upgraded intake (edelbrock performen 2.0) and exhaust (stainless marine)
i am trying not to get burned by my lack of knowledge.
Thank you in advance.
Gary

Those are a great head to start with for an auto application. I would imagine they're good for a boat too. I'd do a mild port cleanup on the runners to clean up the casting flash, rebuild them and go to town.

I'm sure somebody with more knowledge marine knowledge will chime in and give you more insight.

Do i need any special valves/seats etc.
Also got a line fresh on 781 heads with 2.25/1.88 valves installed (built for auto). Any recommendations and advice

My guess would be stainless valves and the proper springs to match your cam.

What are your intentions with the boat? If you are planning to lean on it, a set of inconel exhaust valves would be a good investment. Downside is the cost - $350 - $400 for 8 of them. If just pleasure boating, you may be able to get away with a very good set of stainless exhaust valves. Ferrea makes some nice stuff. I would look to them for both intake and exhaust.

What cam are you running? Depending on lift, you don't want to skimp on the valvetrain. Good springs, retainers, keepers, pushrods, rockers and lifters are all needed to control harmonics in the valvetrain. I considered the GM heads, but when I added up the cost for the new parts and machine work, I was well north of $1100. For another grand I was able to go with a set of AFR 265 ovals, which far outflow the GM heads, especially on the exhaust side. This included the upgrade to inconel exhaust valves. Something to consider. Brodix, Dart, etc., also make some good heads that will make real power.

781 or 049 castings are the sought after oval portsn the drag racing world. I just got my brother in laws all steel 72 Chevelle with a 461 BBC doing 7.23 at 95 mph in the 1/8 and I've still gotta dial in the suspension. This motor has a set of 781's that I bowl ported and that car hauls the mail!!

Think i am going to look at a set of 781's this weekend already upgraded to 2.25 / 1.88 stainless valves. Used take-offs (car) but pics look to be good condition. I am taking some barsol and check for leaky valves. If all looks ok i will probably buy. Found on craigslist for asking $600 will try for $500. Take them to machinest for final checking and surfacing. Need to decide how much material to remove.
Like i said have stock 454/330 strock cams & 8.5:1 compression flat top pistons and would like to remove enough to get to about 9.75:1. Any ideas what the chamber cc's required for this?
Not trying to make race engine just adding some spunk and freshness to engine.

they are great heads, use a performer RPM intake or something close, yes change the exhaust valves to inconel...

781's and 049's are good heads with a lot of potential. That being said, it is very expensive to reap that potential. You stated you are putting them on a 330hp 454, please keep in mind that motor has crappy cast pistons, a crappy cast crank, and crappy cast rods. If you aren't upgrading the cam, or plan on upgrading the cam, you may actually lose a fair amount of torque as well. The stock peanut ports that were typically on the 330's had excellent torque with the small cam that they came equipped with. To sum up my rant: Yes, they are good heads. Yes, they work well in marine applications, but you need to take care of the cam as well to see any benefit or you may very well see a loss. Another quick note, CC your existing chambers, then CC the replacements. 781's are open chamber and usually end up around 122 +/1 CC. It will probably drop your compression, which will get even worse with a better cam......

I've been in your position b4. I think it's a waist of money to buy those heads. You will see little to no performance gain. If you have heads get them freshened along with the bottom end and call it a day. Otherwise if you are really wanting to change the horsepower of the motor and see a difference on the speedo you are gonna have to break out the wallet and hide the bank statements from the wife if you are married...

it would be difficult to get that compression with those 118 cc chambers. look for a set of alum heads with the chamber size you need.

What current casting number do you have??

There was a $2900 502 for sale this week. Prosystems carb and such.

Too bad.

Current casting # 360 peanut heads not looking very useable trashed out and tired. Bottom redone 2 yrs ago. I am freshening-up the stock engine not buying any real performance parts, read alum heads, just putting the boat to good running order for 1-2 years.
I saw the 502 and the 509 and would like to have but i need to swap the alpha for bravo before adding any "real" power.
I found some recent rebuilt 781's for $250 my head shop said they would replace valves with stainless 2.25/1.88 and cc and machine heads for compression correction for around $400. I thought this to be a prudent direction.
Am i missing something? I am asking 'cause i really am no expert at this.
Thanks and as always any all sugestions welcome.

Those 781's will blow your 360'sw out of the water and with a tad of machining they will hit your comp ratio. Do an RPM Airgap intake and go have fun. This will really wake up your engine.

It has been sugested to use inconel exhaust valves. My question is what is different about them, when are they needed and why? Thanks again

If you cut the heads enough to raise the compression you will most likely have to cut the intake to match. The 2.25 valves may be a waste on that small bore motor and just cost you some low end torque. You might be better off with some closed chamber heads with 110 cc combustion chambers.

We are running the 781 heads on a 461 BBC in an all steel Chevelle and the engine is a monster! It pulls like a freight train in the eighth and will be in the 6's with some tuning....all steel and full interior I might add.

781 heads are great, with a bit of work done to em.

What compression, what gears, what cam ? what have you compared them to ?

For the car?

It's a sleeper so I can't divulge too much. It's a hydraulic roller, single plane, 750 carb, turbo 400 built by myself, 4.56 12 bolt posi, all N/A.....no gas.

As for peanut port heads....they are considered open chamber heads also, but to get the actual volume they need to be measured. But....they are VERY close in size to the 781's. Everything I can find is stating within 5cc. I'd machine .010 off the 781's to have a clean mating surface and bolt them up.

You missed the point, in your car you have low gears and a 3 speed,

I realize that, but those peanut port heads start to choke the engine off around 4500 RPM's.

at 650 done the 781s are good buy. at 500 a set plus work, you would not be able to justify not spending a little more for alum. Inconel valves handle the extreme heat of sustained full throttle use only a boat or airplane will see. but if engine spends it's life at 4k or lower, stainless valves will live. you can not justify ever spending money on peanut heads unless they are in a 34 hatteras.

^^^Well said^^^

Ran 781 on a 454 and a large cam and efi setup. Ran well and strong.

Anyone ever run the 820 castings? They have similar ports to the 781 and 049, but a smaller combustion chamber - generally around 112-114 cc, versus the 119 cc of the 781/049. This can help out if you are trying to bump up compression a little bit on a flat top engine.

You are also going to to need special head gaskets and pay close attention to cooling ports if going on a Gen V/VI block I strongly recommend the Cometic. You are going to need new rocker arms and possibly pushrods depending on set up height. Compare accessory bolt holes cause some may need tapped to 7/16. You will need to get new valve covers or modify the drip rail inside your original ones and may need to run a double gasket. If your pushrods are the right length make sure guide plates are matched to your diameter as the stock are 5/16 and alot of the 781 heads ran a 3/8 pushrod.

I have the 781's on my engines..twin 509's dyno'd at 495 HP. with edelbrock air gap dual plane manifolds and crane flat tappet cams 236 [email protected] 551 lift 100 over on the valve length ferrol valves
my machine shop did not go with 219/188 valves sizes. They went a bit smaller because of the water jacket too close to the exhaust ports.. Running 1 piece push rods and comp cams stamp steel rockers with roller tips and stock chrome valve covers with drip rails.

Thats the issue many face on the budget flat top engine upgrade for peanut port, other than buying a set of aftermarket heads with a 100 or 110cc chamber. the valve sizes on the peanut and oval are the same and the gen 5 peanuts often still have some meat on the exhaust seat .
with some ambition and some fresh carbides they can be reworked to make good power but its a sloppy messy proposition.

mine are large oval port.. If you ground out too much meat in the exhaust port eventually it starts to leak. The original heads that came with the boat both went bad, both were leaking from the exhaust ports after pressure testing. So this time we went not so large on the valve sizes and no deep porting...The problem with new heads is that most if not all of them like world products, dart have raised the exhaust ports 1"....SO after you install your exhaust manifolds and risers nothing lines up again. 1" at the bottom changes a lot on top of the engine. Years ago I had Gil exhaust on a single big block with new heads. Gil made wedge plates for this type of situation. Try and get a wedge plate for stainless marine exhaust...or many others. lots of luck.

I think Brodix makes an aftermarket head that flows pretty decent, and still has the exhaust ports in the stock location. The heads are aluminum, however, so might be an issue on a raw water cooled application.

Yes, the RR (Race Rite) series for BBC's.

You'll never get to 9.75:1 with a 454 and a flat top. I don't know how you are getting 8.5:1 with a flat top and peanut port heads. Even with a 100CC chamber and a zero decked block, you'll be lucky to see 9.25:1. A stock 330HP merc was 8.0:1

I ended up with 781's .030 shaved from heads giving me chamber of 108cc and .023 in the hole on flat top pistons. 30 over bore. Don't have a calculation on compression but guessing 8.5 - 8.75 on compression.

That would make a little more sense if your heads cc at 108, and the block is .030 over.

With that combo, you're about 8.4/8.5 ish with a typical .040 head gasket. You could get that up a bit with a thinner cometic head gasket, or if the block is going to be machined, have the decks milled a bit. Nothing wrong with a 8.75:1 engine. Mercury did it on many engines. I'd enjoy the 87 octane fuel and run it.

8.4/5ish did you run that through your computer or is that an educated guess?
Any idea what I would pick up with a thinner head gasket?
Thanks

Merlin made the majic aftermarket boat heads . Under a grand . Cc your oval ports , use the drugstore kiddo syringes if you cant get a moroso acrylic or comp big glass, 9cc can be the difference between yea and nay
Big john got over 500 out of peanut ports at under 5000 rpm , yea he could make hummers do wheelies in street trim , but the peanuts its mostly in intake port volume and cam cause your exhaust is still going to suck anyway
Your never going to be king with a bbc and flat tops but with some science you can get within spitting distance of the mag on wet exhaust boat app without pulling the motor

Did you cc those? I've cc'ed probably 7-8 781 heads (exhaust issue mentioned above got me), and I've never seen one below122 cc chamber - and that one had been shaved previously. Starting with that, you can't get to 108, not enough deck thickness. Online, they list 781s at lower cc's, but those are inaccurate when considering everybody's actual cc readings.

I personally did not cc them, the machinist told me that is what they cc'ed at. He said he measured therm.