I got a set of 781 casting heads, and am wondering how good they are, and if i should put some money into them or move on. if they are worth keeping what should i have done to them, they will be on a 396 BBC that is either .030 or .060 over, eagle h beam rods and stock crank. i am hoping for 400-450 horse, enough to get a 67 rs/ss into the 12's. thanks

 

Open chamber good flowing oval port heads. Have some 2.19/1.88 valves installed with some port and polish work and they'll do fine.

781 and 049 are the best factory oval port heads.

Save your money on the H beam rods. I beam will do fine for what you intend to do. 7/16" rod bolt rods would be the best but 3/8" rod rod rods with ARP bolts should survive.

 

welp, its too late on the h-beams, they are alredy on order. they were advertised as lighter then the i beams and only a few bucks more where i got them. thanks for the help on the heads.

 

its probably out of the question and i understand that, but if theres anyway at all you can afford it go with a 454 or if you have the cash go with a 502 the larger bore will allow the heads to flow better. a 454 vs a 396 with equivalent parts only difference being a "proper" cam is a totally different animal.

as has already been said put bigger valves in it, my heads guy said it was worth more than i expected on the bench. the other things you might do to the heads is have them angle milled down to around 109 or 106 cc's so you can just get by with a very minimal dome or even a flat top piston. i dont like large domes because its my idea that the shape slows flame travel. not only that domed pistons tend to be more expensive at least where i shop.

i know you didnt ask but, for the love of god dont be afraid to throw some compression at it large engines like large cams, and that dictates higher compression. i'm sure bret or one of the others here can tell you everything you need to know if you choose to do business with them. good luck in any case, sounds like a sweet project.

 

how much compression would you consider too much with iron heads, 10.8 ish ok with a large cam? and who is bret? where is he from? thanks

 

BBC head/piston design isn't the same as a SBC. Using a dome piston to bump up compression is fine on a BBC. The open chamber head design is prefered because it unshrounds the huge valves beter than a closed chanber head. Milling the head to increase compression just causes more problems in the piston to valve clearance area depending on what pistons you use and how much lift is on the cam.

Maximum compression is the same as on a SBC. Typically 10:1 for premium pump gas but every engine is different so you'll never know until you try it. You only need enough octane to eliminate detonation.

I use 119cc chamber oval port heads on my race car. They're Merlin heads but roughly the same as the 781's but just better castings. I use a huge dome piston to get 13:1 compression but then I also run alcohol which is just about impossible to get detonation with. A set of aluminum Canfield heads are waiting to be installed.

You just have to watch what pistons you use with those heads. LS6 dome pistons won't fit without a little bit of grinding done to the combustion chamber on one side. All that should be checked anyway when the engine is mock up assembled.

 

They are good heads if ported correctly with a good valve job. Used in 74-75, as best as I remember.

Rich Krause

 

Many 454 pickup trucks from that era came with those heads so there are hundreds of thousands of them still out there. I've scrapped a couple myself when I dropped valves and had the head of the valve punch a hole in the head.

I still have 3 sitting in my garage.

 

Not really any motor will gain from a small chamber with either a flat top or having the piston take up part of the chamber volume. The same rules of SBC stuff apply on a BBC, but you do have to use domes sometimes on BBC to get any decent compression. With what you have now (468cubes and 113cc) then with a flat top 9:1 is do able. Anyway that you can prevent hot spots and detonation means that you can run more compression for a given combo. Domes are one way to reduce the amount of compression you can run on a motor.

Oh and with the right cam specs you can get what you are looking for with LESS piston to valve problems. P to V also has NOTHING to do with max lift.

In my book the best way to get compression in a BBC is with cubes. A 496 is a easy motor to come up with on a BBC block. Scat makes a nice cheap 4.250 stroke crank. Milling the heads to 106cc, putting a flat top in there and then getting 496 cubes will be a much better motor all around and you will have 10.2:1.

10:1 huh, well why can guys run 13.2:1 on 92 Octane then? Look up Dynamic Compression Ratio. I regularly build and design cams for 11.5:1, 12:1 and 13:1 STREET motors that run on pump gas. They all work fine too.


Honestly I think that WS6T3RROR has some good points here.

Bret

 

thanks for the reply bret, but i dont have a 454 bored to 468, i have a 396 that will be bored out. i was looking at a set of je pistons that with these heads will give a 10.8 cr. its not like this is going to be a daily dreiver, its going in a 67 rs/ss and will only be driven in nice weather.

 

Your idea for the 396 combo sounds pretty straight, but why not up the cubic inches while you can, like a 427 with a niece set of rectangular port heads. You seem to already have the right idea for pistons and the H-beam rods for making the bottom end pretty strong, but check out www.competitionproducts.com, and have them send you a catalog. I bought a 4.25" stroke Elgin forged crankshaft through them for $350, and the price is the same for a 4"(454crank) to make your engine a 427. Also, check out their cylinder heads. I almost had a set of stock oval ports rebuilt for my 489ci bb, but after pricing their heads, I got a set of Canfield 310cc aluminum rectangle ports for $1399 complete, ready to bolt on, about $600 more than what it was going to cost to rebuild the stock pieces. Keep in mind, that if you do go with the 454 crank, the engine would then need to be externally balanced with a damper and flexplate for a 454. Competition products has a nice 454 SFI approved damper for $100, and you can get an SFI approved externally balanced flexplate for around $70. Just ckeck with your machine shop for how much they charge to balance the rotating assembly. I'm sure your on a budget, but if you can swing the extra $2000, the power potential would be well worth it. Good Luck on the build up!

 

i talked to my machinest the other day and he suggested getting a set of aftermarket heads due to the fact that the amount of work that would be needed to get any worth while numbers would be money better spent on new heads. so im looking at a set of AFR magnum 305's.

how much machine work would need to be done to the block to fit a 454 crank? are the rods the same length?