First off, hey motornuts! Its been a few years since I've had time to post, so I started all over. Well, lets see.. The 357 in my original BB car needs to go so the 454 i have laying around can move in. I have a .030 over 454 block # 3999289, and the original 396/427 heads off the nova # 3919840. The ports have been nicely ported, but I haven't seen the bowls.
I belive they are 2.06/1.77 valve, rec. port heads with 107cc closed chambers. They were used on the L-78 396's and 427's. I'm looking to make 450-500hp and over 500 ft. lbs. on a pump gas friendly BBC, not too hard right? So what do you guys think about those heads? I have many more questions, but I know that I came to the right place!

 

Compression is king, so first figure out what your compression ratio will be. That will be the combo of piston configuration (dish,flat top or dome) and cc of cumbustion chamber. If you want to run 93 octane pump gas shoot for 10.5:1 compression ratio. If you only have 8.5:1 compression it is a lot harder to make big power. A good intake is a must! Low end power go with a dual plane intake. High rpm power go with a single plane. You will also need a stout cam if you are going to make that kind of power. If you don't have AC on the car, then you can still run a pretty wicked cam, because then the only thing else that should need vacuum would be power breaks (if equipped). I am by no means an engine expert, but I know some people who are. Maybe try calling a local engine shop and ask them for the best cam specs for your motor. Also look up the 1970 LS6 454 specs on the cam. They were in the neighborhood of 10.75:1 compression and they had a wicked cam because AC wasn't even an option on an LS6 Chevelle. They even made all this power with a low rise intake. So yes, it is possible to make 500 horse with those heads, just need to find the right combo for the rest of the engine components.

 

They are indeed L78 type... also used on L71/L72 427's. they have big valves, 2.19/1.72 I believe.

With the way muscle car prices are exploding, there is probably somebody out there that is looking for correct date code heads, for their L78 or L71/72 resto, that you could relieve of a nice chuck of cash. Suggest you research values carefully.

For all out performance, those heads aren't the best. Oval port (modified stock or aftermarket like Edelbrock RPM's) can make 500 hp and run a lot better on the street (more torque) than factory rectangular port. Aftermarket large oval or rectangular port are best for serious track efforts. So if you sell the 840's for large $$$, you can either buy good aftermarket ovals for a 500hp street/strip engine, or get bigger port heads for 600 hp.... and probably have cash left over.

 

The car that it is going into has no a/c or power anything, so vacuum doesn't matter to me. I'd like to use these, considering my money. If I do use them would I need big a hyd. roller to get the power I want? Also what are some info on oval port heads? How about the ones GM sells through their performance division?
If I use these heads, 10:1-10.5:1 comp, and a ~550 lift hyd. roller cam, dual plane intake, etc... Will I fall short of my goals?

 

500-550hp is very easy with a 454.... very streetable.

As far as compression is concerned, you need to be more concerned with your dynamic compression than static. Dynamic varies based on the intake valve closing event. Close the valve late enough and you could get by with alot more static compression.
Not to confuse the matter, but you need to decide on a camshaft that will meet your requirements and create a dynamic compression of 8.5-9.0:1.

If you're confused about dynamic compression, there's a good deal to read in Advanced Tech. Just do a search.

-Mindgame

 

Whats it typically cost to have the machine shop do a rebuild on a 454 and a set of heads? This would include Boring, align boring, cleaning, balancing, rod reconditioning, and assembly on the block. The heads probably will need new guides and seals.

 

I have a set of the -840 heads on my 427.
They will kill your low end torque unless you get the compression up
and run more cam than you are thinking.To put it in perspective,
my motor has 13.5-1 comp and a flat tappet Crane .630 lift cam.
With 4500 stall and 4.88 gears, they work well.
On a typical street motor, you are probably better off with -781
open chamber oval port heads.I have both types and they both work
well.

 

Machining costs vary but it should be less than $2000 to have the block worked and heads machined. Like I said, all depends on who's doing the work.

The rectangular port heads can work great on the street. They'll make plenty of torque. The problem most people make is in using too low a compression and a larger cam. That will make the low end go to mush. You need to use a camshaft that will provide good dynamic compression. 10.5:1+ is fine as long as the cam timing keeps the cylinder pressures up. Like I said... 8.5-9.0:1 dynamic, good tuning and adequate cooling will make for an engine with more average low-midrange torque.

-Mindgame

 

If you're wanting an 'all stock' GM parts motor that runs like the dickens....I have a decent formula that has track time on it.....but my puter at home took a dump and its on there so I'm waiting to get back to it.

Email me and HOPEFULLY by next week I'll be back in my old puter and can pass this info to you....