Hi all, I have a question for the Big Block builders out there. I just purchased a 72 Chevelle with a 454 that needs a rebuild. Car needs a "little" work. (read: the car is completely disassembled) I've built several small block Chevy's before, some for daily driving, some for street high performance, but never have I built a Big Block.

My question is this, what is a good high performance street combination that will survive in the heat of the desert, won't have too bad street manners, but also will be able to lay down some good numbers when I take it to the track.

Cam?, piston type?, compression?, want to use a 2000 stall convertor in a Turbo 400.

Any advice is appreciated.

do you plan on going fuel injection?

No Fuel injection, Holley 750, or 800. Don't know the head type yet, Oval or rectangular port, but I figure I can get 500 lb-ft out of it, and at least 430 hp and still be very streetable.

Yea, should be a sweet setup. Unfortunatly, Im not to good with building a motor so I can offer no advice. Good luck.

i'd suggest a couple of things, none by any means a definitive answer:

1. investigate your advance curve...this is what i like to call the heat fence. depending on how the advance is set up, the burn occurs either sooner or later relative to the piston at top dead center. the sooner it happens (more advanced), the more heat sinks through the piston/combustion chamber and into water jackets and lubricant. the more retarded the setup, the hotter the exhaust gas temperature is, because the burn happens sooner to the opening of the exhaust valve.

in terms of power, the best way i've seen this described is likening the piston/rod/crank assembly to a bicycle pedal and crank sprocket. if you push down on the pedal when it's at top dead center, it's difficult to get it started, but has a huge potential to grunt off of the line (torque - retarded); if you push down when the pedal is at 3 oclock (assuming the sprocket runs clockwise) you have more potential for rpm (hp - advanced). the degrees at which the piston is pressed back down are far more subtle, and entirely different, but the analogy i think is a good explanation of advance as it relates to power.

2. exhaust port size. the smaller your exhaust port, the more off the line low end grunt you'll have. conversely, the larger the port, the more horsepower potential. port size also determines how much heat sink occurs. small ports = higher operating temps (my scout is a perfect example), and also increase exhaust gas temperatures. these factors build on one another.

so my suggestion would be to go moderate compression (requires less advance and hence less internal heat sink potential), moderate to retarded advance curve (great low end torque), large exhaust ports (tempers that off the hook torque and provides some good hp potential).

bottom line - if you have the cubes to make it happen, it shouldn't be that tough to go very mild on everything but the head ports and get some serious power that'll run on pump gas (even maybe 87 octane!), produce good torque and subsequently yield good hp as well.

that's the beauty of the big block. it allows you to make hairball power without building the living piss out of the whole thing.

i'd also suggest to get a copy of desktop dyno for the pc, and fiddle around with the numbers in it using these concepts to see how slight you can go and still produce power. it's all in the combo, don't forget. you don't need any over the top components with that many cubic inches to do what you're looking to do.

hope this will at least serve as a starting point for a discusson on building a bbc. if i were you, and i had to invest in one expensive item for the engine, it would either be a good set of heads or a programmable advance ignition system (serious power available here with a little tinkering, plus gives great duality to the car - one program for street, one program for race).

jason

Hi Quick,
I just rebuilt mine a couple a years ago and stayed too conservative. I didn't want too much cam because of my power brakes and A/C, however I found out later I could have done more. What is your plan, ditch the A/C? Drive on the freeway? Here is what I would do if I did it again.
1. HEADERS!! Best HP imrovement you can make.
2. Aluminum heads. My engine stays warm forever and the parts weigh a bunch.
3. More cam. Mine has .475 lift and 212 degrees @.050 compared to the stock one at .430 lift and 202 degrees @.050. I should have gone to over .500 lift and around 220-228 duration @.050. If really want to step up I would do a roller cam, verrrry nice.
4. Better intake, I have a Edelbrock Performer waiting to go on.
5. A GOOD electronic ignition.
Edelbrock has a great "Performer" package that I should have done had I known. It is a intake and cam kit with a nice power band.
Also what Jason said, get a desktop dyno program, they are actually pretty close and it will save you time. I have one and built my "dream" motor, you change things and see what it does for your power curve and max hp figures, worth the money.
My car weighs 4,400 lbs and runs the 1/4 at 14.70 so far, I have 3.30 gear in it with a posi so it is very streetable.
If you would like PM me and I can take you for a ride to give you an idea what my BB is like.

I had a couple more thoughts. First, Jason explained the exhaust ports/valves well, the same thing can happen with a header that is smaller or larger. If someone is going to modify the heads, like porting, make sure they dont open the exhaust port too much, this can cause poor street driveability. A large exhaust port is good for wide open throttle, but terrible for everyday use, an engine needs some restriction to it to operate correctly. When the exhaust port is opened too far the airflow through the head becomes like a straight pipe with no restriction. Ever have a misfire, try and fix it and all feels well in the driveway then you take it out only to find the miss is still there? Almost the same thing, no load and it is gone, load on it and it is back. Make sense?
And of course the last option here I would recommend is, CRATE MOTOR! Save yourself some time and money and look into it unless you want the pleasure of building your own motor. By the time I got done with mine I could have bought a crate motor and been driving,it would probably have more power too.
My motor was wasted and needed complete machining, heads had to be re-done, then there was my time to clean, assemble, paint, and install the motor. How much is your time worth?

Thans for the advice guys, I think I'm going to take it easy on this engine. Since it is going to be driven alot I think I'll try to keep the lift down around .500 and the duration around 220 - 230 @ .050.

What kind of heads are you using on your engine LS4_454? Oval or Rectangular port? I heard the ovals work best for street.

Yes mine are oval port heads and I have heard the same thing. In fact the guy who smogged my Chevy drag races boats (Eddie Knox) and he was telling me some guys were taking their rectangle ports and filling them back in to make them oval, I guess they liked the way the flowed on a bench. My engine was rated at 345hp back in '70 (at '70s standards) which makes mine a LS4, there was also a 390hp LS5 and I think those got rectangle ports and electronic ignition, better intake and exhaust. If you are going to keep your engine mild, here is a site to think about down the road, they even have kits for carburated cars:
[url=www.procharger.com]www.procharger.com[/url]

Also, go to Silvas Radiators on Indio Blvd and get one of their aluminum ones, I should have stepped up when I did mine. My engine doesn't run too hot, even with the A/C on, but it takes a while to cool back down after a hot soak and the aluminum radiator would probably cool it back down faster. Just a thought.