[MEJ1990TM]

I have recently asked about that four bolt main 454 I am going to build some day. Between the compression, and the rectangular port heads that 454 will be no where near an economical car to drive on trips. If I have the money some day I would like to build a more economical big block I could swap in for going on longer trips.

I'd like to build something that still has some get up and go (425 or so HP) but still maintain some economic value. Lower compression so it could run on pump gas, and oval port heads to save on fuel consumption.

Here is what I had in mind.

Block and Internals
- Either two or four bolt mains. (Won't be hammered around so it would just depend what I could find)
- Stock bore/stroke 454
- Forged crank, rods, and pistons
- LS6/L78 solid lifter cam
- Would like to run about 10.25:1

Heads/Intake
- Closed chamber oval port heads (2.06 Intake, 1.72" Exhaust)
- GM double valve springs
- GM rockers
- GM cast iron high rise intake
- 750 or so Holley
- Either Hooker Comp or M/T Super Scavenger headers

I know it will be quite a while before I could attempt this. But I'd like to have it done and broken in by CB next year. Actually with the gains I've made with my business it may actually be sooner rather than later. But I guess I'll see.

What kind of power would what I have mentioned here be good for? I know the rectangular port heads would help for more top end, but I'm more focused on mileage than I am on brute horsepower.

Now that I have this typed up that is pretty much what the LS5 that is in the '70 was when it was in the car. With the exception of the Holley, the LS5 had a 650.

I should have come here to the performance section quite a while ago. I've learned quite a bit about what works with these big blocks since I've started reading in here. Thanks in advance for any help. I'll just have to save this thread for a reference when I get around to putting together the hypothetical engine.

 

[mr 4 speed]

Michael,you can build a flat top 454 and use closed chamber oval port heads. You'll end up around 8.8 to 1 compression at a minimum (up to 9.25 to 1 depending on head gaskets,chamber size,etc.) and still get away using the LS6 cam.
And don't let anyone tell you different as the 1971 LS6 that only came in Corvettes had 9 to 1 compression and still made 425 HP
And you can burn 87-89 octane....and run in the 12's if you flog it at the dragstrip.
Your gas mileage may vary

 

[30-A rider]

Michael,you can build a flat top 454 and use closed chamber oval port heads. You'll end up around 8.8 to 1 compression at a minimum (up to 9.25 to 1 depending on head gaskets,chamber size,etc.) and still get away using the LS6 cam.
And don't let anyone tell you different as the 1971 LS6 that only came in Corvettes had 9 to 1 compression and still made 425 HP
And you can burn 87-89 octane....and run in the 12's if you flog it at the dragstrip.
Your gas mileage may vary

I agree with Mr 4 speed. I would like to add for a budget build you do not need a steel crank as a cast crank will do just fine. You also do not need to limit yourself to a solid flat tappet cam. Lets face it, if you going flat tappet you can go solid or hydraulic and considering this is a budget fuel efficient build, a hydraulic will require no adjustments once broken in compared to a sft. I think if you truely want a street performing BBC with best fuel economy Id consider a gear vendors unit or an overdrive trans as well.

 

[MEJ1990TM]

I see what you are saying.

The car will be built to be somewhat economical for trips, but I also want it to be something that can get out and go with some application of the right foot. The cast crank will work, but will it hold up as well as a forged one at 6500 or so RPM? It is more leaned to fuel economy, but I guess I've got some standards that I don't want to go back on. The solid flat tappet cam, and forged internals are two of them.

Just stubborn I guess.

I do appreciate the input though. :beers:

 

[RB69SS396Conv]

1. It makes not the slightest difference how many bolts are in the main caps, if they're the factory ones. Use whatever you can get.

2. Those archaic stock cams are long since superseded. Nobody that wins runs stuff like that any more, in fact didn't when they came out, even. As a species, we have actually made progress in understanding how cams work, and in figuring out ways to build them, in the last 35-40 years since those were introduced; not to mention, alot of the surrounding environment has changed since then. People's gas mileage expectations, fuel octane, the compression ratio you yourself have stated you want to run, the speed limit, and so forth. Those ancient cams are therefore a bad choice for a driver, and doubly bad for the rest of your combo.

3. There are few brands of springs in the world that I distrust more than GM. UNDER NO CIRCUMSTANCES WHATSOEVER would I ever run their springs in a car with anything more than a stock bottom-option hydraulic cam, and even then, ANY other springs will run better. Get modern springs as recommended for whatever modern cam seems to be the best match to your driving style.

4. Same for GM rockers. They might as well be made of rubber. They do a PITIFUL job of transferring the cam lobe motion into valve motion. They are altogether a bad idea. Again, you can make a VAST improvement on even a bone-stock motor by upgrading them; no sense in handicapping your dream motor with that garbage.

5. Most of the rest is good. There are lots of good stock heads (although 2.19"/1.88" valves will make a BIG improvement in a 454), a Holley 750 should be plenty, and some of the older iron GM intakes aren't too bad for street drivers.

6. You don't mention what car weight, gears, and converter (if any) this will be used with. That info is CRITICAL to making intelligent parts choices, especially the cam. Just jamming some romantic-sounding part with a hallowed name from days of yore isn't a good way to optimize the setup to your total package.

7. Mr 4Speed's suggestion isn't a bad way to go; that's what alot of us used to do back in the day. Take off the 781s (regardless of their intake port size), and put on 396 heads. Good for most of a full point of CR, for relatively little $$$. OTOH, if you're already going to buy forged pistons, run the 781s or 049s that your 454 came with, and get the best of both worlds.

8. Decide decisively between

Won't be hammered around

and

6500 or so RPM

BEFORE building.

 

[MEJ1990TM]

I came up with this combo because that is what the '70 LS5 car basically had, aside from a little more carb. The LS5 car has an M22, and 3.31 posi. My plans are for the same M22 and a 3.73 posi. It's got a TH400 now, but that will last only as long as it takes to get a four speed.

I don't necessarily consider 6500 RPM to be hammering the car around. The L78 that is currently in the '70 will hit that without any trouble. It's got GM rockers, springs, cam, lifters, and push rods. Actually the whole engine is GM aside from the pistons. But I am open to whatever will get the most power wise, and not sacrifice the gas mileage any more.

The engine will be going in a ,presumably, '71 Chevelle stock weight. So probably close to 4000 lbs or so.

Thanks for the suggestions, I will keep all this stuff saved away for when this actually happens. I am going to run that LS6 in the car most of the time, but for long trips I'd like to have another BBC that I can swap in.

 

[mr 4 speed]

I respectfully disagree with #2 and #4....the stock LS6 cam has recently taken a fellow TCer's LS6 car to 115 MPH in the pure stock class.I believe he is running stock rockers too.
Stock Eliminator motors run stock rockers as well.