408 Big-Block Rebuild, Part 5 - 1967 Chevrolet Chevelle SS

We bolt our $4,300 408 big-block (402 with an 0.080-inch overbore) to the dyno to see what our combo was capable of.

Patrick Hill Jan 28, 2014 0 Comment(s)
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Well, the day of reckoning finally came. Our “small” big-block was ready for the dyno. We’d finally see if the stuff we picked out made for a good combo of horsepower and torque for the street, while staying fairly budget friendly when it comes to big-block builds.

408 Big Block 2/16

With our 4.185-inch bore and stock 402 stroke, we have a total of 408 cubic inches. The heads are factory 820 oval ports, with enlarged valves and some port and bowl work. Our net compression is right around 10:1, still pump gas friendly, and when we try out some aluminum heads later on, we can manipulate chamber size for a boost in compression, but still stay pump gas friendly thanks to the alloy heads. But that’ll be later in this engine’s life.

We made five runs total, with all the data presented here. Our intake is the factory cast iron, 360 HP 396 intake for the ’67 model year, our ignition a single points type, and most everything else as original as possible. We know there’s a lot more to be had from the 408, but we wanted to leave more on the table so we’d have more stories to write for the magazine later on. And for the guys who want more power but also want to keep a factory stock appearance, this build can be used as a road map to build a similar engine. Total cost (sans carb): $4,282.95.

Flat Tappet 3/16

1. Because we’re running a flat tappet cam, we needed to run a high zinc content engine oil after our initial break-in. For maximum durability and protection, we went with AMSOIL’s Z-Rod 20W-50 synthetic oil. A high-zinc formulation to prevent wear on flat-tappet camshafts and other critical engine components. Z-Rod is made with a proprietary blend of rust and corrosion inhibitors for added protection for engines that see long periods of storage and inactivity.

Amsoil Oil 4/16

2. For oil filtration we went to AMSOIL again for one of its Ea oil filters. AMSOIL Ea oil filters (EaO, Ea15K) have one of the best efficiency ratings in the automotive market providing a filtering efficiency of 98.7 percent at 20 microns. Ea filters designated with product code Ea15K are recommended for 15,000 miles/one year, whichever comes first, in normal or severe service. Ea filters designated with product code EaO are recommended for 25,000 miles/one year, whichever comes first, in normal service or 15,000 miles/one year, whichever comes first, in severe service

Holley 4777 Double 5/16

3. For the first runs on the dyno, we started with a 650 cfm Holley 4777 Double Pumper carb. Our intake is the factory ’67 360 HP 396 cast iron intake with a Holley flange.

Mixture 6/16

4. After getting the engine fired up, Kevin set the mixture screws to factory spec, along with the idle setting. We started with the front jets at 68, and the rear jets at 76.

Single Point Ignition 7/16

5. For ignition on all our test runs, we used the factory single-point ignition system, with 12-degrees base advance, and 42 degrees total advance.

Peak Horsepower 8/16

6. After running the engine long enough to bring the oil up to temp, Kevin made the first pull. We ended up with a peak of 401.9 HP at 5,600 rpm, and peak torque of 424 at 4,000 rpm.

Lunati Flat 9/16

7. For those who missed our previous stories on this build (October-December ’13 Super Chevy) we selected a Lunati flat tappet, solid-lifter cam, part no. 30110512. It features a 112 degree lobe separation, with .550-inch lift on the intake, .570 lift on the exhaust, with the stock 1.7 rocker ratio. Duration at .050-inch is 238/248. Lash settings cold are .020-/.022-inch. Along with our cam, we also got a set of Lunati’s premium 70984 lifters that feature a laser drilled hole in the face of the lifter to provide a little extra oil to the lobe of the cam, along with the factory splash oiling system.

650 Cfm 10/16

8. After our first run, we decided to change the jets in our 650 cfm carb to see what would happen.

Holley Assortment Kit 36 11/16

9. For all our carb tuning possibilities, we had on hand Holley’s jet assortment kit, part no. 36-181. This kit comes with nearly any jet you would need to tune a Holley carb.

76 70 12/16

10. We decided to leave the rear jets at 76, and increase the front jets 70. This change gave us a peak HP of 396 at 5,500 rpm, and peak torque of 425 at 4,000.

Holley 750 Cfm 13/16

11. Figuring that our 650 cfm carb was a bit small to keep the big-block happy, we switched to a Holley 750 cfm 80803HB Ultra HP Double Pumper carb. The Ultra HP features an aluminum body and fuel bowls in Hard Core Gray hard coat anodized finish, and black billet metering blocks.

74 14/16

13. We hit the jet kit again, and switched to 74 jets front and rear. Another run, and our air/fuel ratio leaned out to 11.8, with peak power of 403.9 at 6,100 rpm, and peak torque of 423.8 at 4,000. Still, 11.8 is way too rich for our engine.

76 76 15/16

12. We started out with jet setting of 76 front, 76 rear. Our first run gave us peak HP of 394.8 at 5,600 rpm, and peak torque of 429.1 at 3,800 rpm. We checked the air/fuel data, and it showed us being pig rich, with a ratio of 11.3. This was too much fuel, robbing us of power and torque.

Final Run 16/16

14. We changed to 72 jets front and rear, getting our air/fuel ratio leaned out to 12.5, just right. Our exhaust gas temps were running near 1,200 degrees, so we knew leaning the carb out more wouldn’t do much good, and increase the risk of melting something. Our final run we started at 3,400 rpm, and went to 6,800. This gave us a peak of 411.8 horsepower at 5,800, and peak torque of 451.7 at 3,400. After 6,500 rpm, the engine fell off a cliff power-wise and started hitting valve float. We can shim the springs up for increased pressure to combat this, but with our cast crankshaft, we really don’t want to be pushing the engine past 6,500 that much anyway. But the end result was what we were expecting Next up will be dropping the motor back into the AMD/Super Chevy ’67 Chevelle, and seeing what the chassis dyno has to say. Then it’s off to the drag strip!




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