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)
View Full Gallery

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!

First Run

Carb was a 650 cfm Holley Double Pumper, timing 12-degrees base, 42 total. Timing stayed the same for all runs. We knew the carb was too small, but we wanted to get a baseline before going bigger.

RPM HP TQ
4000 323.1 424.2
4100 330.6 423.5
4200 336.0 420.2
4300 340.7 416.2
4400 347.0 414.2
4500 348.8 407.0
4600 360.0 411.0
4700 361.1 403.5
4800 361.0 395.0
4900 366.4 392.7
5000 371.1 389.8
5100 376.2 387.4
5200 384.4 388.2
5300 389.5 386.0
5400 395.3 384.5
5500 395.7 377.9
5600 401.9 376.9
5700 399.6 368.2
5800 392.0 355.0
5900 380.2 338.5
6000 381.2 333.7
AVG 368.7 390.2

Second Run

We changed the front jets to 70, and left the rears at 76. This took us backwards overall, and after some discussion, we decided against any more jet changes with the smaller carb.

RPM HP TQ
4000 323.7 425.0
4100 326.5 418.3
4200 335.2 419.2
4300 343.2 419.2
4400 344.9 411.7
4500 354.8 414.1
4600 356.4 406.9
4700 361.1 403.5
4800 362.1 396.2
4900 366.7 393.0
5000 375.6 394.5
5100 374.8 386.0
5200 378.1 381.9
5300 384.7 381.3
5400 392.0 381.3
5500 396.0 378.2
5600 395.1 370.5
5700 392.4 361.6
5800 391.1 354.2
5900 378.4 336.8
6000 382.3 334.7
AVG 367.4 389.0

Third Run

This time we switched to a Holley 750 Ultra HP Double Pumper. Jets were 76 front and rear. Air/fuel ratio ended up at 11.3 with this setup.

RPM HP TQ
4000 312.2 409.9
4100 315.0 403.5
4200 324.2 405.4
4300 330.1 403.2
4400 336.6 401.8
4500 346.9 404.9
4600 350.5 400.2
4700 349.9 390.9
4800 356.2 389.8
4900 358.6 384.4
5000 361.6 379.8
5100 374.2 385.4
5200 374.2 378.0
5300 374.2 370.8
5400 379.2 368.9
5500 390.9 373.3
5600 394.8 370.3
5700 382.8 352.7
5800 379.6 343.7
5900 384.0 341.9
6000 395.6 346.3
AVG 356.4 384.5

Fourth Run

Jets were changed to 74 front and rear. Air/fuel came up to 11.8. This netted us nearly 14 lb-ft of torque and 7 horsepower.

RPM HP TQ
4000 322.8 423.8
4100 325.0 416.4
4200 334.7 418.5
4300 338.5 413.5
4400 347.3 414.6
4500 352.0 410.8
4600 355.1 405.5
4700 361.3 403.8
4800 364.6 399.0
4900 366.3 392.6
5000 375.3 394.3
5100 377.9 389.2
5200 381.3 385.1
5300 385.6 382.1
5400 391.3 380.6
5500 395.9 378.1
5600 398.2 373.4
5700 398.8 367.4
5800 397.0 359.5
5900 393.8 350.6
6000 402.2 352.1
AVG 369.8 391.0

Fifth Run

Went to 72 jets front/rear. Air/fuel improved to 12.5. We decided to start as low as possible on the dyno (3,400 rpm) and go to the spec ceiling for our cam, 6,800 rpm.

RPM HP TQ
3400 292.4 451.7
3500 297.5 446.4
3600 300.5 438.5
3700 308.5 437.9
3800 314.8 435.1
3900 323.0 435.0
4000 332.5 436.6
4100 338.5 433.6
4200 343.7 429.8
4300 353.5 431.8
4400 354.6 423.3
4500 360.0 420.1
4600 367.3 419.4
4700 374.7 418.7
4800 372.4 407.5
4900 375.4 402.4
5000 382.7 402.0
5100 388.4 400.0
5200 391.8 395.8
5300 397.6 394.0
5400 407.9 396.7
5500 408.0 389.6
5600 411.1 385.5
5700 411.5 379.2
5800 411.8 372.9
5900 409.2 364.3
6000 411.0 359.7
6100 405.4 349.0
6200 409.1 346.5
6300 418.7 349.0
6400 408.8 335.5
6500 399.7 322.9
6600 370.1 294.5
6700 343.9 269.5
6800 327.1 252.6


Summary

We felt really happy with the results. The 408 was making just over one horsepower per cubic inch, we had a strong, flat torque curve for most of the operating range, and when you consider that this was all done through factory oval port heads, a points ignition, through a factory cast iron intake, the power numbers were excellent. With some basic mods in the future (stronger ignition, better intake, better heads, etc.) we’re confident we can have the 408 making over 500 horsepower without changing the cam. As it sits, this engine will have no trouble propelling our ’67 Chevelle to fast times and a lot of fun.


Parts List (All prices from Summit Racing website)
30110512 – camshaft $192.97
70984-16 – lifters $188.97
73121K3 – valvesprings and retainers $179.97
86603-8 – seat spacers $23.76
93110 – Timing set $109.97
8200-16 – Pushrods $172.97
15350-16 – Rockers $289.97
70461352-8 – connecting rod $521.97
CRB162 – rod bolts $13.97
CRS100 – locators $15.76
CRH140 – rod bushings $87.76
Manley Valves – Intake $109.97, Exhaust $109.97
Alternate Piston Set Price: Keith Black Hypereutectic $364.97
Machine Work – $750
Assembly Work – $1,000
Initial Engine Price - $150


Additional Sources

APE Racing
863-698-4374

Sources

Lunati
662-892-1500
www.lunatipower.com
AMSOIL
Superior, WI 54880
800-777-8491
www.amsoil.com
Summit Racing
Akron, OH
800-230-3030
SummitRacing.com
VP Racing Fuels
San Antonio, TX 78265
210-635-7744
www.vpracingfuels.com
Holley Performance Products
Bowling Green, KY 42101
270-781-9741
http://www.holley.com
Auto Metal Direct
Buford, GA 30518
866-684-5942
www.autometaldirect.com
Cometic Gasket
Concord, OH 44077
440-354-0777
http://www.cometic.com
Bad Attitude Engines
352-528-5386
http://www.badattitudeengines.com
Rollins Automotive
352-335-7223
http://www.rollinsautomotiveinc.com
« Prev 1 2 Next »

MORE PHOTOS

VIEW FULL GALLERY

COMMENTS

subscribe to the magazine

get digital get print
TO TOP