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

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

COMMENTS

subscribe to the magazine

get digital get print
TO TOP