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400 HP 305!!

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Submitted by: Ed Hilker May 1997

This is a summary of a 400 HP buildup of the good old L69 9.5:1 V-8. I found this article in the July 1983 issue of Hot Rod.
Check it out.

First, the goodies:

L69 9.5:1 short block w/ 350 rods
Comp Cam  224 deg.@.050", .501" net lift, 110 deg. lobe separation.
RHS 041 heads, 59.0 cc, 1.94/1.50, mild porting, polished chambers and exhaust ports, Manley Pro Flo valves, Crane roller rockers
Edelbrock Victor Jr. intake, minor-work in plenum area, port matched
650-cfm Holley double-pumper
Hooker 1 3/4" primary tube headers
MSD Extra Duty distributor, Blaster 2 coil
Hamburger windage tray and scraper inside stock oil pan

Engine Dyno numbers:

RPM     Horsepower      Torque
3500           210               314
4000           243               319
5000           270               320
5500           316               331
6000           361               344
6500           378               305
6850           386               296
7250           402               287

Chassis Dyno numbers:

RPM     Horsepower
7000           300

The photos in the article were taken during a rebuild after the 305 spun a bearing a month after the putting the engine in an 3rd generation Z-28.

The article claims a true 10.6:1 compression ratio.  When block work was done to bore and hone everything, the deck surfaces were not parallel and the cylinder bores were out of square. The authors felt that the late-model blocks seem to be made of inferior material that is dimensionally unstable during hard usage.  Pushrods some .100" shorter were used to correct a slight rocker arm geometry problem.

The authors were "genuinely" surprised at the amount of power and the degree of driveability the package displayed.  In early testing, the Z28 ran 106 mph in the 13-second bracket.