|
Tech Tips
305 CID TPI Engine & Camshaft
Courtesy of 3rd Gen Member ~ Vader
Your original 1986-1992 Chevrolet TPI engine should has the following characteristics:
Automatic transmission
1986 LB9 V8 9.5:1 compression,
5.0L(305CID), 2.73 standard rear axle ratio Horsepower-195@4000 RPM Torque- 295@3200 RPM TPI induction system.
1987 LB9 V8 9.3:1
compression, 5.0L(305CID), 2.73 standard rear axle ratio Horsepower-190@4000 RPM Torque- 295@3200 RPM TPI induction
system.
Manual transmission
1987 LB9 V8 9.3:1 compression,
5.0L(305CID), 3.08 standard rear axle ratio Horsepower-215@4400 RPM Torque-295@3200 RPM TPI induction system.
All 305 TPI (LB9) engines (1985-1992) came with one of two basic cam grind profiles. An easy way to identify the
type of cam on an LB9 car is to look at the tach: the lesser cams have a yellow line at 4500 and red line at 5000;
the hotter cams have a yellow line at 5000 and red line at 5500. All camshafts 1987 and later use hydraulic roller
lifters.
|
Cam info on 3rd Generation F-bodies
|
|
Model
|
Tach
|
GM P/N
|
Lift
|
Duration
|
Lobe
|
|
Yelw
|
Red
|
In.
|
Ex.
|
In.
|
Ex.
|
Sep
|
In.
|
Ex.
|
|
1986-87
305 AT (LB9)
|
4500
|
5000
|
10088155
|
.350
|
.384
|
179
|
194
|
109.0
|
108
|
-112
|
|
1987
305 5spd 350 AT
(LB9-L98)
|
5000
|
5500
|
14093643
|
.404
|
.415
|
202
|
207
|
114.5
|
115
|
-114
|
|
305 LM1
Police Pack.
|
|
|
14093640
|
.383
|
.404
|
191
|
202
|
112
|
108
|
-116
|
|
1988
1989
305 AT
|
4500
|
5000
|
10088155
|
.350
|
.384
|
179
|
194
|
109.0
|
108
|
-112
|
|
305 5spd
350 AT
|
5000
|
5500
|
10066049
|
.415
|
.430
|
207
|
213
|
117.0
|
116
|
-118
|
|
1990-1992
305 5spd
305 AT
|
4500
|
5000
|
10088155
|
.350
|
.384
|
179
|
194
|
109.0
|
|
|
|
305 G92 5spd
350 AT
|
5000
|
5500
|
10111773
|
.413
|
.428
|
202
|
207
|
114.5
|
116
|
-116
|
All varieties from 1985-1991 used MAF sensors instead of speed density sensing
for fuel metering control. Fortunately for you, the MAF is more accurate. Unfortunately, it is more costly to repair
and maintain, and the costly MAF sensor is susceptible to destruction from vibration and backfire.
The engine uses self-aligning rocker arms with a stock ratio of 1.5:1. Performance and economy can be improved
by installing 1.6:1 ratio rocker arms. These must be of the self-aligning type, and if you are going to the trouble
of replacing the rockers, you should probably spend a few extra bucks for roller rockers. The OEM valve springs
can be retained with 1.6:1 rockers if the original camshaft is used.
Another shortcoming of the design is poor flow through the intake air plenum. More improvement can be realized
by clearing the excess material from the throttle body area floor and matching the ports to the runners than by
installing a larger throttle body or air foil. And the modification only takes time and a few gaskets, not a lot
of aftermarket parts.
You should also check the PROM installed in the ECM. This is the chip that programs the brain. GM upgraded many
PROMS after initial release of the vehicle, and the upgrades address many driveability and performance issues discovered
by owners.
There is information in the GM TSB database, and on
this website regarding upgraded PROMs, and your local dealer service
department should be able to help you. I installed a Hypertech PROM in my 86 because of some difficulties I had.
I later discovered and installed the GM replacement (purchased for less than half of the Hypertech chip) and found
even better performance than the aftermarket PROM. And the GM PROM retains 50-state emissions legality guaranteed
by GM.
|