1.8L GSi Cam Swap
I installed the 1.8L GSi Cams. Was an easy swap-well it was real easy with the engine out of the car, only took 15 minutes.
UPDATE: I swapped out the 1.8L GSi cams and the RS solid lifters and installed the IMARK cams and hydraulic lifters. The engine is a lot quieter now, but I am a little dissapointed in the performance at this point.
Here is all the information I have on Isuzu Camshafts:
| Year |
Cams |
Lift (Lobe height) |
Lift Duration |
Intake open/close |
Exhaust open/close |
| 1989 1.6L DOHC (I-Mark RS) |
Hydraulic Lifter |
39.02mm |
252/252 |
13BTDC/59ABDC |
64BBDC/8ATDC |
| 1990-92 1.6L SOHC |
Solid Lifter |
36.22mm |
??/?? |
??BTDC/??ABDC |
??BBDC/??ATDC
|
| 1993 1.6L SOHC |
Solid Lifter |
Intake/Exhaust
35.53mm/35.89mm |
??/?? |
??BTDC/??ABDC |
??BBDC/??ATDC
|
| 1990-91 1.6L DOHC |
Solid Lifter |
38.18mm |
246/246 |
16BTDC/50ABDC |
54BBDC/12ATDC
|
| 1991 1.6L DOHC Turbo |
Solid Lifter |
38.74mm |
250/250 |
20BTDC/50ABDC |
63BBDC/ 7ATDC |
| 1992-93 1.8L DOHC |
Hydraulic Lifter |
38.89mm |
244/244 |
7BTDC/57ABDC |
58BBDC/ 6ATDC |
*Note that the lobe heights listed here are the MINIMUM heights to be within Spec. Actual lobe heights may be higher.
Understanding cam specs and their affects will help you select the best cam for your specific engine. The four important camshaft specs to understand are duration, lift, centerline, and separation.
Lift Duration
Duration refers to how long a valve is opened in relation to crankshaft rotation. This open valve time period is expressed in degrees of crankshaft rotation. So, a cam specification of 244 degrees duration simply means the cam holds the valve open for 244 degrees of crankshaft rotation.
As a general rule, more duration can be helpful in high RPM engines but not low RPM engines. The extra degrees of open valve time in high RPM engines gives the air flow a little more time to get into (or out of) the cylinder in spite of the piston's stroke. However, at lower RPMs, more duration can cause less power because the valves will be open at the wrong time in relation to the piston's stroke up or down in the cylinder.
Lift (Lobe Height)
While Lift duration refers to how long the valve is opened, lift is used to determine how wide the valve is opened.
If the valves are not opened wide enough, they will cause a restriction for the air trying to enter or exit the cylinder. However, opening the valve past a certain point will not increase the flow to (or from) the cylinder.
Centerline
The cam's centerline specification is used to tie the valve timing to the crankshaft's rotation. This spec is expressed as the number of degrees the crankshaft must rotate from top dead center until the cam has rotated to the peak (or centerline) of the lobe.
The centerline spec and the duration spec can be used to calculate when the valves open and close in relation to the crankshaft's rotation. When the valves open (or close) relative to the crankshaft's rotation is known as valve events or valve timing.
Understanding the effects of valve events or valve timing is the real secret to understanding engine performance. For the engine to run at its peak performance, the valves must open and close at the correct time in relation to the piston's position and the crankshaft's speed.
Separation
Separation refers to the spacing between the intake lobe and exhaust lobe on the cam shaft. The SOHC cam on the Isuzu engine is the only one that will have this from the list above. This spacing (or separation) is expressed in degrees on the cam, not on the crankshaft. So, a 108 lobe separation means the intake and exhaust lobes are 108 degrees apart from each other on the cam shaft.
This spec by itself really doesn't mean anything. Separation, just like centerline, is another way to tie the duration to the crankshaft rotation and end up with valve events. This spec is a little more complicated though, because it is in cam shaft degrees and the crankshaft rotates two degrees for each one degree of cam rotation. Also, if the cam has been installed either advanced or retarded, the valve events will be different.
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