07-03-06, 04:03 AM
I am just curious if anyone knows the changes with the northstar, inparticular the 2005 with the 20 extra hp in the STS. I drive a 99 and I know they changed it some in 2000. Would someone care to give me a history on the changes after my 99 STS? I had the head gaskets go out on mine, did they finally fix that problem?
What did they do to get the extra 20 hp?
07-03-06, 09:31 AM
In 2000 the compression was reduced to 10:1, and roller cam followers were added. There's some other small changes as well. The 320 HP STS has Variable Valve Timing, so that's the reason for the extra 20 HP over your '99. But the 2005-up STS is a RWD engine, so there's a bit different with that one.
They also made change to the head bolts. Changed the thread pitch I believe.
07-03-06, 06:40 PM
^also changing from the FWD version offers better breathing room for the intake and the exhaust (I believe its a true dual pipe setup rather than Y split). The engine also has a 10.5:2 compression ratio in the RWD platform. Intresting enough in the change to the RWD drive engine cadillac once again suggests using 91 octane and up for full performance and fuel economy. Basically try it on premium, then drop to 87 or 89 and see if you can notice a performance drop, if you don't, you OK to use it and still will be getting full performance.
"STS Manual" states:
If your vehicle has the 3.6L V6 engine (VIN Code 7),
use regular unleaded gasoline with a posted octane
rating of 87 or higher. For best performance or trailer
towing, you may choose to use middle grade 89 octane
unleaded gasoline. If the octane rating is less than
87, you may notice an audible knocking noise when you
drive, commonly referred to as spark knock. If this
occurs, use a gasoline rated at 87 octane or higher as
soon as possible. If you are using gasoline rated at
87 octane or higher and you hear heavy knocking, your
engine needs service.
If your vehicle has the 4.6L V8 engine (VIN Code A),
use premium unleaded gasoline with a posted octane
rating of 91 or higher. You may also use regular
unleaded gasoline rated at 87 octane or higher, but
your vehicle’s acceleration may be slightly reduced, and
you may notice a slight audible knocking noise,
commonly referred to as spark knock. If the octane is
less than 87, you may notice a heavy knocking
noise when you drive. If this occurs, use a gasoline
rated at 87 octane or higher as soon as possible.
Otherwise, you might damage your engine. If you are
using gasoline rated at 87 octane or higher and you hear
heavy knocking, your engine needs service."
07-06-06, 03:01 PM
If you goto Caddyinfo.com, Bruce has all the differences from year to year listed.