AZ455

I think I may be answering my own question with this one, but was curious to hear what those of you who know for sure have to say about this.

In the 1974 CSM, Tune-up Specifications page (6C-13) there is a list of many many of the same engine, 350 or 455, with different engine codes and vehicles they were installed in.

I notice that most of the 455s have a different timing specs. For example...

455 [UV, UX] CUTLASS - 14° @ 1100 RPM + 26° MECHANICAL @ 3000 RPM

455 [UL, UA, UC] CUTLASS, WGNS., 88&98 - 8° @ 1100 RPM + 18-22° MECHANICAL @ 3600 RPM

SO, what I see is that the same 455 (I assume?) with the same compression ratio installed in two different vehicle types that have different initial and total timing. The large cars start with much less initial and end up with less total when the mechanical advance is all in than the Cutlass only spec.

My question is, are these differences due to installed rear end gear ratio and weight of the vehicle they are going to be used in? I figure the Cutlass can get away with 12/14° since it's lighter, and there is less engine load to get it moving. Even the Toronado spec is 10°, no idea what it's final drive ratio is though. Am I way off here?

The main thing that brought this to mind is I am running my Delta 88 at 12° initial, when my spec is 8°, and I am getting some pinging under hard acceleration. I plan on attempting to remedy this by using premium fuel (don't want to run 8° initial, I like the extra power).

Sorry about the long post, thanks for reading.

joe_padavano

Keep in mind that in addition to different vehicle weights, these engines have different cams, different mechanical and vacuum advance curves, etc. A lighter vehicle (or one with steeper gears) can use more advance since the engine will rev faster. Lugging the engine in a heavy car will lead to pinging.

oldcutlass

Timing is also something that you need to experiment with. Set it to what the motor likes, as all the literature is a guide.

AZ455

Thanks guys. That is what I figured. Although I did not know the same year 455s had different cams depending on vehicle application.

I reset my dwell and made sure timing was at 12 deg still, put in some 91 octane, pinging is gone. This engine is a slug from 0 to about 10mph at 8 degrees, can't live with that.