What is correct initial timing for 1957 250hp FI?

[Duke W.]

Re: What is correct initial timing for 1957 250hp FI?

How about the technical information you can download from the GM Heritage Web site. Are the 905 specs there?

Duke

[William C.]

Re: What is correct initial timing for 1957 250hp FI?

Per Delco Remy Service 1D-186, dated 1-1-62, '905 Specs are 1-5 degrees @800 rpm, 13-17 degrees @ 1550 rpm, 19-23 degrees at 3200 rpm, and 26-30 at 5000. All figures are crank degrees and engine rpm, to simplify things if you don't have access to a distributor machine. Readily available info.

[Peter R.]

Re: What is correct initial timing for 1957 250hp FI?

I wasn't aware of the data available from the GM Heritage Center web site, but I found it, downloaded the 1957 data, and looked at it. A lot of good information. There is centrifugal advance data for a couple of V-8 distributors, but not the 905. There is a Corvette supplement in the data, but only a footnote about the 905, not specs.

As far as the Delco-Remy Service info, where does one find that? Thanks for the 905 specs. Those data are in crankshaft degrees, so I divide them in half for distributor degrees? When I read degrees of advance using the timing light and the harmonic balancer mark, which type of degrees am I reading--distributor or crankshaft? When we're aiming for 36 degrees of total advance, is that distributor or crankshaft degrees? This can be confusing.

[William C.]

Re: What is correct initial timing for 1957 250hp FI?

OK, the distributor runs at half engine speed, so the advance specs I gave you are as measured with a timing light on the engine. The published specs are not real useful unless you have a distributor machine in your garage, but not too many of us have that so I generally try to make the info something that could be used by a person with a tach and a timing light. If you have a distributor machine and need the info, divide the rpm and advance by 2, or email me and I can scan the info and email you a copy. As for finding the Delco service info. it's in my personal library as a result of visiting many auctions and buying distributor related info over the last 40 years or so. If you really feel a need for a copy, I'd likely try a literature dealer or regular visits to the fleabay. Using a timing light you are looking at crankshaft degrees, and crank rpm as provided in my message.

[Peter R.]

Re: What is correct initial timing for 1957 250hp FI?

Ok, Bill, thank you. That helps. So it would appear that when I'm seeing a max advance of 18 degrees (with around 4 initial), I am having a problem with this distributor. I will proceed to pull it out and take it apart to see what's going on. I'll let you know.

[Peter R.]

Re: What is correct initial timing for 1957 250hp FI?

Well thanks for all the great help and advice. Wow!!! I just got back from driving the car in the neighborhood. Problem fixed!! What a nice driving car now--a real cruiser. Sunday I pulled the distributor, disassembled it, cleaned everything thoroughly, with special attention to the centrifugal advance mechanism. The weights and other parts of the centrifugal advance mechanism didn't really look all that bad but were uniformly covered with a thin coat of gray grime. At first I almost thought that gray was their natural color and that everything was fine, but after further disassembly and application of a little solvent, I could see it was grime. After the cleaning, I coated all friction surfaces with a light coat of ignition lube (a 25-30 year old tube). Apparently the weights were just sticky enough to limit the advance to only getting 18 degrees total, which included 4 degrees initial. That's what was causing a lack of power, backfiring (it sounded like backfiring into the intake, but maybe not), and general rough running above 2000 rpm or so. I still have to tweak the dwell a bit, but this is by far the best day since I got the car almost 6 weeks ago. Thanks again.

[Alexander C.]

Re: What is correct initial timing for 1957 250hp FI?

Great to hear!