Initial timing specs for 1975 400 small block

[Billhilly]

I finally got my truck on dual fuel (petrol/propane) and am having timing issues apparently...The PO put a 400sb out of a mid 70's truck in. Casting number is 330817. I'd really like to find what the OEM timing specs were, especially initial. My repair manual that covers the right era says 'look at the sticker under the hood'.... Helps alot!
One of you guys with a squarebody must have a 400sb in there. Or point me to the right place on the net. I can't see anything at this stage. Thanks!

[leftybass209]

Is that 400 bone stock, or do you suspect the cam has been changed? If the cam were changed, you will most likely need to play with the timing a bit.

Try to find a chassis manual for the 75 trucks.

[geezer#99]

According to my 1976 motor auto repair manual, all the 400's had an initial timing of 8 degrees.
The manual also has some dizzy specs if you can get the number off yours if it's a stock one.

[leftybass209]

What I got in the GM 1976 manual was 2 degrees BTC for a Cal. Emissions 400, and 4 degrees BTC for a Federal Emissions 400. 8 degrees for a 350.

Distributor advance is 2 degrees difference between the two, maxing at 20 or 22 respectively.

[Billhilly]

Thank you guys! Yeah should of said, motor is stock, dizzy is an MSD 8361. Looks like I'm going to have to change the advance stop bush (need less centrifugal) and make up something to limit the vacuum advance as well. Fun times!
As I said my Haynes manual explained how to adjust the dizzy, but had no actual numbers at all. So 4 and 22 is quite a bit less than I've got....... This propane deal is just different again funnily enough!

[davepl]

I'm normally the guy yelling "Do whatever the factory did" but they likely had that thing super-retarded to keep the exhaust hot so that the AIR injection and new catalytic converters worked.

Unless you're feeling nostalgic, I'd aim for what runs best, maybe starting around 8 BTDC, to be honest...