1. I have a 78 F-150 w/351M, I found out FoMoCo retarded the cam on these motors four degrees, can I take this retardation out by replacing the timing set with an aftermarket set (double roller, gear, ect.) or do I have to change out the cam and timing set?
2. what's the difference between "open & closed combustion chambers" in cylinder heads? Any info helpfull.

i have a 79 with a 351m and from what i understand
some aftermarket timing sets for the 400, 351m and the 351c
fix this... now it depends on what year the set is for.. i found that everyone that fixes "factory Retarding" says *Not legal for sale or use on pollution controlled motor vehicles. i priced an edelbrock true rolling timing set (part no. 7821) to fix that problem at 94.00$ canadian, and yes it can be used with the stock cams. if your motors in good shape i hear its a good way to wake that m up, also you should think about a 4bbl intake manifold to put on there... from what i hear you'd get more power and better gas mileage. i have a performer 400 to bolt onto mine, just havent gotten around to it.. ill let u know how it works when i do put it on.

1) Looks like <font color="blue">79f1504by4</font color> took care of that.
And, yes, the 4° change (advance) in cam timing will make a good bit of difference. [img]images/graemlins/burnout.gif[/img]

2) Open and Closed chambers refers to the design/shape of the combustion chambers.
Open are more of an O shape, while closed are more D shaped.
I don't recall the difference in CC's of each, but the open are considerably larger,
hence lower compression with every else on the engine staying the same.

Here's a shot of what a "closed" chamber would look like, albeit, my 351W, not 351M.
Note the "D" shape.


Ah ha! [img]images/graemlins/grin.gif[/img]
Here's some good reading for you.

Thanks 79f150, I was not sure if the cam had anything to do with it or if I could just do the chain &amp; gears for now. It does have a Edelbrok intake, 4bbl carb, &amp; headers.But as far as I know that's the only mods done to the engine, I bought it a couple years ago from the second owner (he had almost 13 yrs), he only used it for work &amp; to haul fire wood.
I found timing sets at Summit that are adjustable from $50-$130 + S&amp;H.
Thanks WD40, when you explained it I knew what you ment just never knew there was different names for combusttion chambers.