Does anyone know what the maximum valve lift I could have with the stock valve springs on a 1978 351M? I don't really want to change the springs if I don't have to since they are almost new.

 

>Does anyone know what the maximum
>valve lift I could have
>with the stock valve springs
>on a 1978 351M?
>I don't really want to
>change the springs if I
>don't have to since they
>are almost new.

Generally the upper limit to stock valve springs is .500" lift.

 

I just had my 400m rebuilt at an engine shop I wanted the same thing your talking about he told me that a 458 inch lift is the highest you can go without having to change your springs mine does very well with this cam I was impressed.

 

fastredford,

My Ford books list installed height spec for the 351M/400 valve springs as 1.820" and solid height spec as 1.33". That would allow a maximum valve opening of 0.490".

Some '78-'79 M-blocks had a shorter exhaust valve spring with installed height of 1.68" and solid height of 1.20". Those springs would allow a maximum exhaust valve opening of 0.480".

If you're going to change the cam, I recommend changing the valve springs (and retainers, seals, etc.) too. If your existing valve springs have seen a lot of use, they could be too weak to keep up with a good new cam.

BubbaF250

1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.