I have a 351w in my 95 mud truck. It is the original motor with 180k miles on it. The thing runs great, doesn't smoke, leak, or burn any oil. I already have some head work done to the stock heads (larger exhaust valves), and a free flowing air intake (K&N FIPK) and full headers/exhaust. It is a speed density motor, and short of changing to Mass Air and doing a complete rebuild, I was wondering it if was worth going to a different cam (live an RV cam) and roller rockers to get a little more umph out of the old girl.

I am gathering parts to do a complete motor swap next year, but until I can afford that build, will I just be wasting money? Also, what would be a good cam to swap in? I have been looking at the Ford Racing Z303 cam (duration@.050": 228deg/228deg, lift: .552"/.552") even though it is for the 86-95 Mustang 302's, it should fit and work in the 351w, right?

 

Forget the FMS alphabet cams, you definitely need mass air to run them. To have any chance of decent operation on the SD computer, the cam has to have 114+ LSA and under 220 duration at 50 thou. Also consider that valve clearance will be an issue with longer duration cams, the pistons have no valve reliefs. As well, the stock heads stop increading flow after 0.500" lift.. even ported with bigger valves, so any more cam than that is wasted. The stock intake will also limit power production above 4500rpm, so everything is working against you at this point. Something like the Comp Cams 35-349-8 is about all the motor can take advantage of without an SEFI conversion, heads and intake upgrade.

 

Thanks. I knew that the stock intake is limited in how much it will flow. Which is one of the reasons that when I go to the stroker motor, I am switching back to carb so I can tune a lot easier and a whole lot cheaper. I do like the consistancy of the EFI, but cost to upgrade is nuts, especially for an off road use only truck.

 

Typically, the change to a higher exhaust-to intake valve size bias is for nitrous or forced induction, where more complete exhaust scavenge is required, due to higher cylinder pressures- it helps with exhaust reversion and contamination of the incoming air/fuel charge. Is this the reason for larger ex. valve only?


Pete

 

For more specific 351W performance ideas try the 351W forum...

 

It was an easier way to make the stock motor breathe a little better. Not set up for NOS (not yet anyways), and the larger valve is really not much bigger than stock, just slightly with a little porting to reduce some restrictions that the factory does for emissions reasons.