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I have read alot about this topic over the years and I have done this mod in the past but, I personally didn't see any advantage to using the 351W heads on my 302. In my opinion that seemed to be a step backwards.I didn't really notice any major power gains after doing the swap. It wasn't until I started doing some research that I found that most all of the early 351W heads have a larger combustion chambers which will effectively lower the compression ratio.'69-72 351W heads have a 60.4 cc combustion chamber as compared to a '68-70 302 2V which has a 58cc chamber or a '68 302 4V which has a 53.4 cc chamber. See the difference? So if all I was going to gain was the larger valves,then why not just put the larger valves into a set of 302s? I'd get the compression I needed and the flow capabilities I desired. I do this sort of thing for a living and I have compared the early 351s with the early 302s and in most ways the two are identical, with the exception of the valve sizes,cobustion chamber volume,and head bolt diameter. Runner volumes appear to be the same as well as port configuration. So after I did my research I went ahead and built up my 4V 302's.I did a mild bowl blend and port match, just like I had done on the 351 heads, and used the 351W valves,springs and hardware. With the extra compression, I noticed a major power increase right away,which is what I was after in the first place. This is only my theory and I'm sure someone will tell me that they have had great success with the swap, but in my own experience I didn't acheive the power gains that I was expecting and it left me a little disappointed.

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Thanks for the input.
I wonder why most aftermarket heads have cc's equal or larger than 351 w heads? Not only that but in my impression porting 351 w will get you flow numbers that are around what the aftermarket ones do.

If I use my 351 heads I'll be sure to mill them down a little. I did some reading on 351 W early heads, ford performance is saying that the intake is 1/8 inch larger and that the oval combustion chamber provides less shrouding.
 

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I am in the process of doing the 351W head swap onto a 289. The first thing I learned doing the research is the drop in compression. Since I'm building a new engine from scratch, I've elected to go with flat top pistons to compensate for the loss in compression due to the larger CC of the windsor heads. This way I don't have to shave the '69 heads (therefore, not effecting their resale value) and get all the advantages of the W heads without the one negative. One of my reasons for doing this swap is because I got a really good deal on these '69 heads that already have screw in studs and guide plates (and an equally good deal on the roller rockers).

I agree that without either shaving the heads or increasing the compression, there would be little or no gain with this swap.

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I built a stock 289 2V for my convertible.
For my fastback, I built a 302/351 Heads, Edelbrock F4B Intake, Edel 650 Carb and headers. I ported the heads to match the headers.

The difference in these motors was night/day, well beyond what the 4V/headers combo would add. That car had so much torque it was scary. I sold the car and kept the motor.

I'd do it again in a heartbeat.
 

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I also have made this swap many times...the 351 heads are a good choice but only if you have them milled, or swap out the pistons..but then again..I would ever use a set of used heads..302 or 351's without milling them..too many years of use takes it's toll...so milling is always my first step..if for no other reason then to true up the heads.



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I'm doing the 351W head swap... Got a set of 1970 heads... the biggest thing I learned was...

CHECK THE DATES OF ALL YOUR PARTS!!!

I have a 1978 302 these are going on. The heads have a volume of 68.4 cc!! My 351W heads are at 60.4 cc or something close. My volume went down, meaning compression went up. I went from an 8.4 to a 9.5. Always check these things.

Seems most everyone thought I was going to have a drop in compression because they assumed I was using a stock Mustang 302... (from the 60's).. Nope.

Rich
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'66, 302-4bbl, Granada disk brakes, etc, etc...
 
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