Ok, now I'm really confused. I've had friends tell me that I could swap out the 302 heads with 351 heads. Yesterday, a mechanic friend said that I couldn't do that. I asked if he was sure so he called another mechanic that specializes in Fords and he agreed saying that the heads won't fit. Is he right? Not that it matters, I've decided to stick with the original heads. More of an FYI.
Your mechanic and his "specializing" friend need to find different jobs... Yes, they will fit. That's all we had back in the bad old '70s and '80s. I ran a set on my 302 for many years. With the available aftermarket heads we have nowadays I don't think it's worth the time and effort to build up a pair of 351Ws.
They will fit but 351 heads use 1/2" head bolts and 302's use 7/16 head bolts so the holes for the bolts on 351 heads are bigger. You can get adaptors to take up the extra space in the holes for 7/16 bolts.
I did this swap on a 289 HiPro back in 70.....................you can buy the bushings from Summit.........I would recommend this as it centers the head on the block. Remember, when using any other 351w head than the 69/70 4brl head you will loose compression.........at least 1 to 2 points because the later heads are open chamber............the early heads have a much smaller combustion chamber.....................and you will most likely end up using steel shim head gaskets to keep the compression as high as possible. Also, use the 351w intake gaskets as the water outlet on the head is a L shaped port unlike the 302..................if you don't it will leak. You will also need to change over from the rail rocker to a screw in stud............I don't remember how much has to be milled off the pedestal.............and while you are at it port the intake/exhaust and add bigger intake valves, I think I used 1.94's from the stock 1.8........it's been a long time. By the time you have had this done work you could have purchased a set of aluminum heads which will really wake up that tired ole 302............IMHO Also, I think I would get to know some guys who really understand Fords, as it sounds like you friend and his friend are "shadetree mechanics" with little knowlege of SBF's.
I wasn't really talking about what you "can feel".. only that adding compression to an older smog motor is the single most important factor in waking any motor up all across its rpm range... idle to redline. No cylinder head will do that through flow numbers alone. Compression is universally good for any internal combustion engine up to the fuels allowance. You typically gain higher average power with heads through shifting the range higher up the rpm curve. Especially true with higher end heads. With compression you get it EVERYWHERE and that my friend lets you have your cake and eat it too. IMHO, the most beautiful thing about higher compression is that it makes even a larg'ish cam seem smaller and allows for a fatter torque curve.. without losing peak power up top(although you will peak earlier if the intake/carb/exhaust is already restricting the current cam/heads). Well.. that and the beautiful sound of healthy 10+ CR engine. PS. I would be looking for some used aluminum heads.. or going to higher compression mid '66, or earlier, 289 heads. Really easy to build a stock headed 350 horse 302(that still has tons of low-end torque) with just a little port work and some milling. Even 400 horse isn't out of the question if you really like to rev it. Plus, I can tell you from experience that it really stings another guys ego to see stock parts under the hood of a car that just showed him its tail lights. That's gotta be worth something too. lol
Ford dealers actually sold special bolts for this swap over the counter, slightly longer 7/16" bolts with an integral washer. That's what I used when I did mine.
That's the way many did it. Ford's contention was that you loose some thread length by using washers with stock head bolts and it would be better to have the bolts install deeper. I know of a couple people that didn't even use washers... LOL
I think we may be misleading somepeople on here that compression is the key to HP. Compression is only a small part of making HP and if you were to to take a stock 210hp 302 with it's 9.0 to 1 CR and put say 11.0 to 1 CR pistons in I would venture a guess of only 5% gain in HP............and even with a 302 that makes 310hp and change from 9.0 to 13.5 I can't see making more than 10% more power. My old 408 had 14.5 to 1CR and when new was probably around 650hp (I believe it was setup to run Alcohol and race gas)..................we dropped the CR down to 13.5 to 1, changed the cam and headers and made about the same HP with less compression...............642hp to be exact. So, depending on what you are going to do with the motor, compression is only a part of equation. I have personally never experienced a 40HP gain although I have never taken a stock motor and just added compression..............usually it has been a motor making over 400hp...................and even then it has still been in the 5% range.........................................just from my own personal experience.
No need to dig too deep between the lines of what I wrote above as I was merely generalizing. And of course it just depends on the motor and level of parts already bolted on it.. but I have added 1-2 points of compression to stock motors well more than a few times.. and with properly matched tuning it will literally wake them right up. Night and day difference. To me.. "night and day" STARTS at around 30 horsepower and goes up from there within this particular context. And I won't even get into the potential part throttle mileage gains that a point or two of compression and more agressive timing adds during cruise mode. 3-4 mpg is REALLY easy to find with proper tuning.. and even more is available with tire size or gear ratio changes.
Sorry, wasn't trying to dig deep, just wanted to make a point that compression is just one of the keys to unlocking HP.:Handshake
yep.. no doubt... it's just the foundation from which we build on. The way I really look at these types of lower budget builds.. is that once you tally up the cost to freshen up a set of larger chamber smog heads.. it's almost downright silly to not find a tighter chambered design and take a step up from where you're already at when the price is so close. Plus it sets you up for even larger HP jumps down the road when you add bigger cams/intakes/headers to take advantage of the better pumping efficiency. 1.5 - 2 points added now.. will keep it from becoming a turd down low when you add all that extra airflow potential. IMHO, adding compression is quite literally the best bang for the buck you can do to a lower compression motor since you will see gains everywhere. That's what the factories did on all their high-performance versions since larger valves and bigger cams alone just won't cut it. And the increase in efficiency and part throttle power can be easily used to overcome the higher cost of the premium needed to run it. That is, if you can fight the urge to stop jabbing the throttle too often for chirping tires and enjoying all that newfound torque that compression will add.
