The problem with the typical sbf 289/302 head is that they don’t breath well especially on the exhaust side. As you found out it starts to lay down around 4000 rpm. The object of installing a cam to make more HP is to move the point where the engine makes it’s peak power to a higher RPM. This means you’re moving more air/fuel in the same time period this making more power. When you do this you’re also taking away lower RPM power. If you install a cam designed to make more power at a higher RPM with a set of cylinder heads like the sbf that don’t make power past 4000 RPM, you’re still not going to make more power. What you will end up with is a motor that makes less power everywhere and performs poorly. It all has to be matched, intake, exhaust, cam, heads, gear ratio, shift points and converter stall speed if automatic.

You can buy heads that flow better or modify the stock heads to flow better. You could easily have as much invested or more in stock heads then just to buy a set of aftermarket heads. With better breathing heads, you don’t need as much cam timing either for your HP goals. You’ll end up with a motor that has a much broader power band then sticking in a big cam on poor flowing heads even if both make the same peak power.

The other thing with a larger motor, you don’t need to rev them as high. That’s why Americans like big V8’s. They just loaf along quietly. Before automatic transmissions big engines were used so you could drive most of the time in high gear and not constantly shift.

In my 66 I have a Explorer GT40P. The GT40P heads are probably the best mass produced sbf made. Over a stock 289/302 they’re probably worth about 30 hp. That’s enough to make a nice difference. I run a stock Mustang 5.0 cam and with the better breathing heads it makes a nice broad power band that will very easily rev past 5000 but will cruise at low speed in 4th with a 2.80 gear ratio with no issues.

When picking a cam the absolute best thing to do is call several cam companies. You’ll get FREE EXPERT advice. They will ask you all sorts of questions about your car and how you drive. You will get the right cam this way.

6sally6 wrote:

Have you "modified" the ignition curve in the distrib.? Lighter springs etc.?
Lotsa power locked up in the duraspark....FoMoCo set them up for better gas mileage and didn't worry too much about performance.
Get the full advance in by 2000 rpm and a total of 36*.
Tell me you have already done this!!.......Don't make me upset with you!!

Thanks but i do not have spring in my distributor .  i think are in the 302's....
Lotsa power locked up in the duraspark.   What this means ? 
i will do for sure step by step  the distributor . i would never upset Sally  

Alessandro - here is a link about recurving Ford distributors to advance the timing quicker.

https://www.modmotortech.com/forums/internal-external-engine-22/ultimate-duraspark-ignition-timing-guide-598/

The hydraulic cam 289s don't really like to rev.  Its sounds crazy since the engine is so small, but Ford built them to make as much low speed torque as possible, and they actually do an amazing job of it, with over 300 lbs/ft.  The downside is they are done right around 4,800RPM.  You can rev them higher, but get nothing out of it.  With a Performer intake, 500cfm Edlebrock carb, JBA headers, 2-1/2" Magnaflow exhaust, and recruved distributor with 38 degrees total timing I find mine pulls strong to about 5,000, but that's about it.  I know I'd have to change the cam and/or heads to get any more power out of it.  I had a strip trip planned for late October, but after making the trip the track was closed due to cold weather (?) and "high winds" (didn't feel any wind that night to speak of).  One thing I was going to play with after getting a consistent launch was shift point.  Previously in stock form, crazy as it sounds it wanted to shift at 4,500RPM.  That's how I got my best times out of it, which were a string of mid 15s. 

You can measure the circumference of the damper with a flexible tape measure, then divide the number by 360, take some tape and a ruler and mark off timing marks based on your result.  Then just sick the tape around the damper starting at 0. 

I've done this a couple times when a timing tape wasn't available.  FWIW, its nice to have marks at 90, 180, and 270 too in case you ever need to lash the valves.