Thread: 351 Cleveland needs more hp

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No man, your questions are very sensible.

Ok, you've got points........get the appropriate Pertronix kit, and sure, step up to a hotter coil. It will fire your plugs better. Talk to Pertronix for their recommendations. You may want to step up to better plug wires at the same time to take advantage of the new spark.

As for vacuum advance distributors versus mechanical advance.......here is all you will really need to know about that subject. Most cars come from the factory with distributors that have both mechanical and vacuum advance to advance the timing as needed. Race cars generally use only mechanical advance, and some guys try to run them on the street, but quite often the car will overheat because it isn't getting advanced properly at low speeds, and a retarded condition occurs. This makes the car run hot. You have vacuum advance, so don't mess with anything there.

Your Cougar most likely has what is called a 9 inch rear end. That number refers to the diameter of the ring gear. (you can't see the ring gear, it's inside, so don't sweat that piece of info) You could also have an 8 inch rear axle.....also refers to the diameter of the ring gear. Of the two, the 9 inch is stronger and more desirable, but even if you have an 8 inch, you will be fine in the hp you are putting out.

Here is how you tell which one you have: Take a 9/16 inch deepwell socket and try to put it on the two or three (I forget) bottom nuts on the very bottom of the rear end center section. This part is called the pumpkin in common terms by car people. If the socket will go on those nuts straight on, you have an 8 inch. If it will not go on, and you need a box end or open end wrench to remove those nuts, you have a 9 inch.

Now, how do you go to a deeper gear ratio? Two ways. You either remove your axles then remove the pumpkin (by removing all of the nuts around the perimeter) and you either replace the entire pumpkin with one that has already been fitted with the desired gear ratio, or.......you take your old pumpkin to a shop that does hi performance work and you have them remove your old ring and pinion and put in the new set. I like keeping the old pumpkin and buying one already set up, as you may want to go back to the 2:75's some day for gas milage reasons.

Your old axles do not get replaced in this switchover. You mention not being mechanically inclined, so for the first several steps you may want to seek out a small garage that has a good reputation in your area to do things like the rear axle swap.

Not trying to steer you into any particular direction, but gears are a great place to start, and you will feel the difference immediately. However, gas milage will suffer, but hey, we have to keep those guys in ski lodges, don't we???



If it were me, I would put in either 3:50 or 3:70 gears. Both are tame enough to be ok on the street, but will still give you a noticable kick off the line, especially with the automatic. My roadster runs 3:90's and it is perfect for me, as I am running 30 inch tall tires which drop the ratio to maybe 3:70 or so.

Next point. Ford used either 28 spline or 31 spline axles on these units. 28 is considered weaker, but still fine for your application. When you pull out the axles, count how many splines are one one of them. That will be the same type you need to buy to replace the old pumpkin.

I see guys on ebay selling rebuilt rear ends, ready to install, all the time. If you pay attention to their feedback rating, you should be able to buy with some degree of confidence from them.