As we started planning the stroker buildup on our 351 Windsor block we got to the head selection process and like millions of car guys before us were a little taken aback  by the sheer volume of selection available for aftermarket performance heads. Any given speedshop will quote you on a half dozen heads for any given application you are after with prices ranging from $900 a set up to $2500 a set and beyond. For some of us, by the time our $2500 heads get the valve train installed and put onto the motor they will probably be the most expensive piece on the car. So are they worth it?

Why the massive selection of heads? Why all the different specs? What do they actually offer over each other? Back 20 years ago guys would port up a nice set of 69 Windsor heads due to their huge valves and be off and running so why the big jump to such variances in aftermarket pieces? Well the fact is that the heads of your small block Ford are the true key to unlocking the hidden horsepower of your motor. Just tossing on a “stock” valve train and bolting even the cheapest set of aftermarket heads to your engine will give you an easy 30-40 horsepower gain. What we are going to attempt to find out is what heads make what differences where so that we can find the right heads for our 383 stroker build.

When working on or choosing a set of heads you want to start with something that is right for your application. Going with too big of a head or chamber will actually rob you of low end horsepower since they hardly start working until they hit 3500 RPM or higher. We’ve decided that our car is going to be a street car slash daily driver. We are looking for performance from idle to 5500 RPM. Our engine stock came with a compression ratio of just under 9:1 and we are looking to move that closer to 9.5:1 for that little extra oomph. Since we are building up a stroker block we also have to consider exactly what dished pistons we will be using to allow for better valve clearance especially at higher RPMs when narrow tolerances can be highlighted by a floating valve or worse.

Let’s look at some of the “stock” choices for our 351. First there is the old standby 69 Windsor heads. These things are getting real hard to come by these days and when you do find a set they are generally used and abused or the seller wants an arm a leg and a half a pound of flesh for them. The 69 heads stand out because of their massive intake and exhaust valves. With the intakes running 1.84” and the exhaust at 1.54”, these were the biggest ports that Ford put on their small blocks including all of the GT and cobra mustangs right through into the latest generation of Mustang heads. Just to give you a fair comparison, the 5 litre cobra mustangs of the 80s sported a similar intake of 1.84” but the exhaust valve was only 1.46”. Yeah I know we are talking about fractions here but untill you put these bad boys on a bench flow tester and look at the results you can’t truly appreciate the massive difference that little bit makes.

Before we start looking at the actual flow numbers here I wanted to interject some facts about the improvements in head technology over the last 40 years. I think it would be pretty lame of Ford’s engineers if they hadn’t found some significant improvements in basic head flow and chamber design in the 40 years since the 69 Windsor heads were produced right? The fact is there have been some very significant changes in the head flow and even though the exhaust port on the 69 Windsor is slightly larger than the stock 5 litre head from 87 the improved flow technology gives it a better flow result. This is good news for us in that we all don’t have to run around for months looking for an old set of Windsor heads to bolt on. Keep in mind though that if you do happen to have an opportunity to grab a set of 69 Windsor heads, there are one hundred and one articles floating around the Internet that give detailed porting and polishing walkthroughs to unlock at least another 10-15% flow with them.

The first comparison I checked into was the cast iron GT40P head. It’s very similar to the GT40 head but with better sparkplug placement closer to the center of the chamber. Unfortunately that really makes them a bear when it comes time to put exhaust manifolds on your car so if you end up wanting to try the GT40Ps make sure you look into headers and special plug wires first to save yourself a ton of grief. The flow was measured at each tenth of lift up to .6 for each head. The 69 Windsor intake port flow numbers from .1 to .6 lift consecutively were 58.7, 105.6, 152, 171, 181.5, 189 with exhaust port numbers of 51.8, 90.4, 106.8, 112.9, 114.8, 115.4. By comparison, the GT40-P heads produced these numbers 61, 128, 169, 195, 196, 193 on the intake ports and 52. 90, 123, 135, 139, 142 on the exhaust side. Obviously big advances were made in the exhaust port design in the GT40 head as it produced an easy 20-25% gain on the exhaust side even with the slightly smaller valves.

Ok so all we know at this point is that if we come across a set of 69 Windsor heads they wouldn’t be too bad with a little porting and polishing and even better if we came across a cheap set of GT40 heads. These are the numbers that those of us with small pocket books will probably have to be content with. Now let’s take a look at what happens when you can drop an extra couple grand on a real set of decent aftermarket heads.

First up are the AFR 165cc heads for the Ford 351 small block. These guys sport a 1.9” intake and 1.6” exhaust port setup. The flow for these heads metered as follows: N/A, 123, 186, 225, 250, 250 and on the exhaust they ran NA, 115, 153, 178, 185, 191. The clear difference from these heads to the stock heads is their ability to just crack wide open and stay wide open granting as much flow as possible as quick in the cycle as possible.

Now let’s check out the Edelbrock Victor Jr. heads. With an intake diameter of 2.05 and an exhaust of 1.6 I am already sure these things are going to punch out some crazy airflow numbers. Here they come: 63.7, 127.3, 177, 229.2, 268.8, 288 and exhaust ran 54.1, 106.8, 151.6, 181.5, 205, 217. Let’s chart these guys:

No real surprises here. Bigger valves generally mean bigger flow as long as they are coupled with a decently engineered head. Always get flow test results for any head you are considering purchasing. The results can be surprising sometimes and will often show signs of good or bad engineering. You can put as big of valves into your head as you want but if the channel design is inhibitive you will never truly unlock all of that hidden horsepower in your car.

There are literally 20 or 30 sets of aftermarket heads out in the market today for your small block Ford powerplants. After searching for weeks for the right ones for my stroker I am still not finished digging. The one piece of advice I can pass on to all the rest of you guys though is dig up as much info as you can on heads you are looking at. I know that if I am going to drop $2000 on a set of small block heads I want to make sure I’m getting every last pony out of them for the dollars I spend.

Good luck in your hunt.