Hello Mustang aficionados,
Recently i've decided to swap gt40 heads I have onto my 69 302 block and came across the subject of steam-holes. I know there have been many threads about the steam-hole dilemma, but in my hours of reading, I did not find many that provided a good account of just what was going on with the steam holes and why it should even matter. So, being in the unique position of having an old 69 block as well as a 96 5.0 block in-front of me, as well as multiple sets of heads, I decided to put together a guide demonstrating the differences in the blocks and heads. Ultimately, its so you can make an educated decision on what's right for you. Disclaimer: I am not a ford engineer nor master engine builder. I can not account for all renditions of 302 blocks and heads out there, but my goal is to provide lots of pictorial evidence for which you can compare your combination to. My hunch says most blocks will fall into these two categories. 289's i'm not sure on, as they supposedly had different steam hole transfer ports then the 302's did.
Steam-Holes, What Are they?
What many refer to as steam-holes on 302 engines are these water passageways that appear on the block and head. They differ in location based on the generation of block. The images below show the block and cylinder with their accompanying steam holes. Figure 1 demonstrates the 69 302 with 68 302 heads, and Figure 2 demonstrates the 96 5.0 roller block with Gt40 heads. notice the steam holes and how they differ in location between the two blocks, while other passageways are the same.
Next I will be comparing the steam-hole locations with the FELPRO 9333PT1 gasket in place. This gasket will work on all blocks from the 260 to the 351. We are interested in 302's from 68 to 2000 or whenever the last 5.0 left the assembly line. Pay attention to the different steam-hole port locations used in the gasket between the blocks. Figure 3 Is the 69 Block with the 68 head and Figure 4 is the 96 block with GT40 head.
Next I will overlay the GT40 head onto the 69 302 block, where I intend to install it. Take note of where the two steam holes would end up. They would not line up at all. Also note, highlighted in green, that the 69 block has coolant ports not utilized in either head.
So what does this mean? If I were to install the GT40 head onto my 69 block, passageways that were intended to be used in both components would now be rendered ineffective. In my research, I had found some threads with individuals claiming that ford had actually completely done away with the steam holes in later blocks, determining there was no need for them. I believe this to be false, as ford had only changed their location, not function. But what does this mean? What is the result if they are mismatched?
The Steam-Hole Debate
Here's the reason I spent so much time researching. In almost all my threads existed those who adamantly believed the steam-hole was a necessity, and those who did not. It seemed there existed people who never drilled holes and have had no issues, who never drilled holes and had issues, and who drilled holes and never had issues. The biggest issue with the steam holes I believe, are individuals who do not want to drill into their block or heads to add them if they don't need to. Adding features that are not currently there can be a little daunting. I myself was in this boat. As a foreshadowing, let me express the task really isn't hard at all. I was all but ready to go down the path of not drilling the holes if other's hadn't and experienced no overheating issues, until I read one post that changed my mind. In this posting, the user had stated that not drilling the holes does not guarantee you will overheat, what not drilling the hole grantees is that you may develop isolated hot-spots around cylinders that can lead to issues such as detonation in a single cylinder and even head-gasket failures. Your temperature sensor can be fully immersed in coolant up top, and read ok temperatures while a cylinder may be experiencing an airlock around it due to trapped air, and it could get much much hotter in that localized zone. This immediately made sense to me, and is the reason I set out to do this analysis. Hopefully what is clear to me is clear to you now with the pictures above. The gt40 heads on this 69 block isolates passageways in the block and head that should be exposed to each other. Just because some people claim to run fine without the holes, doesn't guarantee I will, as every combo is different in terms of heat generation within the cylinders and detonation thresholds. Even without detonation, you could have cylinder distortion occurring due to un-even heat distribution within the cylinder. So for me, I determined adding steam holes was a necessity.
Adding Steam Holes
It seems people approach this task in two ways, drilling into the block or drilling into the heads. To me it seemed like drilling into the heads would be the route with the least risk. If something could go wrong, heads are a cheaper replacement item than the block. But if you sit an think about it, adding the steam-hole in either the head or block does not prevent you from later using an older head on the block or gt40 again on the 5.0. The gasket will isolate the incorrect steam-hole from use. I elected to go the head route.
First I sat the heads next to each other as seen in Figure 6. It seemed to me that if the water passageways were the same in both heads, I could just simply add the hole to the GT40's. But I needed to confirm that I would be drilling into the coolant passageway and not the intake runner, because on inspection, it looks like you'd be drilling straight into a runner. Figures 7&8 demonstrate me using a ziptie in the GT40 head to see if it seemed like the passageway would lead right under the spot the steam-hole would need to go. It seemed like it did! The ziptie went straight down with no deflections.
Trusting the ziptie test, I removed the dowels from the engine block and used them to align the head-gasket on the head. I then used a sharpie to mark the steam hole locations and punched them with a center punch. Figures 9&10 demonstrate that process.
Then, I drilled out the first hole with an 1/8'' drill-bit. I used the ziptie to check weather my assumption was correct or I had just ruined a 93 cobra head, luckily I was right! You can see the new steam-hole shares the same water cavity as the old one!
So I finished drilling them all out, then followed up with a 1/4" drill bit to make the steam hole slightly larger than the hole in the gasket. I did this to account for any holes stamping variations that may appear in future gaskets down the road, ensuring the hole won't be partially covered. Figure 12 below shows the holes all drilled. Now the wet cavities in the block and head will be connected just like the good Ford intended.
Hopefully this analysis helps shed some light on just what is going on with steam-holes in-between these two different block generations. Now, these two blocks are literally on the opposite ends of generations, my 69 block is just one year after the 302 was introduced and my 96 is from the last few years of 302 production. That means there is plenty of generations that could have their own quirks concerning passageways. But I do believe, at least in this instance, I have shown that each head has the same coolant cavity that is supposed to interface with the engine block. By not adding the appropriate hole, you are eliminating a feature ford still had on their last generation blocks. Even though some claim to be fine without the steam-hole, the relative ease of adding them makes it practically a no-brainer. Ultimately it's your ride and your call. Thanks for reading!