Gt40 heads on a pre-h.o block: Steam-holes, a guide and walk-through - Vintage Mustang Forums
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post #1 of 15 (permalink) Old 10-27-2018, 04:20 PM Thread Starter
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Gt40 heads on a pre-h.o block: Steam-holes, a guide and walk-through

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.

Figure 1


Figure 2


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.

Figure 3


Figure 4


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.

Figure 5


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.

Figure 6


Figure 7


Figure 8



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.

Figure 9


Figure 10


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!

Figure 11


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.

Figure 12



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!

-Scarlet 302
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post #2 of 15 (permalink) Old 10-27-2018, 04:52 PM
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VERY good read.
I may try this on my pro comp heads.
But scary stuff drilling into brand new heads for sure.....

Dang it, I was just going to slap mine, now you got me rethinking it.



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post #3 of 15 (permalink) Old 10-27-2018, 04:53 PM
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The water jacket holes in the block and heads are quite often much larger than the hole in the gasket. Ford engineers obviously did that to insure that the holes in the head and block lined up with each other and the hole in the gasket actually controls the amount of coolant that flows from the block into the head through the gasket. So when drilling steam holes in the head or the block it is OK to drill those holes oversize but in no circumstance should the holes in the gasket be drilled larger.


Also, my Ford Racing Boss 302 block has siamese cylinders IIRC. Therefore no coolant can flow between adjoining cylinders. In that situation the steam holes serve a definite purpose exactly as you have described concerning "hot spots" around a cylinder.

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post #4 of 15 (permalink) Old 10-27-2018, 05:16 PM Thread Starter
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Quote:
Originally Posted by mikeyhunts View Post
VERY good read.
I may try this on my pro comp heads.
But scary stuff drilling into brand new heads for sure.....

Dang it, I was just going to slap mine, now you got me rethinking it.
I am not familiar with pro comp, i'm assuming they are aftermarket. I would investigate, as aftermarket heads could possibly be handling coolant delivery differently. I know some of the heads such as edelbrock do have spec sheets that ask for steam-holes to be drilled. Best of luck!
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post #5 of 15 (permalink) Old 10-27-2018, 05:28 PM
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Great post! As you said this topic comes up time to time.

Tom

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post #6 of 15 (permalink) Old 10-27-2018, 06:08 PM
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I am in the "don't bother" camp. There is, of course, no steam in an engine operating at normal or even high normal temperatures. Any coolant that comes through these holes never makes it to the rear of the engine block and heads, so has the potential to allow the rear cylinders and rear end of the head to run hotter. If you have good flow this is insignificant, but again, why bother? Coolant at 16 psi doesn't boil until roughly 250F, which is way above overheat condition, 220F.

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post #7 of 15 (permalink) Old 10-27-2018, 06:30 PM
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Quote:
Originally Posted by 22GT View Post
I am in the "don't bother" camp. There is, of course, no steam in an engine operating at normal or even high normal temperatures. Any coolant that comes through these holes never makes it to the rear of the engine block and heads, so has the potential to allow the rear cylinders and rear end of the head to run hotter. If you have good flow this is insignificant, but again, why bother? Coolant at 16 psi doesn't boil until roughly 250F, which is way above overheat condition, 220F.
Okay, I rarely disagree with 22GT, and although there SHOULDN'T be any steam present, the possibility exists, due to the extreme temperatures in and around the combustion chamber, that localized heat CAN cause steam. Also, the coolant flow in a SBF through the block is not from front to rear, but from bottom to top, pretty much equally through all the coolant passages in the deck surface and into the heads.

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post #8 of 15 (permalink) Old 10-27-2018, 06:52 PM
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The only time I have seen mention of steam blocks is in the Edelbrock instruction sheet for the heads I will be installing eventually. They have this:

1. Check the upper deck to see if you have an early or late model block (not needed with 351W): a) Late model 289-302 blocks have the water passages located next to the head bolt location on the deck of the block (This block will not require drilling). b) Early 289-302 blocks, pre-1972, will have the water passages located directly over the cylinder upper deck area and will require drilling 1/8 steam holes as shown in Figure 2.

Does that mean that the later blocks flow the water through different cavities and not use the top ones and hence don't need those steam holes but pre 1972 still use the top water cavities and hence need the steam holes? I will be drilling my block if its missing that steam hole in the number 1 and number 5 block location but it seems as if water flows differently in the 2 blocks?

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post #9 of 15 (permalink) Old 10-27-2018, 07:37 PM
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See the first post. The water jackets, themselves, in the block are pretty much identical. The major difference is that the water passages above the cylinders exit through the "eyebrows" directly above the cylinders on the "early" blocks and on the "later" blocks the water passages exit through the "triangular" shaped holes adjacent to the head bolt holes to the upper left of the cylinder.

My guesses on why they changed the location of the holes would be either emissions-related or to enable the same head castings to be used on both the 302 and 351W as the 351W had the "late" style passages from the get-go.

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post #10 of 15 (permalink) Old 10-27-2018, 07:45 PM Thread Starter
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I think the reason ford has these transfer ports is to rid the potential for air pockets getting trapped in the areas that those "steam-holes" exist, around the cylinder jackets. As you fill your motor with coolant, that coolant has to displace air in the system. Air wants to travel to the highest possible point when getting displaced by coolant. Some of the jacketing in the block itself is located in areas where the only way for that air to escape is up through that transfer port. In a situation like mine, I would have ended up blocking these transfer ports completely. I don't believe these "steam-holes" prevent steam from occuring, I think they are more aptly termed "air-bleed off holes". The gasket punch-outs show how small the holes that exist between these cavities are. They don't flow a substantial amount of water by any-means. What they do is allow that air to move upward out of the block as it fills. Air trapped in cavities slows flow, and can create isolated hot spots, and may never leave the system. Air is less dense than water, so when trapped in an isolated pocket, it has no reason to be displaced even with fluid flowing beneath it. Also technically speaking, steam is the reason a radiator system builds pressure. As coolant heats up it wants to expand, some of the molecules reach the required enthalpy of vaporization, transitioning into a gas state. Enough of them make the transition and build pressure. Eventually the pressure is such that no more molecules can vaporize, because temperature and pressure are what determine that point. Once the system cools, that vapor condenses back into a liquid. It's why expansion tanks are necessary in cooling systems. Even if you filled your entire system with liquid, at operating temperature it will not be at 0psi. Some of the coolant will still vaporize and expand, displacing liquid and reaching the system design pressure/temp.

Quote:
Does that mean that the later blocks flow the water through different cavities and not use the top ones and hence don't need those steam holes but pre 1972 still use the top water cavities and hence need the steam holes? I will be drilling my block if its missing that steam hole in the number 1 and number 5 block location but it seems as if water flows differently in the 2 blocks?
my289, I think it depends on what the edelbrock heads look like. I looked up an edelbrock head for a 302 and have set it together with my gt40 picture. What we notice is they both have the same coolant port set ups with the "steam-holes" for 5.0 blocks in the same locations. The older blocks, as my 69 doesn't have a transfer port or "steam-hole" in that location which makes sense as to why they want older blocks to recieve a hole. My assessment is that even they recognize the necessity of having the air vacated from those locations in the block.

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post #11 of 15 (permalink) Old 10-27-2018, 08:27 PM
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FWIW this is how Edelbrock handled the Steam holes
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post #12 of 15 (permalink) Old 10-27-2018, 08:30 PM Thread Starter
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Oh nice, they combined both ports into one. Clever! I'm more convinced that they are necessary.
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post #13 of 15 (permalink) Old 10-27-2018, 10:08 PM
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I'm also in the "eh" camp with steam holes. I have a '69 block and have had two sets of TFS heads on it, I didn't even know I was supposed to drill my block until I swapped to the second set. Amazing what you find when you read the instructions .

The engine is been running cool since day one.

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post #14 of 15 (permalink) Old 10-28-2018, 02:39 AM
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When I installed Twisted Wedge heads on my 289, I went ahead and drilled the holes in the block, per the instructions that came with the heads. Didn't have overheating problems before and don't have overheating problems now. Good write up!



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post #15 of 15 (permalink) Old 10-28-2018, 05:30 PM
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Seems to me you could just slot the gasket similar to how Edelbrock slotted the heads and achieve the necessary vent for air pockets.

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