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I like your line of thinking kingtal0n. Still curious though that the factory decided to stop connecting all 4. I'm sure there is a small cost savings, but if they could prevent warranty issues from hot no 7s I'd think they'd do it. I don't think they use 4 port steam venting even on their performance and supercharged variants?
So many custom setups, so many sold, so many pictures. And not a single person on the entire internet saying "I put 4-corner steam ports on my LS and it was a mistake". combined with what I know about cooling an engine off and its a no brainer.
I'm not disputing that they sell or that a lot of people, use them. The mere availability to the masses does not persuade me either way, after all look how many fidget spinners, snuggies, and clap-on light switches are out there. People are still buying all kinds of things that have little merit. I'm not saying 4 port steam venting is one of those things - I really don't know. On the surface it seems perfectly appropriate, but then again I see the factory doesn't use this approach. Given they have a lot more access to instrumentation and engineering and they have to warranty even their performance variants, I tend to favor what the factory does.
Here is a quote I've seen going around.
Originally Posted by Pratt & Miller
(Pratt & Miller Engineering New Hudson Michigan) and Dr. Jamie Meyer (head of GM Performance) both say that the rear two should stay blocked off.
I used to advocate having fittings that went to -4an on all 4 steam vents feeding into a coolant swirl pot, which then drained back into the lower hose or return heater line... this is a setup that was used successfully by a few race teams, but it looks like this was a band-aid once I got 'real' information from REAL race teams.
The issue is not flow - the coolant passages flow plenty - it's pressure.* When driven hard, engines need coolant pressure to "scrape" the steam bubbles that form on hot spots in the head off the wall of the passage.* With all 4 ports open, there's not enough pressure locally (in the head) to promote proper heat transfer unless you run your overall coolant pressure extremely high (30psi or so).* Indy and F1 cars run MUCH higher than that, due to higher hp/liter (heat concentration).
The proper setup all my LSx racers are using is, assuming the top of your radiator is below the steam vent port:
*The rear vents blocked off, the front tee'd (LS6-style).
*Radiator cap replaced with "open" cap (free flow through radiator overflow port)
*Steam vent tee and radiator "overflow"/free flow feeding into coolant swirl pot (aka expansion tank)
*Swirl pot has pressurized radiator cap, bottom drains to non-thermostat-controlled water pump return
I don't know if that quote is authentic. I came across it being reposted on a Corvette forum and I have seen it posted a few times. Whether or not it's true, I have no idea.
All this said, there is evidence both approaches work.
In partial support of the 4 port venting concept and simply getting as much coolant flow as you can, here is the C7R engine which uses a coolant outlet manifold that connects at multiple places along the top of the heads. It seems the coolant does not exit the block through the waterpump like it does on the standard Gen III-V engines.
I'm not sure what the coolant or "steam vent" system looks like on the C5R or C6R engines. On those it looks like the coolant exits from the block back through the waterpump like a conventional LS, but I can't tell where or how many "steam vents" there are.
Last edited by -TheBandit-; Mar 7, 2018 at 12:28 PM.
so it seems we should do some testing. Somebody hook 4 corners up using clear hose and valves, then dyno the car under the most brutal condition possible and see what happens in those clear lines with the rear valves closed vs open. (/not serious)
I used to get in the middle of these conversations. I couldn't figure out why every body does it differently yet some people are so adamant the vents have to be connected in a very specific manner or the engine is doomed, doomed I tell you, to certain failure. Or why so many guys are successfully running with all 4 blocked off and zero issues. People had all these convoluted theories, just like this thread, most of which seemed to be pure conjecture.
Finally someone explained that GM had to add the vents because unlike the first gen SBC they put the water outlets on the front of the block below the top of the coolant passages. This allows a dry intake manifold. They aren't steam vents, they are air fill vents. Leaving them plumbed in just makes it more idiot proof when refilling a dry system. Some motors (Dodge diesels) have a petcock valve on the top of the motor that needs to be manually opened when filling the system. Once the air is out the vent is no longer needed.
But I guess some guys still think a coolant passage full of bends the diameter of a coffee stirrer will noticeably improve the flow of coolant through the block. You do realize adding rear vents creates a short cut that allows coolant to bypass traversing the block?
And then there is the dreaded "#7 running hot" conspiracy. Damn. Good old No 7. Must be a Tennessee thing.
I do know this for certain, jacking up the front end of the car and unplugging one of the vents cuts in half the time it takes to fill the system. It lets the air out as well.
^^^....and tying that line into the vent tube on a reservoir installed as the highest part of the closed system (with pressurized cap) allows one to fill the system just by....wait for it....pouring coolant into the reservoir with the car at normal ride height until the coolant reaches the "full" line. Don't forget to open the heater control valve...
I used to get in the middle of these conversations. I couldn't figure out why every body does it differently yet some people are so adamant the vents have to be connected in a very specific manner or the engine is doomed, doomed I tell you, to certain failure. Or why so many guys are successfully running with all 4 blocked off and zero issues. People had all these convoluted theories, just like this thread, most of which seemed to be pure conjecture.
Finally someone explained that GM had to add the vents because unlike the first gen SBC they put the water outlets on the front of the block below the top of the coolant passages. This allows a dry intake manifold. They aren't steam vents, they are air fill vents. Leaving them plumbed in just makes it more idiot proof when refilling a dry system. Some motors (Dodge diesels) have a petcock valve on the top of the motor that needs to be manually opened when filling the system. Once the air is out the vent is no longer needed.
But I guess some guys still think a coolant passage full of bends the diameter of a coffee stirrer will noticeably improve the flow of coolant through the block. You do realize adding rear vents creates a short cut that allows coolant to bypass traversing the block?
And then there is the dreaded "#7 running hot" conspiracy. Damn. Good old No 7. Must be a Tennessee thing.
I do know this for certain, jacking up the front end of the car and unplugging one of the vents cuts in half the time it takes to fill the system. It lets the air out as well.
Oh, there is no question that those 'steam' lines appear to be related to air stagnancy. Of this we are mostly certain. The question that remains is: does the engine frequently have air 'pockets' being induced, and if so, where do they tend to collect, and will it be near the rear in the application? I guess. Something like that.
Always an interesting conversation no matter how many times it's revisited. Thanks for continuing to chime in I hope I haven't come across as combative or arrogant in my posts It's really a topic of interest that I'm sure a GM engineer knows the answers to. Whatever the original intent or potential repurposing it's sure to be debated as long as I keep looking for that damn 10mm socket.
Here's a little stainless steel setup I made when I was using a carb setup, it would still fit under a normal efi intake but not with an ls6 valley cover, have to use ls1 valley cover. So I'm gonna tear it apart and rebend new lines to fit under my fast intake and ls6 valley cover. It's all self contained on the left side water pump port which makes it nice, no line going to radiator. And being stainless it won't rust out like the one truck one.
And I moved it to the upper radiator tank because it looks trouble to tie them together. They are both pressurized outlets (steam port and upper water outlet) but being in two different positions in the system and having two separate "staging areas" (they come from different places) the resulting pressure is probably going to be different where they mix. And that means one could pull or push the other.
Just imagine the lines are full of air instead of water, and it might help you see what I am saying.
I think the salient issue to keep our eye on is this -- if, in fact, the engine is producing 'steam' under certain conditions -- what do you want to do with that/about that? In my mind, I don't want to route that someplace where the thermal energy in that steam/coolant is simply routed right back into the engine, otherwise I've just created a radiator bypass. I'd like to get it the steam/hot coolant out of the engine, and remove the heat from it. In my mind that points to routing it someplace where it can get back to the hot side of the radiator for subsequent heat rejection. If connected to the water pump outlet area, it ends up going to the radiator for cooling. I routed mine into the 'high' line connection between my coolant reservoir and the top of the cool side of the radiator.
I think calling them "steam lines" is a misnomer. More correctly, they are "air bleed lines" since that is essentially their purpose, to evacuate the air trapped in the top of the heads.
its a power plant equation. Of number of KW being produced some fraction is lost and needs to be removed for the operation to continue. If the engine produce a lot of KW (or horsepower) you need to dispose of more energy somehow. So at some point 2x, 3x, 4x the output of factory intended, something about the cooling system is no longer adequate, whether it be coolant passage size, or speed of the coolant, is no longer adequate under certain circumstances such as sustained output (continuous max power production from the plant). So if we set the engine to 99% duty cycle (WOT) for an hour or three days, will the coolant system be designed well enough to reach a steady state (hold some max temp and not have any difficulty holding it) or will it continue to rise in temp until something explodes?
If the max sustained temp vs pressure of the system is high enough to boil it will boil somewhere in the system.
0 PSI 212° F
10 PSI 239° F
20 PSI 259° F
30 PSI 273° F
Everyone should know what a boiling chip is. The concept of forced locational boiling, or forcing a specific surface to generate the bubbles formed in the start of boiling, is known in engineering. I am sure when they designed the heads they said "ok this is where I want bubbles to form if the head gets hot enough to boil water" and took steps. But how often does that happen?
Talon, you have just veered COMPLETELY off course. A cooling system under pressure does NOT vaporize, so your steam theory is bogus. For what you say to happen the system would be at a much higher temp than operating temp; an overheating scenario, which is not what is being discussed here.
A cooling system under pressure does NOT vaporize...
Not so fast.....with enough heat input you can generate steam even under pressure, and you can get localized steam generation under pressure as well. I’ve read both steam and air bleed descriptions from reasonable sources - opinions vary. For me - based on what I’ve read - they seem to serve both functions. But unless it’s a road racing/endurance application or heavy/extended towing application - I don’t think it matters much. For the 99% of my driving that’s light throttle between idle and 2500 rpm - I ain’t a Big Generator of steam. Yes? No.
Not so fast.....with enough heat input you can generate steam even under pressure, and you can get localized steam generation under pressure as well. I’ve read both steam and air bleed descriptions from reasonable sources - opinions vary. For me - based on what I’ve read - they seem to serve both functions. But unless it’s a road racing/endurance application or heavy/extended towing application - I don’t think it matters much. For the 99% of my driving that’s light throttle between idle and 2500 rpm - I ain’t a Big Generator of steam. Yes? No.
Exactly this. The oem truck application isn't going to put 1000kw into the cooling system. the oem didn't plug the rear steam ports to increase high rpm "bubble scraping" fwiw. I think it more likely the real reason something to do with saving money.
I've had nearly every chemistry course my college offers.
Trust me I know how to boil water ;D
Anything can boil, diamond, steel, w/e. In space ur blood boils instantly because no pressure. The boiling is controlled by pressure and electronic interactions between molecules. You can induce some behaviors by using some kinds of electromagnetism, all atoms are basically electric, so saying that it is strictly pressure controlled would be inaccurate.
liquids have partial pressures, a chemistry term which allows scientists to know the rate of liquid to gas transformations per unit time. The gas molecules were liquid molecules that escape the surface. It is given in quantum physics by the molecular velocity, or escape velocity from the group of solid/liquid in question, as a statistical distribution plot. I can take a pic in the physics book if you want one, of the curve. Basically this explains why ice cubes shrink while frozen in the freezer, and why peas and steak freezer burns, it is the water molecules leaving the item in question, escaping as a gas. Even at freezing temps.
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