Is anyone running their LS with the rear steam vents blocked off? I've read this should only be done if the motor sits in the car at a slight angle upwards. I'm installing a new intake manifold and have to delete the original steam vent piping under the stock manifold. I'm curious if anyone else has had problems running the engine hard with the rear vents blocked.

 

I just finished installing my new fast intake manifold, so I didn't block any of the steam ports I actually ran custom lines from the back to the front , will post some pictures later , haven't fully tested yet

 

When I ran the LS6 intake, and then the FAST 90 intake, I kept the 4 corner stock vent piping. I used Hi Spot Dykem blue on the piping, and lowered the intake carefully. You could also use white or red water paint marking pens on the steam pipe. It didn't rock much. But this left lines on the intake that I then clearanced. Just dont get carried away with a die grinder. Doesn't take much. If I were to do it again, I might try a soldering iron to melt the clearance areas. But clearancing worked great. No leaks, vacuum or steam......

 

FWIW all Z06s and 01+ cars with the LS6 intake factory have the rear ports blocked.
On my car I did the easier truck crossover mod to have 4 points of where steam vents out and have some 1/4 coolant hose going over the intake.

I'd rather have had a early LS1 steam kit but they're not common nor cheap and require modifying the LS6 manifold a tad.

 

I did the same thing. You really need that rear cross over to help prevent hot steam pockets from forming in the back of the cylinder heads when run the engine hard at say the track events.

 

does the the c5 ls6 engine have block off plates or pressed in caps? I want to do this tothisengine but dont want to pull heads and punch out plugs.

Thanks

 

I am not sure how the factory heads were done on the '01-05 LS6 engines, but my 243 heads that came from an '06 LS2 in a GTO had rear plugs that held in place to cap screws that were easy to remove. They looked similar to the photos below;

 

Sweet. Really appreciate it! Thank you

 

Although I've never been able to collect any kind of data evidence, I firmly believe with all my heart that the 4-corner fluids flowing out to the top of the radiator is an enormous benefit and possibly in some cases essential to a performance engine.

That said, we could do some calculation. The flow rate of water leaving the head seems to fill my 2-liter bottle with the engine at idle 'pretty quickly' lets say around 40 to 50 seconds.
If we use numbers for 8mm tube, with 0.5m/s to 1.5m/s gentle flow at idle engine pressure coolant differential of a couple psi, it should be around 0.1 to 0.3Liters per second. Our measured flow of 2L/50seconds is slower than that(0.1L/s is only 20 seconds to fill 2L) so somewhere in between the max of the low end of the prediction (0.1L/sec) and empirical estimate (0.05L/sec @ 40 seconds and 0.035L/sec) sounds about right.

In one second, 0.05L of water can take (0.5*4184) = 209J/K of energy input for every *C or degrees K it is raised by
So if the water went up 2*C then that would be 418Joules of energy stored in that 1 second

An LS cylinder head probably has around 10kg of aluminum mass
Specific heat of Al is 900J/kg*K
The head already has water flowing through it. We just want to know what energy removal contribution near the steam ports means to the local aluminum.
Since there are two steam ports, and the ports are isolated near the upper 1/4 corner of each head, I take 5kg/4 = 1.25kg of aluminum in each one quarter volume per steam port.
We can say 1 to 2kg of aluminum to be fair and also compare to the entire head, to make it easy just imagine 1,2,3,4,5kg of aluminum,
since 1kg will handle 900Joules per 1 degree K (or C),
1kg = 900J
2kg = 1800J
3kg = 2700J, etc...

So for our meager idle calculation of 0.05L/second which is 209J of energy removed per degree K in one second,
and our aluminum of say 900 to 2000J per degree K,
Each steam port probably contributes at least 209/2000 = 10% to 209/900 = 23% of the energy removal that would have raised the temp of the head aluminum materials,

That is also assuming the temp of the water went up 1 degree in that second. If it went up 2 degrees in one second, then its
418/2000 = 20% to 418/900 = 46%

A single degree of temp rise per second is quite too much I think for an idle but 1degree/second is a legitimate possibility for a performance session or forced induction, for water which is so close to the source in the head, as the temp rise rate increases the same volume of water plays more and more of a role in heat removal from that region of the heat, which I consider to be instrumental, essential, ideal, etc... like I wouldn't want to leave home without that 10%+ of energy removal rate

 

I haven't needed to work out a heat loss calculation it way too many years

Basically the lack of a rear steam tube crossover tune will allow hot spots to develop in the rear of the cylinder heads.. In simple terms that means steam and not coolant is present in that area of the water passages in the cylinder heads, with no were to vent. Just about all the #7 and #8 cylinder piston ring land failures in factory LS short blocks can be traced to localized overheating due to the combination of tight clearance rings with hypereutectic pistons without the use of a rear steam crossover tube. Why the engineers saw fit to eliminate the rear steam crossover from the LS6 engine in the Corvette (which is never going to be used at the track, right?) but insist that one was present on every LS truck engine (that possible could be working hard pulling a trailer) is beyond my comprehension.

 

back when I was trying to relate anything to do with steam vents, I noticed there seem to be just as many #7 #8 failures, piston cracking at the rear of the engine, even with engines that still have 4-corner steam venting.

Furthermore in engines like the 6-cylinder 2jz-gte, it has the same issue with #6 running lean and blowing stock ringlands.
In the 2jz this is expected to be an issue with the intake manifold, and possibly fuel injector rail, as each runner just as with each injector takes a part of the fuel/air,
This is an example spreadsheet (not actual numbers, just for showing the concept of fluid mechanics flowing down the runner/fuel rail)


As each runner/fuel injector takes a portion of fluids (air is a fluid), there is a change in pressure applied to the downstream runners/fuel injectors.
The change is slight, but, the higher the input velocity (e.g. the more power the engine makes at any instant) the more the pressure changes downstream,
As we find with Bernoulli's, for airflow and fuel injectors this means an air pressure and fuel pressure increase for each runner/injector downstream.
Of course engines are more complex than that, injectors opening and closing quickly and intake valve systems create pressure waves and many disturbances,
However at peak airflow and fuel flow the injectors are open much longer and the airflow demand is met by a relationship of valve closing timing (cam specification is intended to maximize momentum flow at peak conditions if its being done 'right')

In a failed inline 6-cylinder 2jz engine with broken factory #6 I expect to see that it used a lot of boost pressure, and a near-factory intake manifold style, causing the rear most runners to run leaner than the front most, the pressure gradient front to back. It is speculative, yet common enough of a failure that it is quite popular to replace the 'square' intake manifold designs with a 'taper' which gradually reduced the plenum volume towards the rear most cylinders, in order to conserve velocity and maintain equal pressure. Many if not all aftermarket high performance 2jz manifolds take this shape now of a taper , the thinnest parts towards the rear cylinder.

In the V8 intake manifolds especially factory, which seem to rely heavily on acoustic tuning and medium-momentum investments, I feel that this is a potential causative implication for why the rear cylinders run leaner than the fronts, just as with the inline 6-cylinder engines. But unlike the 6-cylinder engines, the V8 does not have a luxury for many taper rear intake manifold designs. Certainly not from the OEM which are popular manifold choices. Furthermore there are potential complications with fuel flow for the same reasons, dead head fuel rails for example seem to work great up until a certain point, but what point? Fuel rail return placement, number of returns, is a consideration in the pressure changes that accompany high output fuel flows with high velocity, approaching 2m/s there are concerns with pressure differences after fuel injectors inline with flow along the rail, and the more injectors there are down stream (dead head has the most, and single return line rail systems) it can be concerning for sure.

While I would love to say that sure, steam venting water has implication in failures, I have not actually witness any concrete evidence of that, which is to say that I've attempted the traditional approach of collecting samples (random sampling from failed engines, the hundreds or so from stock bottom end reliability lists we find all around) that I am not coming up with any p < anything, there is no significant difference in groups with and without steam venting when it comes to failures, the most common cylinder 7 and #8 seem to fail whether the steam vents are intact or not.
That aside, Even if the steam venting contributes very little for cooling, it certainly can remove some air from the head, the high point on the head, speculation again but I believe this is another benefit of using them, and perhaps why they are called 'steam' venting to some?

In general now with 25 year tuning turbo engines I always increase fuel flow to the rear cylinders, 0.5%, 1% and 1.5% respectively in-line for 6 cylinder engines and 8 cylinder engines, something along those lines, and always look at the rear most spark plugs for evidence compared to the front most, they need to look identical after being used in a long duration highest possible output condition. I also impost strict oil temp and air temp guidelines for factory pistons, reliability of the OEM brittle fracture failure materials depends on oil being kept reasonable near the boiling point of water atmospheric, say 212 to 220*F and air temp needs to stay on gasoline below 112*F for E10 generic 93 octane fuels, to help keep from shattering the OEM pistons of any of these engines (Sr20, 2jz, rb26, LSx) which are all capable of 200hp to 250hp/liter on factory pistons for 250,000 miles+ when these and other (air filtering and other details) are set correctly

 

The three things I always thought were darn near "criminal" concerning the C5 from the factory were;

eliminated the rear coolant steam crossover tube with the introduction of the LS6 intake manifold
failure to equip the Z06 / LS6 package with some type of engine oil cooler
failure to equip the C5 with HID projector headlamps