"Zulu" mod

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#1
Looking for opinions/ experiences with this. Opening up the rear coolant port on cyl 6. I have my head off getting machined. Should I do this too while I'm at it?
 

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#2
Opinion. There is no engineering behind this mod. It could easily upset the balance of coolant flow in the block. This sort of thing is best left to people who design engines and have the software tools to model coolant flow. It's a zero sum game. Adding coolant flow in one place takes away from somewhere else.
 

suprarx7nut

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#3
In some ways I feel like this mod is similar to the EGR delete that was popular years ago. The goal was to reduce heat, but in reality in might increase heat to the point of failure.

As pi says, it was designed that way, likely with intention. If Toyota could have reduced aluminum in the casting and improved cooling, They probably would have.

I'd skip that mod.
 
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#4
Not doing it. Thanks. I was wondering why this action wasn't more popular, now I understand why. In Toyota engineers we trust...
 

Hybrid

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#5
Have both the Zooloo mod and deleted EGR (running JDM ECU), have not noticed any adverse conditions.
 

suprarx7nut

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#6
Have both the Zooloo mod and deleted EGR (running JDM ECU), have not noticed any adverse conditions.
If you have the JDM ecu with the EGR delete, that's fine. The ECU and EGR status need to match as the ECUs are counting on the EGR being there or not. My old 90 had a JDM ecu and EGR delete (leftover from previous owner, but I kept it that way). My comment was aimed at those folks that kept the USDM ecu and deleted the EGR.
 
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#7
I know a said I wasn't doing it, but I've seen a few more cases and I've thought about it more. As far as I can reason, Toyota cast the head that way to intentionally run cyl 6 hotter than the rest, and did so for the sake of the EGR, since it's the only cyl that feeds it. I'm not deleting my egr until I get a standalone but I could reasonably figure the only adverse affect would be slightly cooler egr gasses/ temps. Which wouldn't that be a good thing?

Hybrid: If u use your heater, how's that affected? U said no change but I'm just double checking. We have some cool summer/ fall nights and mornings here in MI.
 

Hybrid

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#8
Yep no change I have noticed.

There are so many theories on why there is no hole but a hole in the block and gasket, no one really knows and likely never will. Everyone is using pure speculation on both sides of the fence.

My "theory" is because of the EGR heater being in the general area, so they didn't want coolant effecting it's efficiency and in turn emissions. Am I right?. Who knows.

The 1JZ and 2JZ had a coolant port there also. I also deleted the ISCV and TB coolant path (plugged both ends), so extra capacity on tap now also.
 

Hybrid

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#10
Yep, it is only for climates where the car can see icy/snow conditions. For me in Australia with a climate like SoCal, it is no use. Id rather the coolant stay inside the engine. Also one less loop that could leak, I guess.

People will tell you to just connect up both ends, but they don't understand the engine coolant flow path. Ideally modify the coolant return line that goes behind the engine, but that isn't mandatory (but again more coolant inside the engine)
 
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#11
I'm one of those people that believe in connecting both ends as to not disrupt factory flow too much lol. I live in Michigan USA but I don't plan on driving my car in winter. Ever. Unless it's an emergency. So I'll probably bypass it.
 

3p141592654

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#12
Its an EGR cooler, not heater, and the volume of exhaust gases flowing in the EGR that is the size of a straw is so low that it has zero impact on the heat load of cyl 6. Compared to the flow through the exhaust port of cyl 6 its completely irrelevant.
 
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#13
Its an EGR cooler, not heater, and the volume of exhaust gases flowing in the EGR that is the size of a straw is so low that it has zero impact on the heat load of cyl 6. Compared to the flow through the exhaust port of cyl 6 its completely irrelevant.
I think you misunderstood my theory. You're argument seems to be be based in a theory that Cyl 6 is Heated BY the EGR. I agree, that's ridiculous.

My theory is that the combustion chamber of cyl 6 was denied the additional coolant passage to allow that cyl to run hotter, thus producing higher exhaust gas temps, which benefits the EGR system with hotter, less dense exhaust gases, which would take up more "room" in the intake charge to each of the other cylinders.

You had my cause and effect mixed around I think.
 

Piratetip

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#14
You are still backwards CJgordon.
EGR recirculation by design is to be cooled prior to be taken back into the engine.

Running hotter EGR gas is counter intuitive to it's intended purpouse of reducing NOx emissions.
Lower temperatures reduce that.
 

3p141592654

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#15
Agree with Pirate. EGR is about lowering temperatures to reduce NOx formation. The EGR gas temperature is lowered by the cooler prior to re circulation, so if Toyota's intent was to affect the EGR gas temp they would run cyl 6 cooler no t hotter.

Its interesting to look at the coolant passages in the 7M head. You can see that for each cylinder the exit for the coolant is metered by a small hole much smaller than the head to block coolant interface. This is done to balance the flow and ensure that all cylinders get equal cooling. Drilling holes without consideration of the existing balance will upset thing unpredictably.
fresh_milled_head.jpg
 
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#16
Maybe I am confused. I don't understand how recirculating exhaust gases back into the intake to be combusted again is going to cool anything, even if the exhaust gasses are "cooled" at the rear of the head 1st. Maybe I need to do more research into the function of the EGR. But that's beside the point... Afaik, every longitudinal online engine blows it's head gasket more frequently on the rearmost cylinder. Unless coolant from the radiator is somehow piped to the rear of the head then forward..
 

suprarx7nut

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#17
Maybe I am confused. I don't understand how recirculating exhaust gases back into the intake to be combusted again is going to cool anything, even if the exhaust gasses are "cooled" at the rear of the head 1st. Maybe I need to do more research into the function of the EGR. But that's beside the point... Afaik, every longitudinal online engine blows it's head gasket more frequently on the rearmost cylinder. Unless coolant from the radiator is somehow piped to the rear of the head then forward..
And this right here is why so many people screw around with EGR - they don't understand how it works. No offense meant at all by that. Just saying your mis-understanding is very common.

EGR works by disallowing more fresh combustion. The EGR gas is hot as hell... but it's not as hot as freshly burned fuel and air. And that's exactly what it's replacing when the system is turned on and working. The EGR gasses are essentially inert. They can't ignite. Adding in a little bit of EGR gas fills up space in the cylinder that otherwise would be taken up by fresh air and gasoline. The EGR system allows enough inert gas to enter the intake stream such that less combustion occurs. Less combustion = less heat. That inert air can also absorb some energy in the form of heat, because the EGR gases are cool compared to the burning air/fuel mixture (again, the EGR gases are hot, but not nearly as hot as fresh combustion thanks to the cooled flow path). The USDM ECU is tuned very specifically to account for EGR flow and function. It counts on the EGR system providing a certain amount of flowing gas at certain conditions. Once that balance is broken, you're likely to have more heat in the engine at partial load. That's what kills motors.

Inline motors do seem to have a slight tendency to heat up in the rear, but this is not because of EGR, so much as air flow in general. All the fresh air is at the front of the motor when the car is moving. That said, I don't believe a properly running 7MGTE will have any more risk of failure at 5/6 than the other 4 cylinders. Screwing with coolant flow and/or EGR will certainly put you at risk of killing the motor.

If you want to ensure the rear of the motor stays healthy, focus on a healthy cooling system and keep all OEM ductwork in place and intact. For instance, running without the undertray can significantly reduce air flow to the engine bay. Keep that silly piece of plastic installed is probably more beneficial than any coolant passage or EGR mods.
 

Piratetip

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#18
The EGR system allows enough inert gas to enter the intake stream such that less combustion occurs. Less combustion = less heat. That inert air can also absorb some energy in the form of heat, because the EGR gases are cool compared to the burning air/fuel mixture (again, the EGR gases are hot, but not nearly as hot as fresh combustion thanks to the cooled flow path). The USDM ECU is tuned very specifically to account for EGR flow and function. It counts on the EGR system providing a certain amount of flowing gas at certain conditions. Once that balance is broken, you're likely to have more heat in the engine at partial load. That's what kills motors.
Not to hijack your explanation but what you are trying to say is EGR displaces volume in the cylinder.
Thereby reducing the actual displacement of the engine.
Since the EGR is inert gas the computer does not have to inject as much fuel to maintain stoich 14.7:1 ratio.
You mess with EGR and the computer still reduces fuel flow at partial loads, this causes a lean mixture. Lean mixture = hotter running engine.
Among many other issues.
This is one of those beat the dead horse topics, everything has been said multiple times before, but the misinformation continues to spread.
 
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figgie

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#19
This is one of those beat the dead horse topics, everything has been said multiple times before, but the misinformation continues to spread.
that is because stupidity and ignorance is like a tidal wave, it is hidden underneath in the ocean until it comes close to land then it rears it's ugly head.

There was a reason I had one of my signature as "standing against the wave of stupidity (and ineptitude)"
 
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#21
And this right here is why so many people screw around with EGR - they don't understand how it works. No offense meant at all by that. Just saying your mis-understanding is very common.

EGR works by disallowing more fresh combustion. The EGR gas is hot as hell... but it's not as hot as freshly burned fuel and air. And that's exactly what it's replacing when the system is turned on and working. The EGR gasses are essentially inert. They can't ignite. Adding in a little bit of EGR gas fills up space in the cylinder that otherwise would be taken up by fresh air and gasoline. The EGR system allows enough inert gas to enter the intake stream such that less combustion occurs. Less combustion = less heat. That inert air can also absorb some energy in the form of heat, because the EGR gases are cool compared to the burning air/fuel mixture (again, the EGR gases are hot, but not nearly as hot as fresh combustion thanks to the cooled flow path). The USDM ECU is tuned very specifically to account for EGR flow and function. It counts on the EGR system providing a certain amount of flowing gas at certain conditions. Once that balance is broken, you're likely to have more heat in the engine at partial load. That's what kills motors.

Inline motors do seem to have a slight tendency to heat up in the rear, but this is not because of EGR, so much as air flow in general. All the fresh air is at the front of the motor when the car is moving. That said, I don't believe a properly running 7MGTE will have any more risk of failure at 5/6 than the other 4 cylinders. Screwing with coolant flow and/or EGR will certainly put you at risk of killing the motor.

If you want to ensure the rear of the motor stays healthy, focus on a healthy cooling system and keep all OEM ductwork in place and intact. For instance, running without the undertray can significantly reduce air flow to the engine bay. Keep that silly piece of plastic installed is probably more beneficial than any coolant passage or EGR mods.
Well thanks for clearing that up for me, although I already knew most of it... My concern isn't about the EGR. I'm putting it back on either way. The only reason I bought it up was a hypothesis as to why that coolant passage is blocked. I've seen people open it. I've seen people leave well enough alone. But aside from "Toyota engineers said so" can anyone tell me a functional benefit to leaving it closed vs opening it? I do plan to upgrade the rest of the cooling system as well (aluminum radiator, electric fans, fresh coolant obviously). I'm not trying to sound like a new idiot to modifying cars. I do understand much of their nature and went to school for auto tech. This post got side tracked and became about the EGR whereas I'm actually curious about the blocked coolant port for cyl 6.
 

figgie

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#22
But aside from "Toyota engineers said so" can anyone tell me a functional benefit to leaving it closed vs opening it? I do plan to upgrade the rest of the cooling system as well (aluminum radiator, electric fans, fresh coolant obviously). I'm not trying to sound like a new idiot to modifying cars. I do understand much of their nature and went to school for auto tech. This post got side tracked and became about the EGR whereas I'm actually curious about the blocked coolant port for cyl 6.
Simple

Unless you have done FEA on the flow of that head in both OEM functions and with the mod in place, you are risking in adding an issue where there is zero reason to add one.

In other words, it is your car, do as you please but if you do not have facts, all you are doing is taking a risk and hoping for the best. One of the reasons the 7M have a bad rap to begin with.
 
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suprarx7nut

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#23
Well thanks for clearing that up for me, although I already knew most of it... My concern isn't about the EGR. I'm putting it back on either way. The only reason I bought it up was a hypothesis as to why that coolant passage is blocked. I've seen people open it. I've seen people leave well enough alone. But aside from "Toyota engineers said so" can anyone tell me a functional benefit to leaving it closed vs opening it? I do plan to upgrade the rest of the cooling system as well (aluminum radiator, electric fans, fresh coolant obviously). I'm not trying to sound like a new idiot to modifying cars. I do understand much of their nature and went to school for auto tech. This post got side tracked and became about the EGR whereas I'm actually curious about the blocked coolant port for cyl 6.
Nobody has bard data on this either way. I think you just need to decide who to side with. On one side you have engineers from Toyota that have likely spent their career designing and testing engine flow characteristics. On the other side, you have DIY modifiers and enthusiasts that think they may have found an oversight from those aforementioned engineers. Toyota is just about the epitome of tightly controlled and tested designs and manufacturing, but they aren't (and weren't) perfect.

Maybe Toyota wanted to slow flow at that point near the gasket and speed it up in the head. A wider flow path will reduce speed and a narrower one will increase velocity. Maybe it was a pressure-based consideration. Maybe it was a technical limitation of the casting that they didn't bother rectifying in post-machining. Nobody knows.
 

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#24
It's also worth considering that the internal cylinders 2,3,4,5 are surrounded on two sides by hot neighbor cylinders and they do not have coolant paths separating them due to the tight packing. The same consideration applies to the internal hot exhaust passages.

The end cylinders 1, and 6 should run cooler by virtue of having one side facing the cold outside world. Therefore, if the internal cylinders don't need cooling passages between them I can't see why the end cylinders would (in particular #6).
 

figgie

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#25
...and thinking about this some more.

This might be a left over from the 5M head? I would be curious to see if the 5M had that part opened or closed up.
 
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#26
No hard data either way... I see. We see it works well from factory, one report of no issues formed so far. I agree Toyota engineers are top teir. I want my car to be as reliable and as strong as possible. Because as much as I enjoy working on it, I'll enjoy driving it more. I'm still undecided unfortunately tho I appreciate all the input. Both sides of this argument are practically valid. I just wish there was some data. Maybe even something as simple as a laser temp reading outside the head or on a hose before and after. I prefer to refer to numbers... And their aren't any here.
 

Hybrid

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#27
Everyone should keep an open mind, that would be a good start.

It would indeed be great to get real data, but not sure anyone will ever bother.

A few people have added the Zooloo mod to their head that I personally know, and it has never cause adverse issues.

It may do something, it may do nothing, but there is zero evidence that it causes a negative effect. The latter is backed up by real world usage.
 

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#29
I do agree about being more open to things as so much has changed from the 80's. Many improvements, redesigned parts, both good and bad information from what members have shared on here has been a true blessing for helping soo many 7m/mk3 guys.

I recently picked up a 7m cylinder head from my local junkyard out of a 89 Cressida. I am doing the Zulu mod, ARP headbolt insert mod and machine the head so I can put it in my current 7mGTE motor. If it does not work out I am out $40 for the cylinder head plus some machine shop labor.