Head cooling on cylinder #5 - solutions?

[blue72]

I've taken the morning to do some looking into the gasket/blocked flow thing. I've found that there is quite a bit of variation on both blocks, heads, and gaskets. This is to the best of my knowledge so far, so correct me if I'm wrong.

 

First, the blocks. From my researching (my own engine blocks, and photos on my hd of others) I've seen a few basic block differences as far as water passage holes. The earlier design P-30/N-42 engine blocks look to have more small water passages on the passenger side of the block. The F-54 block has fewer small passages on the passenger side of the block (except cyl #6), but four extra, large passages on the driver side. I don't have a '75-78 N-42 block, and my pictures are small, but it appears to have at least 1 extra hole on the driver side.

 

Same goes for cylinder heads. It seems that the pictures/examples I have of E-31, E-88, and N-42 heads are missing the large, driver side holes, while the MN-47, P-79, and P-90 heads (I don't have an N-47) have them in addition to all of the passages the others contain.

 

Now gaskets. There are 4 styles divided by years. Up to Oct 70, Nov-70-74, 75-Feb 81, March of 81- end of production 83. Makes sense. Not having access to actual Nissan head gaskets I have instead looked at fel-pro and B/A for reference. Again, I only have early and late, not mid, but early has holes in the gasket for the small, passenger side water passages, while the later (F-54 block) head gasket blocks these holes completely, but does have three of the four extra holes on the driver side.

 

I have a few side by side pictures to illustrate: First is an early style head gasket/L-24E/N-42 side by side. The other picture shows a late head gasket/F-54/P-79 side by side.

 

 

 

I admit that I am not a Nissan Engineer, and don't know the exact reasoning for different configurations. It may have to do with siamesed and non blocks, different flow theories, turbo and non applications, better heat transfer, what have you.

 

I'm going to swap P-79 heads on my F-54 block this week, and won't modify my new H/G. I'll assume the Nissan people made it that way for a reason, plus I have the same head gasket in my car now, and it runs fine. (and 1fastz who built my head said it was inconsequential at my power level.) After reading this thread through though I'll definitely be adding some water wetter when I refill the radiator.

 

As a side note, it looks like the metal head gasket zxtman has allows flow of the small passenger side holes, but blocks two of the four large driver side holes, like his pictures show. I assume he's got a F-54/P-90 combo. I haven't seen a turbo specific head gasket listed, so I assume they used the same for N/A and turbo applications, which in my case blocks the small holes, but opens 3 of the 4 large ones. It almost seems like his is a universal gasket for the many 75-83 combos people could come up with.

 

Boy, I too would like to see the plastic head where we could watch the flow with different varieties of gaskets and bypasses. Either that or the 3-D scan with simulated flow data. I'm not picky For now I'd settle for some pics of actual Nissan head gaskets, and maybe some pics of a 280 block and N-47 head water passages for more research.

[ktm]

Ron Tyler and I talked briefly on the phone this afternoon. In the interest of expanding our collective knowledge, I'll post the questions here for open discussion.

 

1) If you do not have a heater core, why not block off the outlet at the rear of the head on the passenger side near #6? If you look at the block, there is a large coolant passage at this area. Wouldn't the outlet in effect cause a "short cycle" with regards to the fluid flow?

 

2) The idea of tapping the head above #5 and #6 exhaust ports into the coolant return gallery that feeds the lower thermostat housing is a good one. However, where should the coolant from these taps be returned? Should they return back to the water pump inlet or the radiator?

 

3) I just had this thought. The coolant system is pressurized at operating temperatures. Why not use this pressure to drive coolant from the bottom of the radiator to the block drain plug? 10 psi of coolant pressure is roughly equivalent to 20 feet of hydraulic head.

 

Discuss.

[ktm]

Ok, I just spent 30 minutes looking at a spare L24 block in my garage as well as my F54 block and the P90 and P90a heads. I think I have a pretty good idea as to the coolant flow.

 

The reason #6 gets the hottest, followed by #5 and then #4 is due to the way coolant reaches #6. The primary block feed from the water pump forces all of the water into the block right at #1 cylinder. The water has to travel from #1 to #6 before going into the head at #6.

 

My first question above was easily answered. There is no short circuiting of the flow. While it looks like it would short circuit, the passage from the large openign in the head to the outlet is rather small. Most of the water will circulate around the head and into the lower thermostat feed gallery.

 

Saying that, I also found a way to get the fresh coolant from the water pump to #6 using the stock configuration.

 

I do not have a camera with me, but conjur the image of the block in your mind or go and look. Right at the main feed into the block, there is a nice flat spot on the side that can be tapped with a 3/8 NPT port. Tap this and then run the line into the outlet on the passenger side outlet by #6 or into the block drain on the driver side.

[TimZ]

The reason #6 gets the hottest, followed by #5 and then #4 is due to the way coolant reaches #6. The primary block feed from the water pump forces all of the water into the block right at #1 cylinder. The water has to travel from #1 to #6 before going into the head at #6.

True, but the water still has to travel back to the front through the head from #6 to #1, so by this logic #6 should be the coolest cylinder in the head.

 

My first question above was easily answered. There is no short circuiting of the flow. While it looks like it would short circuit, the passage from the large openign in the head to the outlet is rather small. Most of the water will circulate around the head and into the lower thermostat feed gallery.

Not sure what you are saying here - if the short circuit you are referring to here is a piece of hose bridging the two hose barbs in the engine that used to run to the heater core, then you would be running the hot water from the back of the block back to the pump inlet.

[X64v]

3) I just had this thought. The coolant system is pressurized at operating temperatures. Why not use this pressure to drive coolant from the bottom of the radiator to the block drain plug? 10 psi of coolant pressure is roughly equivalent to 20 feet of hydraulic head.

 

The whole cooling system is pressurized equally by the thermal expansion of the water (with that pressure being the radiator cap rating). Add in the water pump flow being restricted by the thermostat, and that means the pressure in the block/head should always be higher than in the radiator.

[ktm]

True, but the water still has to travel back to the front through the head from #6 to #1, so by this logic #6 should be the coolest cylinder in the head.

 

Not necessarily. The water in the block moves from #1 to #6 through the block. The water, once it enters the head, circulates around each chamber. The water entering the head at #6 is hotter than the water entering the head at #1. The water in the head at #6 does not recirculate back through the head to the #1 cylinder and then enter the lower t-stat housing. It enters the lower t-stat return gallery that Monzter's sectioned head pictures illustrated (where we would tap into above the exhaust port - see picture below).

 

Not sure what you are saying here - if the short circuit you are referring to here is a piece of hose bridging the two hose barbs in the engine that used to run to the heater core, then you would be running the hot water from the back of the block back to the pump inlet.

 

I was wrong. What I was saying is that the water coming out of the block at the large opening would preferentially flow to the heater port and not the head, thus robbing the head of a cooler source of water than recirculated coolant.

 

The whole cooling system is pressurized equally by the thermal expansion of the water (with that pressure being the radiator cap rating). Add in the water pump flow being restricted by the thermostat, and that means the pressure in the block/head should always be higher than in the radiator.

 

The coolant system can not be pressurized equally, otherwise coolant would not flow. The coolant moves by differential pressure. The pump creates a higher pressure at the outlet and due to frictional losses along the flow path, there is a lower pressure at the thermostat.

 

The pump creates a negative pressure at the inlet side and a positive pressure at the outlet, right where I was talking about tapping. The pressure at the heater port by #6 is at a lower pressure than right after the pump, thus putting a tap where I mentioned would enable cool water to flow from the pump to #6.

[ktm]

I just had another thought. I am thinking of the coolant flow in terms of differential pressures throughout the head.

 

Could it be that the coolant in cylinders #5 and #6 does not actually return to the lower thermostat housing but rather exits via the heater port at #6? The pressure in that hose, especially where it connects to the housing at the front of the block, is going to be lower than the pressure in the head. Reason being is that it is connecting to the inlet side of the pump. The pump is "sucking", or creating a negative pressure, in that line.

 

The pressure in the head around #6 is going to be lower than the pressure at #3, and #3 less than #1 as a result of the increased frictional losses at each cylinder. If the losses are great enough around #6, it could be conceivable that there would be deadspots in the head where equal pressures meet.

 

The lower pressure area provided by the heater port would cause a preferential movement towards the port.

[Tony D]

Bo, I answered your questions in yoru other post, before I saw your PM.

 

The heater hose is a direct shunt, and allows engines to potentially overheat.

 

The flow answer is to tap above the head and return it directly to either the radiator, or the thermostat housing.

 

The water pump imparts velocity to the water, and restriction along the way creates the pressure in the block and head. It is this increased pressure (up to 60 psi on the bottom side of the thermostat at higher rpms!!!) that keeps the nucleaic (give me a break on spelling---reference the grape ape racing document on cooling and how engines overheat for the correct spelling of the term) boiling from starting. It's not just the static pressure from the radiator cap. What the cap pressure does is insure there is sufficient NPSH at the pump inlet to operate correctly at variable speeds that can wing that thing up to VERY high speeds. One of the problems you get is pump cavitation, and a higher static pressure helps with that...but when the engine is cold you can cavitate when you rev high simply because no pressure is built up in the radiator yet, and the lower radiator hose can 'collapse' from the suction.

 

Really, the only time there is real 'suction' at the water pump inlet is before warmup. Once the coolant expands and you build some static pressure against the cap, the pump in merely imparting flow to a system that gets pressure from restrictions along the way.

 

Adding flow to one section may indeed rob flow from another...TimZ's post about the OEM Nissan LD28 pump (or was it JGKURZ...) as it has a larger impeller and fits our front cover.... So if you plan on modifying the flow on the head, I'd consider that upgrade as well.

 

Take a look at what I wrote on the other post...feel free to copy and post to this thread if you feel it's appropriate.

 

I'm jumping all over! BLaaaaah! Walla Walla Walla...

[ktm]

Thanks Tony. Your explanation regarding the pump operation makes sense.

 

As far as the other heater shunt, you confirmed what Ron Tyler and I discussed. I thought blocking this line off would be benefitial as well as tapping the head and returning it to the radiator. I can not return it to the lower t-stat housing as that port is used to feed coolant to the turbo.

 

Thanks again!

[TimZ]

I can not return it to the lower t-stat housing as that port is used to feed coolant to the turbo.

 

That's the lowest pressure point on the engine aside from the pump inlet - where does the turbo return the coolant to?

[Tony D]

That's the lowest pressure point on the engine aside from the pump inlet - where does the turbo return the coolant to?

 

Most people return turbo coolant to the inlet side of the water pump and in that capacity it functions as the 'external bypass line' that normally comes around the front of the block and returns to the suction side of the pump anyway.

 

The system is designed for those two bypass routes (one internal, one external from the lower thermostat housing) without overheating---and as I discussed in the other thread are critical for proper pump operation and proper engine warmup before the thermostat cracks open to let coolant flow through the radiator.

 

When you start the engine cold, that T-Stat is closed, the pressure built by the pump rotation has to go somewhere and that is through the two bypass channels mentioned. Later on the ZX's they added a 'poppett' valve on the 15mm line off the head to the heater for when the engine is revved to sky high rpms before the thermostat is opened...it dumps coolant in a shunt back to the pump inlet keeping the pump from cavitation...and shocks the system with a slug of water from the hottest part of the engine directly into the pump's inlet making it warm up all that much faster.

 

Basically if you take a ZX and start it cold at the top of an onramp to the autobahn, and then immediately rocket down it to top speed and jsut keep going the poppet valve will open and recirculate a LARGE volume of hot coolant to the inlet to make the thermostat open faster as it will see hot water before the block is even fully up to temperature.

 

The internal passages on the earlier cars were designed with the thought that people would take the time to properly warm up the engine before revving it up and taking on top speed runs. By the time the ZX came out---apparently it was realized this was not the case, and they changed the system.

[ktm]

Tim, what Tony said. It is routed back to the inlet side of the water pump. One more thing. It does not matter what the pressure is at the lower t-stat housing for the turbo coolant line. The turbo is lower than the t-stat housing and so is the pump inlet. Water will flow from the lower t-stat housing to the pump inlet by gravity (and siphoning if it must). Actually, the lowest pressure point is not the lower t-stat housing but most likely the top of the radiator once the t-stat opens.

 

Tony, what about tapping the block at the pump outlet/block inlet (where there is a nice flat area on the block and a nice big coolant passage) and routing that to the heater outlet by #6?

 

Also, this statement:

 

"Really, the only time there is real 'suction' at the water pump inlet is before warmup. Once the coolant expands and you build some static pressure against the cap, the pump in merely imparting flow to a system that gets pressure from restrictions along the way."

 

Is confusing me. I was a wee bit tipsy last night thanks to Mr. Walker and glossed over this statement.

 

The system does not get pressure from the restrictions but rather loses pressure at each restriction, roughened surface, transition, bend, etc. The pump must over come these losses by developing pressure at the pump outlet so that the water will flow.

[TimZ]

Tim, what Tony said. It is routed back to the inlet side of the water pump.

 

That works. I was mostly curious - people often get confused about which way the fluid is flowing.

 

One more thing. It does not matter what the pressure is at the lower t-stat housing for the turbo coolant line. The turbo is lower than the t-stat housing and so is the pump inlet. Water will flow from the lower t-stat housing to the pump inlet by gravity (and siphoning if it must).

 

No, it still matters - there is an amount of pressure due to the head of water in the system (density of the water vs the difference in height from one port to the other) that must be overcome, but the water will ALWAYS flow from a high pressure point to low pressure if it has a path to get there. It doesn't have a choice.

 

Actually, the lowest pressure point is not the lower t-stat housing but most likely the top of the radiator once the t-stat opens.

That's why I specified "on the engine, aside from the pump inlet". The pump inlet is by definition the lowest pressure point in the system.

 

Also, this statement:

 

"Really, the only time there is real 'suction' at the water pump inlet is before warmup. Once the coolant expands and you build some static pressure against the cap, the pump in merely imparting flow to a system that gets pressure from restrictions along the way."

 

Is confusing me. I was a wee bit tipsy last night thanks to Mr. Walker and glossed over this statement.

 

The system does not get pressure from the restrictions but rather loses pressure at each restriction, roughened surface, transition, bend, etc. The pump must over come these losses by developing pressure at the pump outlet so that the water will flow.

 

These are just two different ways of saying exactly the same thing. You can't have liquid flow without a pressure difference, and you can't have a pressure difference in a body of liquid without flow.

[ktm]

That works. I was mostly curious - people often get confused about which way the fluid is flowing.

 

Understood.

 

I was thinking about tapping the head above #5 and #6 exhaust ports as discussed earlier in this thread. I would then run the #6 line to the turbo coolant inlet; the #5 line would run to the lower t-stat housing where the turbo previously connected. Thoughts?

 

No, it still matters - there is an amount of pressure due to the head of water in the system (density of the water vs the difference in height from one port to the other) that must be overcome, but the water will ALWAYS flow from a high pressure point to low pressure if it has a path to get there. It doesn't have a choice.

 

Yep. I was typing too fast. I made a similar statement to x64v when he stated that the cooling system was equally pressurized.

 

As you stated that the pump inlet, by definition, is the lowest pressure point in the system, the pump outlet, by definition, is the highest pressure point in the system.

 

These are just two different ways of saying exactly the same thing. You can't have liquid flow without a pressure difference, and you can't have a pressure difference in a body of liquid without flow.

 

After I posted my response, I thought about the statement some more and realized this point.

 

So we are in agreement regarding how the coolant is flowing, its general flow path, etc. The question at hand is how to improve the cooling.

 

I was really hoping someone would chime in on my idea of tapping the block right after the inlet port in the block (right after the pump outlet), and running a line from the tapped port to the port in the back of the head.

[Tony D]

One of the biggest hurdles I have when training people on centrifugal pump theory is that the impeller imparts flow. Pressure comes from slowing that flow, or impeding it...if you impart more flow without enlarging the slowing chamber a correspondingly, or removing restrictions you will get more pressure rise showing.

 

Take a pump and run it free field and you will find you get a LOT of flow...but deminimis pressure. The thermostat opens, and you will see a drop in your block water pressure. When you are operating at higher pressure (higher rpms) and watch pump output pressure..and see it start fluctuating you know you are experiencing cavitation of the pump. Which is why a 16psi cap helps---more suction head to keep feeding the pump and preventing any cavitation (surge in a centrifugal air compressor).

 

When you stop that flow during a cavitation episode, and that block water pressure instantaneously fluctuates, you can instantly form steam pockets. Usually when it cavitates it does so in rapid succession, so your steam pocket can get pretty big, pretty quickly. It used to be common on high load equipment to monitor bock water pressure. You can see the thing start misbehaving and then watch a corresponding spike in temperature.

 

The actual mechanics of 'overheating' are pretty complex, not nearly as simple as many people would have you believe. If you can watch what is happening, you know which way to move to combat it. I think your issue is the formation of steam pockets over the top two hottest cylinders during episodes of either cavitation, or high heat production.

 

In either case, giving those steam bubbles a place to IMMEDIATELY exit the area, instead of loiter and cause problems would aid in your heating issue. You have that steam in there acting as an insulator, and as a result the temps in those two cylinders start rising higher and higher, faster and faster.

 

Put some more flow in there, and let ALL the cylinders vent steam/flow directly to the radiator (see the PM I sent about the FIA and LY cylinder head cooling manifold revisions) should help quite a bit.

 

Once you know you are evacuating the water sufficiently, then you can start thinking maybe you are running 'too lean'.

 

Of course reverse flowing the engine would put the coolest water into the hottest part of the engine like EVERY OTHER PROPERLY DESIGNED HEAT EXCHANGER ON THE FACE OF THE EARTH! What we have here is a holdover from Henry Ford's Ebuillent Cooling systems and the intimations from above of using simple head and thermal siphon actions to cool the engine in a 'total loss' cooling scenario. Since it was all set up to go that way to start, nobody thought about making it an efficient heat exchange under a pressurized scenario.

 

When Chevrolet started doing high specific output engines (for the time, a whole 1HP per CID---oooooh! Wow!) they did some experiments on reverse-flowing the SBC. It was much more efficient and promoted less cylinder bore taper/wear. But they were tooled up for production and already had the stuff amortized. It wasn't until the engine went through a major platform redesign that this revelation (er...from 40 years earlier) was actually implemented. I mean, 'it worked good enough, why screw with it' does have a valid stance, but once you start talking about incremental redesigns, you may as well look at ALL the options.

[X64v]

Of course reverse flowing the engine would put the coolest water into the hottest part of the engine like EVERY OTHER PROPERLY DESIGNED HEAT EXCHANGER ON THE FACE OF THE EARTH!

 

:lmao:

 

Quote of the day, right there.

 

I'm getting ready to rebuild another cylinder head to put on my turbo motor, and am thinking very seriously about tapping 5 and 6 above their exhaust ports and returning both to the pump inlet, giving steam pockets a good place to go just as Tony D said. What does everyone think about the size these lines should be? I will be plumbing in AN line, but obviously a restrictor can be made to any proper size.

 

Also, what about tapping #4 as well? On lots of blown head gasket pics where 5 is blown and 6 is way out of round, I see 4 is quite out of round as well, much more so than 1, 2, and 3. Would it also be worth the little extra effort to tap #4 as well, perhaps one size smaller?

 

I would then run the #6 line to the turbo coolant inlet; the #5 line would run to the lower t-stat housing where the turbo previously connected. Thoughts?

 

I think you're on the right track with #6, as it would be flowing fairly freely back to the pump inlet. As for routing #5 to the lower thermostat housing, I think that's not the greatest idea. While there would be a difference in pressure, the difference would not be very great, yielding less flow. Returning #5 back to the pump inlet as well would flow a lot more water (more on par with what the #6 tap would flow).

[MONZTER]

I'm confused, what’s so funny about reverse cooling a Z head??

[X64v]

Nothing, but the fact that Tony D gets so worked up about it is entertaining.

 

 

 

Edit: I've been thinking about what size to make those taps, taking into consideration total external bypass flow relative to stock, ease of plumbing, and of course cost of -AN fittings. I think I've come to a good compromise for myself: 1/4" NPT ports above #5 and #6, -6 lines coming off each one into a -6 tee, with a -6 line from the tee back into the water pump inlet. This way, the total flow of the ports above #5 and #6 would equal the capacity of a single -6 line, which is about the same capacity as the original bypass circuit from the lower T-stat housing (which I've had blocked for some time now). Therefore, I would not need to upgrade my water pump, as no more water would be bypassed than stock (a single -6 line is 9.525mm, stock is what, 10mm?).

 

Thoughts on this?

[johnc]

Why not just cross flow the cooling on the head? Three inlets on the passenger side, each between two cylinders, and three outlets on the drivers' side between the same two cylinders. Run a dry deck, electric pump, and split the pump output between the head and the block.

 

Or, maybe just increase cooling system pressure like I did. 28 to 30 psi solves most nucleate boiling problems. Or better yet, go with a non-water based cooling system.

[ktm]

"1/4" NPT ports above #5 and #6"

 

I came to the same conclusion about the size. A 3/8" NPT tap results in HUGE hole just to have a true -6 I.D. So I am going with a 1/4" NPT tap with -6 lines.

 

I am feeding my turbo from the by-pass line on the lower t-stat right now. Tony and I talked about my plans and he suggested running the turbo feed line from #5 and not #6.