285 whp!

[shotgunslade]

Rally Bob:

Would really be interested in the insights Jack and team have about the overheating problem with the EG33. I have a sense that the problem is located in the engine, or at the inlet to the water pump. If it is in the engine, there might be a portion of the engine that is inadequately served by cooling channels, and overheats locally, causing local boiling of the coolant and steam pockets in the coolant stream under hard running. A second possiblity is that there are coolant passages that, because of their poor hydrodynamic design, cause local cavitation at high flow. Another possibility would be that at high rpms, the water pump is cavitating. The first problem probably isn't solvable, the second might be solvable by machining some of the coolant passages in the block. The third could be solvable by an electric water pump.

As I have continued to track my SVX, the overheating problem has gotten worse. Maybe I'm driving the car harder, or maybe something is deteriorating. Even the PWR radiator didn't seem to help. At this point, I have given up tracking it. Overcoming this issue is key to my keeping the car. Even though I do have a new track car, it's open and isn't really suitable for heavy rain. I loved being among the fastest cars on the track when it got wet. Loved passing Corvettes. But, soon as it dried out, my radiator boiled over.

Anyway, next year, I'm going to upgrade my closed trackable car alternative. I'll either go into a major refurb of the SVX, if the overheating can be overcome, or buy something different. So, the overheating issue is very important to me. Would love your insights.

[oab_au]

I realise your post was addressed to Bob, but I really do think it is related to the pump speed. Over the years that I have seen engines improved, and the average engine speed raised, it has always been a problem of the pump cavitating to allow the engine to overheat. The fix was to fit a larger pulley to the pump, or fitting an under drive crank pulley, to reduce the pumps speed.

When the engine was designed the pump speed was set to operate at the most effective speed. For the normal SVX this would be about 3000 rpm. As you are road racing with a 5 speed box, you are running at a much higher average speed that is over the effective pump speed, for a longer period.

Gearing the pump down is not an option, reducing the pump impeller would impair its effectiveness. So the best option would to fit an electric pump. Its operation is controlled by the water temp, without the thermostat.
You would have to remove the impeller fins, and reroute the bypass and heater return pipes to return to the inlet side of the pump, but that is not a big job.

It is an easier option to try, than redesigning the cooling system.

Harvey.

[shotgunslade]

Harvey:

Thank you. I really want to keep the SVX, but I want a car that can take a few turns around the track without blowing its top.

[oab_au]

Originally Posted by shotgunslade

Harvey:

Thank you. I really want to keep the SVX, but I want a car that can take a few turns around the track without blowing its top.

Yes I can understand that.

I would like to hear what Bob has found out also.

Harvey.

[oab_au]

Just to explain, as you may not know the full implications of how the effects of cavitation affect the cooling. It is not just that the pump stops pumping.

When the impeller reaches the speed where the molecules of the water are torn apart, forming bubbles of nothing. This is a void where the pressure has dropped dramatically.

With the drop in the boiling point, with the drop in pressure the water around the void instantly explodes into superheated steam. The pockets of steam push the water out of the system overflow.

This can happen in a normally driven pump, when it is revved out. You can see on the inside of the housing, around the impeller track, small indentions where the water has exploded into steam, blowing holes in the casting. Looks like detonation marks on a piston.

As it only happens at high rpms, so it does not last long. Yours would do it most of the time, because you are up in those rpms most of the time.

Harvey.

[RallyBob]

Originally Posted by shotgunslade

Rally Bob:

Would really be interested in the insights Jack and team have about the overheating problem with the EG33. I have a sense that the problem is located in the engine, or at the inlet to the water pump. <snip>

As previously mentioned in this thread, Jack has done quite a few of these mods already. Aftermarket radiator, higher pressure cap, deleted thermostat (restrictor in place), remote electric water pump. All have reduced the overheating to some extent, and certainly delayed it until later in a racing session. But none have cured it 100%.

I had mentioned when I had a chance to look at his spare shortblock while building the oil pan, that I didn't 'like' the appearance of the cooling passages and in particular the inlet at the water pump. Jack's machinist also agreed with this, and spent some time machining the block to straighten the passages and try to reduce some turbulence. So when the new engine is fired up and run, we'll see if these changes have helped any.

Jack had mentioned that he might have it up and running this weekend, maybe dynoed this week.

Unfortunately we won't have a direct HP comparison to before, as Jack had left XXTuning when that company got sold, and now works for EFI Logics with another brand of dyno (Mustang AWD). And apparently the Mustang reads *quite* differently from the old Dynapack they had used before.

[RallyBob]

Originally Posted by SVXRide

Bob,
Nice! What's the total oil capacity now?
-Bill

Almost forgot, the engine now takes exactly 8 quarts, inclusive of the oil cooler and the accusump.

[longassname]

Ya the numbers off the previous dyno didn't seem right. I expect the results off the new one will fall more inline with other dynos.

Did you take any pictures of the new pistons and the engine as it went together?

Originally Posted by RallyBob

As previously mentioned in this thread, Jack has done quite a few of these mods already. Aftermarket radiator, higher pressure cap, deleted thermostat (restrictor in place), remote electric water pump. All have reduced the overheating to some extent, and certainly delayed it until later in a racing session. But none have cured it 100%.

I had mentioned when I had a chance to look at his spare shortblock while building the oil pan, that I didn't 'like' the appearance of the cooling passages and in particular the inlet at the water pump. Jack's machinist also agreed with this, and spent some time machining the block to straighten the passages and try to reduce some turbulence. So when the new engine is fired up and run, we'll see if these changes have helped any.

Jack had mentioned that he might have it up and running this weekend, maybe dynoed this week.

Unfortunately we won't have a direct HP comparison to before, as Jack had left XXTuning when that company got sold, and now works for EFI Logics with another brand of dyno (Mustang AWD). And apparently the Mustang reads *quite* differently from the old Dynapack they had used before.

[shotgunslade]

Harvey:

Rally Bob's proposed cures of the water pump inlet and the restrictor are all consistent with the problems caused by increased water flow due to higher engine rpms. In a closed fluid loop, a pump is merely a mechanism for creating a net positive pressure on the discharge side and a net negative pressure on the inlet side. The sum of these net pressures can be considered the average net pressure for the system. It may not be limited to the pressure rating of the radiator cap, because the radiator cap may not be located at the neutral pressure point in the system, the point where the downstream pressure drop equals the upstream pressure drop.

The faster the pump moves the greater is the lift acrosss the pump, and the greater the positive and negative net pressures on the discharge and inlet sides of the pump respectively. The problem arises when the net absolute pressure on the intake side of the pump falls below the vapor pressure of the fluid at the operating temperature. The fluid then boils. Since pumps don't pump steam very well, there can be a drastic loss of flow, greatly reducing the ability fo the cooling system to shed heat and resulting in rapid overheating. Local poor flow configurations resulting in high turbulence can also result in very local low pressure areas causing localized boiling. The probelem is that the steam bubbles may not collapse completely when they rejoin the main stream and they disrupt heat transfer between the coolant and the block. These local flow conditions are more disruptive, the closer they are the pump inlet, because the net absolute pressure in the line is lower the closer you get to the pump inlet, and the less has to be the negative pressure differential caused by local turbulence before local boiling occurs.

So, an electric pump to avoid excessive lift thru the pump at high rpms, and cleaning up the pump inlet condition and accessible fluid passages at the downstream end of the block coolant channels should avoid the local boiling problem. Can't wait to see how this works. Don't know if the restrictor is needed with the electric fuel pump, unless it moves the pressure balance point of the system farther upstream in relation to the radiator cap, thus effectively increasing the average net system pressure required to blow the cap.

If I decide to redo the SVX, including having an engine built, it will be later this year, hopefully, after we can find out if Jack's efforts are successful.

[dynomatt]

What electronic pumps are you guys using?

I know there's the Davies Craig, but when I looked at relative flow comparisons, the standard pump flowed a lot more.

The manual says

600rpm 20l/min
3000rpm 100l/min
6000rpm 200l/min

The Davies Craig ones I have seen max at 110l/min.

If we have engines running at 5000-8000rpm...and we assume they are cavitating up there, what is the max flow we need to effect proper cooling?


Matt

[svxistentialist]

This pump fluid capacity thing is interesting on a couple of levels.

Looked at one way, the more horsepower an engine produces the more redundant heat is made, so the cooling system needs to keep up. This would imply that rally Imprezas, that produce 300-400 hp which is 50% to 75% more than the EG33 on two thirds the cubic capacity, these must have already overcome the engine heating problem.

So the simplistic question is, would a pump from an Impreza rally car shift more litres per minute or be a better pump in any way? [If so, could one of those be made to fit?]

Looked at on another level, and shotgunslade described the problem very succinctly, is the primary problem here the inability of the EG33 block water passages to flow efficiently to the feed side of the pump when the engine is running at high revs full time on track?

And if this second scenario is the real problem, as increasingly seems to be the case, then what are the principal differences between the water flow capability of the EG33 block and the 2.0 block that cause this restricted flow/cavitation in the EG33?

If this can be identified maybe some machining or adjustment can be made to improve things.

Does anybody know the stats on the Impreza pump used in high hp cars, and if it can be substituted?

Joe

[SVXRide]

Originally Posted by RallyBob

Almost forgot, the engine now takes exactly 8 quarts, inclusive of the oil cooler and the accusump.

Bob,
Thanks for the info! Any chance we can get a little more detail on the machining mods to the block? Did they do anything to the crossover pipe?
Thanks.
-Bill

[TomsSVX]

Has anyone thought about how fast the fluid is moving? What are the chances that the pump is not caviating, it is flowing well, and the big problem is the coolant is simply moving through the radiaor too fast to cool down enough?

Tom

[shotgunslade]

Tom

Doesn't work like that. Heat transfer is equal to the the mass flow times temperature differential, times specific heat:

Heat = (mass flow) * (temp Diff.) * (specific Heat)


You have two generalized systems for heat transfer here: block to coolant and coolant to air (radiator).

For the sake of argument, lets assume the temperature of the water entering the radiator is fixed. Also assume that the volume of air rushing past the radiator is fixed as is the air temperature. Raising the fluid flow rate through the radiator will do two things, it will reduce the heat flow resistance at the boundary layer between the tube walls and the fluid and it will slightly raise the logratihmic mean temperature of the fluid in the radiator. It will raise the temperature, because heat loss on the air side of the radiator is pretty fixed, so that putting more coolant through the radiator reduces the temperature drop of the coolant as it goes thru the radiator. Both of these will tend to increase the heat loss from the fluid to the radiator. So, even though you have a higher temperature of coolant leaving the radiator, because you have a larger flow volume, you have actually slightly increased the heat loss through the radiator.

The heat gain within the block is also fixed, and is not really a function of fluid flow. Heat generated by engine operation at a constantly engine operating state will be pretty much the same no matter what the coolant temperature (within reason). So, the temperature difference between the fluid entering and the fluid leaving will be equal to:

(Fluid Temp diference ) = (Engine heat gain)/ ((fluid flow rate) * (fluid specific heat))

So, so the coolant temperature rise through the block is directly proportional to the amount of fluid going through the block.


The short version of this is that raising the fluid flow rate causes 2 things to happen: the temperature rise through the block is reduced almost in direct proportion to the increase in coolant flow rate. The temperature drop through the radiator is also reduced almost in direct proportion to the increase in fluid flow rate. These two things almost cancel out one another. The almost is important, because raising the fluid flow rate improves heat transfer between fluid and tubing, and because raising the fluid flow rate makes the mean temperature of of the radiator higher compared with the fluid inlet temperature. Both of these two slighly increase the overal heat transfer of the system.

This discussion assumes that the coolant fluid stays liquid. If it boils, heat transfer rates crash.

So, we need to look for boiling.

[TomsSVX]

good description Dan, it was just a quick thought the other day while i was reviewing the thread... The fact that the coolant temps dont gradually climb and tend to spike leads me to follow the assumption that the coolant is able to boil...

I think we need to be looking at a possible hot-spot in the block in which flow is not optimal where coolant can get caught and allowed to boil...

Care to swing by with your car so I can run a couple tests?? I haven't had overheating issues like you have and I would like to make sure there are no issues with the cooling system.

Tom