Water Pump Flow Rates

[GTRNUR]

Where this thought came from is that I have been experimenting with different pully sizes on my open deck engine (which has the N1 water pump). I am also thinking of putting 3 temp sensors in the spacer plate of my next engine to get a picture of what is happening cooling wise around each of the cylinders. (Ala the Jun super lemon R33.. Too much data is just enough).

Im trying to track down some REAL flow data for the RB water pumps. Seems that oil pump data is everyhere to be found, but there is little said about the flow capabilities of the various coolant pumps.

The most that seems to be out there is:

The VL/RB30 pumps are 6 blade and all RB20/25/26 pumps are 8 blade. N1 is 6 blade with an anti-cavitation disc.

Search results have come up with this quote below... about the only moderately *useful* bit of information. Others comments posted claim the N1 pump has higher flow, but do not offer an explanation or any real data other than the belief that N1 = Race car stuff = MORE POWER = MORE COOLING.

I've always seen people in high hp/high rpm applications (Nissan RB26 N1 water pump for example) try to decrease cavitation for better cooling going around a track at the expense of low rpm flow due to the design of the blades.

Also of interest is that the RB20/25/26 pumps are turned at a lower average speed due to the pulley size being larger, compared with the VL/RB30 pumps. Which stands to reason as the skyline engines are designed to rev more. So turning the pump slower will mean less cavitation risk at higher RPM, whilst possibly achiving a lower flow rate.

So the thinking is, that a stock pump/pully configuration will actually be more "streetable" for most applications, as it will provide more flow at lower RPM. Resulting in a more even engine temperature (less variation) from the block to the head.

It also stands to reason the N1 pumps whilst being able to maintain sufficent coolant flow at 9000 rpm on an RB26 configured engine, may also just barely deliver enough coolant flow at low speeds. Which leads me to think the N1 pump is not at all suitable for a big torque stroker engine, as sufficent coolant flow may not be possible when the engine is operating around 1500-2200 rpm. Especially in very hot climates. But on a smaller displacement engine that typically revs around ~3000+ in typical in traffic driving, the N1 is adequite.

There is also the Patrol RB30's to consider. They run a smaller pully size again than the VL's but on the same pump. Granted a big part of the reasoning behind this is to turn the fan faster so the engine will get propper cooling when spinning all 4 weeks and bogged to the axels in mud.

Im interested in hearing everyones thoughts, and if you have actual flow data by all means post it up!

[DVS JEZ]

Honestly i think that wins the longest opening post without pictures.

What is the main reason for working out the flow of the pumps? Have u got a stock and a n1 to compare? Might have a different pitch om the blades

[GTRNUR]

Ok.. a picture... N1 vs stock. And as we all probably know, the RB30/VL pumps resemble a vl pump but without the disc supporting the blades.

Flow data is important for a number of reasons.

1. Higher flow reduces hotspots, and temperature differentuals in the engine.

2. Higher flow will pull in cooler water from the radiator more easily and faster into the hot coolant circulating within the engine blocks galeries, of course flow limited and controlled by the thermostat.

3. As a result of 2, higher flow will more quickly result in a stabilised engine temperature when loads change suddenly from light to heavy resulting in more heat.

4. More stable engine temps over varying operating conditions mean that the tune of the engine will not drift as much based on sensor corrections and compensations... so the car will be nicer to drive, run better and make more power more reliably.

Ideally you want as much flow as you can possibly get, without pump cavitation, and without robbing too much power from the engine.

Coolant flow rates should be matched to the operating speed and maximum working speed of the engine. If we were able to see an actual chart of the pump flow rate, pullies could be sized appropriately to achieve maximum flow at engine redline before cavitation sets in, thereby achiving the highest flow possible at low working speeds. I hope that makes more sense.

[bubba]

No flow data here but the reason I put an OEM RB20 pump on my 3L instead of an N1 pump is purely due to the many opinions that they are designed for sustained high rpm's.

[turboedsloth]

No flow data here but the reason I put an OEM RB20 pump on my 3L instead of an N1 pump is purely due to the many opinions that they are designed for sustained high rpm's.

The OEM pump? i thought it would have been the other way around, especially for track work

[bubba]

The OEM pump? i thought it would have been the other way around, especially for track work

Sorry, meant the N1 pump is designed for sustained high rpm which is why I opted for the OEM RB20 pump as the 3L was in my daily driver (at the time) so I didn't want any issues when getting stuck in traffic on the way to work.

Also, chuckie had a custom impeller made for his water pump by Terry Stacy, looked like a trick bit of kit, very similar to the N1 setup. No idea on flow rates etc though.

[wlspn]

The other thing to consider is, if the coolant is pumped TOO quickly, it will pass through the radiator before it has had a chance to be thoroughly cooled...

Could be the N1 pump is 6-bladed, not 8 to stop the water rushing through the radiator too fast at high RPM/track conditions

[wlspn]

Also just to mention, on my RB25, I use cheap RB30 water pumps.

Have come across both 6 & 8 blade...

Would seem the only difference between the cheap ($60 odd) pump & N1 is the anti-cavitation disc (& materials used, etc)

[turboedsloth]

I think with the cheaper pumps the different aftermarket companys that make them vary with the blades. One of the companys my other job deals with do the 8 blade water pumps. Think the brand is Trueflow, it doesnt have the cavitation plate either

[linkems]

I was reading your build thread just the other day which is very impressive by the way , and noticed you mentioning something about using the 300zx pulley to speed up the pump. Well i used to own a z32 300zx and when fitting an underdrive crank pulley, it was a good idea to fit an overdrive waterpump pulley to keep the waterpump operating at the correct speed. If your trying to speed up your pump this might be an easy solution.

Clicky

[Tony de Wonderful]

Flow data is important for a number of reasons.

1. Higher flow reduces hotspots, and temperature differentuals in the engine.

2. Higher flow will pull in cooler water from the radiator more easily and faster into the hot coolant circulating within the engine blocks galeries, of course flow limited and controlled by the thermostat.

3. As a result of 2, higher flow will more quickly result in a stabilised engine temperature when loads change suddenly from light to heavy resulting in more heat.

4. More stable engine temps over varying operating conditions mean that the tune of the engine will not drift as much based on sensor corrections and compensations... so the car will be nicer to drive, run better and make more power more reliably.

Ideally you want as much flow as you can possibly get, without pump cavitation, and without robbing too much power from the engine.

Coolant flow rates should be matched to the operating speed and maximum working speed of the engine. If we were able to see an actual chart of the pump flow rate, pullies could be sized appropriately to achieve maximum flow at engine redline before cavitation sets in, thereby achiving the highest flow possible at low working speeds. I hope that makes more sense.

As I understand it you need to consider pressure in the system also, because pressure helps stop steam pockets from forming which lead to hot spots.

You could increase flow rate by removing any restriction/restrictior (such as a thermostat) but this would reduce the pressure and could lead to worse cooling by virtue of steam pockets forming.

Also flow paths and flow split between the head and bottom end should be considered. You might be able to flow 'smarter' ,rather than flow faster, to cool the engine as well or better, and this won't rob HP.

[Tony de Wonderful]

double

Edited April 12, 2011 by Tony de Wonderful

[Tony de Wonderful]

Double.

Edited April 12, 2011 by Tony de Wonderful

[Tony de Wonderful]

The other thing to consider is, if the coolant is pumped TOO quickly, it will pass through the radiator before it has had a chance to be thoroughly cooled...

Could be the N1 pump is 6-bladed, not 8 to stop the water rushing through the radiator too fast at high RPM/track conditions

Apparently that is 100% not true.

It would probably cool a given unit of water faster because you get more turbulence.

You are flowing more units of water per unit of time so this compensates for a unit of water 'dwelling' in the radiator for less time.

Trying poring boiling water or your hand, first slow and then fast and get back to use about cooling rates!

[chuckie]

Hi,

heres few of my Pump,

[GTRNUR]

I was reading your build thread just the other day which is very impressive by the way , and noticed you mentioning something about using the 300zx pulley to speed up the pump. Well i used to own a z32 300zx and when fitting an underdrive crank pulley, it was a good idea to fit an overdrive waterpump pulley to keep the waterpump operating at the correct speed. If your trying to speed up your pump this might be an easy solution.

Clicky

I have something very similar to this sitting on my loungeroom table at the moment. I'll be fitting it next weekend to see how it goes.

Stock RB26 is a 135mm diameter

RB30 is 115mm (approx... its on the car so hard to measure)

Z32 underdrive is 100mm.

I figure since the N1 pump is used on engines that rev to 10k, and if I only use 8k gearing it up a bit to increase flow whilst gaining the benefits of the anti-cavitation design through mid range and top end RPM is worth a go. I'll re-measure the balancer side on the weekend and workout the exact ratio increase.

Its cooling down now at my end of the country now too. 35+ degree days arent happening anymore, so I might have to wait another 9 months before I can properly start experimenting with this again.

As I understand it you need to consider pressure in the system also, because pressure helps stop steam pockets from forming which lead to hot spots.

You could increase flow rate by removing any restriction/restrictior (such as a thermostat) but this would reduce the pressure and could lead to worse cooling by virtue of steam pockets forming.

Also flow paths and flow split between the head and bottom end should be considered. You might be able to flow 'smarter' ,rather than flow faster, to cool the engine as well or better, and this won't rob HP.

Yes pressure is required to eliminate hot spots and air/steam pockets, but removing restrictions isnt going to help increase flow. The system is closed and pressure of the coolant system has nothing to do with the flow rate of the pump. Its all about thermal expansion of the liquid, and the relief pressure of the radiator cap alone determines system pressure. The only way system pressure could effect flow would be if the coolant viscosity changed with pressure or temperature.

The restrictions after the pump that limit flow are the galleries in the block and the head, however its pretty safe to say that virtually all RB blocks of the same family will flow a simular rate given an identical pressure.

Edited April 12, 2011 by GTRNUR

[GTRNUR]

Hi,

heres few of my Pump,

Great looking impeller you have there. I guess you had to slot the disc and tig weld the blades both sides of the disc. And then probably machine it round and flat again. Very fiddly work.

[GTRNUR]

Apparently that is 100% not true.

It would probably cool a given unit of water faster because you get more turbulence.

You are flowing more units of water per unit of time so this compensates for a unit of water 'dwelling' in the radiator for less time.

Trying poring boiling water or your hand, first slow and then fast and get back to use about cooling rates!

I agree with you there Tony, except for the boiling water test...

Most people with something serious under the bonnet are also already running a tripple core radiator as well and typically have twice the coolant capacity and much more cooling surface area. If you factor in this with the fact you are generally going faster at a higher RPM and your cooling systems efficency goes up exponentially with speed.

[bubba]

Also, chuckie had a custom impeller made for his water pump by Terry Stacy, looked like a trick bit of kit, very similar to the N1 setup. No idea on flow rates etc though.

Hi,

heres few of my Pump,

There ya go

[Tony de Wonderful]

I agree with you there Tony, except for the boiling water test...

Most people with something serious under the bonnet are also already running a tripple core radiator as well and typically have twice the coolant capacity and much more cooling surface area. If you factor in this with the fact you are generally going faster at a higher RPM and your cooling systems efficency goes up exponentially with speed.

Well that is my point that fast flow rates don't mean 'the water doesn't get a chance to cool in the radiator'.

My boiling water comment was to demonstrate that heat exchange would still occur at higher flow rates.