Water Pump Flow Rates

[Tony de Wonderful]

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.

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.

Well no the radiator cap sets a maximum pressure at one part of the cooling system only. The pressures seen upstream of the radiator are going to be higher because of the sum total of frictional losses; the water pump has to force that water through all the galleries etc and that creates frictional losses before it gets to the rad. My understanding is you might have 30 psi in the block or so.

[wlspn]

OK, so silly example but all I can think of right now (it's been a hard day )

It's summer, 40-something degrees, you're all sweaty & hot...

In this scenario would you rather sprint past a fan or SLOWLY walk past it?

Obviously the more time spent in the airflow (by walking slowly) the cooler you will get...

This is ignoring said turbulence, etc though.

Not being a smartarse, just trying to understand some peoples theories better.

Also the N1 pump (anti-cavitation plate aside) with 6 blades...

Would it flow coolant faster or slower than a stock item? & in your opinion why?

[GTRNUR]

OK, so silly example but all I can think of right now (it's been a hard day )

It's summer, 40-something degrees, you're all sweaty & hot...

In this scenario would you rather sprint past a fan or SLOWLY walk past it?

Obviously the more time spent in the airflow (by walking slowly) the cooler you will get...

This is ignoring said turbulence, etc though.

Not being a smartarse, just trying to understand some peoples theories better.

Also the N1 pump (anti-cavitation plate aside) with 6 blades...

Would it flow coolant faster or slower than a stock item? & in your opinion why?

Getting a little off topic here, but anyway...

Assuming you are walking in a slow circle past a fan first, and then past a furnace. What you will experience is a nice cool down, followed by a heat up cycle again. Going slowly means more cooling time when in front of the fan, and also more heating time when in front of the furnace. The result will be that for a given time your body temperature would have the largest temperature variation from its hot to its cold state.

Now if you were to run the same circle (and assume you dont generate any of your own body heat). Hot, Cold, Hot, Cold, etc very fast! You will have less time to cool down per fan pass, and less time to heat up per furnace pass. This means your temperature over time will vary less from its hottest to its coldest temp.

As for which wins the thermal battle, that is determined by how efficent the fan is and how much heat the furnace generates. We have left out the thermostat here as well, which is designed to maintain a maximum level of cooling. So by varying the fan speed (in our little story), we could limit the cooling rate and vary the average body temperature.

The limited information that I have come across so far is that the 8 blade pumps flow the most, then its RB30, and then N1. Still this was just a comment that someone made on a forum thread somewhere, no data was provided again. And it wasnt from someone with a knowledgable reputation like Trent of Status either. I dont think the differences between the RB30 and N1 can be identified in just a picture. Blade angle and exact size are instrumental to how it works, what and pressure it will achieve at the pump.

[Tony de Wonderful]

OK, so silly example but all I can think of right now (it's been a hard day )

It's summer, 40-something degrees, you're all sweaty & hot...

In this scenario would you rather sprint past a fan or SLOWLY walk past it?

Obviously the more time spent in the airflow (by walking slowly) the cooler you will get...

This is ignoring said turbulence, etc though.

Not being a smartarse, just trying to understand some peoples theories better.

Also the N1 pump (anti-cavitation plate aside) with 6 blades...

Would it flow coolant faster or slower than a stock item? & in your opinion why?

You need to consider the system as a whole not just a given unit of water in the radiator and how much time it spends there

Put it this way if you pumped slow enough you would have a stone cold rad but the rest of the system would be boiling hot/overheating.

It's not just the turbulance either, because the faster you pump the less time a given unit of water spends in the rad and this means it cools less. This actually makes the radiator more efficient because cooling rates are faster when the temp difference between the rad and outside air is highest. It sounds like a paradox but it is becase you are feeding in units of hot water behind the unit in question; the whole system cools at a faster rate.

.

[sucram]

I seem to recall that the N1 flows less then stock

Reason being is that on the track, too much flow of water gives less time for the radiator to transfer heat. So N1 was better suited to engines that are more track orientated (live their life at higher rpm) and Normal is better suited for street driven low rpm cars.

Its been a while since I looked at one side by side

To work it out you would need to measure the area of the blades, angle/profile and the pump speed (rpm/pulley size)

If you removed your thermostate completely, your engine will run hotter. In traffic, highway and on the track. Flow needs to be balanced with the effectivness of the radiator used.

If you have a street car that is used as a track car as well, these can be the hardest to set up especially if you do track days when its 40 degree's outside. The problem is compounded if you have a high hp car

-Larger radiator (volume)

-Stock fan (flows the most but sucks engine power)

-Multi pass set up

-Header Tank (more volume, easily beeds air)

-Diffuser to direct air through the core instead of under/over/around

-100% water transfers heat better, (run sweet F all coolant if your lazy like me and dont want to change for meets)

-Water wetter works but hates coolant (about 4 deg drop)

This is pretty much what you will need to consider if you want something you can drive every day as well as doing track work. Its been a couple of years since I raced bikes and even longer since I raced cars but nothing has changed much for 45 deg days and 60 deg track temps. You may even need to run an N1 pump with stock pulley for the road and under driven for the track (or vise versa). Even machining down the impeller is an option but you would need to experiment and test to see if that is the direction you want to go with the pump you decided is best for ya

[GTRNUR]

My final analysis.

As has been covered, here-say says that the stock 8 blade pumps flow the highest, followed by the RB30 pumps, and then the N1 pump. As for actual flow data, none seems to exist.

However, it is known that the standard pumps works as designed on the standard motors and the N1 pump work well on modified motors that rev. It is fairly safe to say that being an N1 part it will have been designed to be effective on an RB26 at 9000 RPM. Though we can all be sure it is the pump of choice for engines that rev to and past 10,000 RPM.

It has been my experience that even stock GTR's struggle to keep cool in traffic driving conditions on a hot day (36+ in the sun), when the aircon is running. Unless sustained speeds above 80km/h can be maintained, temps tend to run away up to 85-90 degrees, which is well above that which the thermostat is trying to regulate too. This is because ambient air temps are too high to sufficently pull enough heat from the coolant.

The goal of what I have been trying to achieve here is to get a cooling system optimised to the point that it actually can maintain engine temps at a thermostat regulated temp, even on hot days and also with a modified engine. And according to my latest test data I have come very close. The other factor I am trying to achieve is that my stroker engine produces usable power much lower in the RPM range. Cruising in 5th or 6th at 1800-2000 rpm at light throttle at 80-100k's is where I am picking up great fuel economy, so I am trying to balance the cooling system to be effective at this speed. On long drives (in the heat) it is effective, but add some stop-go traffic and it takes some driving to pull that heat back out of the coolant again.

I believe it is also safe to say that the pump flow rate vs RPM are not linear. Though going on what we know with the N1 pump, it is likely to sustain flow at a higher RPM without (or with less) cavitation, while still flowing less than a stock pump at a lower RPM.

This table show the crankshaft RPM and the associated RPM of the pump for each type of pulley.

Crank Size Belt Speed/Ratio 2000 3000 4000 6000 7000 8000 10000

RB26 140mm 4PK875 1:1.07 2140 3210 4280 6420 7490 8560 10700

RB30 114mm 4PK850 1:1.315 2630 3945 5260 7890 9205 10520 13150

VG30OD 100mm 4PK835 1:1.5 3000 4500 6000 9000 10500 12000 15000

I have tried these combinations on my RB315. At present I have a billet VG30 overdrive pulley on the pump and it seems to be producing the best result (for my application). Crusing around yesterday in 35 degree heat with the air con blazing a nice 20 degrees, engine temps only crept up to 74 degrees when stuck in traffic. Cruise below 70km/h was 72 degrees and at 80 degrees temps dropped to the 68 degrees of the Nismo thermostat.

I am still using a clutch fan with the standard R34 fan which also is obviously picking up speed as a result of the pulley size change, though there is no noticable loss in response. I put that down to the engine having torque to spare, or also the fact that once rolling and incoming air is essentially flowing into the front of the engine bay naturally, the fan is pretty much free spinning anyway.

The engine still retains the water to oil heat exchange, so I am also seeing lower oil temps which is nice. Generally they max out at 80 degrees after sustained driving, which is ideal as above that viscosity does tend to drop off rapidly. (still using mineral oils for the moment).

I'll add that back when I had the RB26 in the car, crusing at 100k's in 5th would produce much higher oil temps than cruising at the same speed in 6th. I'd put this down to the oil that was squirted to the bottom of the piston crowns pulling more heat from the engine at higher rpm. Or more accurately at higher RPM more heat was generated. So while my stroker engine revs much less than a stock engine does at cruise speeds, the seems to be being transferred to the coolant via the block more.

Then there is also the grey area ive introduced with a tomei oil pump too... As it is very likely that the oil squirters in my engine operate virtually all the time, as even at 1800 rpm the oil pressure is 4kg/cm so the squirters will be operating.

So for the moment my current setup will remain with the VG pulley for the remainder of summer. Considering I tend to shift gears at no higher than 7000 RPM generally, pump speed shouldnt be an issue. But in winter I believe I will swap to the RB30 pulley, and still maintaining propper engine temps.

My opinion would be that for any stroker engine that is intended to stay below 8000 rpm, keep a stock pump. And for 3lt engines switch to an RB30 pulley. And only run the VG30 underdrive pulley if you live in an hot climate, and when you do, limit the use of your maximim RPM or risk throwing belts or breaking the pump.

There are those out there that claim they want to maximise response and minimise the power and response losses from driving the standard cooling system. Really though, all the power and response in the world is pointless if you can not used it for more than 5 minutes without it overheating. So a cooling system should always have capacity too spare to properly cool your engine for its given performance.

[WHITER33GTS-T]

Just to put another option out there. Did you think about going a electric water pump setup..?

I was just searching to try find flow rates for the different pumps as the ewp kits im looking at flow either 80 or 115 liters per minute

[STATUS]

i had a r34 gtr that was getting hot in traffic....tried evrything then pulled the pump as a last resort and found it to an N1 pump... fitted a std gtr item and it fixed the issue.. put the n1 pump on our drift car and it worked fine. In a street car it just didnt flow enough at lower rpm... thats the only real work comparo ive done

[GTRNUR]

Yes, that pretty much sums it up. Street cars should not have N1 pumps.

[discopotato03]

Well this is my opinion so maybe food for thought .

A cooling system has a finite ability or capacity if you like to reject heat and if you overstretch it nothing will the prevent the system temperature rising .

With radiators the cores are designed to have thin tubes with turbulators inside them which gives a lot of surface area to transfer heat in the coolant to the air passing over the tubes/gills . The turbulators are there to "agitate"the coolant enough to prevent laminor flow and reduce the boundary layer insulation effect .

I'm not sure if its possible to pump coolant "too fast" through a properly designed radiator for a given application .

We really have to lose the multi core urban myth because if anything deep thin core tubes make the best use of a heat exchangers physical size . You don't see "multi core" intercoolers for this reason .

As was mentioned a big difference in air and coolant temperature makes it easier for a cooling system to attemp to run at a constant temperature which is naturally why fewer cars overheat in winter like now . If theres problems in the system engines still can its just that it can get by generally with less capacity before problems become obvious .

And to specialist parts . Nismo like Ralliart make things like coolant thermostats that open at lower than standard temps and no doubt water pumps designed not to cavitate at higher average engine speeds than the manufacturer expects road cars are expected to use .

Using them is fine when an engine is worked harder and rev'd higher than roadies generally are , its not at all surprising to me that issues arise from using specialist parts in road cars - driven like road cars . I believe its a case of thinking that the people who designed the things in the first place somehow screwed up - which they didn't .

Personally I don't think a water thermostat that opens at 68C and actually regulates at that temperature is a good idea on a road car because no manufacturer deliberately designs a road car to do that and you have to wonder if oil temps get to where they need to be .

Would I be right in thinking people do this with the idea that when everythings cooler they have a greater temperature buffer before they think temperatures get out of hand ?

I would add that if the heat exchanger/s were up to the task then this extra buffer by running cooler is more of a negative than a positive .

Now I don't want to start a Nissan/Mitsubishi war but I think the later Evos are good examples to look at because they were not short changed when it came to cooling water oil and air . A 6 like mine std has an 82 degree opening thermostat and because they run a separate oil cooler they chose to use a thermostat for oil as well and its opening temperature is 100 degrees C . They are a transverse engine meaning have to get air to all three cores and out again because if you cant get the air out more can't get through .

With Skylines and RB engines from memory the coolant thermostat opening temp is about 76 which by todays standards is not very high . I remember some Fords running water thermostats up at or near 100C and I'm only guessing but I suspect this had to do with getting up to temp and running pretty warm for emissions and consumption reasons .

I would not be panicking in a hard worked engine if the water temp got to 100C provided the system pressure was high enough to stop the coolant actually boiling . Its not the highish coolant temperature that damages engines its the water coolant boiling and turning into a gas (water vapour) and the gas pockets allowing very high localised temps in heads and blocks - to the point of warping/cracking/gasket sealing failure .

Nismo and probably Ralliart sell higher pressure rated radiator caps to raise the cooling systems pressure which raises the cooling waters boiling point . Remember , free standing water at sea level meaning 1 bar or one atmosphere boils at 100C and the higher you go the lower the air pressure is and the lower the water boiling point becomes . If you could raise the atmospheric pressure waters boiling point would rise and this is why cooling systems run at higher than atmospheric pressure .

Oil coolers . It is convenient to run a water/oil heat exchanger because the only extra plumbing is coolant to/from the heat exchanger . It has the slight plus that at cold start the water heats up faster than the oil does and because of the heat exchanger the water speeds up the oil warm up process . Its a good system but the down side is that a hard worked eigine , particularly a turbocharged one , dumps a LOT of heat into its lubricating oil and some of this is taken out at that oil/water heat exchanger . Its not generally a problem at standard power/heat outputs IF everything is working as when new . Manufacturers generally don't build tons of extra cooling capacity into road cars though homologation specials in the days of production based race cars often got lots of extras for homologation purposes .

Now I don't know what up spec GTRs got but I think whatever that was should be considered a STARTING point if your going to work these cars hard .

Dual purpose . If it were me Id be looking at a higher capacity all aluminium radiator for starters and leaving a correctly functioning std OE water thermostat alone . I'd also make sure EVERY rubber hose that see's coolant was new or as good as and consider a higher pressure rated cap . The radiator is important because if those composite tanks , and 99% of the time is the hotter inlet side , fails and dumps your coolant its bad news for the engine .

The greater heat rejecting radiator if correctly designed and fitted with dump more heat than a std one if the coolant themostat increases the flow enough to pass water through it . Remember a water thermostat is a minimalist device meaning it sets the MINIMUM temp not the maximum , if it decides the temp is geting higher than it likes it opens further till it can't open any more and then its up to the system to sink or swim . It cannot control maximums .

Rambling aside the working higher capacity radiator allows the water thermostat to regulate minimum coolant temp until the water and oils heat output gets beyond what the higher capacity radiator can deal with .

Oil coolers . EVERY turbo engine can use an oil cooler of some sort but the oil/water ones only really do the job as long as the water cooling system can cope with the engines heat output .

If there is somewhere you can fit an independent or air to air oil cooler in the place of the oil/water one then suddenly you have a sometimes significant heat input removed from the water cooling system .

If you splash out a little and get a thermostatically controlled oil cooler adapter system you don't get the cool oil drag through the engine of a car thats being driven sedately , and it warms up a bit faster .

Its common for these to have thermostats set at around 100C which is logical because no one would want to run oil that couldn't cope at 100-110 degrees centigrade . Again the oil thermostat is a minimalist device and the control valve is a shuttle type so its not a valve that can close and stop oil supply , if it failed it just won't regulate the oils temperature .

The other thing is that ambient air will always , normally , be cooler than engine water so the heat transfer process will be better provided it has good airflow through it .

Oil . I reckon if you really like your engine you'll try to run it on a good synthetic oil and preferably a real or group 4 one rather than hydro cracked mineral oil .

The good ones are not terribly viscous at cold temperatures so you don't get the oil drag when cold and pump more freely at stat up . They can also withstand slightly higher temperatures before their film breaks down so give a bit more latitude/safety margin for your engine .

Summing up . Water pump for the intended speed range of the engine ie the cars use and its gearing .

Higher capacity radiator for increased heat rejection ability .

Std OE thermostat .

Healthy oil radiator/cooler with a thermostat so it doesn't overcool .

The result should be cooling water running somewhere in the 76-90C range and oil probably in the 90-115 deg range which is completely normal . All thats really changed is the radiators and oil coolers heat rejection capacity and the control mechanisms , thermostats , keep the fluid temps in their correct operating ranges .

With water pumps and engine water jackets there is an optimum pump speed that works best but sadly engine driven water pumps have to work over a wide speed range . Water flowing too slowly doesn't absorb and transport the heat away terribly well and if its too fast it isn't there long enough to absorb enough heat .

Ideally a pump run at a constant speed would be good for the pumps efficiency but I don't like the idea of using an electric pump and attempting to control the coolant temp with water flow and no water thermostat .

And lastly I think its true to say that possibly up until the last 5-10 years if not longer manufacturers were striving to make performance engines work well and reliably , nowdays the affordability and green aspects are taking us down a different road of using no juice/making no exhaust/noise/having no longevity/much reduced fun factor .

The engines run hotter and have longer service intervals and their safety/longevity relies on everything working absolutely 100% . When they don't they die very quickly and expensively and become throw aways .

My 2c , A .

[bubba]

Anyone have any knowledge on coolant flow through RB blocks and heads? or a coolant flow diagram?

Trying to figure out what the water outlets on the underside of the plenum are for and where they come from (i.e. trying to figure out if I can block them off with no adverse affects).

[Beer Baron]

Yes, that pretty much sums it up. Street cars should not have N1 pumps.

agree completely. I don't have proof but have asked GTR 'experts' in japan about this years ago. at low-mid RPM stock water pump outflows an N1 pump by quite some margin. personally I would only use N1 water pumps on circuit cars. some people also run oversize pulleys AND an N! pump which makes it even worse. my 32 track car has a beautiful sard triple core radiator, still has stock shroud and clutch fan but with the N1 water pump getting stuck in traffic in 30degree heat sees water temp starting heading north rapidly. not nice. definitely for a street car a standard 26pump is the go. or if using the N1 pump consider doing what you've done and run an undersize pulley to give it some rpm, and then perhaps swap it out for a bigger pulley for track days where it's going to get sustained high RPM. it's only a 30min job to change the pulley.

[Simon-S14]

had a read thro this.. good info here.

I need a new pump and i want to get the one with the highest flow. its looking like the Stock Rb25/26 one is the way to go. I will be using it in my drift car that see's a lot of sustained rpm, i considered the N1 however the other issue the car will also spend time sitting in line up after a run and this is where ive been having temp issues also. So i need to factor in low RPM flow also.

what would be the best pump and pully combo for my rb25? redline is 7K rpm

[TerribleOne]

So would there be any issues in using an RB30 pump on a mild RB25? (cooler, exhaust, boost)

[GTRNUR]

what would be the best pump and pully combo for my rb25? redline is 7K rpm

Your best off with a standard rb25 pump and pulley. 7000 rpm isn't a lot, and you will find that your average RPM will still be around 5000 where peak torque is.

So would there be any issues in using an RB30 pump on a mild RB25? (cooler, exhaust, boost)

It would depend on your climate and what your doing with the car. If its a street car and your average ambient temps are below 30 degrees then it would be fine.

[JonnoHR31]

had a read thro this.. good info here.

I need a new pump and i want to get the one with the highest flow. its looking like the Stock Rb25/26 one is the way to go. I will be using it in my drift car that see's a lot of sustained rpm, i considered the N1 however the other issue the car will also spend time sitting in line up after a run and this is where ive been having temp issues also. So i need to factor in low RPM flow also.

what would be the best pump and pully combo for my rb25? redline is 7K rpm

stock 25 pump withe the standard pulley will be fine

[BenRThirtyFour]

i have a rb25 r34 cooler, gtrs hks turbo 18psi and do the odd track day once or twice a year other than that its a daily, would a RB30 pump with 6 blades be better than a 8 blade standard rb24 pump. i live in cessnock where it gets down to 0 degreese in winter come nights and 40+ in summer, at the moment it is running at 85-90 degreese and

[KiwiRS4T]

68deg is too cold. The alleged purpose of the Nismo thermostat is to facilitate even warming of the engine by promoting flow earlier - it is not designed to hold temperature at 68deg and in fact no thermostat can. Ideal temp is probably more like 90deg.

[GTRNUR]

i have a rb25 r34 cooler, gtrs hks turbo 18psi and do the odd track day once or twice a year other than that its a daily, would a RB30 pump with 6 blades be better than a 8 blade standard rb24 pump. i live in cessnock where it gets down to 0 degreese in winter come nights and 40+ in summer, at the moment it is running at 85-90 degreese and

Stick with the standard pump. The R34 pump is a more efficent design than the old RB30 one. Also the NEO engines are designed to run at 90 degrees. The NEO thermostats open at a hotter temp than the older designed RB26's and RB25's.

[Shibbby]

Sorry for the thread bump, I would normally use Taark for genuine OEM parts however stock for rb water pumps is 6 weeks out.

Has anyone found a guaranteed genuine water pump supplier for a decent price that they can recommend?

Kind Regards