I am busy working on a new motor to rev nice and high (8500rpm)

Just wondering if you guys do anything to the waterpumps on your higher reving A-series motors? I know loads of motors (sr20 and RB as well) have cavitation problems at high rpm so they actualy slow the pump down a touch in setups where it will have the hell rev'd out of it,

Just wondering if there is a "done thing" to do to water pumps in the might A series

I got a smaller crank pulley made when I got my harmonic balancer done to slow down the pump and alternator, but it's a race engine so is barely ever running below 4000 rpm.

Yeah, good idea, im already using the pretty small A12 pully on it,

The reason I ask is that I run a CA18DET radiator on my my A15 and around town even if its seriously hot (35c) its fine, sitting at 4000rpm on the highway its fine, but if I drop a gear from 5th to 4th and hold it at 5000rpm (obviously now with reduced load but higher RPM) it heats up from 1/4 temp gauge to about 1/3 (the only time it ever raises it at higher RPM and its not load dependant), when i am at the track she goes up to about 1/2 way on the gauge... Sounds like a bit of cavitation/restriction with the pump spinning much faster than normal.

Could well be...... With my small pulley and 77 degree thermostat, the temp never rises above 80 once moving, and I've never had a problem with overheating at idle either.

Sounds good!

do you know roughly what diameter your new pulley is?

Thanks!

Just a quick note: I run the stock pully set and rev the car to 8000 RPM's regular. I use the GX 3 core Rad, the motor is A12 putting out around 92-95HP. Most of the time the motor runs between 4500-7800, the temps here are as high as 106 F (42-45 degrees?) out May and September events.

Tom

Yes, I had heard you only need a mod if it is between 8,000 and 10,000 RPM.

Rallytwit, Do you know what pump design your using? there are a few different impeller designs available,

I must actualy get around to putting my oil temp and water temp gauges in,

Its only after 4-5 laps of our 2 mile track (quite complex track) do I notice my coolant temps climing to half gauge, Probably also time for me to get my oil cooler in there to help stabilize the temps a bit.

Are you currently running a thermostat? If so it might finally be just getting up to temp. If not, and you are running a restrictor plate, half way up the guage (assuming it's actually calibrated so that equates to around 180F - then it's nothing to really worry about.

If you aren't running a restrictor plate, get one in there, it'll 'preload' the pump and actually help prevent cavitation. There is the school of thought that this will also slow the water down and give it more time to conduct heat away, but I'm not sold on that being different at all - since if the water was travelling through twice as fast, and the water only picked up half as much heat per litre, it'd still be even stevens overall.

Aside from preloading the pump a little, and preventing cavitation 'at the impeller' itself, it raises the water pressure inside the block (possibly up as high as 15psi on top of radiator cap pressure) which _does_ make it better at conducting heat, since it's denser, and furthermore, this raised pressure really prevents any chance for tiny air/steam pockets to develop and lead to a localised hot spot.

As to how large to make the hole in the restrictor plate, there's actually an easy 'cheat' to be had here. Simply get a 160F thermostat, and cut the entire 'guts' out of it, - the spring, and moving valve section, leaving the 'top' washer section - hey presto instant restrictor plate, and of the right size.

Be aware of course that although a couple of % power can be found running around 160F, you also shorten engine life, they last longer (mostly due to being able to boil off, or evaporate (since they are below the 'true' boiling point) water vapour that inevitibly gets into the oil in trace amounts, but also because being slightly warmer, petrol is less likely to condense on cylinder walls, washing away the micro oil film, and increasing ring/bore wear and also oil contamination from the petrol itself.

I am running a functioning thermostat, OE replacment which is 165degF/74c for our climate. 25.3mm opening. I use the car as a daily run about and at the track so I prefer to run a thermostat.

The reason I was worrying is that I push a tiny bit of coolant out between races, I was running a 1.1bar cap but it was a crappy cap, I have now upgraded to a Nismo 1.3kg cap but havent been able to test it out as I am busy building the motor to make another few KW's. The CA18 radiator is pretty large so I would presume that it would be just fine for a fairly hard core A15.