Mailing List flyrotary@lancaironline.net Message #63635
From: Neil Unger <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: water pump and alt speeds
Date: Sat, 19 Aug 2017 08:13:22 +1000
To: Rotary motors in aircraft <flyrotary@lancaironline.net>

Mat,  those pulleys are what I thought I bought, but I find that I have a 2 inch alt. pulley which will require the alt to get up to approx 20,000 rpm AT 8000 Engine rpm.  This is unnecessary and takes a lot of HP on its own for no need or result.  The load is such that the fan belt will not drive it over 6000 RPM.  I say that as it could also be the water pump but I think not.  First step will be to drastically reduce the Alt speed to around 1:1 engine speed.  Will be interesting.  Thanks Neil.


On 8/19/2017 1:36 AM, Matt Boiteau wrote:
From the rx8club group, they say the stock generation rx8 water pump will start cavitation around 6000-6500rpm using stock pullies. This guy simulated the pumps and got around 7000rpm.


On Aug 18, 2017 02:19, "Neil Unger" <flyrotary@lancaironline.net> wrote:
Gents,

                   I am getting belt slip over 6500 engine revs and suspect that the water pump and alt speeds are too fast and taking too much power to drive.  I will measure all pulleys tomorrow, but just need some speeds to work towards.  I have been told that an alternator can happily run between 3000 and say 8-10,000 even up to 30,000, but the higher speed will chew 15 HP and achieve nothing in extra charge especially when I only have to run avionics and charge the battery.    Water pump has a speed whatever that is over which it just cavitates and does nothing. What is that speed for the RX8??  Neil.


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