Radiator cap, alloy head max temp


So I’ve searched, admittidly I’m not so good at searching...

Anyways, I can’t find what radiator cap pressure people run. I’ve seen 1.6bar/23psi, to me it seems bloody high given stock is 1.1bar/16psi. 10psi = 10degrees, which is a bad trade off unless you are slide to the limit already and only need a few more degrees to get you across the line.

Mind you if the head is happy to take the 260degrees+ then I can run it.

Looking for direction from the experienced blokes. Cheers!
not meaning to be rude
but have you water tested the current rad cap.?
If it opens and closes at the set temp I see no need to replace it.
Johnnie, I think you may be referring to the thermostat when you say "opening and closing at the set temp".
The rad cap's job is to bypass coolant under pressure at a particular pressure, for example 1.1 bar.
These are two different functions of cooling system control.
I'm trying to clear up any possible confusion . . .
As Frank mentioned, 1.6 bar cap is a proven workable upgrade to safely raise the boiling temp of the coolant, without risking heating damage to the cylinder heat.
Hi kiwi. My mistake. You are correct. Thank-you for correcting me and preventing confusion
No worries mate, we are all learning and if you're not learning, you are not doing anything!
For people with mechanical aptitude it's their obligation to help others learn. Our good friend C10 is a prime example of this,
He passes on so much vital and worthwhile info it just amazes me how much energy and zeal he has!
He's an inspiration to all of us here to actively pursue the Hayabusa High Knowledge.
So if you're reading this Bryan, be assured every bit of time and effort you put in to sharing with us is vital and appreciated by me and most likely all of the Busa Family, go you buddy!!
So I am going to assume a rad cap pressure tester is not made, or at least easily found, for a cap as small as one on a Busa. So as was already said. For a 10.00 investment in a new cap why fiddle around and risk damage.
Thank you all for the kind considerations.


Just so you know John, you can pressure test your entire water system. You replace your cap with a tester... we’ll just google it. You will see.

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