Radiator cap pressure

[Duckhnter83]

What's everyone's thoughts on the best pressure cap to run and why?

[RCJ]

27lbs the higher pressure raise the boiling point.A higher boiling point gives more margin for error and helps prevent detonation.Tried a 31, the radiator started leaking in an inner core.

[Matt49]

Run the highest pressure cap that the rest of the system will allow. Meaning you want the cap to be the first thing to pop but not so soon that it can't assist with raising the boiling point.

[brad hibbard]

I agree with Matt
the more the better but there are limits
for every pound of pressure you will raise the boiling point 3 degrees---that is a plus
ALSO as you increase the pressure, the coolant (water) becomes more efficient in dissipating the heat from the engine block and heads----that is a big plus and the real reason for increasing pressure

lets go back to the boiling point for a second
water under no pressure boils at 212 degrees and that is at seal level----
we usually race at locations well above sea level which lowers the boiling point
using round number lets say our water is going to boil at 200 degrees
a 20 pound cap will increase that to 260 degrees---
If your running your engine hotter than 260 you should be back at the trailer cooling it down and not worried about how much pressure you have on your cap

so that takes us to the efficiency of the water verses the metal
increasing the pressure will increase that efficiency

now here is where we can cross the line
lightweight radiators can and will swell their fins with excessive pressure----combine that with some extra heat from time to time and now a perfectly good "LOOKING" radiator does not move much air ----consequently we get hot and then hotter and so on

I have heard a thousand times ---"my radiator is not that old and looks perfect"
change the rad and all heating issues are gone

sorry for the ramble
around 25 is good 30 is a bit high

Brad

https://www.race-1.com

[PushinTheLimit]

For a 604, what is the "too hot to race, have to come in now" temperature?

[RCJ]

We always called that the ''checkered flag better be waving temp".I'm not a crate guy but, if the temp is high 1 minute and the next time you look it has went down considerable.That is it, the motor has pushed enough water out to start having air pockets.This point will be different if a guy has a 27lbs cap and 15% anti freeze than a guy with a 13lbs cap and straight water.A guy on a lower octane fuel will get in trouble faster than a guy with more octane.We've won races at 250 degrees in street stocks.240 as long as the temp is not fluctuating, after that I start worrying.

[PushinTheLimit]

Good info... I put a new radiator in and cut a small opening on my front valence this year to see if that would help my temps. Last year I would regularly see 230-240 on a 1/3 mile race with the GM 4-blade fan. We just ran a 4/10 mile track 40 lap feature with only one caution the whole time and the max I seen was 215. Sounds like I'm good right now.