NASCAR teams often run 40 PSI caps, their seals, hoses, etc. are all excellent and replaced often. Every maximum PSI gained allows 2 degrees F higher temp before boiling.
So, a 21 PSI cap, vs. a 40 PSI cap allows an additional 38 degrees F before boiling over.. (in theory)
Mind you, they replace hoses every race, vs. us leaving a hose on for 10,000 miles or more.... have better skills, spec block to intake manifold clearances way tighter than what we get out of the box from Edelbrock, etc.
Reasioning is that they can run higher temps without boiling over, and therefore can duct tape the radiator opening more to allow better aerodynamics. Their biggest fear seems to be Yellow Flag situations when the cars are running slowly... with much less air flow thru the radiator. At race pace, you'll see them running nose to tail, under yellow, they stagger themselves side to side to get the most cooling possible.
Makes me wonder if there's a rule that dis-allows using a chain to roll up and down a window shade type radiator blocker like the Birdcage Masarati's had in the mid 1950's
I run a 22 PSI cap on my 351 Windsor in my factory Five Daytona Coupe... main reason is after a lot of stop and go driving, I get some heat-soak issues when I stop to run an errand. I let my radiator fan stay on til the radiator drops down to 170 degrees F, so at least 40% (?) of the coolant gets down to 170... so I get back into LA traffic with at least some 'cooler' coolant.
I tend to run about 140-175 degrees on the freeway depending on outside temp and how fast I'm going.... then in town in stop and go it jumps up to the 190 degree range pretty quick (measured inbetween radiator fins at the top of the radiator nearest the inlet) After a lot of stop and go and or stop light driving with the 16" fan running, when I shut down the radiator CAN boil over from heat-soak.... I custom made a huge 4X4X18" aluminium overflow-expansion tank and that resolved
'lost fluid' issue I had when I had a smaller tank. Seems like a common problem that many people think is another problem... (not enough volume in the overflow tank.. if you often have to add fluid to your tank, just get or build a bigger tank... I haven't had an issue all summer long now.)
By the way I would NEVER run a cap without a safety release cap.... 212+ degree coolant rushing thru a hose to the overflow is WAY better than escaping onto your hand as you remove a standard cap.... not sure how those are even legal to sell... seen plenty of 3rd degree burns when I was a cop back in the day... horribly painful... seen complete forearms burnt to the muscle... be careful out there, folks... (in the past when working on friends cars, I would grab the cap, and see if I could 'stand the heat' for about 30 seconds... then I would deem the coolant cool enough to open the cap, and I always had a rag around the cap... still foolish...
So, a 21 PSI cap, vs. a 40 PSI cap allows an additional 38 degrees F before boiling over.. (in theory)
Mind you, they replace hoses every race, vs. us leaving a hose on for 10,000 miles or more.... have better skills, spec block to intake manifold clearances way tighter than what we get out of the box from Edelbrock, etc.
Reasioning is that they can run higher temps without boiling over, and therefore can duct tape the radiator opening more to allow better aerodynamics. Their biggest fear seems to be Yellow Flag situations when the cars are running slowly... with much less air flow thru the radiator. At race pace, you'll see them running nose to tail, under yellow, they stagger themselves side to side to get the most cooling possible.
Makes me wonder if there's a rule that dis-allows using a chain to roll up and down a window shade type radiator blocker like the Birdcage Masarati's had in the mid 1950's
I run a 22 PSI cap on my 351 Windsor in my factory Five Daytona Coupe... main reason is after a lot of stop and go driving, I get some heat-soak issues when I stop to run an errand. I let my radiator fan stay on til the radiator drops down to 170 degrees F, so at least 40% (?) of the coolant gets down to 170... so I get back into LA traffic with at least some 'cooler' coolant.
I tend to run about 140-175 degrees on the freeway depending on outside temp and how fast I'm going.... then in town in stop and go it jumps up to the 190 degree range pretty quick (measured inbetween radiator fins at the top of the radiator nearest the inlet) After a lot of stop and go and or stop light driving with the 16" fan running, when I shut down the radiator CAN boil over from heat-soak.... I custom made a huge 4X4X18" aluminium overflow-expansion tank and that resolved
'lost fluid' issue I had when I had a smaller tank. Seems like a common problem that many people think is another problem... (not enough volume in the overflow tank.. if you often have to add fluid to your tank, just get or build a bigger tank... I haven't had an issue all summer long now.)
By the way I would NEVER run a cap without a safety release cap.... 212+ degree coolant rushing thru a hose to the overflow is WAY better than escaping onto your hand as you remove a standard cap.... not sure how those are even legal to sell... seen plenty of 3rd degree burns when I was a cop back in the day... horribly painful... seen complete forearms burnt to the muscle... be careful out there, folks... (in the past when working on friends cars, I would grab the cap, and see if I could 'stand the heat' for about 30 seconds... then I would deem the coolant cool enough to open the cap, and I always had a rag around the cap... still foolish...
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