Posted By: HR5058
radiator cap psi - 04/18/11 02:42 AM
How important is the PSI rating on a radiator cap on a drag only car? What PSI is everyone running? Thanks Chuck
radiator cap psi
Posted By: sam64
Re: radiator cap psi - 04/18/11 02:51 AM
i've been told for every 1 pound of pressure at the cap it raises the boiling point 7 degres.most racing caps i think are 20 psi.
Posted By: MR_P_BODY
Re: radiator cap psi - 04/18/11 03:14 AM
A drag race you shouldnt need much pressure at all...
unless you have a temp problem.... the higher pressure
works great on the street
unless you have a temp problem.... the higher pressure
works great on the street
Posted By: HR5058
Re: radiator cap psi - 04/18/11 03:18 AM
Thanks Sam and P. I have a 14lb and wanted to make sure not to light. Chuck
Posted By: cagebob1
Re: radiator cap psi - 04/18/11 04:23 AM
with a race only vehicle I cut a small slice out of the gasket on the radiator cap. this effectively eliminates any pressure in the cooling system. ever see a car blow a rad hose in the lights? ever see a engine block have the freeze plugs pop out from a combination of stress from the stock engine mounting points and a small amount of cooling system pressure? this eliminates that possibility
Posted By: Quicksilver440
Re: radiator cap psi - 04/20/11 04:42 AM
I run a high pressure cap...But mines street strip, 22 psi
Posted By: moparacer
Re: radiator cap psi - 04/20/11 04:58 AM
Quote:
A drag race you shouldnt need much pressure at all...
unless you have a temp problem.... the higher pressure
works great on the street
What Mr P said.
I usually run a 13 Psi cap but have run as low as 7.
Posted By: Sport440
Re: radiator cap psi - 04/21/11 03:59 AM
Quote:
How important is the PSI rating on a radiator cap on a drag only car? What PSI is everyone running? Thanks Chuck
I think its very important. A high PSI cap on a race car is extra insurance to prevent a boil over blow out. Most of us who race deal with heat issues.
Dont run a cap that puts you on the edge of a boil over. With a cap 1 psi short of preventing a boil over, the water vapor pressures can double
I run a 16# cap, it should be good for around 240* before it blows.
Posted By: MR_P_BODY
Re: radiator cap psi - 04/21/11 04:16 AM
Quote:Quote:
How important is the PSI rating on a radiator cap on a drag only car? What PSI is everyone running? Thanks Chuck
I think its very important. A high PSI cap on a race car is extra insurance to prevent a boil over blow out. Most of us who race deal with heat issues.
Dont run a cap that puts you on the edge of a boil over. With a cap 1 psi short of preventing a boil over, the water vapor pressures can double
I run a 16# cap, it should be good for around 240* before it blows.
You are suppose to have a over flow can... watch it
to determine if a higher cap is warranted... on my
car I have 2 caps on the system... yes 2... one is
on the radiator basically as a plug and then I have
a small reservoir that my return lines from the heads
goes to... that is the highest point so I made it
so a cap is there... I believe thats a 7# cap...
the over flow is empty except when I had a bad seal
on the old cap
Posted By: HR5058
Re: radiator cap psi - 04/21/11 04:26 AM
Thanks all. Good info. I usually run through the traps at about 210 so I believe I am safe at 14 psi cap. Thanks again, Chuck.
Posted By: MR_P_BODY
Re: radiator cap psi - 04/21/11 04:36 AM
Quote:
Thanks all. Good info. I usually run through the traps at about 210 so I believe I am safe at 14 psi cap. Thanks again, Chuck.
FYI... there are 2 styles of caps, a recovery style
that will suck fluid back into the rad IF you have a
tube down in the over flow can... then the NON recovery
style (old style)... easy way to tell is if you hold
the cap in the normal up right position... does the
metal disc dandle down... thats the recovery type
and if it doesnt thats the old type
Posted By: Sport440
Re: radiator cap psi - 04/21/11 04:45 AM
Quote:Quote:Quote:
How important is the PSI rating on a radiator cap on a drag only car? What PSI is everyone running? Thanks Chuck
I think its very important. A high PSI cap on a race car is extra insurance to prevent a boil over blow out. Most of us who race deal with heat issues.
Dont run a cap that puts you on the edge of a boil over. With a cap 1 psi short of preventing a boil over, the water vapor pressures can double
I run a 16# cap, it should be good for around 240* before it blows.
You are suppose to have a over flow can... watch it
to determine if a higher cap is warranted... on my
car I have 2 caps on the system... yes 2... one is
on the radiator basically as a plug and then I have
a small reservoir that my return lines from the heads
goes to... that is the highest point so I made it
so a cap is there... I believe thats a 7# cap...
the over flow is empty except when I had a bad seal
on the old cap
Im not sure I understand your head return line system resevoir 7# cap system. Whats your cap psi on the rad?
Yes, all cars are required to have a overflow can. Ive got one too.
A boil over is a violent event in terms of pressure. Preventing this with a stronger psi cap from the get go is a good idea adding extra safety insurance.
Once a boil over occurs the Vapor pressures skyrocket. Prevent that boil over with a few extra pounds at the cap . Priceless
, 
Posted By: polyspheric
Re: radiator cap psi - 04/21/11 04:50 AM
The gauge temperature and thermostat level don't tell what's happening in the head's water jacket around the exhaust valve and spark plug.
As water temp goes up, the thermo seals the engine system (more or less) until its cracking temp is reached. That pressure has been keeping the water in the exhaust area from boiling, and when the thermo opens that water boils immediately (your gauge still shows 180° etc. but at the exhaust it's 230°).
The only thing that keeps it liquid is cap pressure.
As water temp goes up, the thermo seals the engine system (more or less) until its cracking temp is reached. That pressure has been keeping the water in the exhaust area from boiling, and when the thermo opens that water boils immediately (your gauge still shows 180° etc. but at the exhaust it's 230°).
The only thing that keeps it liquid is cap pressure.
Posted By: Sport440
Re: radiator cap psi - 04/21/11 04:56 AM
Jeff, 
Posted By: MR_P_BODY
Re: radiator cap psi - 04/21/11 04:59 AM
Im not sure I understand your head return line system resevoir 7# cap system. Whats your cap psi on the rad?
Yes, all cars are required to have a overflow can. Ive got one too.
A boil over is a violent event in terms of pressure. Preventing this with a stronger psi cap from the get go is a good idea adding extra safety insurance.
Once a boil over occurs the Vapor pressures skyrocket. Prevent that boil over with a few extra pounds at the cap . Priceless,
My pics are too large to post but I have 2 lines
coming from a manifold on each head to a box/reservoir
with a cap on the box... the radiator has a 15# but
the reservoir has a 7# that is the low pressure
point of my system (remember I run W-9 heads so
they are different than most heads)
Yes, all cars are required to have a overflow can. Ive got one too.
A boil over is a violent event in terms of pressure. Preventing this with a stronger psi cap from the get go is a good idea adding extra safety insurance.
Once a boil over occurs the Vapor pressures skyrocket. Prevent that boil over with a few extra pounds at the cap . Priceless
, My pics are too large to post but I have 2 lines
coming from a manifold on each head to a box/reservoir
with a cap on the box... the radiator has a 15# but
the reservoir has a 7# that is the low pressure
point of my system (remember I run W-9 heads so
they are different than most heads)
Posted By: MR_P_BODY
Re: radiator cap psi - 04/21/11 05:14 AM
Quote:
The gauge temperature and thermostat level don't tell what's happening in the head's water jacket around the exhaust valve and spark plug.
As water temp goes up, the thermo seals the engine system (more or less) until its cracking temp is reached. That pressure has been keeping the water in the exhaust area from boiling, and when the thermo opens that water boils immediately (your gauge still shows 180° etc. but at the exhaust it's 230°).
The only thing that keeps it liquid is cap pressure.
Almost all the time that surface temp is much higher
than that but in a minor distance its cooled back
down... the gauge is showing the average of the engine
and rad itself
EDIT
once the stat opens
Posted By: mac56
Re: radiator cap psi - 04/21/11 10:26 AM
22 psi here.
Posted By: Crizila
Re: radiator cap psi - 04/21/11 02:40 PM
14 lb cap for me. That gives me a boiling point of 254f ( staright water ). - slightly high pressure than what my thermostat housing gasket seems to be rated at 
Posted By: HR5058
Re: radiator cap psi - 04/22/11 11:38 PM
Checked and I have the recovery type. Tube down in recover tank. It is a 16 and not a 14 but based on all good info, I should be good as I dont let the engine get that hot. I usually like to leave about 180 and by the time I hit the strip I am at 210. My alternator only starts to charge at about 4500 rpm and above so I dont like the fan and pump running much after I get to the pits. I am going to an electric vacuum pump, so the next question is do I run it all the time or just at WOT so not to kill my battery? Thanks Chuck
Posted By: MR_P_BODY
Re: radiator cap psi - 04/22/11 11:55 PM
Quote:
Checked and I have the recovery type. Tube down in recover tank. It is a 16 and not a 14 but based on all good info, I should be good as I dont let the engine get that hot. I usually like to leave about 180 and by the time I hit the strip I am at 210. My alternator only starts to charge at about 4500 rpm and above so I dont like the fan and pump running much after I get to the pits. I am going to an electric vacuum pump, so the next question is do I run it all the time or just at WOT so not to kill my battery? Thanks Chuck
Fix your charging first... if I was running a ele
vac pump it would be running all the time going down
the track and on the way back to the pit..... JMO
Posted By: Sport440
Re: radiator cap psi - 04/22/11 11:57 PM
Quote:
Checked and I have the recovery type. Tube down in recover tank. It is a 16 and not a 14 but based on all good info, I should be good as I dont let the engine get that hot. I usually like to leave about 180 and by the time I hit the strip I am at 210.
My alternator only starts to charge at about 4500 rpm and above so I dont like the fan and pump running much after I get to the pits.
I am going to an electric vacuum pump, so the next question is do I run it all the time or just at WOT so not to kill my battery? Thanks Chuck
Even if you have a bigger alt pully, your Alt should charge way before 4500 rpm. Thats a problem that you need to checkout.
On the vacuum pump question, if you dont have any other assist after you hook it up, I would run it all the time.