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Re: radiator cap psi
[Re: HR5058]
#975339
04/17/11 11:14 PM
04/17/11 11:14 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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A drag race you shouldnt need much pressure at all... unless you have a temp problem.... the higher pressure works great on the street 
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Re: radiator cap psi
[Re: HR5058]
#975344
04/20/11 11:59 PM
04/20/11 11:59 PM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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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.
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Re: radiator cap psi
[Re: Sport440]
#975345
04/21/11 12:16 AM
04/21/11 12:16 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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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
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Re: radiator cap psi
[Re: HR5058]
#975347
04/21/11 12:36 AM
04/21/11 12:36 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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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
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Re: radiator cap psi
[Re: MR_P_BODY]
#975348
04/21/11 12:45 AM
04/21/11 12:45 AM
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Joined: Jan 2003
Posts: 6,591
Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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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 ,
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Re: radiator cap psi
[Re: HR5058]
#975349
04/21/11 12:50 AM
04/21/11 12:50 AM
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Joined: Oct 2007
Posts: 4,205
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,205
New York
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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.
Boffin Emeritus
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Re: radiator cap psi
[Re: Sport440]
#975351
04/21/11 12:59 AM
04/21/11 12:59 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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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)
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Re: radiator cap psi
[Re: HR5058]
#975356
04/22/11 07:55 PM
04/22/11 07:55 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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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
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