just put a new race rad in my Comet and as of right now it had an outlet which i plugged with a brass fitting, But in the NHRA book it states all cars must have a minimum 1L overflow container...but do i need one if i have it plugged? or is that just for the stock vehicles that have the hoses coming out and leading to the ground?
The overflow is designed to relieve excess cooling system pressure. If you plug it, you risk finding the weakest link in your cooling system. You can use a container to catch it and return it to the system when it cools or you can use the original vent hose and periodically check your coolant level for street use. NHRA specifies a catch can to prevent coolant contamination of the track if the system burps. If you plug the vent, something will give, releasing coolant on the track and making you not so popular on raceday.
The other guys have covered this pretty well, and if it were my car I would unplug the overflow and use a catch can even if you only drive it on the street.......................on the strip it is manitory. Just a short story about my Maverick; when it was built for B/SM in the late 70's they took the catch can rule to the extreme..................they ran an aluminum tube from the overflow on the radiator, plumbed it all the way along the inside of the frame into the trunk. They then used a stock windshield washer overflow plastic container and mounted it to the cage in the trunk. When I talked with the original owner he told me he just wanted to make sure there was no possible way any water/antifreeze could leak out infront of the rear slicks causing an unusually slippery ride down the track. This is alittle extreme, but I will not change it...................and it's a conversation piece at the track when people are looking at it, or it goes through tech.
I did the same thing with my circle track cars running on pavement with 10 inch slicks - I ran a line to a 1 gallon catch can behind the rear end and then out to the ground - we were only allowed straight water but I didn't want it under our rear tires - now under someone else's tires - that was a different story LOL!
The Short answer is Yes you have to have one. It only makes sense. Plus if you have the vent blocked off there is no way for the rad to relieve pressure.
Just dump it with no catch can... and the first time you get antifreeze/water mix or water only under the slicks at 100+ mph, you'll wish you'd have put a catch can on it to begin with. Besides....with a puke tank on it, the system will never have to be refilled if it's set up right. The radiator, when it cools down, pulls enough of a vacuum to overcome the radiator cap's seal and it will draw coolant out of the tank and into the radiator. Without the tank, it just needs to be refilled once in a while. Takes one more maintenance point off of the schedule-not JUST a safety issue. All cars since the 70's have them.
Heres mine that I added when I put the fan in. Sorry best pic I have. Grabbed it out of the compund at work. I think its an older Dodge truck or van. Its long and fit perfect on the left of the rad. Painted it black and left a white strip unpainted as a window for level. Something like this one here. This is a Jeep bottle I think.
