Cooling system expansion tank??

[GH]

I am having trouble blowing bottom radiator hoses off at speed. The engine is a big block Chevrolet, electric water pump, large cross flow radiator, no thermostat but have a restrictor with a 3/4"-7/8" hole. The engine had a roots blower in 04, now has turbos. Do I need an expansion tank in the system to take care of pressure buildup? I do have a recovery tank with a very small hose going from pressure cap to recovery tank. Any suggestions or comments...

[Dynoroom]

What kind of electric water pump are you running? Lots of people run them at the salt but everyone I've run on the dyno never builds pressure, it does boil the water though on a full hard dyno pass. So I don't run electric water pumps. If you are making good power use a belt driven pump. I think if you look around you'll see some belt driven pumps on some pretty fast cars too. JMO

[Sumner]

What kind of electric water pump are you running? Lots of people run them at the salt but everyone I've run on the dyno never builds pressure, it does boil the water though on a full hard dyno pass. So I don't run electric water pumps. If you are making good power use a belt driven pump. I think if you look around you'll see some belt driven pumps on some pretty fast cars too. JMO

Mike are you talking about in-line electric pumps with a large water tank or the electric pumps that mount on the front of the motor in place of the normal pump or both??

Thanks,

Sum

[Dynoroom]

Both.

[Bob Beatty]

GH,  My experience with electric water pumps agrees with what Mike is telling you.  The electric pumps will supply plenty of volume but not sufficient pressure to handle conditions such as steam pockets that tend to form at hot spots particularly in the heads.  The minimum pressure needed to prevent steam pockets from establishing themselves seems to be in the 25 to 28# range.

[Bob Drury]

-Speedway motors makes a nice belt driven unit for sprint cars.  I run a J.F.K. which is similar.  I am not sure if they are still in business, but their phone is or was (818) 767-8573.  I think they sell for around three hundred bucks.

[1212FBGS]

seams to me that there is at least 25# of pressure if it is blowing hoses! I run an electric pump on my liner that fees both motors and don't have a problem.
isnt the bottom hose that is commin off the feed hose to the pump? where is these restrict-or at in the system? could you have blown a head gasket pressurizing the system

[Bob Beatty]

It is not a matter of pressurizing the system in the case of eliminating steam pockets.  What seems to be important is pumping the water through the system under enough pressure (or with enough pressure behind it, if you prefer) so as to blow through a potential steam pocket before it can form.  
A typical area where you run into this situation is the water jacket between the two adjacent exhaust valves in the center of the small block Chevrolet head.

[dwarner]

Ed Pink told us that you cannot put enough water in the heads. You must eliminate steam pockets/hot spots.

Use a JFK style, belt driven pump.

DW

[Rex Schimmer]

Stewart Van Dyne of Van Dyne Engineering, who has built some pretty big HP motors, has a "rule of thumb" for water pumps: 10 GPM/100 hp. So if you piece is making 800 rpm then you need a 80 GPM pump and I can bet that most of the electric units would have a hard time making 30-40 GPM. As for pressure, the more pressure you run the higher the boiling point of the water so the more difficult it is to have a steam pocket, but fluid velocity i.e. flow rate through the head is very important here because if the water is not flowing thru the head fast enough it will be subjected to high heat in the hot areas for a longer time and turn to steam.  Back in the 80s when I was doing IMSA racing there was a team, Electromotive out of El Segundo that ran a Datsun 300 Z turbo and they were getting close to a 1000 HP, reliabily out of the Datsun straight six! Their water system operated at around 100 psi just to keep the water from boiling when the turbo was on the boost.

If you are blowing hoses you probaby need to first look at the inlet and outlets of your system and make sure that each has a good bead on the end, if you are just slipping the hose over a straight tube, without a bead, you will always blow hoses. What is your system cap rated at? If you have a 25 psi cap maybe you should have a 17. Better to let the water boil at a little lower temp than to blow the hose and cooking the motor. Water pumps do not make much pressure, the pressure that they make is what is required to push the water past the resistance caused by the water flowing through the engine cooling system and no more which is why most people put a restricter in the outlet of the water pump, or a thermostat. Water pumps are centrifugal pumps which means that they have specific areas of pressure and flow at which they are the most efficient and as you increase the pressure typically their efficiency drops off, i.e. the flow drops off also, but this does not mean that a water system that is at 25 psi is going to have a water pump that is less efficient because the inlet to the pump is also at system pressure so the pressure that determines the pump efficiency is the difference between the inlet pressure and the outlet pressure which is again caused by flow restrictions in the cooling system.

Rex

[desotoman]

Around 5 years ago, one of the guys in the club was running a big block on the dyno. It was normally aspirated and had 15-1 compression. They were circulating the cooling system with a electric pump. They encountered problems on the dyno, I forget the exact problems they encountered, (I think it was detonation) but I do remember they changed to a standard belt driven water pump and the problem got solved. As I remember they were after more volume to make sure there were no areas where air would get trapped.

[Rex Schimmer]

Just to add a little more regarding water pumps I called Stewart and Van Dyne Engineering and he had some info on inlet and out let pressure for a water pump that he insturmented on his dyno while testing an engine. A note is that his dyno water setup is not "closed loop" i.e. the water outlet from the engine does not go directly into the pump inlet, his pump was drawing from a reservoir. Using a direct drive pump at engine speed at 5500 rpm the outlet pressure was 22 psi, and again this pressure represents the pressure required to push the water through the engine at the pumps flow rate at 5500 rpm and its efficiency at 22 psi.

Another thought about water pressure, if you run really high water pressure, 50-100 psi, the increased pressure will actually reduce the stress in the cylinder block caused combustion. Useful thing to do if you are running a blower or turbo.

If you are looking to build a big motor to run at the salt and are looking for a good water pump Stewart has a high volume unit that is based upon the Offy turbo pump from the days that the Offies were making 1200-1400 hp. (Shameless plug:) Van Dyne Engineering is in Huntington Beach 714-847-4417.

Rex

[dieselgeek]

THanks for the excellent input guys!!


At first I thought we were blowing around the headgasket (have seen this a lot in drag racing with forced induction motors), but there was no sign of this happening anywhere but with the coolant pressure issue...

but I've since done some reading and am finding the same thing you guys are telling us.  It's funny how much easier it is to build a drag motor and tolerate these kinds fo thinggs, versus building something that makes similar power but has to run WOT so much longer...  I'm learning a lot of valuable lessons here.


-scott

[hotrod]

Just curious for the folks running recirculating tanks, ( I guess this would apply to radiator systems to) has anyone tried pre-pressurizing the system cold to raise the boiling point.

That way you could run a 30  psi coolant system even though the temp never exceeds 160 -170 degrees and prevent nucleate boiling in the hot parts of the head.

Larry

[SPARKY]

  I hurt a set of BBC Alum heads by not running a Mechanical pump and a pressurized system...my research---and I called lots of Folks...

My set up now:
Best Stewart pump---with a drive pulley arangment that the water pump turns about 5500 max at 8000.

Heat exchanger with 11 gallons in box with additional 12-15 gallons 1 pass-pumped through resevior then overboard.

A bleed off  de-aeriation tank.

A prepressuring Schreeder valve.

using only distilled water

fill & seal the system and "let it Burp for 6 weeks to get as much air out of the water as possible before running.