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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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Posted: February-01-2016 at 9:32pm |
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Does anyone know what the water pressure should be with a 302 1978 ford engine. Thinking of installing a gauge to show pressure just after the RWP. Would rather see a difference in pressure BEFORE the temp gauge takes off. Couple lakes I plan to go to have a weed problem and thought this might be of value Thanks
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Keep it as original as YOU want it
1978 Mustang (modified) |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Duane,
I don't feel reading pressure off the RWPor any other place in the system is the way read flow. I don't feel you understand you can have pressure with NO flow!! There are some externally mounted ultrasonic flow meters out there .but I feel you are overestimating a problem. The simple way to make sure you're getting water is to monitor your temp gauge. You do have one correct? |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10686 |
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Hi Duane
I don't know what the pressure would be but I'm rather amazed at what Pete can determine about your understanding of pumps and fluid flow from one simple question. Plenty of pressure gauges for outboards that could be used. With both a pressure gauge and a temp gauge you would have the best indication of whats going on., but I feel you probably know that already. I'm sure the pressure would vary with speed and you would get used to knowing the readings at any given speed.and if you sucked up some weeds and lost pressure that would be your first indication of problems before the temp gauge even thought about responding, but I feel you know that already too.. A friend has a pressure gauge on his speedy go fast bass boat that he swears by. KenO |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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I've handled a few fluid dynamics projects in my life so here was my first thought. Cap the discharge of any type of pump. You get pressure and no flow!! A pressure gauge is not a good method of determining flow. Here's just one example I ran into. It was the installation of 5 water cooled compressed air dryers. These were cooled off a cooling tower but even if city water was used the same would apply. The contractor installed pressure switches on all 5 dryers. The idea was to shut down the refrigeration when water flow wasn't enough to prevent a high head trip. It didn't work since as explained there were times when there was pressure with no water flow. I retrofitted all 5 dryers with flow switches. I still feel monitoring the temp gauge is the best method. |
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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Thanks Ken, I have a pressure gauge on both my Ranger bass boat and my Bass Tracker. Big Mercury on one and 30 hp Johnson on other. One utilizes a 30 psi and the other a 10 psi. I am just trying to narrow down what pressure I would use. On both boats I get a loss of pressure before the temps go up. I prefer to catch it before it gets hot.
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Keep it as original as YOU want it
1978 Mustang (modified) |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10686 |
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Hi Pete Take away the water supply to that pump which is Duane's scenario and what happens to pump discharge pressure? KenO |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Ken,
You are correct. I'm sure thinking backwards! Duane, Are you thinking about a remote gauge so you can read pressure at the dash? Maybe a pressure switch triggering ether an audible or visual alarm? |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10686 |
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Aw hell Pete, It's one of them age things
That's coming from another guy the same age KenO |
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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Pete, Thanks for your reply. And yes to all the above. Dash mounted gauge if feasible. If I knew the normal operating pressure then I could pick the correct pressure switch if an audible device was utilized. (ie. piezo buzzer)
I thought you were confusing an open versus closed outlet system. Anyway, back to the original question, short of just hooking up a 30 psi gauge and checking pressure, do you know what range I would be dealing with? I am rebuilding my dash now and all thoughts would be welcome. Either poplar or cherry and stain it to closely resemble the vinyl original. I have plenty of poplar, cherry, and oak of the width required. I have both a 12" Powermatic and an old 24" Cresent planer. Some boards in stock are 26" wide. Also using boards to replace my "ski locker" boards. Thanks in advance Also thanks to KenO |
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Keep it as original as YOU want it
1978 Mustang (modified) |
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backfoot100
Platinum Member Joined: January-03-2007 Location: United States Status: Offline Points: 1897 |
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What's the difference if you use a 10 or a 30 PSI gauge? In Ken's loss of intake water scenario, both guages will drop to 0. So if the 10# guage is pegged under normal operating conditions what does that hurt?
Personally, seeing a guage such as this being either pegged high (good) or pegged low (bad) is going to be much more effective then trying to read a specific PSI number. I think even an audible alarm would be much more sufficient under the circumstances. The actual engine temp is far more important and your ultimate goal anyway. |
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When people run down to the lake to see what's making that noise, you've succeeded.
Eddie |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Duane,
If you do go with a gauge, I'd go for a 0 to 15 psi. With the cooling being an open system, I don't feel you will see anything close to the 15 psi plus, you will get some pressure drop up to the dash. Poly 1/4" tubing would be my choice for the run. So, you're one of the non original guys!! |
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74Wind
Grand Poobah Joined: August-02-2011 Location: Georgia Status: Offline Points: 2101 |
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Just a thought, but if you are indeed able to install an audible alarm, then a viewable Guage would seem unnecessary, and you could avoid another hole in the dash.
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1974 Southwind 18
1975 Century Mark II |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Duane,
I'll suggest it again and also agree with Eddie that an audible alarm is a better choice. Plus, a pressure gauge in the dash sure isn't very original! EDIT: plus Jeff with the alarm! |
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Gary S
Grand Poobah Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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Am I missing something,I thought a pressure gauge on an outboard was merely for when your jacking up the motor and running on that ragged edge trying to get that 1 last mph. Seems to take the fun out if your worried about everything IMOH-----
Next on the bucket list is to get the first pull on Nautique # 1 |
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phatsat67
Grand Poobah Joined: March-13-2006 Location: Indiana Status: Offline Points: 6149 |
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Gary likes to give his HM a rest sometimes and let other boats parade him around the lake.
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desertskier
Platinum Member Joined: December-19-2006 Location: Az Status: Offline Points: 1114 |
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During our ProTec replacement discussions it occurred to me that the ProTec temp switch could still be used to interrupt the ignition voltage and turn off the motor. If it is possible to install the switch in your engine cooling system it could be used to turn off the motor when it reaches 210 degrees. Route the ignition voltage through a normally closed relay, the control line goes to 12V and the ground goes to the switch. When the temp switch activates it closes and connects ground and opens the relay and turns off the motor. The only downside I see to this is a possible safety issue. But in the rare instance that your engine is overheating I think it is worth the risk. Just another idea to consider.
ProTec temp switch |
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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Not really Pete. But if one 2" dia. gauge can save my engine then I don't feel that I have broken any laws. And if I knew the answer to my question then I would not even have to install the gauge, but it would give me an idea of what range pressure switch to use. Since my engine is out of the boat I cannot check it myself. Thanks again, Duane |
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Keep it as original as YOU want it
1978 Mustang (modified) |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Didn't I read you were talking about wood for the dash panel? Faux wood grain vinyl is available.
Since what is really needed is alarm to be triggered at a very low or zero psi, the pressure switch can have a low range. I'd say 0 to 60 or lower. If you find one, do check the on/off hysteresis as that will affect the trip point. |
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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[/QUOTE]
Didn't I read you were talking about wood for the dash panel? Faux wood grain vinyl is available.QUOTE] Yea, I know and in my opinion it looks like cheap faux vinyl too. |
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Keep it as original as YOU want it
1978 Mustang (modified) |
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DrCC
Grand Poobah Joined: April-12-2004 Location: at home Status: Offline Points: 2867 |
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I have water pressure, but it seems it works better with volume.
. because it's wired to the stereo. |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10686 |
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Hi Duane
I built my low tech redneck rig to measure water pressure at the discharge of the RWP. and also at the suction( actually between the hull suction and the trans oil cooler) It's on a 351 but that shouldn't really make any appreciable difference. The short answer is that you better get a 0-30 pound gauge. The longer answer is below RPM Suction Vacuum Disch Press 1000 1" hg 1 psig 2000 5"hg 4 psig 3000 7"hg 9 psig 4000 8"hg pegged the gage but had 15 psig at 3700 If you do the math for 5000 rpm you would have about 25 psig. It seems your engine should have no trouble hitting 5000 rpm. This is with the pump running at the same speed as the engine, that's how my PCM is, not sure how your commander is but I'd guess it's the same or awful close. Hope this helps. KenO |
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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Thanks for the reply Ken, that is what I was looking for. Duane
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Keep it as original as YOU want it
1978 Mustang (modified) |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10686 |
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Glad to help Duane.
I was a little surprised at the numbers but didn't really know what to expect. Checked twice with 2 different gauges too, just to be sure KenO |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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I was surprise too - at the high end!
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10686 |
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I guess the pump laws for centrifugal pumps really do work for these little pumps.
You might say the impeller in there was well seasoned too, but it was in good shape with no pieces parts missing |
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shierh
Gold Member Joined: April-29-2015 Location: Florida Status: Offline Points: 605 |
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engine temp and water flow, pressure is no issue. Only place that will block flow is your risers and you should be pulling every couple of years and acid washing. Replace them every 5 years or so.
If you want to completely clean your block of rust you can try to circulate Evapo-Rust through it. Get 5 gallon bucket from Northern tools, less than 100 and put a bilge pump in it and circulate through block with thermostat removed. let run 24 hours. Will need to put return from exhaust back to the bucket. I plan to do this once i change it over to heat exchange. |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Ken, My comment on the high pressure at the high RPM wasn't based on a centrifugal. I've engineered quite a few rubber flex impeller pumps so the comment was based from pump performance charts. Typically as the pressure increases with RPM, the max head is reached and that's when the impeller blades bend to a point where they are no longer in complete contact with the cam. |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10686 |
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Found some info that says this pump (Sherwood g21) puts out about 22 gpm at 4000 rpm and tails off very slightly from that point upwards probably due to impeller blade bending as Pete said..
It's really more of a positive displacement pump till the blades bend over like Pete mentions
No pressure info other than my results but that makes me think it won't go much over 15 or 16 psig With a 30# gauge, I'll know the answer. KenO |
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