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mattyboy
07-30-2011, 02:55 PM
I am adding about 4 inches onto the oil pressure sender connection. the existing ford extending tube is about 4 inches long with 1/4 thread on the block side and 1/8th on the sender side. I need to wire in an oil pressure safety switch for the new electric fuel pump. In order to make the sender and the switch fit between the risers, power steering pump and the oil filter I'll need to add another 4 inch tube and a T fitting. The sender and the switch will be about 8 inches from the block . will doubling the length of the tube make a change in the pressure reading?? somewhere in the back of my mind the principles of electronics keep bugging me current resistance

mrfixxall
07-30-2011, 03:35 PM
I am adding about 4 inches onto the oil pressure sender connection. the existing ford extending tube is about 4 inches long with 1/4 thread on the block side and 1/8th on the sender side. I need to wire in an oil pressure safety switch for the new electric fuel pump. In order to make the sender and the switch fit between the risers, power steering pump and the oil filter I'll need to add another 4 inch tube and a T fitting. The sender and the switch will be about 8 inches from the block . will doubling the length of the tube make a change in the pressure reading?? somewhere in the back of my mind the principles of electronics keep bugging me current resistance


No! pressure that close wont make a bit of differance, think of it this way,,mechanical gauges used long copper tubing and that did not effect the pressure reading..just make sure you use brass fittings.

300EVIL
07-30-2011, 03:37 PM
That shouldn't be a problem. If you think about how far the tubing has to run for a mechanical oil pressure gauge, an extra 4" of void to compress would be insignificant.

300EVIL
07-30-2011, 03:39 PM
What he said..... :yes:

Beat me to the post.... :pimp:

mattyboy
07-30-2011, 04:04 PM
thanks guys

the ford extender is steel from there on out everything is brass

300EVIL
07-30-2011, 04:59 PM
thanks guys

the ford extender is steel from there on out everything is brass

The only other thing I'd worry about is mechanical fatigue of the fittings due to engine vibrations. You are essentially creating a fulcrum with a weight at the end. You may want to look into a way to secure the end of the sender to maybe one of the intake manifold bolts with a piece of flat stock. Just thinking out loud...

Gary S
07-31-2011, 09:00 AM
The only other thing I'd worry about is mechanical fatigue of the fittings due to engine vibrations. You are essentially creating a fulcrum with a weight at the end. You may want to look into a way to secure the end of the sender to maybe one of the intake manifold bolts with a piece of flat stock. Just thinking out loud...

+1 and don't forget it's not going to break at idle either :eek: It will happen at 5 grand and by the time you realize it,too late.Junk motor and a bilge full of oil. Don't use brass as it can break even easier,thats why the original Ford extension is steel.

mattyboy
07-31-2011, 02:08 PM
got it mocked up in brass. the motor was never meant to have power steering or these center risers on it. i have to engineer a connection for the dip stick tube and some kind of support for this too

mphatc
07-31-2011, 09:27 PM
Matty,

way too long . . this will fail . . the small 1/8" pipe will fracture at the threads dumpiong lots fo oil into the bilge if it happens quickly, or a slow leak that will empty your sump while not letting you know you have low oil pressure.

I suggest using a ss nipple off the engine block, to a tee for the two sensors.

http://www.mcmaster.com/#stainless-steel-pipe-fittings-and-pipe/=df7s42

Schedule 80 . . and a support backet off the exhaust manifold.Know that the Ford sensor requires a good ground path as it is a single wire sensor, so pipe sealant needs to be considered.

Mario L.

Gary S
07-31-2011, 09:54 PM
Matty I have a friend with a Correct Craft who destroyed his stroker doing the same thing. I think you'd be better to mount the senders to the boat or the block and connect an Aeroquip type hose.By the time his fuel pump shut off because of the low oil pressure,the engine was toast because it was running off the fuel in the float bowls. Here is the link,it's about half way down the page. http://www.correctcraftfan.com/forum/forum_posts.asp?TID=5635&KW=brass&PID=144388&title=a-351w-stroker-from-scratch#144388

300EVIL
07-31-2011, 11:00 PM
Without looking at mine, is there any space left to re adapt the stock extension by drilling and tapping new NPT locations on it and mounting the sender and pressure switch independently? If not, the aeroquip hose as mentioned above will be the best method but simple bracing would most likely also work.
Good Luck!

mattyboy
07-31-2011, 11:42 PM
evil no where near the same setup as yours. if the previous owners would have left well enough alone none of this would be necessary. KISS

300EVIL
08-01-2011, 01:37 AM
if the previous owners would have left well enough alone none of this would be necessary. KISS

HA! Yeah, been there. KISS indeed.

mattyboy
08-01-2011, 08:26 AM
Evil, yes KISS a lesson or philosphy I wish the old owners would have lived by.

the original owner as he grew older tried to civilize the boat. the original hi-po 289 must have blown up and a newer 1987 5.0 HO was put in. At this time the owner decided to get power trim , power steering and i guess he ( most likely his wife) didn't like the noise so corsa capt call exhaust was added as well. the problem stems from the fact that Holman Moody never planned for these options. when they added the pulleys for the power steering they had to engineer the pulleys to make the HM water pump work. then to get capt call they added center risers which displaced the dipstick on the newer 5.0 it's on the side not the front. then found out they needed an electric fuel pump as the newer5.0 doesn't have a spot on the timing chain cover for a mechanical pump.their solution just lay a $9.95 automotive pump in the bilge wired hot once the key was turned on.

so my plan was to go back to original as possible without altering the boat too much. I do like the 280T with trim and the setup for the 280 is made for the power steering so without changing the steering setup the power steering must stay. the capt call scrapped the old merc trim pump scrapped for a new Volvo pump. so now this close to finishing I am running into some of the same issues the old owner did. he must have just said **** it doesn't matter as long as it works. I am leaning more towards doing it right and doing it once.

so some stooopid questions

do they make an all in one pressure sender/safety switch?

is there another place to get a pressure reading?

is there another way to wire a safety switch to keep the fuel pump from being wired On when the key is on?

last resort today I will try and mock up a 1/4 black pipe setup to see if they will fit vertically closer to the block behind the power steering pump.

we'll see

300EVIL
08-01-2011, 12:47 PM
is there another way to wire a safety switch to keep the fuel pump from being wired On when the key is on?


Well, If you don't mind spending more money, this would be ultimate...
http://revolutionelectronics.com/Fuel_Pump.html

What's nice is that it primes the system for 3 seconds before starting and rely's on receiving a tach signal pulse to tell the pump to keep going just like a modern day auto. Worth $60? That's up to you. It would eliminate the need for the pressure switch though.

mattyboy
08-01-2011, 01:19 PM
scrapped the 1/8th senders and fitting went to 1/4 black pipe this should work, will keep and eye on it.

mattyboy
08-02-2011, 09:28 AM
Mario,

I have no doubt in my mind that the brass 1/8th pipe would have failed it didn't survive being removed without breaking exactly where you said.

Lowflyn
08-02-2011, 09:22 PM
I have a related problem - elec fuel pump not working, after rebuild - It has been pointed out that I may have a faulty safety switch, functioning off the oil pressure.....

Where is your switch located??? I just checked your photos - Is the 3 prong sensor the switch for pump cut off???? I do not I have one.... Yet I have the same old style can type sending unit..

mattyboy
08-02-2011, 11:24 PM
I have a related problem - elec fuel pump not working, after rebuild - It has been pointed out that I may have a faulty safety switch, functioning off the oil pressure.....

Where is your switch located??? I just checked your photos - Is the 3 prong sensor the switch for pump cut off???? I do not I have one.... Yet I have the same old style can type sending unit..


I have a ford small block the switch is located on the front right side of the motor near the oil filter. yes the 3 prong sensor is the switch. from what I gather the switch has a lead to the S post on my 2 prong remote starter solenoid and then a connection to the IGN circuit that closes when there is more than 5 psi in oil pressure. so the pump will work when cranking then when the key is released to the on posistion and oil pressure has built the pump will stay on. have you hot wired the pump? to see if it works

gcarter
08-03-2011, 10:53 AM
Matty, your boat is looking really good.
I like it. All your efforts are really paying off.

mattyboy
08-03-2011, 04:33 PM
Thanks George :)