The Dodge Challenger Message Board

Hi my 318 small block with some modifications has oil pressure at 60 psi when cold at the idle but after it gets hot between 80-90 deg C pressure drops to 30 psi, during dribe when hot it is like 40-45 psi. Is it to low or i should not worry ? I am using 20-50 oil, all the bushings and high volume oil pump are new.

Second question is about power valve in the carb i have vacum around 18-19 inches at the idle, what power valve i should be using in my carb.

Thanks for any suggestions.

Wojpi wrote:Hi my 318 small block with some modifications has oil pressure at 60 psi when cold at the idle but after it gets hot between 80-90 deg C pressure drops to 30 psi, during dribe when hot it is like 40-45 psi. Is it to low or i should not worry ? I am using 20-50 oil, all the bushings and high volume oil pump are new.

I can never remember what oil pressure is supposed to be. It is so much per 1000rpm or something. I really need to find out again and write it down! But it does not sound dangerously low at the moment.
What oil filter are you using and is it clean?

Second question is about power valve in the carb i have vacum around 18-19 inches at the idle, what power valve i should be using in my carb.

Whatever the carb came with will do. It is only really critical in cars with big cams and very low vacuum. If the car struggles up steep hills and goes very lean then drop the valve rating.

According to the 1975 Chilton's Manual ( covers car from 1968-1975 ) The oil pressure for every engine from the 170 cid 6 cylinder to the 426 Hemi should have 55 PSI at 2050 RPM.

I looked it up.

The stock valve pressure relief spring in the pump results in 45-55psi max.

If you want more there is a higher pressure spring available from MP part number P3690944 although I don't know how much more it gives you.

MP recommend you have 50psi pressure at 5000rpm min. Plus 10psi for every 1000rpm over that.

The lowest you should EVER let pressure get (even at idle) is 15psi. If it ever gets down to 15psi switch the engine off straight away.

Did you recently have your engine re-built or install new main bearings? If so did you use full groove main bearings? 30 P.S.I. hot at idle, is perfectly acceptable. Mine is 25 psi@750 RPM Hot, full groove mains, hydraulic roller cam, pushrod oiling to the heads, yours is rocker shaft oiling I assume as per LA engines. As long as the pressure "shoots up" as the engine RPM's increases it's fine. BTW, you must have "loose" clearances to be able to run 20W-50 oil in your engine, mine doesnt run right unless 10W-30 is used, I used 15W-40 in it during the summer months but switched back to 10W-30 Year Round, it has pretty tight clearances comparable to modern engines, but has full groove mains, which are not used in production engines.

There is an adjustable pressure relief spring for big blocks if you would rather be able to fine tune it.

The black relief spring that fits slant six and B-RB (not LA) oil pumps puts out penty of pressure. No need to fine tune it.

Today i did some test.

When i start engine cold i got 60 psi at the idle, that is set to 800 rpm

until 70 deg C of engine temp is keeps that way, When i reach around 80 deg C pressure at the idle drops to 40 psi, during drive aroound 200 rpm there is 60 psi, when i reach 90 deg C at the idle i have 35 psi and around 55 psi during drive at 2000 rpm.

The engine was rebuild recently, I am not sure which type of bushings they have used, but it was done by Sixpackspeedshop in Belgium. As for now it is all good. My little 318 puls 14,4 s for 1/4 mile on street tires and the car has all equipment in it the weight with me in is 3750 pounds, and i have 3,23 gears, i was using 255/60 tires.

Do you think if i use 275/60 tires my ET can be worse ?

What kind of power this engine can be putting ?I have never checked it ?

Wojpi wrote:When i start engine cold i got 60 psi at the idle, that is set to 800 rpm

until 70 deg C of engine temp is keeps that way, When i reach around 80 deg C pressure at the idle drops to 40 psi, during drive aroound 200 rpm there is 60 psi, when i reach 90 deg C at the idle i have 35 psi and around 55 psi during drive at 2000 rpm.

Nothing to worry about. Keep the oil temp below 90 degrees C though. That is too hot. You need to be closer to 80 degrees C.

180*F is the ideal temp. That is 82*C. The hotter the engine gets the thinner the oil gets as you have found.

My little 318 puls 14,4 s for 1/4 mile on street tires and the car has all equipment in it the weight with me in is 3750 pounds, and i have 3,23 gears, i was using 255/60 tires.

Do you think if i use 275/60 tires my ET can be worse ?

A wider tyre will give you more grip. But the 275 will be almost one inch taller so you will have slightly higher gearing. One probably offsets the other.

What kind of power this engine can be putting ?I have never checked it ?

To work out what power your engine is making I need the mph at the 1/4 mile.

From your ET of 14.4 and your weight I can tell you that you are making almost 250HP between the tyres and the track surface.
So you are probably making at least 320hp at the engine. Not bad at all for a 318.

But your mph will tell more.

As to the speed it is sth about 100 mph at the finish line, it is the reading from my speedometer so may not be very accurate. We have the timing done by Tag hauer but unfortunatelly they do not measure the speed.

You need to club together and make them measure speed as well. That is the only way to see what HP you are making.

You need that so you can see the difference between what you should be running and what you did actually run. So you can see how much you are loosing with gears/tyres/suspension/chassis etc.

If you did do 100mph through the finish line you could in theory run a 13.6.

You could also be making about 350hp at the crank.