Oil Cooler sizing: Is AN8 too small? Options

[Eddie914]

I'm adding a front mounted oil cooler to a '71 914 converted with a 2.7 liter six. I am planning on using -12 size hose.

I have an old oil cooler that has AN8 fittings and lines.

Is this cooler too small?
Will there be too much restriction due to the smaller line sizing?

The cooler is made by Behr. Six cooling plates. Core is 4" x 18".

Thanks

Eddie

'71 914 2.7

[J P Stein]

-8 is too small, IMO.
-12 is gud.

[machina]

where you live it may be enough but you won't know till you try.

Wouldn't work down here in FL though.

Sound like that cooler is too small for flat 6 application.

dr

[Jake Raby]

too big of a line kills the pressure..
I run #10 to the cooler and #8 out of the cooler to the case.... Reason being that it tends to hold the oil in the cooler longer and helps control temps better! was good for 30 degrees on the last time I tried it... Your limiting factor is the size of the smallest orfice in the system, you could run -20 and its not flowing more than the smallest orfice!

[Rusty]

Jake,

I understand what you mean about the smallest hole regulating flow. (at least that's how I interpreted what you said)

But why would larger lines mean less pressure? For air compressor lines, I can see that's true - air is very compressable. Oil isn't. Once the passages are full, shouldn't pressure be constant?

-Rusty (IMG:style_emoticons/default/smoke.gif)

[Jake Raby]

It has more volume, and takes more PSI to build on a gauge... I have seen guys run front coolers and drop 20 PSI pressure from what they had.

You'd think that once its bled that pressure is pressure it would still be the same with the same given resistance to flow, but it does seem to be impacted by hose diameter.

On my lifter test fixture I'm using -14 oil hoses, but it needs alot of oil and it has twin oil pumps ran in series between the engines to move the oil through both filters and coolers...

[SirAndy]

Once the passages are full, shouldn't pressure be constant?

more friction because of more surface? (IMG:style_emoticons/default/confused24.gif)

but what do i know ...
Andy

[scotty]

I run -12 (lines and cooler). -8 may be a tad small, making the suction pump work harder (or some such gobbledygook)

...you're in for some fun times driving that thing! (IMG:style_emoticons/default/biggrin.gif)

[J P Stein]

The 6ers have a 2 stage oil pump. Pressure & scavenge. The idea of larger lines on the scavenge side(where the cooler is installed) is to lessen the work of the pump. Engine oil pressure is not effected as long as the scavenge side of the pump is allowed to do it's work.....It's a volume deal.
You don't want the case to fill with oil.
-16 is actually mo better.

[Jake Raby]

ah, a 547 engine is the same way... It has -14 from the factory.

[Mark Henry]

I get a lot of my stuff at the local Parker Hose store and I told him that the guys were using an-12 lines. He said "no way that's too big! Even transports don't use that size, real hard on the pump bud."

I know that the /6 guys swear by the an-12 size and they say that you might install a /6 in the future, so the /4 guys should install an-12 lines as well.

Is there any hard data on flows etc, out there?

Also I've seen coolers out there that look like they could become an air trap, is this a problem? (IMG:style_emoticons/default/unsure.gif)

[J P Stein]

The only hard data I have found is on the 964 (3.6L)
oil pump.

It supplys 65 liters per minute to the pressure side.
The pressure varies per rpms. 1 bar per 1000 rpms is the rule of thumb.
The scavenge side has 1.84 times the capacity.

A good example would be: Go turn on your garden hose full blast (IMG:style_emoticons/default/biggrin.gif) That's about 4 bar thru a 1/2 inch ID line.

The 911 oil pump is a piece of work.

I would stay away from that Parker Hose guy.

[rdracrdave]

On a dry sump system the oil pressure in the lines really means little because the oil is simply being dumped into a non pressurised tank. The only issue there is the stress on the pump and the recovery time for the tank volume. ( I.E. running the tank low on oil because of a restriction in the lines .
Like a too small oil cooler oriface.)
lots of guys use -12 lines and oil coolers and seem to be satisfied ,but I allways use -16 lines and coolers .
There are lots of -12 oil coolers from the Nascar guys on Ebay for very little $ . You may want to go that route.
Dave

[banderson]

Pressure drops off with every restriction that is in its path. If you add a new feature, odds are, it will drop the pressure slightly. If you add hose to the front and back again, there will be a small pressure drop from each fitting, each foot of hose, each bend, etc. Add them up and you get the total pressure drop. If you have a major restriction in one place, and minor ones elsewhere, the minor ones still add up to the total. And, IIRC, pressure drop is exponential with flow rate or tubing size.

Its just like electricity; resistors in series.

It makes no sense to me to have –10 lines to the front and –8 lines retuning. Just put the biggest ones in there that you need. What do you need? Haven’t got a clue. Read a different post. But beware of the laws of diminishing returns. If pressure drop is exponential with tubing size, then if –10 is enough, there is no benefit to –12.

If the pump is sucking fluid, then that section is usually limited to atmospheric pressure (14.7 psi). Therefore, a larger tube makes sense to avoid cavitations.

[machina]

I don't have no fancy book learning but I thought the more restrictions, the higher the pressure, not the inverse.

Makes sense to me that restrictions would increase the pressure, just like with arterial sclerosis.

Also, just because a cooler has -12 or -16 fittings on it doesn't mean that you should use that size lines with them. Many manufacturers use one size only and sell you the step down adapters for your application.

I would use what has worked for other folks.

dr

[Mark Henry]

I would stay away from that Parker Hose guy.

I don’t like bad advice. Who did you buy your hose from…Jegs? I’ve already priced an-12 SS line and fittings from him, he came in $200 less than the delivered price from any US supplier I’ve seen. He (and I) never said he knows anything about P-cars. He just knows hose, I tell him what I want and he makes it up.

The 911 oil pump is a piece of work.

It's a nice unit but the 911 has a very simple pump, it's almost the same as a /4 pump, it just has an extra side. If you want to see a work of art look at a Bombardier snow-groomer pump, it powers everything on the machine, including the tracks. It’s worth 25K and has more moving parts than your engine.

The only hard data I have found is on the 964  (3.6L) oil pump. It supplys 65 liters per minute to the pressure side. The pressure varies per rpms. 1 bar per 1000 rpms is the rule of thumb. The scavenge side has 1.84 times the capacity.
A good example would be: Go turn on your garden hose full blast (IMG:style_emoticons/default/biggrin.gif) That's about 4 bar thru a 1/2 inch ID  line.

Now, that's real data. How many bar do I have if I increase the gardenhose size to 3/4 inch? (IMG:style_emoticons/default/biggrin.gif)

(IMG:style_emoticons/default/wacko.gif)

[Joe Bob]

Well....the Pegasus and BAT 30mm conversion fittings have -16AN and -12AN on the other side. So one would think that would be the standard(s) for high end racing.

Manfred and Frank are getting -10AN becuase that was what was in there and what I have used in the past.....they will be running a 2.0 and a 2.2 engine(s).....Old Blue has been running VERY happily with -10AN as well....

The Rocket....which was a CIS/964 cammed 3.0 ran
-10AN as well.....so.....none of the hot climates that I ran in....including Willow Springs in the 100F heat saw the need for anything else.

I'm a -10AN guy I would guess....

[TimT]

On the 911's with front mounted oil tanks, we typically use -12 to the filter/thermostat/tank/cooler and -16 or -20 as a return to the engine from the tank.. I think the real reason for the -16 or -20 line is just for extra capacity.

The -16 line and fitting get really expensive, a piece of aluminum pipe 1 1/4" dia (I think) is cut and -16 ends are welded on...but then the -16 fitting are really expensive too...

Using pipe you dont have to worry about the return hose collapsing..

I buy stuff from these guys sometimes.... its take offs from NASCAR... good prices etc..

[TimT]

oops kind went of topic from the /4 question... (IMG:style_emoticons/default/blink.gif)

[Rleog]

just to expand on what Brett was saying above..

resistance varies by the 4th power of the radius of a tube, and directly by its length. Reducing a tube to half the diameter increases resistance to flow by a factor of 16.

Bob G.