Oil cooler flow rate???

Gumba11 · 04-27-2005, 06:25 PM

Hey all,

I had some custom oil coolers made and now the question of flow has come up. Pressure drop accross the cooler is not as big of a deal as flow here because the coolers are on the scavenge side of the system. Flow is very important because the oil is airated that runs through the cooler means the flow is paramount due to a loss of efficiency.

Now the real question. Does anyone know the flow rate of a front mounted oil cooler from either B&B or Fluidyne? Any info you might have would be great.

Thanks in advance.............................C

Jim Sims · 04-27-2005, 08:09 PM

Flow will depend on pressure drop. The scavenge side doesn't have a lot of pressure so big diameter lines and large flow passageways in the cooler (and hence low pressure drop) are important in the 911 external oil cooling system. Contact the oil cooler vendors; they may have graphs showing flow rate versus pressure drop for a given weight of oil at some specified operating temperature. Jim

Wil Ferch · 04-28-2005, 05:16 PM

Ahh...I think this is backwards *if* the scavenge pump is a positive displacement device that I think it is....

..meaning therefore...pressure drop will be a function of flow rate which is essentially constant in a positive displacement pump....

Wil

Jim Sims · 04-28-2005, 08:19 PM

Any real flow system has friction which requires a certain amount of pressure difference (pressure drop) across it (depending upon flow through it) to overcome that friction. Flow rate and pressure drop are only constant if the pump is turning at a constant speed and the oil is flowing at a constant rate. Positive displacement pumps also have slip (leakage) and other volumetric inefficiencies.

Gumba11 · 04-28-2005, 09:15 PM

Found out the flow rate on the B&B. They claim 20 GPM. This number seems a bit high to me but that is the number we are shooting for with my custom coolers.

I find out tomorrow if the ones that are already made for me are enough. If not its back to square one.

Thinking back I could have made things more simple by just getting a B&B cooler, but they wouldnt be free now would they.

Sponsors kick a$$!

.........................................C

P.S. Thanks for the input guys!

Wil Ferch · 04:10 PM

Jim:
Maybe we're splitting hairs here....but the point about constant flow was meant "at a given RPM"....certainly the "system resistance" of the lines and pressure drop through the cooler ( itself) must be overcome. This resistance ( delta-p) is different when different flow rates are applied. But the pressure drop ( of the "system") ..."is what it is"..at a given flow rate. The pump needs to overcome this.

Common convention says that when "flow is a function of pressure drop"...this is usually taken to mean the pump is backing up on its performance curve ( more flow/less pressure....less flow more differential pressure)....as in a centrifugal ( and not positive displacemnt) pump. It was in that context that I said what I did..

Wil

Early_S_Man · 04-29-2005, 03:42 PM

I think your flow rate would depend on which oil pump was fitted, and the size of the lines to and from the thermostat.

The cooler can only reduce flow through the scavenge system, not improve it ... compared to the trombone loop, which is the same size as the lines. If the factory engineers did their homework as I suspect ... none of the coolers fitted to production cars can be improved upon by fitting a replacement, fender-mounted aftermarket cooler, in spite of all of the advertising hype!!!

A center-mounted cooler with non-restrictive fittings and adequate airflow is the only real way to improve oil cooling in the scavenge circuit!

Wil Ferch · 04:21 PM

Which brings me back to a question I posted before but never got a good response...

The scavenge side picks up a lot of "air" as part of the mix it pumps around....very inefficient. The engine mounted cooler, OTOH....is on the pressure side of the circuit and pumps a full volume of liquid oil ( little or no air). BA says that people have used this circuit ( in lieu of scavenge) for aux cooler duties and have therefore been able to use "smaller" helicopter coolers to good effect.

Why then...are we all still going with the scavenge side which need these big coolers and big spaces to mount them??

Pure racing Porsches of yore used the pressure side for coolers....no ?

Wil

Gumba11 · 04-29-2005, 06:11 PM

None of this has been truely informative. I am sometimes disappointed when the forum gets a little too technically groovy about things. Rather than just answer the question in simple terms people tend to want to reinvent the wheel or split atoms when it really isnt needed.

I got the answers I needed from B&B in about 2 minutes on the phone. What he said was clear and concise. No theorys discussed. No B.S.

I say this not to lash out but only because I have seen others here that ask very simple questions and have said this very same thing. I only echo their thoughts.

Simple really can work on occasion.

Thanks............................................ .C

Jim Sims · 04-29-2005, 07:34 PM

20 GPM at what input pressure (assuming the exit is exhausting to normal air pressure)? If B&B didn't provide an inlet pressure or a pressure drop across the cooler then just stating 20 GPM is not very informative. One can get 20GPM through a lot of coolers but some of them may require a 50 hp oil pump to do so if the pressure drop is excessive. If B&B said 20 GPM fender mounted on a 911 with the engine at 4500 rpm and 30 weight oil at 190F then that is a useful number and has an implied pressure drop built into it.

Gumba11 · 04-29-2005, 10:19 PM

Long story short, you almost repeated what B&Bs engineering department told me.

Thanks ...................................C