Dry sump breathing on 351W V8
Discussion
Hi all
I'm racing a 65 Mustang with a Roush 351W enigine (410bhp). Good oil pressure and temp and good water temp. No smoke from exhaust and engine pulls well.
BUT: the dry sump was pushing oil into the expansion tank (front of engine bay). Up to 2 litres in a 45 minute race. At first it looked like the pipe to the expansion tank was located incorrectly from the oil tank (in cockpit). So moved it to the top of the tank and away from the scavenge pipe returns (it runs twin scavenge and one pressure line) and removed rocker breathers which I did not think a dry sump should have.
It still pushes oil into catch tank at the same rate.
I may have slightly over filled the system but not by 2 litres.
Compression seems ok in engine / cylinders.
Question: should I have rocker breathers (some schools of thought say yes others no).
The tank could be too small but I am presuming the people who originally fitted it knew what they were doing (but I'm not convinced)
What else could cause the overflow and what options could I try to stop the problem?
I'm thinking of putting a catch tank in the boot for the oil so at least it wont be in the engine bay and using the front tank for rocker breathing??
aaaaarrrgh!
Help required
Gail
I'm racing a 65 Mustang with a Roush 351W enigine (410bhp). Good oil pressure and temp and good water temp. No smoke from exhaust and engine pulls well.
BUT: the dry sump was pushing oil into the expansion tank (front of engine bay). Up to 2 litres in a 45 minute race. At first it looked like the pipe to the expansion tank was located incorrectly from the oil tank (in cockpit). So moved it to the top of the tank and away from the scavenge pipe returns (it runs twin scavenge and one pressure line) and removed rocker breathers which I did not think a dry sump should have.
It still pushes oil into catch tank at the same rate.
I may have slightly over filled the system but not by 2 litres.
Compression seems ok in engine / cylinders.
Question: should I have rocker breathers (some schools of thought say yes others no).
The tank could be too small but I am presuming the people who originally fitted it knew what they were doing (but I'm not convinced)
What else could cause the overflow and what options could I try to stop the problem?
I'm thinking of putting a catch tank in the boot for the oil so at least it wont be in the engine bay and using the front tank for rocker breathing??
aaaaarrrgh!
Help required
Gail
Is the oil in the catch tank very foamy? Does the oil tank have some kind of de-aeration device built into it? It's possible the oil tank isn't big enough. Certainly the catch tank is too small at 2L as the regulation size is 3L. Have you contacted Roush to see what they say? What grade of oil are you using? Not least are you certain the engine is breathing the oil rather than being surged from the main oil tank to the catch tank? Photos? Worse case scenario is a broken piston ring but you say the engine isn't smoking.
You mention expansion tank ? What is this ?
A 2 stage pump probably should be enough to scavenge the engine and cover it's breathing too.
are there any breathers on the engine at all ? either open to atmos, to a can or with a check valve to prevent too much vacuum in the crankcase ?
Your catch can that the oil tank breathes into. Is this mounted higher than the oil tank ? What size lines etc ?
A 2 stage pump probably should be enough to scavenge the engine and cover it's breathing too.
are there any breathers on the engine at all ? either open to atmos, to a can or with a check valve to prevent too much vacuum in the crankcase ?
Your catch can that the oil tank breathes into. Is this mounted higher than the oil tank ? What size lines etc ?
Hi All
Not sure about the tank but I am going to look at it in more detail as several people say it may not be baffled enough although I presume its a shop bought part designed for the job! Catch tank is higher than the oil tank. Currently no rocker breathers. Most designs suggest that the scavenge pipes create a vacuum so there should be need to breath rockers. Oil is Joe Gibbs #6.Has been changed twice now since I bought the car. Breathing was a bit better today at Rockingham in qually. Didn't check after race as needed to get home but will do later in week.
Not sure about the tank but I am going to look at it in more detail as several people say it may not be baffled enough although I presume its a shop bought part designed for the job! Catch tank is higher than the oil tank. Currently no rocker breathers. Most designs suggest that the scavenge pipes create a vacuum so there should be need to breath rockers. Oil is Joe Gibbs #6.Has been changed twice now since I bought the car. Breathing was a bit better today at Rockingham in qually. Didn't check after race as needed to get home but will do later in week.
The Pace system in my Pinto engined Escort does the same. It seems to be an oil flow differential in that slightly more oil is returned to the tank than exits. I have changed tanks, hose diameters, breathers with little success. My races are 15 minutes and I just empty the overflow tank periodically and keep the main tank half full.
Your engine doesn't make oil.
You should set your tank level when the engine is warmed up, run it at high enough rpm to have the scavenge stages working at max flow for long enough to replicate the scavenge flow on track, then switch off and dip the tank.
If you don't do that you will always overfill the tank.
Oil in the overflow catch can on dry sump systems is usually down to either too much oil in the tank or you are using a badly designed breather outlet. Some of the more popular tanks in use are very poorly designed at the breather outlet.
You should set your tank level when the engine is warmed up, run it at high enough rpm to have the scavenge stages working at max flow for long enough to replicate the scavenge flow on track, then switch off and dip the tank.
If you don't do that you will always overfill the tank.
Oil in the overflow catch can on dry sump systems is usually down to either too much oil in the tank or you are using a badly designed breather outlet. Some of the more popular tanks in use are very poorly designed at the breather outlet.
Kinkell said:
The tank I used at first was from a factory rally car made by a certain Mr Gomm. I have tried various levels of oil in the system with the same result. After wet weather races the overflow tank is always empty due to less revs being used.
Less corner g is why it's empty. If you are using less revs in the wet you aren't doing it right. LS said:
If that is a reply to me, how much money do you want to put on it?
I don't do pissing contests on the internet.You may have a Gomm tank, but its not unusual for them to be messed about with and functionally ruined or have the wrong ports used.
Gail, having re-read your opening post its most likely your breather outlet in the tank is not correct. If you want some help take some pictures of the tank as best you can, both with all the pipes on and of the internals of the tank. You can email me them if you prefer.
I have a lot of experience of dry sump systems (and FIA spec race cars of all types) so may see something that can help.
Edited by anonymous-user on Monday 27th July 17:14
jsf said:
If those top two hoses are direct into the top of the tank and that's your breather out and in, its never going to work.
You cant breath the tank to the engine, the final breather out has to go to atmosphere (via a catch can if running to most race regs)
The smaller top pipes breathe out, so what else do you suggest to allow it to work properly and not pump oil into the catch tank. OP's system diagram is same as mine.You cant breath the tank to the engine, the final breather out has to go to atmosphere (via a catch can if running to most race regs)
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