NASCAR ENGINE DRY SUMPs and CRANKCASE Vents

spookypt · #1 (**permalink**) 05-11-2011, 10:32 PM

Hi everyone, I'm chasing some info....

My cobra basically is running a NASCAR Spec 351w. 4 stage dry sump with all the bells and whistles 13:5 comp bla bla..

What I'm curious about is my dry sump pulls substantial vacuum and yet it isn't fitted with a crankcase vent. It has a vent on teh DS Tank but essentially teh engine is sealed. So at high rpm (say 8500) what stops it sucking its guts in. (Gaskets etc)

I'm planning on fitting a Moroso Crankcase vent (+12) off the rocker cover and set inside a catch can to eliminate the potential for this to happen.

I also understand without this its bloody hard to get piston ring seated?

What do the NASCAR guys do?? Do they have a vent off teh rocker covers?

Spookypt

Jac Mac · #2 (**permalink**) 05-11-2011, 10:51 PM

They seem to run them exactly as you have it now, 'They' want to run with a negative crankase pressure for several reasons, if you vent the covers or valley you will destroy the way its setup & yes if its fitted with low tension ring packages you might have problems, but I imagine unless your car is going to be treated in similar fashion to a nascar racer that you might have a few other problems to iron out anyway.

spookypt · #3 (**permalink**) 05-11-2011, 11:06 PM

Quote:

Originally Posted by Jac Mac

They seem to run them exactly as you have it now, 'They' want to run with a negative crankase pressure for several reasons, if you vent the covers or valley you will destroy the way its setup & yes if its fitted with low tension ring packages you might have problems, but I imagine unless your car is going to be treated in similar fashion to a nascar racer that you might have a few other problems to iron out anyway.

I understand that negative crankcase pressure increases HP..... so I figure this is one of the reasons...?

Why do you suggest I'm going to have other problems??? We don't race on banked circuits like NASCAR but we do run on our circuit tracks pretty hard.

Spookypt

Ant · #4 (**permalink**) 05-12-2011, 02:30 AM

I have a similar setup to what you mention, but have modified the engine for the road and mainly track, comp ratio 10.3, this engine is sealed dry sumped, and has coated racing pistons with thinner rings but running normal tension. I have well over 600bhp at 6800rpms out of this 373, plus 525ft Ibs torque, so wheel spin will be the biggest problem.

My inlet valley has a removable plate with -10an size bung and as I am not running Nascar and 8500rpms, I will route a breather hose to the puke tank. On the engineers forum a guy had a lot of trouble with leaks etc until he ran a breather for semi serious fun and racing.

750hp · #5 (**permalink**) 05-12-2011, 06:25 AM

Spook, I've added a few of my thoughts in red. I haven't heard of the value of introducing extra air into the engine (via a breather), only to suck it out with one stage of the dry sump pump. Seems like it'd be the same as putting a humidifier and a dehumidifier in the same room and letting them fight it out

Quote:

Originally Posted by spookypt

Hi everyone, I'm chasing some info....

My cobra basically is running a NASCAR Spec 351w. 4 stage dry sump with all the bells and whistles 13:5 comp bla bla.. And sounds TOUGH!!!

What I'm curious about is my dry sump pulls substantial vacuum and yet it isn't fitted with a crankcase vent. Have you measured it? Most guys are running 10 to 15" of vacuum with a vacuum control valve such as http://www.gzmotorsports.com/vcv102.html

It has a vent on the DS Tank but essentially the engine is sealed. As it should be, and as the pump is designed.
So at high rpm (say 8500) what stops it sucking its guts in. (Gaskets etc) Usually the only gasket that is at risk of being sucked inwards is the rubber seal at the front of the oil pan. Doesn't seem to have been a problem with SBF motors in the past.

I also understand without this its bloody hard to get piston ring seated? Vacuum in the crankcase sucks the rings out to the cylinder walls, so it helps with ring seal.

spookypt · #6 (**permalink**) 05-12-2011, 03:51 PM

Craig Mate can I ring u tonite to discuss. Pm me your moby no!

spookypt · #7 (**permalink**) 05-12-2011, 04:20 PM

750HP, we expect my 4 stage DS is sucking up to 20 of mercury at full melt which is alot! We reckon its sucked in part of a manifold gasket. With the BIG heads the manifold gasket with those poxy steel wedges is a joke...

We are going to run exactly what you have proposed (CC Vent set to 12 of Merc) and set it to 12" of Merc Vacuum so once the vacuum exceeds that it can suck in some atmosphere and reduce the chances of sucking in gaskets and will ultimately help increase piston ring seal. Current leak down tests are BAD!

My question still remains though.....Do the NASCAR RACE Guys have a set crankshaft vents to suck in some atmosphere after reaching a certain point.
The vents don't release air into the atmo they only allow atmo into the engine so I assume if they do that they don't run the vent inside an externally mounted catch can arrangement to avoid oil spew etc.

I've read up a bit on the net and many seem to get mixed up between PCV and Crankcase Vents.... Entirely different animals!

I'd love a pic of a NASCAR RACE ENGINE with a crankcase vent set up shown if anyone has one!

SpookyPT

vector1 · #8 (**permalink**) 05-12-2011, 06:16 PM

don't know what the nascar guys do but i run a blowoff valve on one of the valve covers, keeps the gaskets in good shape if you lose ring control or build crankcase pressure for some reason.

i run a vented crankcase, but am going to use a peterson vacuum regulator to limit vacuum to 12". vacuum does make power.

don't make any vacuum if you are breaking the engine in, the rings will not seat correctly from what i have read.

why are your leakdown numbers so bad? with a lot of leakdown you might have problems pulling a vacuum.

spookypt · #9 (**permalink**) 05-12-2011, 11:32 PM

Leakdown is an issue as I have only just built the engine and have not as yet bedded the rings. Managed to have a major oil leak on start up and haven't progressed much further from there.

I'm going to get in touch with Marcus Ambrose and see if he can send me a pic or 2!

spookypt · #10 (**permalink**) 05-15-2011, 04:43 PM

"Hi Matt, in NASCAR today, engines run with around 20-psi vacuum in the crankcase. Dry sump pumps have their scavenge sections designed to create vacuum. A check valve is added to suck air into the crankcase to prevent excess vacuum. Regards Marcus"

olddog · #11 (**permalink**) 05-15-2011, 05:53 PM

Quote:

Originally Posted by spookypt

"Hi Matt, in NASCAR today, engines run with around 20-psi vacuum in the crankcase. Dry sump pumps have their scavenge sections designed to create vacuum. A check valve is added to suck air into the crankcase to prevent excess vacuum. Regards Marcus"

I see this mistake a lot, and don't want to see miss-education given to the next person. Don't mean to be disrespectful to anyone. I'm just a bit anal.

Vacuum is typically measure in inches of mercury ("Hg) or sometimes inches of water column ("H2O) for light vacuum.

1 atmosphere is generally accepted to be 14.7 psi, which is the most vacuum possible on earth. Since vacuum is the absence of pressure, absolute pressure can only go to zero. It is not possible for absolute pressure to be negative.

spookypt · #12 (**permalink**) 05-15-2011, 08:35 PM

Olddog, that is true.... Would I be correct in saying then...

"in NASCAR today, engines run with around 20 inches of mercury vacuum in the crankcase. Dry sump pumps have their scavenge sections designed to create vacuum. A check valve is added to suck air into the crankcase at 12 inches of mercury to prevent excess vacuum damaging gaskets and help piston seal etc"

Thoughts?

olddog · #13 (**permalink**) 05-16-2011, 04:30 PM

Sounds good.

Morris · #14 (**permalink**) 05-21-2011, 10:44 AM

Pay attention to the Seals in the motor..... as with high vacuum in the crankcase

The motor has to be built for high vacuum. and the lips of seals have to be facing the right direction.

Morris

spookypt · #15 (**permalink**) 05-22-2011, 06:35 PM

Ye Morris correct. And done!

here's what I'm using now. Fully adjustable. Now set to 12 inches of Mercury! Once the vacuum exceeds this it sucks in atmo to ensure this isn't exceeded.

vector1 · #16 (**permalink**) 05-23-2011, 07:55 AM

do you put a filter on that part?

spookypt · #17 (**permalink**) 05-23-2011, 04:33 PM

An interesting question....? Apparently not though.

scottj · #18 (**permalink**) 05-23-2011, 05:47 PM

This is a filtered vacuum regulator from from Peterson:

This is what I have always run, a pop-off valve:

I'd be very surprised to see a 4-stage pump produce 20 in/hg.

Ant · #19 (**permalink**) 05-23-2011, 07:53 PM

Quote:

Originally Posted by scottj

I'd be very surprised to see a 4-stage pump produce 20 in/hg.

Would a 3 stage Peterson pump with two std scavenge sections pull enough vacuum for me to consider a relief valve, any thoughts!

scottj · #20 (**permalink**) 05-24-2011, 05:43 AM

Quote:

Originally Posted by Ant

Would a 3 stage Peterson pump with two std scavenge sections pull enough vacuum for me to consider a relief valve, any thoughts!

I ran a 3-stage SCP pump on the Cobra for a while. We didn't try to pull vacuum... ran it vented. A good quality 4-stage is the minimum we would use to run it sealed.

We'd see 10-12" with a 4-stage Barnes on the Late Model engines. That's why we didn't run regulators, only pop-offs. We'd see a little more than that with 5-stage and gerotor-style pumps.

Scott