Does anybody here run a vacuum pump on their street car? Are there any issues with running one on the street? I've read both yes and no. I'm trying to fix what I believe is a crankcase pressure issue on my car causing my rear main seal to leak. I have a crate 528 hemi in the car and it has a moroso positive locking breather (part # 68788) on each valve cover and no pcv system. The breathers are just vented to open air; not hooked to a evac system in the headers, as I've read they don't work well on street cars with a full exhaust. I'm believing that this is causing my issue and thought about running a vacuum pump to relieve the crankcase pressure. Any real world experience on street cars and how well they hold up? Thanks for the help

You're trying to resolve a street issue with a race solution. Why not just install a PCV valve !?!?

But doubt the PCV will solve his leak nor will a vacuum pump. The PCV is a great thing for the environment and one would not be able to breathe in any major metropolitan area had they not been mandated by the fed's

The PCV's function is to recycle the blowby fumes back into the intake system, mix them with the incoming air/ fuel and reburn them. It does not create a "vacuum" in the engine as the other air inlet is open to the air cleaner.
Putting a vacuum pump on a street the motor will require an inlet that varies with Engine load / RPM in order to create and maintain a vacuum that does not start sucking the seals, gaskets and oil in

Vac pump is not for street use unless you are running open headers. You’ll creat over pressure within the crankcase causing you all kinds of Ills. PCV valve

I wasn't sure if adding a pcv would have been enough venting for the crankcase pressure, that's why I never added one after I bought it. This is why I was looking into a vacuum pump to help relieve any crankcase pressure. I have seen vacuum pump regulators to help control the amount of vacuum applied to the engine. I've just always heard mixed reviews about street use and that's why I was kind of hesitant on adding one. I'm just willing to try anything to fix the oil leak since the car isn't even drivable with how bad it is and I think I've narrowed my issue down to excess pressure in the engine.

I've installed one on my Hemi during it's current rebuild but have not run it yet. I've ran them on the street with other engines without a problem so I don't anticipate any issues now.

I will say they really only work well when the engine is sealed up good. If there are current major leaks where it can draw air in you will be moving a ton of air through the pump to create a vacuum and along with that, oil.

A rear main seal should not leak, period
Trying to band aid it will only make you mad and drive you nuts
You need to take the time to find out exactly what is causing your oil leak, remove the dust cover from the bell housing and see if oil is being slung out from the crankshaft flange onto the front of the flex plate or is it leaking from the side seals and being blown around by the flex plate and converter.
I've seen guys chase a rear oil leak thinking it was the rear main seal when it was the rear cam plug, also when leaking from the rear of the valley cover or the rear of the intake valley cover by the Hemi intakes or Max Wedge intakes and even rocker arm covers leaking and dripping down and getting blown around all over the trans and the rear of the motor
My S/P bracket motor has a GZ vacuum pump on it, before adding the pump the 12 quart aluminum oil pan would seep a little oil out of one of the welds a tiny bit setting or running, not enough to drip though. It doesn't do that anymore with the vacuum pump, I don't know if it sucked in some dirt with the oil and plug the leaky weld or not
Take a close look at your motor and find out exactly why it is leaking and then fix that

how would it only blow out the rear main seal and nothing else..like the front seal, valve cover, oil pan etc...or pop the dipstick out.

Weakest link always goes first.

My thinking is this, if the blowby is so bad it's blowing oil out the rear main seal even with two breathers venting the pressure he's got more problems than an oil leak.

PCV positive crankcase ventilation

THIS

A vacuum pump will help seal up the engine but it will also have its own problems. It needs to be mounted in place and you need to run a belt to it as well as the various hoses, filters, baffles and puke tank. The puke tank needs to be checked on a regular basis. If you're up for all the extra hassle, cost and maintenance then go for it.

The reason that I was believing that it's crankcase pressure is that the engine only has 150 miles on it and it's already had 6 different rear main seals (different brands, one piece, two piece, tried everything) put in and two different retainers and it still leaks. I doesn't leak right at startup; it usually runs for about a minute or two and then it starts leaking badly out of the seal to where it's almost a steady small stream of oil. I've checked all plugs on the back of the engine, valve cover gaskets and everything is dry up top. I can see it leaking right at the lowest point of the seal/ crank flange area. This I why I was thinking it was too much pressure building up; no leak at first and after a minute or so of running, too much pressure builds up and the rear main is the weak point. I'm not trying to band aid anything with the pump, I'm just willing to try anything at this point so that I can drive my car.

I think I'd be doing a leakdown test.

Perform a cyl .leakage test & make sure your getting proper ring seal,with only 150 miles you may have not have properly broken in your rings yet or there is another possible ring seating issue,simple test.

I would try to hook up a manometer to the engine (off the dip stick tube might work) and see what you have for pressure in the crankcase. As mentioned, if you're only leaking from the rear main, I would suspect something wrong back there. Crankshaft seal surface good? If the engine has high pressure, like mentioned, might not be broken in yet. Perhaps broken ring, etc. I'd check pressure first so you know what to look for.

I had a customer years ago that went through a similar ordeal with a 340. He finally brought the car to me. Knowing that he had changed the rear main seal, pan gasket and oil pan several times and pan gasket several times, the first question I asked was,
who assembled the motor? He said he did. Next question, Are you sure the galley plugs are sealed and tight? He said yes I distinctly remember doing them myself.
OK, so we proceeded to replace the rear main and pan gasket 1 more time. In the process I reinstalled his original oil pan.
Primed it, fired it up and within a short time the leak appeared.
Fortunately it was a 4 spd and we were able to drop the inspection cover on the bottom of the bellhousing.
I proceeded to shoot two full cans of brake clean up onto the the back of the motor. After several minutes I poked around pretty thoroughly with a wadded up paper towel. It was desert dry.
We started the motor again and shut it off as soon al the leak appeared.
using the same paper towel I went up the back of the motor staying away from the rear main area. The towel came back with fresh oil.
I commented, Oil does not run uphill.
We removed the trans flywheel etc with him watching. The RR galley plug was only finger tight.
To my knowledge the car has never leaked a drop of oil and that was almost 18 years ago.
I mounted one of his new pan gaskets to a board and put "Think outside the Pan John " on it.

Not sure what you have going on but, if you have that much crankcase pressure to blow out the rea main seal with open breathers you have other problems like ring seal. And breaking it in further is not going to resolve it.
One can attach a fuel pump tester / vacuuum gauge to the dipstick tube, and seal the breathers. Start the motor and see how fast the gauge builds pressure. If it pegs immediately you have a ring problem. If not start looking elsewhere. Any chance of sneaking a inspection camera up in the back of the motor area ?

I know it gets mistaken for other leaks alot, but It's definitely not leaking anywhere else. I pulled the transmission out to check and I also have an inspection camera that I used. Everything is dry above it. I even dropped the engine back off at the engine builders shop, he said he went through it, changed the seal again and put in new rings because apparently they weren't seated and as soon as I put the engine back in the car and started it up, it instantly eaked again.

Oil will only leak past where it isn't sealed
The motor is talking to you, the hard part is understanding what it is saying
Step back, do three complete right hand revolutions and then do 3 the other way and sit down and think how it can leak
Make sure you know exactly where it is leaking from this time before you start to fix it, take your time and FIND IT
Once you got that figured out, FIX IT
There is no magic on motors and our cars do have problems that are hard to figure out, especially when your learning about them the first time, TRUST ME, we have all had to learn about them the hard way
Take your time and find it