Vacuum pumps/ leaks

Any of you have experience with vacuum pumps on your engine? I have one SSB electric pump on my car, and all I can pull is 9in of vacuum at idle / 5in at WOT.
I tried TWO of those pumps hooked to the engine today, and got the same readings as with one pmp(!). 9-10" at idle, 5-6 at WOT. I've pressurized the engine and tried to find leaks with soapy spray water, but.. not a bubble.
The OEM crank seal arrangement is such that they can be removed horizontally from either end of the crank. I don't know if there's any outer lip on the seal, but if there was that wouldn't lose seal due to vacuum sucking IN on the seal's lip. And if you can change them from the outside horizontally with a tool that is just a puller, then there shouldn't be a lip on the inside of the seals that deforms with vacuum. I'm just posting in case there's an obvious place to look for a leak that I'm missing...
The mains ARE cross-bolted, and there's no gasket of any kind for the cross-bolts, just metal-metal contact.
I think the cross-bolts are likely suspects myself and will try to coat the heads of the cross bolts with something as they sit in place on the block.
Any ideas where the leak might be other than just up past the OEM rings ?

can you give a little more info about the motor and such.

I'm thinking it could be the rings, but not sure at this point.

Well to tell you the truth, no one that I know is using a vacuum pump on this engine, so I'd like keep specific information to a minium. It's kinda my secret weapon..(?)
That doesn't help much perhaps, but basically it's a 100% OEM engine internally,with only 2000 miles on it.
If one pump will pull 9in of vacuum while seeping through the ring end gaps, two pumps working together should have done something. Maybe not doubling the 9in but, at least 13in or 15in or something.
The rings and their end gaps are a fixed quantity. They wouldn't be sucked open more as vacuum increased. (it would seem)
By the way, sticking a short hose and gauge on the vacuum pump produces an instant 22in of vacuum that doesn't leak at all when the pump is shut off. Meaning the pump doesn't leak. Also when I put my thumb over the hose end at 22in and crack an ever so slight opening in the end of the hose, the vacuum drops right down to 9in. Like 2 pinholes in size will do it.
Previously, with just the one pump connected , I noticed the vacuum gauge needle fluttering as it approached and stopped at 9in. I'd guess that's an indication of something repeatedly opening and closing due to vacuum and allowing a leak. I think I noticed the flutter starting earlier with 2 pumps running together.
On the other hand, when the single system is hooked up it'll bleed right down to 2in or less when I shut off the pump.
Maybe there's a shop around with one of those leak detector machines that use smoke to reveal a leak.
The rings and/or end gaps may be suspect, but the fact that it only takes a leak the size of 2 pinholes or so to plummet the vacuum from 22in to 9in almost rules the rings out in a sense.

When you say it was fluttering, when does this happen? At an idle, as the rpms are decreasing, or as the rpms are increasing?
An intermittent fluctuation at idle means you have either an ignition miss or a sticking valve.
If the needle fluctuates as you increase the engine speed, you have either an ignition miss, a blown head gasket, a leaking valve or a weak valve spring.
Other then that, you got me!

Thanks for the replies. My vacuum leak question is for the crankcase. The symptoms you list are more for vacuum leaks when the gauge is attached to the intake manifold.

Sorry, I wasen't more of a help. Good luck, let me know if you figure it out.

I can probaly help you out on this but do need some info, from what i can see from your first post the engine is in a production car and still a stock engine or slightly modified , the first is it an inline 4 or 6 or a V-8, the reason being it has to do with crankcase volume , second normally aspriated or boosted or other LOL.The way the system is working right now seems about right for most of the electric pumps that are available out there,they really dont have the CFM volume to keep up with the ring leakage that you would have in a production engine , on a small cubic inch comp eliminator they work ok but really leave alot on the table. Post some more info or drop me an e-mail and I can be more specific on the info for you.

It sounds like you have achieved an equilibrium with the blow-by from the rings; possibly also from the valve stems/guides. The last post has a good point about the number of cfm your pumps are capable of pulling. Try using a larger, better pump at least to find the leak source -- most of the industrial vacuum pumps that I have used would easily pull 25" or better.

When you are looking for leaks with soapy water how are you able to check the valve stems/guides? That would be an internal loss on a running engine.


Any of you have experience with vacuum pumps on your engine? I have one SSB electric pump on my car, and all I can pull is 9in of vacuum at idle / 5in at WOT.
I tried TWO of those pumps hooked to the engine today, and got the same readings as with one pmp(!). 9-10" at idle, 5-6 at WOT. I've pressurized the engine and tried to find leaks with soapy spray water, but.. not a bubble.
The OEM crank seal arrangement is such that they can be removed horizontally from either end of the crank. I don't know if there's any outer lip on the seal, but if there was that wouldn't lose seal due to vacuum sucking IN on the seal's lip. And if you can change them from the outside horizontally with a tool that is just a puller, then there shouldn't be a lip on the inside of the seals that deforms with vacuum. I'm just posting in case there's an obvious place to look for a leak that I'm missing...
The mains ARE cross-bolted, and there's no gasket of any kind for the cross-bolts, just metal-metal contact.
I think the cross-bolts are likely suspects myself and will try to coat the heads of the cross bolts with something as they sit in place on the block.
Any ideas where the leak might be other than just up past the OEM rings ?

Thanks for the replies!
The pump CFM issue is a valid point, but you'd think hooking up two electric pumps as I did would have covered that base adequately.
HP, I have been told that the size of the engine/crankcase volume makes a difference. Even when using mechanical pumps.
I'll just say that the crankcase volume is as large as you'll find, and certainly contributing to the problem.
The crossbolts don't use any sealant or gaskets so I've gotta believe that even the closely machined fit between the main caps and block that stops oil from leaking out isn't enough to stand up to high vacuum. SOME air must be sneaking in here and there past the crossbolts.
Other than sealing the crossbolt heads to the block with silicone, I'll just have to be content with what I'm getting I guess. How much more HP is there above 7in of vacuum or so(?), is the other side of the coin. That's still a serious emptiness going on inside the crankcase. So, for $250 and the option to turn it off and on at will, that's a pretty good HP bargain.
The car's not a dedicated drag race car, just something I do now and then. I'm always looking for an edge against the competition.
If I ever pull the engine apart I'll take a look at some other areas.
I like the on/off convenience of an electric pump. It's still a puzzle why 2 pumps didn't really do any better than one pump, and kind of indicates that I need to find my leak before even a monster Moroso pump would help.
I did find one aftermarket vacuum cap I'd added that had a pinhole leak in it(!). Though replacing it with a good one didn't give me much more than 1 extra inch of vacuum at most.
Anyway, thanks for the interest! I'm anxious to get to the strip next year and see how the car runs with the pump.

Thanks for the replies!
... So, for $250 and the option to turn it off and on at will, that's a pretty good HP bargain...

First, you should feel lucky to be able to pull that much from an electric pump. Those racers I know which use them, can only get 3" at any time. As for your vacuum goal, you really don't want to run more than 16" of vacuum. You start to run into oiling problems at the top end of the 1/4.

Next, you can't turn off a vacuum pump on a motor which is sealed up for its' use. Where do you think all that pressure goes when the pump is off? Through your gaskets maybe?

Lastly, all of those racers I know who ran the electric pumps, now use mechanical pumps. Does that tell you anything?

Mark

Well thanks. I'll just have to do the best with what I can get from it. I've already been able to turn it on and off using a valve similar to what racers use in pan-evac systems. That valve closes under vacuum but allows venting of the valve cover when the pump is off. I want to do it better than that, so I'll add something like a nitrous solenoid or two to allow me to turn on the pump AND close off atmospheric venting at the same time.
If I were racing only I might consider a mechanical pump. But I've seen some tests where unless you were using the biggest pump available, the vacuum still wasn't pver 10in. Thanks

what's the benefit of a vacuum pump?

.... But I've seen some tests where unless you were using the biggest pump available, the vacuum still wasn't pver 10in. Thanks

DynodDon,

I run an Aerospace Components 3 vane pump. I have some friends that work at Aerospace and after a year of street driving and racing I brought it in and had it tested. It pulled over 14" @6000 rpm. They also sell a 4 vane pump. I know of four people who run them on the street and they all have no problems.

MustangRoadRacer,

Where do I start at how they help? Mainly they give you more HP by helping the ring seal. Also, you will never have an oil leak again. There are many articals out on the topic.

Mark