Is 10" of vacuum in crankcase normal?

starchiefus · Dec 27, 2007

Hi Guys.
I have 10" of vacuum in the crankcase measured through the dipstick tube and when i remove the oil fill breather the engine will stumble and die.

I have 16" of vacuum in the manifold, I'm getting ready to remove the carb and valve covers to check the gaskets, and maybe the manifold, already replaced the pcv valve and also the oil fill breather-open type. just wondering can the engine have an internal leak somewhere?

Engine is a recent 289 rebuild with a 302 rotating assembly, using 86 e6se heads and an 84gt manifold making up the core engine parts, along with a 62 4100 600cfm carb.

Also a little off topic, but once i get the leak fixed is the 4100 a good carb to use or should i go to a smaller carb like the holley 390cfm(the cam is a mild one-crower#15206) for improved throttle response and mileage etc.

Thanks/Steve.

D.Hearne · Dec 28, 2007

You really restricted the engine with those heads and intake and cam. You might have the exhaust crossover rotted thru in the intake. You may as well go smaller too on the carb, as that 600 cfm Autolite is more than too big with your build.

starchiefus · Dec 28, 2007

But the engine should be fine as a daily driver/cruiser right? I used those heads because i wanted to lower the compression so as to use 87octane gas and liked the simplicity of the pedestal rockers, same with the cam wanted good idle and vacuum, the engine will rarely see over 4000rpm.

I will check the the crossover under the manifold, If it is rotted and i need to replace it do any of the basic level edlelbrocks, wieands etc offer any improvement over stock? I have the original 67 4brrl manifold still, just used the 84 because it was aluminum.

Thanks again for info and advice.

65ShelbyClone · Dec 28, 2007

Yeah, it should be a good driver, especially with a smaller carb. If you need to replace the intake, an Edelbrock Performer is like an aluminum version of a stock 4v manifold. The Weiand Stealth is also widely regarded as an excellent dual plane intake, but it will cost more than the Edelbrock which can usually be ordered by the average parts store.

As for the high crankcase vacuum, Do you have a PCV system and valve hooked up or a breather cap connected to manifold vacuum?

D.Hearne · Dec 28, 2007

In Weiand's brand, the intake you'd want with that build would be an Action Plus, not the Stealth. The Stealth is damn near identical to the Edelbrock RPM. Ford Racing also markets the Performer and RPM in their own name. That iron intake would also be a good choice, it's just about 20 lbs heavier.

Scott Amann · Dec 29, 2007

Curious

What IS an average manifold vaccuum for a 289?

Cobain03 · Dec 29, 2007

do you have power brakes?

D.Hearne · Dec 29, 2007

There is no average. You don't have a 289 any longer anyway, it's now a 302. Yours should be higher than what would be average, with the parts combo you have.

Scott Amann · Dec 29, 2007

Sorry to confuse the current thread - maybe I should have started a new one?
Stock 289, 2v, no power brakes. What should vacuum be pulling?

starchiefus · Dec 29, 2007

Yes I've replaced the pcv valve,hose and breather and yes i do have power brakes, but I disconnected them and plugged the manifold so as to remove as many of the external vacuum hookups as i could.

Out of interest i completly removed the pcv valve and replaced it with a regular breather (open type) the vacuum dropped to about 6" in the crankcase but when i removed the vac gauge from the dipstick tube the engine stumbled and died.

Will try and pull the manifold later today or tomorrow and check it out.

I've checked up on the two manifolds recommended as replacements Action Plus and Stealth both spec from idle up to their respective top rpms one low rise and one high rise, now i have to use a 1" spacer for my AOD tv linkage to clear the centre runners would the stealth still be ok for me to use on my mild combo? so i wouldn't have to use the spacer because its a high rise manifold and gives me the linkage clearance i need or am i still better of using the Action Plus with a 4 hole spacer?

Thanks again for the helpful advice and suggestions.

65ShelbyClone · Dec 29, 2007

Something that just came to mind is a leaky intake gasket drawing air from the lifter valley. Usually it's accompanied by noticeable oil consumption and/or smoking, but it's a possibility.

If you need extra space between the carb and manifold to fit the TV cable parts, you'll probably have to keep the spacer with either intake manifold. A high rise moves the carb and runners up higher.

D.Hearne · Dec 29, 2007

Just from looking at pics of both, you'll need the spacer with either one. Summit's pics of the Action Plus show a Stealth intake. The Action Plus actually looks identical to a Performer and the stock 4 bbl intakes.

jbuening · Jan 2, 2008

Is the vacuum needle constant or does it fluctuate a lot? Keep in mind that the PCV valve acts like a vacuum leak, how much it drops the crankcase readings I'm not sure. I do think the 16" hg manifold vacuum is a bit low, but this depends on what you are idling at.

starchiefus · Jan 3, 2008

needle does not fluctuate on intake or dipstick tube, idles smoothly at around 900rpm, removed old intake last night but unfortunately the intake gaskets ripped so i could not check how well they were sealing, the cork end gaskets looked ok though.

I received the new manifold today and will install per instructions using a bead of silicon sealer instead of the cork gaskets, does that sound right? Might get it all installed this weekend if everything goes well. will update if i do.

Thanks.

D.Hearne · Jan 3, 2008

Before deciding on whether or not to use the end gaskets, set the new intake down onto the new gaskets (don't bolt it down, just set it in place) and look at the gap under the ends, if it's larger than the end gaskets, a bead of RTV isn't going to seal any better. Check the fit with the head side gaskets too.

jbuening · Jan 4, 2008

I threw away the end cork gaskets and used a large bead of silicone. Be sure to get enough in the corners as well, as this is a common place for them to leak. Definitely sit the intake on before using silicone to see how large the gap is.

bnickel · Jan 4, 2008

i see one small problem here that no one else seems to have cought. you say you're running a pcv valve AND an open crankcase breather/oil fill cap. you can't do that, that cap needs to be closed to atmosphere, otherwise you're just sucking air through it, effectively creating an open vacuum leak. vacuum in the crankcase isn't a bad thing as it helps the rings seal, that is what the pcv valve does, but if the other end of the system, the crankcase breather, is open to atmosphere it won't function correctly. just FYI.

if you have the stock closed air cleaner still you can use an oil fill cap that has a hose that goes to the air cleaner and most aftermarket air cleaners have a provision for the crankcase hose from the filler cap as well, you need to run one of those as well, but whatever you do you need to get rid of the open breather cap if you're running the pcv valve.

you didn't say whether or not you're running headers or manifolds but if you're running the stock manifolds you should really consider switching to a set of GT 40-P heads instead of the e6 heads....the e6 heads suck bad, the absolute worst head ford ever made!!!!!!! the P head isn't the greatest performance head but for a basically stock engine like yours it's probably one of the best heads there is, especially if you're on a budget.

hope that helps you out some with your problems.

BTW, 16 inches of Hg at idle isn't bad depending on what cam you have.

jbuening · Jan 4, 2008

b, I'm not so sure about that. The stock system uses a PCV valve on the passenger valve cover and the oil filler on the drivers side valve cover. The oil filler still has the the tube that goes to the air cleaner to recirculate unburned fuel gases. This is basically an enclosed filter that uses steel mesh (people often use coarse steel wool in restos). It still creates a large vacuum leak like an open filter unit. I'm running a PCV on passenger and an open on the drivers side with no ill effects. AFAIK, numerous people run theirs the same way.

bnickel · Jan 5, 2008

jbuening said:
b, I'm not so sure about that. The stock system uses a PCV valve on the passenger valve cover and the oil filler on the drivers side valve cover. The oil filler still has the the tube that goes to the air cleaner to recirculate unburned fuel gases. This is basically an enclosed filter that uses steel mesh (people often use coarse steel wool in restos). It still creates a large vacuum leak like an open filter unit. I'm running a PCV on passenger and an open on the drivers side with no ill effects. AFAIK, numerous people run theirs the same way.

the stock system is still closed to atmosphere though. even the hi-po 289's had a tube that ran to the bottom of the air filter, still providing a system that was closed to atmosphere.

i'm very aware that a lot of people run their systems similarly, as a matter of fact mine is pretty much the same way right now too, even though i have the stock air cleaner base and the stock oil filler with the tube running to the air cleaner base, but i have a hi-po lid on the air cleaner so the tube on mine is pretty much open to atmosphere as well. i've been meaning to fix that on mine but keep forgetting about it.

the point is that for the PCV system to function "as designed" the system needs to be closed.

also, did you know that you can "tune" an engine with different pcv valves? in some cases you could see as much as 10hp just by swapping pcv valves around. it's true.

i still think he may some sort ov vacuum leak, but it's worth checking the pcv system. his valve could be stuck open all the time or opening more than it should at idle anyway.

D.Hearne · Jan 5, 2008

You're wrong Bnickel. I run my PCV systems all the time with an open cap. Never was a problem. The PCV valve itself is the check valve for the vacuum leak. The setup on my Ranger is different from any other, the valve covers have two holes each. I run a PCV valve in each in the front hole and the two rears are run to a "T" and the fresh air is drawn thru one of those "ricer" style vavle cover filter caps ( these are sold in the ricer section at the local Advance Auto Parts) The cap/filter is hidden behind the carb. The PCV's are also run to a "T", then into the carb base.

Is 10" of vacuum in crankcase normal?

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