I modified my 80 T-bird 5.0 engine wise and with the changes (such as a bigger cam and Edelbrock RPM Airgap intake) I noticed my vacuum is quite low at an idle. Around 11" when the engine is warm.
I think it should be at least 13" at idle or ideally about 16" for good power brakes. I can't find any vacuum leaks and now wondering ...could my loss of vacuum be caused by my vacuum controlled headlamps?
While the car runs the headlamp door will stay open just fine. However when I disconnect the battery (such as storing it over the winter or working on it a few days) and let the car sit a few days, the headlamp doors will open up.
Is that indicating that there is a leak, or is it normal for most vacuum controlled headlamp door to open up after a couple of days?
The 79 I had would keep them closed for about a week, I'd call it normal for them to creep open. Has nothing to do with the battery bring disconnected or not since they are controlled by a valve in the headlight switch.
Thanks for the reply. Your totally right, I could had left that reference to unhooking the battery out. I must have been trying to hard to think this out and yea, it had nothing to do with it.
But mine headlamps are the same way, maybe about 6 days and they will open up.
The cam is the likely cause of low vacuum at idle. Aggressive cam designs do not make vacuum at idle due to extra time when both the intake and exhaust valves are both open at the same time.
I guess it could be cam alone. The thing is I expected my cam to drop my vacuum some... only its not a super crazy set up. I didn't think I'd be seeing only around 11" at idle in gear.
I have put maybe 200 miles on my 80 in the 6 or 7 years ive had it and the headlight doors stay shut while it sits. I would guess you have a small vac leak
You can install an electric vacuum pump. Done finished fixed case closed plenty of vacuum and all is good in the world
I thought about one of those vacuum pumps that companies like Summit and Jegs sells. Various companies put their name on it such as COMP Cams etc, but I read that they don't work quite as well as most guys had hoped for. That sort sells for between $200-$300 bucks.
I read they are pretty noisy ...but I'm not so worried about them being loud, since my engine with headers is very loud anyway and will likely drown out the pump running. The main concern is reading about how they often keep running and wont shut off or other problems associated with the relay valve. These all seem to be made in China and are kinda pr0ne to quality control issues. At least this is what I have been reading. Some seem to get better reviews up around the $300 price range.
Better ones are more around $440 from Summit Racing but that's way about budget for me.
I wish I could get more info on how some guys use pumps off "Buick Diesels" I might be wrong about that... (maybe I mean to say mid 80's diesel ford escort) or ones off VW Passat's. I found some info on those sort of set up online and they can be found for under $50 used. I just wish there were some good info that went into a little more detail such as the actual pumps to find, parts needed, etc.
Those diesel units have no volume because they are so small. You can install a juice can supplimental vacuum can. moroseo makes them. They store engine vacuum at a high level when deaccellerating and work fairly nice. Otherwise you need a pump. I have used electric pumps and they work fairly well. But NOISY.
Thanks for letting me know about the diesel pumps. I wont waste time trying to go that route then. I think I'm going to just add a decent electric pump ...and like you said earlier... be done with it. Maybe a vac can too, just for good measure. I think about all the money spent and it only makes sense to have good brakes as priority number one.
What cam are you running? Unless it's a huge cam with stock heads you should be making more than 11" of vacuum at idle. The cam in my Thunderbird (Comp Magnum 266HR duration @.050 210 intake/215 exhaust, lift .533 intake, .533 exhaust) makes 16.5"-17" of vacuum with much bigger than stock heads.
I used a set of 289 heads off a late 60's truck, to bump up compression to almost 9.5
I ported and polished them but nothing that should be causing issues. Here are the cam specs:
Cam Style: Hydraulic flat tappet
Basic Operating RPM Range: 1,800-5,500
Intake Duration at 050 inch Lift: 218
Exhaust Duration at 050 inch Lift: 228
Duration at 050 inch Lift: 218 int./228 exh.
Advertised Intake Duration: 278
Advertised Exhaust Duration: 290
Advertised Duration: 278 int./290 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.471 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.471 in.
Valve Lift with Factory Rocker Arm Ratio: 0.471 int./0.471 exh.
Lobe Separation (degrees): 114
Camshaft Manufacturers Description: Fair idle, low midrange torque/horsepower. Works best with 9:1 and higher compression, gearing, and 2,000+ stall. Largest cam with stock converter.
http://www.summitracing.com/parts/sum-3601/overview/make/ford
(Just a side note: I still have the stock torque converter in it but will be swapping to a TCI Breakaway2,400 stall speed, when I get to it. Its been sitting in my garage for a long time.
I only mention this because I found a reference to having vacuum issues if you run a sock converter with a warmed up cam, yet I can't see how that makes an impact on vacuum.)
Looking at those cam specs you should have around 15-16 inches of vacuum at idle. It's not so radical that you only have 11 inches at idle. Do you have any vacuum leaks anywhere else in the system? A brake booster leak can be big. The easiest way to find out if you have a leak somewhere is to block off all the vacuum ports at idle and get a reading.
At 114 you should have more vacuum than you are getting. That cam is mild
Wow, I was expecting a much bigger cam, given the problem you seem to have... Has your power brake booster been replaced? Could the booster be leaking?
I'm pretty sure the booster is alright. I bought this booster used this summer out of an 87-93 Mustang 5.0... replacing my leaking 1980 booster.
I also upgraded my master cylinder to an new aluminum cylinder w/1” bore from a Lincoln Towncar.
When I installed the Mustang booster, I went through all the recommended ways of testing it that I was aware of, (holding pedal down and shutting the engine off and stuff like that) and it all seemed just right.
Maybe I need to go back over testing procedures again.
Do these headlight covers have springs pulling them open and vacuum pulling them shut?
Uhhh.... I'm not quite sure. I seem to recall seeing springs attached to the doors and I know they work off vacuum but as far as how they open and close, I'm unsure.
I just went out to the car and warned it up to 180 degrees, then used a special tool I have to crimp each of the vacuum lines, one at a time.
1. I crimped the port coming off the front drivers side on my Edelbrock carburetor, right past the vacuum gauge connection (this hose line feeds my vac operated headlamps). I have a mechanical advance MSD distributor, so I don't use the carb port that would be hooked up for vac advance. The unused port is capped off. The vacuum remained about 11 inches when in drive.
2. I next squeezed off the vac line that comes off the rear of my Edelbrock RPM Airgap manifold. This runs to my vacuum can for the headlights and splits off to my C4 transmission's modulator. The vacuum remained about 11 inches when in drive.
3. I crimped the main vac line going into the brake booster. It comes from the back of the carb...still no change.
4. I finally sprayed nearly 1/2 can of starter spray around my carbs base, all around the plastic spacer that I'm using between the cab and manifold and around all the intake runners and the engine didn't surge one bit.
Just to see...I sprayed a little into the air cleaner and heard an immediate difference, so I'm very certain I don't have any leaks.
Usually you check the engine vacuum with the engine idling hot in park, not drive. My idle RPM is about 580rpm in drive, 120rpm lower than the idle in park (700rpm). That results in a reading 1-2 inches lower than the reading in park (16.5-17 in park, 15.5-16 in drive).
I always thought it was done in drive, so perhaps I should have kept it in park.
However, in park and heated up, with an idle of just under 900rpm, my vacuum gauge is reading about 13.5" .... and between 11" and 11.5" in drive at about 675rpm.
That still seems about 1.5 inches low, at least.
Maybe I need to pull the valve covers and go over setting valve lash. I read if they are set too tight, that will result in low engine vacuum, however I did recheck them this past summer (when I replaced leaking valve covers) and despite some slight adjustments, they all seemed set properly.
I'm using Comp Cams magnum steel roller tip rockers and locks...maybe I should just go through them once again for piece of mind.
As long as your rockers are adjusted at around 1/2 turn past zero lash (if using stud mounts) you should be good on that front.
I haven't given up on this situation, only its currently about 18 degrees outside and snowing at the moment. I think this will be a spring weather project....If I only had room in my garage.
It's -1* here right now. 18* is plenty warm to do work ;).