I bought a recently rebuilt used engine for my 62. Guy told me it had a mild cam, but after installing the engine I only have about 10" of vacuum and therefore have the dreaded hard pedal syndrome. I installed a vacuum canister and it helped but not where I want it to be. The other problem is the stock torque converter in the COM and theres really no option to have a stall without a custom one or swapping transmission (I do plan on a 4r70w soon). Because of all this I've even considered going to manual brakes... Unfortunately I dont know the build details of this engine. I did do a compression test and got about 130psi per cyl. I know the heads are C8aeh and it has an Edelbrock performer intake. Im now considering going back to an oe cam. Need a little help in diagnosing the problem (vacuum leak?) and some suggestions.
I would consider doing a leak-down test, as 130 is a weak number. 10" of vacuum is also low vac for a "mild" cam. It sounds like it's running lame. Was the vacuum steady? Was the engine warm, and throttle wired open for the comp test?
If you don't have a leak-down tester (cheap and easy to make though), then add a couple pumps (couple teaspoons) of oil from an oiling can to the cylinder being tested and comp test again. If the test is markedly better, you have a ring issue. If not, you may have a valve issue. A leak-down will tell you about the innards.
I agree, however, on the other hand, if the chain was very badly worn, or the guy used a multiple position chain and installed a decent cam late, that would do it too.
Sure, but I was hitting the easy stuff first, that initial testing would also dictate if those were directions to go. The vacuum gauge diagnostics alone should reveal incorrect or late cam timing if it's a factor. Leak-down would reinforce that.
:tup:
David
Engine was warmed up when doing compression test but I only held the throttle open one time to see if I got a higher reading and it didn't make a difference. I will retest it and get my hands on a leak down tester also. What is a good compression reading? Don't think there's any used parts on this motor, it came with a nice custom oil pain (rear sump), previous owner definitely didn't skimp out but then again I'm not 100% sure.
I redid the compression test and made sure the throttle was WOT and engine warmed. Heres what I got:
Cyl 1 – 150 psi
Cyl 2- 130 psi
Cyl 3 – 145 psi
Cyl 4 – 130 psi
Cyl 5 – 150 psi
Cyl 6 – 150 pis
Cyl 7 – 150 psi
Cyl 8 – 142 psi
I have atleast 2 cylinders on the same bank that are 20 psi low, I managed to borrow a friends Snap on leak down tester and will do a leak down test here shortly. Do I need to have the engine at running temp just as the comp test? If the problem is in the valves, I have my original 62 390 complete engine that I can use the heads off of, would those be a good alternative to the C8aeh heads Im currently running?
I havent done the leak down test yet but did check the vacuum again and have a video showing the bouncy vacuum. Im thinking I have either a decent vacuum leak of the cam isnt upto par. The 20 psi in those two cylinders doesnt seem that bad too me.... http://vid301.photobucket.com/album...trim.F0A9F514-AF61-4C00-8204-B1DE5D383790.mp4
That cam sure doesn't sound too rowdy, matter of fact it sounds real nice
Some questions for the brake issue
- What do you have your initial timing at? Also, is the distributor recurved? A little more initial can bring vacuum up and on top of that, having a stock distributor recurved can make a HECK of a difference part throttle for drivability and power to boot
- Do you know that the booster isn't bad? I only bring it up because my 71 F100 needs a booster rebuild, it works, just not as well as it could
I personally would not swap the cam though, especially to stock, you may end up with something unhappy on fuel. What I might do though, is advance the cam, but it takes some care, checking clearances, etc, but if you degree it, and we know your basic setup, you could end up with a bit more vacuum and low end power to boot. (Depending where you are know)
Vacuum diagnostic is indicating retarded ignition or late valve timing, but needs a couple more inputs. See vacuum diagnostic references here. Both the theory articles and the linked video simulator are helpful.
Im leaning forwards valve timing or a vacuum leak. My initial timing is at 16 degrees in that vid and about 38 total. I'll try it at 20 initial and see where vacuum goes. If we're talking valve timing, is that being off a tooth or possibly an adjustable timing chain thats off?
Without knowing what the cam is, it can be a few things.
- Worn timing chain and gear - effectively retarding the cam, doesn't seem it to me, the engine sounds pretty good
- A cam with late intake centerline (FYI Fords of yesteryear used to retard the cams as late as 114 ICL, most modern cams are 104-108)
- A cam that was installed retarded to get more top end
- A cam that was not degreed and just ended up late due to tolerance stack
It would be real nice to know what cam was in it now, because it is possible that advancing the cam 4 degrees makes all the difference in the world, but it'd be a guess without knowing
At 16 BTDC I don't think 20 will get you much.
Have you tried adjusting the a/f mixture, but even that will only get you 1-2 inches
Youre saying to get rid of the caninster?
I set the AF with the vacuum gauge and the 10-11" of vacuum was the best I could get. Besides checking the carb gasket with carb spray, what can I do to check the intake manifold for leaks? How tough is replacing the intake manifold gasket? I may just do it for peace of mind. Also I've never checked the valve clearance, thinking it might be time.
Are you able to degree a cam? It would be the best information you could have. You'd know what the cam is and where it was indexed, it'd likely give you enough information to explain why and what to do next
Of course if you like the way the car runs, you could also put an electric pump to help it or go manual brakes
As I said, I'd be amazed if you have a vacuum leak.
If interested, buying a degree kit, and learning how to use it, may save you the purchase of another cam. Worst case, it allows you to make sire the next cam is what you think it is, and installed correctly, so no loss other than effort.
Now, I will say though, if there is any way the previous owner or builder can tell you what's in it now for a cam and/or if it was degreed, we might be able to just recommend advancing it, how much determines on what cam it is, and where it is now.
Canisters have their place, as anyone who owned a 1953 Buick with vacuum operated windshield wipers will attest. When you stepped on the gas, eliminating vacuum, the wipers nearly stopped! I think the canister was invented shortly after, to handle accessories.
It was not designed to provide vacuum to power brakes, however. Those boosters use the vissitudes of intake vacuum to work properly, which is why my 1965 booster takes vacuum from the intake instead of the canister. Nor will a canister work for modulating automatic transmission. It also does not work to power a vacuum gauge, something I discovered myself, when my self-installed gauge kept reading 17" no matter what the engine was doing, check valve or not.
This is my thinking on the matter, there is a place for vacuum canisters but serving these 1960 era boosters is not a one of them. I might have missed something though, I have before!
something I discovered myself, when my self-installed gauge kept reading 17" no matter what the engine was doing, check valve or not.
This is my thinking on the matter, there is a place for vacuum canisters but serving these 1960 era boosters is not a one of them. I might have missed something though, I have before!
I have only used one vacuum canister and it was from Comp Cams I believe, been a while. It was on a 55 Chevy with a 600 hp solid roller 462 inch Rat. It absolutely helped the power brakes, it's the only time I have tried one though
Again though, need to be sure that the booster isn't bad too, wouldn't be the first time
Ok I got a chance to do a leak down test on cylinders 1-4 and theres virtually no leaks! I heard a little air coming out of the dip stick tube and some coming out of the front of the engine, close to the distributor, actually there was a little air coming out of the distributor shaft, it wasnt completely tightened but nothing out of the exhaust or carb. Heres a pic of what the test revealed. I think the bottom end and heads are in good shape, with valve covers off, everything looks like new.
I bumped the timing up to 20 degrees initial and it does seem to have more power and didnt notice any pinging. Can I keep upping the timing as long as theres no pinging/detonation?
If I were you, I would map the curve and see where you are. Nothing wrong with 20 initial, but if it is a stock distributor, it could add a lot more timing and do it at high RPM, which could cause some damage
If it runs well with 20, Measure the distance from 10 to 20, and mark 30 and 40. Then break out the timing light and go up in 250-500 rpm increments and read your timing with the vacuum advance disconnected If you have a dial back light it's even easier. As long when it stops advancing, you are 38-40 degrees or less, it''' likely be happy. If it advances past that, you should probably go inside the distributor and limit total
The two reasons to map it all the way up is that you likely have more power in that motor if the curve is slow and you want to make sure you know how much total you are getting. Stock distributors are slow, but give too much total, so you lose power on the street AND add danger LOL
Another thing you could consider is to check your balancer, and likely do this first. Make a piston stop through the #1 spark plug, turn by hand until it hits, mark the balancer, then turn the other way and mark it. Measure 1/2 way between the two marks, that is the real TDC, see how close it is to the TDC mark on the balancer. If it is off, you could have a mismatched balancer/pointer combo or a spun balancer, which would make all the timing settings inaccurate.
Then go back and map the curve and see where you are
Thanks Stang. It is a stock distributor but with a Petronix 1. I will check the curve and TDC on the balancer with a piston stop. I did use my original 62 crank pulley because the newer three groove wouldnt line up with my power steering pump. I have checked for TDC with a screw driver and its pretty much spot on. Also what do you mean by measuring between 10 and 20, 30 and so on? Measure on the balancer? Mine only has one mark, its a circle that I put some whiteout on it to make it visible but no actual degree marks.
If it only has TDC on it, then measuring is a bit tougher. I assumed it had the standard 0 - 20 or so that the 70s balancers have.
Might be best to put a timing tape on it after you verify TDC
As far as a stock distributor with Pertronix, you can assume that going inside will help immensely. In fact if you may just want to pull it apart and dig in.
- If its an early distributor, look at JC's posts about his distributor tuning
- If its a 70s distributor, see here
(Psig Quote)Note the trapped canister vacuum is never greater than the peak manifold vacuum, but holds it, and so can be higher (relatively) if manifold vacuum changes.
correct .. I just didn't spell it out.....
Puttster ...
think of it as having 2 air compressors charged to 120 Psi , then unplugged..
one having 5 gallon tank other being 20 gallon tank...
which one will run out of air First and which will sustain higher pressure longer???
Checked timing at different rpm's and I got a total of 40 degrees but its all in at around 2800, kind of quick dont ya think? I'm going to order a piston stop and make sure my timing is correct. The guy I bought the engine from said it came out of a mid 60's truck with an AOD.
2800 isn't quick, it's good, or even slow by some standards. However, for a full size car it's about right, as is the 40 degrees.
If you are concerned, most iron head chambers and standard quench distances like 38-40 on an FE, so you could pull 2 degrees of initial out of it if it pings, but you are likely in a good place if it doesn't and it'll likely steal even more vacuum
My hunch is still, if your brake booster is functioning properly and you don't have the booster vacuum shared off the PCV, then you likely could advance the cam 4 degrees to get more vacuum. However, I'd be leery to do it without cam info, because two things could happen.
1 - You leave some on the table. For example: If it's a 114 LSA cam on 108 and you go to 104, you might even be able to go farther
2 - You get too close to the intake valve hitting For example: If its a 108 LSA cam on 104 and you go to 100
I have regularly seen cams as far forward as 102 in an FE, and it does make a significant difference in vacuum, torque and idle, but to do so blindly would likely be a mistake
Thanks Stang, I will have to drive her as is for now and some time in the future plan on degreeing the cam. In the mean time Im going to focus on getting disc brakes on the front.
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