I freshly built a 312 for my car. I have read the archives and cannot find info regarding the engine vacuum to cam advancing changes.



I tow a T@B trailer with the car. The trailer weight is 1500 lbs dry and 1900 fully loaded. The car has FMX hybrid transmission with 57 wagon Ford 9 inch with 3.25:1 gears. Power disc brakes Granada setup and 64 Ford wagon rear drums 2.5"X11"



I am looking at advancing the camshaft about 4 degrees to get better bottom end, engine is wild and will spin tires at each shift except start off.



The question I have is if I advance the camshaft for better bottom end torque how will this affect my vacuum for my power brakes? Do you think I should go less than 4 degrees as I can set it at 2 degrees on the Roll-master chain? Any other ideas?



I don't have a degree wheel however I have lots of dial indicators and used them to get TDC and valve over lap on #1 and #6

The dampener is new and right on for TDC. When the valves were in overlap I found it was advanced about 0.5 degrees on the dampener, engine vacuum is about 17" and compression 135# even across, valves setting at .017" cold



Details of engine below.

The engine is .030 over with flat top pistons, block decked to 20 thou above piston, heads milled 3 thou, (thickness still showing 1.00" on calibration blocks) engine set up to get about ~.040 piston to head clearance to run steel shim gaskets.

C1TE rods, aligned, shot peened, side polished, balanced big end/little end, re-sized, ARP bolts, new bushings,

ARP head bolts and ARP main studs

crankshaft .010/.010 Best gasket seal and all rotating assembly full balanced

camshaft is Isky E4 with new lifters and new 1.54:1 rockers and shafts, heavy push-rods and Rollmaster timing chain.

heads are ECZ-G with new stainless valves, hard seats, 105# valve springs and one piece retainers, no porting done,

wide back exhaust manifolds,

B intake manifold

C6PF Autolite 4100 carb 1.08 venturis

MSD distributor, coil and wires.



thanks

marv

I'm not sure how advancing the cam will affect vacuum.



17inhg should work fine. Do they not seem to be working right? Do you feel like you need more bottom end?


Lawrenceville, GA

I do not want to reduce the engine vacuum by changing the cam advance as 17" is just enough for the brakes to operate properly. Any decrease in vacuum and the brakes will be heavy to push.



When I hook onto the trailer the old 292 had better low end power, however once rolling this 312 is no comparison to the stock 292. I would like to get the power band lower to about ~2200-2500 rpm. Now it is about 2800-3000 rpm when the engine comes on strong. The torque converter is still the stock 62 cruise-o-matic solid case converter. I don't want to change that unless necessary

marv

marvh

   I will guess and it is only a guess that advancing the cam will give more vacuum. You can check by adjusting the valve lash tighter and looser and see what that does for you. Also I think your compression at 135 PSI is too low. I would expect 155/165 at least.

Marv:

I'm sure you already realize that you have too much cam for towing purposes, since you want to advance it.  Just think about the brake booster situation.  When you are using the brakes, the throttle is closed and the engine is revving.  Vacuum is highest then.  Cam position probably has no effect under those conditions.  As stated above, vacuum should improve slightly at idle with 4 degrees advance.

John - "The Hoosier Hurricane"

I think that cam should have the power start much lower. 2800 to 3000 almost makes me think its retarded, or maybe even the grind is incorrect. The compression pressure might also indicate that but it could also be that the rings haven't seated yet. Invest in a degree wheel.


Lawrenceville, GA

The brakes work good when traveling, actually effortlessly. When coming to a light and engine drops to an idle the pedal does get heavier.



John: that info on improving idle vacuum is what I was needing as it will give me a light brake pedal at an idle. I was afraid I might be going to a heavier pedal at idle.



When I picked this Isky E4 cam it was the mildest Isky cam and the closest to the original 57 cam I could find so should work if I advance it and lower the power band, as well, as others have said advancing will improve the compression. I don't want to go to that B8A replacement camshaft as they are pathetic.



With the info I have gotten I think I should be close. Looks like this weekend has a project.

thanks everyone, anymore comments is appreciated.

marv

Marv:

Is there a check valve in the vacuum hose connection at the booster?  I think there should be. If there is, and it is holding, then the booster may be losing vacuum internally while sitting at a light. 

John - "The Hoosier Hurricane"

Yes there is a check valve at the booster.



I have not pulled the hose off after running the engine to see if still holding. The booster is new however still can be at fault.

What rpm is the 17”Hg vacuum reading being taken?

 

To reitterate what John says, advancing the camshaft will increase the intake manifold vacuum at idle.  The torque band will also come in at a lower rpm but how much lower depends upon the amount of advance.  Stated in more detail, advancing the camshaft closes the exhaust valve earlier during the overlap cycle which minimizes an internal engine vacuum leak and provides a net gain to the overall vacuum readings.  Advancing the camshaft also closes the intake valve earlier after bottom dead center which increases cranking compression and this in turn increases the torque being produced by the engine.

 

As Pete mentions, your cranking compression readings are low for your particular combination.  Without degreeing in your camshaft with a degree wheel, it’s questionable exactly where your camshaft is installed but sounds like it’s on the retarded side now based on the compression readings.   Loosening up the lash to 0.022”-0.024” and rechecking manifold vacuum should give you an idea of how much more vacuum is available by advancing the camshaft.  I’ve experimented with as much as 0.025” lash on the E4 camshaft in my 272.  Loosening the valve lash reduces the amount of overlap between the intake and exhaust valves and basically reduces the amount of vacuum leak through the exhaust port at the expense of exhaust scavenging at higher rpms.  I have the Isky E4 in a 272 with 8.0:1 cr and it pumps out 155 psi cranking compression with ECG heads and that’s with the E4 camshaft installed at 104° intake lobe centerline (cam is ground on 108° lobe centers).  Your 312 should be pumping at least as much if everything else is equal.

Lorena, Texas (South of Waco)