Camshafts, vacuum and power brakes

[ladenedge]

Hello. First time poster, long time lurker..

I just bought a new power brake setup from Tom's. Unfortunately, it looks like my camshaft might be a little too big to supply enough vacuum: I'm reading about 8-10 at the booster (Tom's recommends 18+ at the booster).

I want to keep the PB setup if I can rather than going back to a manual.. so I put the Bronco in the shop today for a tune-up, hoping that the timing was off (8 seems pretty dang low to me). So, questions:

• is there such a thing as an electric vacuum booster?
• how good are vacuum reserve canisters (eg. this one)?
• I've heard that vacuum assists (of some sort) can "retard the engine" - how is this possible, and what does this mean?
• any other ideas?

Thank you all very much for any help!

P.S. Does anyone know of a good page that talks about what one can learn by looking at a vacuum gauge?

 

[daddyg]

What cam are you running? I have a edelbrock performer, but I have ran it with my power brakes yet. It's still on jack stands in my shop. I would consider hydroboost if you can't get enough vacuum. I should be cheaper than any of the solutions you mentioned plus it supposedly stops alot better than vacuum powered brakes. There are several threads on here discussing it. Just do a search.

 

[TOFIC]

This problem is dirt common in your set of conditions. No real cure.
Another area that has the same problem, slow turning diesels, as they do not develop enough vacuum to activate the vacuum cylinder.
there is only one cure
Hydroboost.

Sorry to say this, and I am not pushing this because I know it, what you are experiencing is why I started looking at hydroboost.

TOFIC

 

[Steve]

is there such a thing as an electric vacuum booster?

I suppose you could install an electric or belt driven vacuum pump, but that's expensive.

how good are vacuum reserve canisters (eg. this one)?

They're fine, and most newer cars have a vacuum canister somewhere on them. However, that won't solve your problem. If your engine only gets 8" of vacuum that's all you'll get with or without a canister.

I've heard that vacuum assists (of some sort) can "retard the engine" - how is this possible, and what does this mean?

Actually, depending on how you installed and plumbed it, and your distributor, it should advance it, not retard it. That's only true if you have a vacuum advance distributor. If not, it would have no effect on engine timing.

any other ideas?

Hydro-boost brakes.

 

[mtkawboy]

On my 68 Z/28 stock eliminator drag car i put a plug in the line to the booster and experimented with different size holes in it until they worked decent. Start small and work up. May sound stupid but it worked. Worth a try, dont cost anything

 

[ladenedge]

Well, I do have power steering already, so maybe hydroboost wouldn't be too difficult. I also found some electric vacuum pumps, but they run about $300, apparently. Seems like it might be better to return/sell the PB booster, skip the vacuum pump and put that money into hydroboost..

And in the meantime, try out that plug idea.. heh.

 

[broncnaz]

Really sounds like your cam is to big what grind is it? If your engine is stock then you have bigger problems than brakes. You may want to consider swapping the cam out unless its really suited for your needs which a cam that big in a bronco would lead me to believe that your doing some type of racing, If not there are better cam choices out there especailly for a street driven bronco. I run a decent sized cam and have a single plane manifold and still pull 16in hg at idle. Timing does effect vacuum but I dont think you'll gain 8-10 in hg even when its turned up to about 12 degrees. Your best option is probably Hydro boost if your going to keep that cam. I wouldnt really waste the money on an electric pump and I doubt if you would be happy with a cannister

 

[ken75ranger]

Summit carries electric vaccum boosters. If you feel like yard scrounging almost all Ford PSD have them to run the a/c controls

 

[grs44310]

What is the limit on cam grind before you start dropping vacuum to a level that won't make the brake function properly? I'm getting ready to rebuild my engine and I'm not sure what cam to go with but I want it to be a runner on the street and still be able to climb some dunes and blast some mud.

 

[76Broncofromhell]

I'm at 298/308 duration at .530 lift and I get about 10 inches of vacuum. It all depends on your heads, manifold and cam grind. It hauls ass but doesn't exactly idle as smoothly as a stock engine.

I'd say once you get over 265 duration your vacuum goes to hell. Add in some high-flowing heads and a mean intake and you have no vacuum under 1500 RPM.


I had the same problem with my vacuum boost, so I ditched it and went to hydroboost and never looked back. I did my whole conversion for under $200 and almost broke even when I sold the stock power brake unit.

 

[68ford]

freightliner uses electric vacum pump to run the blend doors and such on the heaters and a/c units. they only turn on when vacum drops below certain number of inches, it would work great for that little extra, im going to use one so my wipers will work going up a hill since i dont want to spend my life savings on a vacum fuel pump.

 

[SnwMnkys]

Advertised duration doesnt really mean anything since it varies from Manufacturer to manufacturer. You need to find out the Actual duration, and even then that sometimes doesnt matter. Its your Lobe Seperation angle that really effects vacuum.

 

[tabascom16]

I'm at 298/308 duration at .530 lift and I get about 10 inches of vacuum. It all depends on your heads, manifold and cam grind. It hauls ass but doesn't exactly idle as smoothly as a stock engine.

I'd say once you get over 265 duration your vacuum goes to hell. Add in some high-flowing heads and a mean intake and you have no vacuum under 1500 RPM.


I had the same problem with my vacuum boost, so I ditched it and went to hydroboost and never looked back. I did my whole conversion for under $200 and almost broke even when I sold the stock power brake unit.

Broncofromhell,
My dads bronco has a 304/314 solid lifter cam. Its nice to see someone else running a very large cam. Its a blast once you get it about 2500RPM and 4000 to 5000 RPM is no problem for a cam like this with plenty more torque to give out. Do you have problems with the plugs fouling?

 

[broncow72]

www.ssbrakes.com
They have the vacuum pump you are looking for. Not cheap though. I think for the price of the vacuum kit you can put together a hydroboost and sell your existing kit to someone more suited for a vacuum booster set up.

 

[broncnaz]

What is the limit on cam grind before you start dropping vacuum to a level that won't make the brake function properly? I'm getting ready to rebuild my engine and I'm not sure what cam to go with but I want it to be a runner on the street and still be able to climb some dunes and blast some mud.

Most of the RV/4x4 Grinds will still run your power brakes your best bet is to call the cam manufacturer and make sure the cam you want still runs your stock systems.
Most of the 4x4 cams will suit your needs just fine.

 

[76Broncofromhell]

Broncofromhell,
My dads bronco has a 304/314 solid lifter cam. Its nice to see someone else running a very large cam. Its a blast once you get it about 2500RPM and 4000 to 5000 RPM is no problem for a cam like this with plenty more torque to give out. Do you have problems with the plugs fouling?

No I don't have any plug fouling problems. I can lug the piss out this stroker and it keeps on kicking I'm running BF42C's in there. It sounds like he's over jetted or has too big of an accelerator pump if that happens that or he's running too cold of a plug. I'm running 79's in the front and 80's in the rear for jets.

 

[SeaBiscuit68]

Summit carries electric vaccum boosters. If you feel like yard scrounging almost all Ford PSD have them to run the a/c controls

Pardon, not feeling sharp at the moment, what's PSD?

 

[Steve]

Pardon, not feeling sharp at the moment, what's PSD?

PowerStroke Diesel.