Cam vs Vacuum Question

[73' mach 1]

I'm trying to decide on a cam for my 73. I'm a fan of a nice choppy idle and wanted to know how big I can go before I'd start to run into vacuum issues for my brakes. I'm aware that they make a vacuum module to help increase vacuum when needed but I'd rather not go that route. 

Now I would not want to sacrifice power for sound so I'm looking for a balance here. Here is some info for the rest of the setup. It's a 351C, flat top -3cc pistons, stock crank and rods, heads will be cleaned up with 2.07 and 1.65 valves, compression should between 9.5-10:1. The rest of the engine is 750 quick fuel slayer carb, blue thunder intake, TKO 600 trans and 3:89 gears. 

The car is will be a fun street cruiser so I would think I want a power band anywhere from 2K up. So again the question is at what point does cam size become an issue with our cars for braking. How big can I go to still make good power, have a nice choppy idle and be safe for vacuum. Thanks

 

[Don C]

I don't believe you will be able to get the idle you're looking for and still have functioning vacuum powered brakes. I believe that something in the 280° to 290° advertised duration range is as big as you can go and still have enough vacuum. That will give you a lopey idle but not that aggressive choppy idle you want.

Four possible solutions:

Manual brakes

Vacuum pump

Hydroboost power brakes - http://www.mustangandfords.com/how-to/wheels-tires/mdmp-1206-hydraulic-brake-assist-system-install/

Electric power brakes - http://www.mustangandfords.com/how-to/engine/mump-0905-electric-high-power-master-cylinder/

http://www.abspowerbrake.com/ehpm.html

Ford started using hydroboost brakes on Thunderbirds first and then on SN95 Fox body Mustangs and vans, so there are a lot of them around.

I don't know as much about salvage yard electric power brakes or if any can be used for swapping. I believe most are a combined system where the electric brake booster, the master cylinder, and ABS system are integrated.

 

[73' mach 1]

How safe are the vacuum pumps? I didn't know they used them on some cars from the factory. I guess I could live with lopey to be on the safe side. I wasn't really crazy about the idea of running the pump but if its just as safe I'd consider it.

 

[Don C]

Hella makes reasonably priced replacement vacuum pumps that should be very dependable

https://autoplicity.com/9491523-hella-724807080-vacuum-pump-sprinter?gclid=Cj0KEQjwqtjGBRD8yfi9h42H9YUBEiQAmki5OrPj-5xOTqOSQb104smntO4JndGtqKzqVmGJX2nHlIQaAt8p8P8HAQ

I believe most OEMs also use a vacuum reservoir and external switch, so if you want to go with OEM/salvage yard equipment you'll have to do some digging to make sure you have a complete system.

I don't have any experience with aftermarket vacuum pumps, so can't make any recommendations.

 

[73' mach 1]

Hella makes reasonably priced replacement vacuum pumps that should be very dependable

https://autoplicity.com/9491523-hella-724807080-vacuum-pump-sprinter?gclid=Cj0KEQjwqtjGBRD8yfi9h42H9YUBEiQAmki5OrPj-5xOTqOSQb104smntO4JndGtqKzqVmGJX2nHlIQaAt8p8P8HAQ

I believe most OEMs also use a vacuum reservoir and external switch, so if you want to go with OEM/salvage yard equipment you'll have to do some digging to make sure you have a complete system.

I don't have any experience with aftermarket vacuum pumps, so can't make any recommendations.

Sounds good Don, thanks for the advise with what you've provided.

 

[jbojo]

I have a similar setup as far as pistons, compression(CR 10.5:1), and rear end. You mentioned that you wanted a cam to be in the power band at 2k, With that rear you will be around 2000rpm at 40mph in 3rd depending on the tire that you use. I have a 290 duration cam and it makes about 12.5 - 13 inches of vac at idle so not enough for power brakes. At 2000 rpm my car makes about 18 inches of vac so I went with a vac can. At start up brakes are ok but as soon as you go down the road I have enough vac in the reservoir to operate the PB. I was considering an after market vac pumps however they are loud and big and I didn't have room in the engine compartment plus the extra wiring that needs to be done. The OEMs in todays cars seem to use smaller pumps so I would go that route if you want to stay with a pump.

I can show you where I put the reservoir if you are interested.

 

[73' mach 1]

I have a similar setup as far as pistons, compression(CR 10.5:1),  and rear end.  You mentioned that you wanted a cam to be in the power band at 2k, With that rear you will be around 2000rpm at 40mph in 3rd depending on the tire that you use.  I have a 290 duration cam and it makes about 12.5 - 13 inches of vac at idle so not enough for power brakes.  At 2000 rpm my car makes about 18 inches of vac so I went with a vac can.  At start up brakes are ok but as soon as you go down the road I have enough vac in the reservoir to operate the PB.  I was considering an after market vac pumps however they are loud and big and I didn't have room in the engine compartment plus the extra wiring that needs to be done.  The OEMs in todays cars seem to use smaller pumps so I would go that route if you want to stay with a pump.

I can show you where I put the reservoir if you are interested.

I incorrectly posted with the 2K I just meant to say mid band power with it being a street car. The tire height that I'll be going with will be 26.6". I don't know the trans ratios in the TKO 600? It's good info for some real life results with that duration vs VAC. Just how loud are these things? Do they run constantly or could it be set up to kick on and off based on VAC needed? So you've never run into brake issues with having the reservoir?

 

[jbojo]

I have a similar setup as far as pistons, compression(CR 10.5:1),  and rear end.  You mentioned that you wanted a cam to be in the power band at 2k, With that rear you will be around 2000rpm at 40mph in 3rd depending on the tire that you use.  I have a 290 duration cam and it makes about 12.5 - 13 inches of vac at idle so not enough for power brakes.  At 2000 rpm my car makes about 18 inches of vac so I went with a vac can.  At start up brakes are ok but as soon as you go down the road I have enough vac in the reservoir to operate the PB.  I was considering an after market vac pumps however they are loud and big and I didn't have room in the engine compartment plus the extra wiring that needs to be done.  The OEMs in todays cars seem to use smaller pumps so I would go that route if you want to stay with a pump.

I can show you where I put the reservoir if you are interested.

I incorrectly posted with the 2K I just meant to say mid band power with it being a street car. The tire height that I'll be going with will be 26.6". I don't know the trans ratios in the TKO 600? It's good info for some real life results with that duration vs VAC. Just how loud are these things? Do they run constantly or could it be set up to kick on and off based on VAC needed? So you've never run into brake issues with having the reservoir?

No issue with brakes so far.  These pumps can be used with a vacuum sensor switch so that the pump will only come on when it drops to around 15" vac and cuts off around 19".  No personal experience with the pumps only what I read in reviews.

 

[Don C]

They are on demand pumps. My wife and I have a small motorhome that is built on a Mercedes Sprinter van chassis and powered by a diesel engine. The brakes are vacuum boosted with the vacuum supplied by a vacuum pump. It is completely quiet from inside (but my wife says I'm hard of hearing, but she hasn't complained about any noise).

 

[jbojo]

They are on demand pumps. My wife and I have a small motorhome that is built on a Mercedes Sprinter van chassis and powered by a diesel engine. The brakes are vacuum boosted with the vacuum supplied by a vacuum pump. It is completely quiet from inside (but my wife says I'm hard of hearing, but she hasn't complained about any noise).

Yeah my F250 diesel uses a pump too and I really don't hear it but maybe because of the diesel noise itself.  The ones built in by auto manufacturers are small and quiet, the after market from summit for example are larger and what I have read noisy.

 

[flstf09]

Yes the Summit pump made by CVR is big and noisy.

 

[Duncan Mach72]

I can recommend an aluminum flywheel over a steel one, that will make your idle choppier without costing you vacuum. Plus, throttle response is much snappier. The only time I would go back to a heavy flywheel is if I had a racier cam & was seriously trying to lower my 60ft time on slicks. With those gears + the TKO600 low, you have plenty of torque multiplication so you won't have a problem pulling away.

 

[73' mach 1]

In the end I think I'd rather be safe than sorry. If the cam I go with requires a the pump than I'll just do it. It's not like its going to run all the time. We'll see...

 

[CalgaryChris]

I'm considering going hydroboost route but not sure how I feel about having no brakes without engine running

http://www.ebay.com/itm/NEW-039-71-039-73-Mustang-Hydroboost-Power-Brake-Booster-/301871368092

 

[Don C]

You'll still have brakes with the engine not running, but it'll be like vacuum booster power brakes and require a lot of foot pressure. The accumulator in them should provide power braking for one or two stops if the engine dies while driving down the street.

Vacuum booster with a vacuum pump or electric booster brakes will provide you with power brakes until your battery dies.

 

[73' mach 1]

I can recommend an aluminum flywheel over a steel one, that will make your idle choppier without costing you vacuum. Plus, throttle response is much snappier. The only time I would go back to a heavy flywheel is if I had a racier cam & was seriously trying to lower my 60ft time on slicks. With those gears + the TKO600 low, you have plenty of torque multiplication so you won't have a problem pulling away.

For myself I think I'll keep the heavier stock one for street use.  With it being a 5 speed I prefer to keep the rpm's from dropping so fast.

 

[Spike Morelli]

I'll throw in my .02 cents here. Purchasing too big of a camshaft is THE most common mistake people make. Seems everyone wants to idle up to the stoplight next to that Camaro sounding like a Pro-Stock. The truth is that if you have a stick and manual brakes ( like most race cars do ), you can run as aggressive a grind as your engine likes, but we're talking street useage, aren't we? The rule of thumb in engine modifying, is that you can enhance a milder grind cam with better breathing ( i.e., heads, intakes, headers, etc, BUT, you will do your engine a dis-service by trying to choke down a large cam to make it more streetable, rarely are the results acceptable, and this train of thought includes Band-Aid fixes like vacuum pumps. Don't get me wrong here, I love rumpity engines, but, I've made the mistake before on my own stuff growing up. Now that I build engines for a living, I always advise pragmatically to chose the cam you think you want, then go at least one step milder, customers are much happier. Anyway, properly operating brakes are way more important than the sound of the exhaust.....especially if you're driving near me on the road....my life may depend on the other person's brakes!