compression help

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71Swingerman

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I have a 78 stock 360 with indy x heads, 2.02 and 1.60 with combustion chamber 62 cc`s. running a mp 268/272 with .450/.445 lift, performer rpm intake with 650 elddy carb. Problem is I added power front disc brakes but they don`t stop as well as I think they should. Not sure of compreson ratio. Any info on any of the above will be a great help, thanks.
 
You have a performance cam, it's probably not creating enough vacuum to operate the booster correctly.

You really need a minimum of 14 inches of vacuum for them to work properly.

I would suggest getting, if you don't have, a vacuum gauge.

Tune the carb to get the highest reading.

Your other alternative is to add Hydro-boost OR go back to manual brakes.
 
your eng combo sound solid. I had that mp cam, and up graded to the mp .474/280 cam and was a lot happier. I had a 2500 stall converter but that cam had more bottom end and top end then the .450 lift. and with the RHS head it will breath better then the stock X head i had on mine.
I had manual brakes.
 
Rhoades lifters can help increase your vacuum. I ran them on one of those cams for years with 19" vacuum.

That is not that big of a cam, you should get more vacuum. Pretty close to a stock 340 cam. Are you sure that you don't have it tuned right, or a vacuum leak somewhere....
 
Bad Sport said:
You have a performance cam, it's probably not creating enough vacuum to operate the booster correctly.

You really need a minimum of 14 inches of vacuum for them to work properly.

I would suggest getting, if you don't have, a vacuum gauge.

Tune the carb to get the highest reading.

Your other alternative is to add Hydro-boost OR go back to manual brakes.
Click to expand...

Not so sure that 14 is enough , maybe with a real good brake booster , I have 15 and the brakes ain't that great, new rebuilt booster , thinking of going manual
 
My engine idles at 6" of vacuum, and my power brakes work excellent on my 1970 E-body. Rebuilt factory booster, 11 3/4" Police/Taxi rotors and Dr Diff's eco no rear disc brake kit.

Not really sure why they work so well on such low vacuum, but they'll drag the car down from deep in the triple digits with ease. They work great around town too.

I have the exact same brakes on my 1968 A-body with a manual < 1" master cylinder bore. That system gives much better feedback during critical light braking situations and doesn't require excessive peddle pressure to lock them up, but it is more effort than the power brake system to go into lock up.

Both cars weigh roughly the same. If my 1970 didn't come factory with power brakes, I wouldn't hesitate to run this same system with the manual set-up.
 
Put a vacuum canister in to hold a reserve for your brakes; OR the $64,000 question...did you change master cylinders when you put the disks on?? There is a difference between drum and disk master cylinders......
 
Thanks everyone for all the info. I checked the carb mixture screws and adjusted the and now I have 30 plus at 750 now. the brakes work some better but after you hit the brakes o
the first time the petal is hard. Thanks again. If anyone has more info it is surly welcome.
 
Did you degree the cam when you installed it?
What is your vacuum at idle?
Have you advanced the initial timing at idle to see if vacuum increased?
 
71Swingerman said:
Thanks everyone for all the info. I checked the carb mixture screws and adjusted the and now I have 30 plus at 750 now. the brakes work some better but after you hit the brakes o
the first time the petal is hard. Thanks again. If anyone has more info it is surly welcome.
Click to expand...
30 + With that cam ? Sounds high , that's more than a stock 340 . You sure the gauge is working properly
 
You would be hard pressed to ever see 30 psi vacuum with the engine braking in a manual car downhill at high RPM! Maybe the OP meant 20? I hard to work hard at it to get more than 28 psi down a mountain in a /6 LOL !

The last post indicates that there is adequate residual vacuum in the booster just for one use that is being bled out on the first brake application, so suspect a problem in the booster's vacuum/vent circuit. If you have the throttle open with low vacuum and apply the brakes successively, you will eventually bleed out all the usable vacuum from the booster.... but with a good check valve, you ought to get 2-4 good brake applications, not 1.

Be sure that you check the brake booster on the passenger compartment side to make sure the pressure side vent filter is not clogged. Air has to flow in from that side to allow the diaphragm to work. And see if the check valve on the vacuum side is working.....do you even have a check valve?
 
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