[team423]

we just built my 352 went .30 over .567 hydrolic roller cam,performer rpm intake,holly 750,headers,2 1/2 in pipes,3.0 gear.. 10.1 compression..i got some questions about vacuum it only puts out 5 at idle but puts out 15 at 2500-3000 rpm should it not do 15 at idle to??any advice will be greatly appreciated..thank

 

[Mroldfart2U]

Not for sure, but the cam spec that you gave, that maybe close to correct. Cam has a lot to do with idle vacuum...

 

[puttster]

Sounds like you have the gauge plugged into the carburetor above the throttle plates where the ported vacuum for the distributor and vacuum secondaries is taken. There is not much vacuum up there at idle. At full throttle it runs up to 15-20. Try a lower port, like the intake manifold.

 

[team423]

mroldfart2u the cam is a comp retro muther thumper .567 intake .552 exhaust..puttster i was off a little in the first post sorry,,we had it connected to the carb at first and it pulled 5,,then we went to the intake and pulled 7..and thanks for all the good info u have been giving me,,thanks again

 

[puttster]

I agree with MrOld. Hope you weren't planning on switching to power brakes!

 

[team423]

Is that low of vacuum normal?

 

[galax-z]

the valve overlap is what gives you the 'thump thump' and kills the vacuum. whats the duration?

 

[team423]

i think its .006 if iam reading it right..Or .050

 

[rambuttt]

Comp makes a bunch of Thumper cams although I didn't see a retro one listed. But the ones I did see all had LSA's of 107*, which is race car territory, and huge intake/exhaust duration splits. It all adds up to a racy sounding engine that is supposed to have a rough (low vacuum) idle...mostly show with very little go, IMO.

Any engine modified to that degree is gonna need a dizzy re-curve to match the new cam specs as well...and a higher stall converter.

 

[team423]

Cam part# 33-601-9... Car idles good and sounds great,, starts quick, just didn't know if the vacuum was ok cus it is kind of low at idle..

 

[rambuttt]

The terms "idles good" and "low vacuum" do not go together...usually. If you are happy with the cam, you'll just have to live with the "as designed" idle...huge overlap, tight LSA and 235/249 duration = low vacuum AND high RPM operating range. Bottom line, I'd say the idle vacuum is pretty much as expected.

 

[Mroldfart2U]

With these adverised specs:
Cam and Lifters, Hydraulic Roller Tappet, Advertised Duration 291/311, Lift .567/.551, Ford, 352-428 FE, Kit,

I would say, yep the low vacuum is 'normal' ... WOW what a cam... and X2 on the power brakes... lol

 

[team423]

i love the cam,,so i will just deal with the low vacuum,,it sounds freeking awsome and runs great...thanks for all the good info guys..