From stock to 1.6 rockers ?

[jrust]

Hi guys, here's my question and I'll try to explain this as best as possible. Will changing the rocker assembly raise or lower the vacuum? Here's my build, with a mild engine setup I have about 15" of vacuum at idle, I installed the new stealth heads and went with the Crane 1.6 aluminum rockers, got it all bolted in and it sound sweet but now it's down to 10" of vacuum at idle. The biggest problem is once I drop into gear it wants to die and my new toy is given me another headache! Thx. James

[purple charger]

What diameter push rods did you use?  I am using 3/8" and had to have them clearance. I am going to be going the 440 source 1.5 roller rockers instead of 1.6

[firefighter3931]

It could be a vacuum leak. The 1.6 rockers will change the engine charahteristics somwhat but i wouldn't expect a 5in drop in idle vacuum with no other changes (cam/carb/intake manifold etc...)

If your ignition timing is retarded it will also reduce idle vacuum....make sure it has enough advance at idle.


Ron

[mally69]

What diameter push rods did you use?  I am using 3/8" and had to have them clearance. I am going to be going the 440 source 1.5 roller rockers instead of 1.6

WOAH, before you go using 440 sources roller rockers, I would think twice about that one. I had 2 rollers break on me and I ended up swallowing a valve the second time. And on the second one that broke I had my new stealth heads on there and it junked one of those.

[purple charger]

What diameter push rods did you use? Did you have any clearances issues if using 3/8"?

[mally69]

I used the pushrods with the cups that 440 source sells and I beleive they are 3/8.

[Rob R]

Well you put more more cyl head on it and increased the lift by .040 so it only stands to reason that the carb will need to follow suit...if you have a Holley on it I'd go up at least 2 jet sizes and give it some more bleed...66 to start