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Howdy, I have a 1974 Chevy C30 with a big block 454 that has a mild cam. My timing is set to 4 degrees before TDC. It has 16 inches of mercury for a vacuum reading at idle when at operating temp. The spark plugs are all burning evenly and with no signs of oil, lean condition, rich condition, etc. The motor has 89,000 miles on it and was rebuilt some time ago before I owned the truck. My question comes to play when I removed pcv hose from the carburetor to take the vacuum reading. all of a sudden some slight wisps of white smoke…more like steam came from the valve cover breather filter on the other side. As i remove the pcv valve to see if its the same on the drivers side same thing. When I rev the motor up from idle, this steam/smoke puff increases and then let off throttle it dies back down to a trickle. I put the pcv hose back in the carb and it goes away completely WOT or not. Motor makes no bad sounds and does not overheat, has great oil pressure(25-60 depending on rpm), and does not stall out at lights or bog down at all(this is a manual trans Muncie 465). Is this normal blowby?
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What you describe sounds fine to me given that you’re approaching 100,000 miles. I would say something about your manifold vacuum in/Hg, but not knowing anything about the replacement cam I’m unable to comment. Enjoy the Q-jet howl!
Not much to add here except that when you’re done adjusting the timing, you might also want to adjust the idle mixture screws. Hook a vacuum gauge to intake vacuum and slowly turn the screws at the base of the carburetor until you get the most vacuum. These screws have springs under them. In your case I’m guessing you have a quadrajet which has 2 of these in the front at the base of the carburetor. Rev the engine every once in a while to see where the vacuum settles. 16inhg seems low to me for that engine. I think you might be able to get close to 20 if it’s tuned right.
As for what you were seeing, I think it’s normal. Older engines are just like that. Get it tuned right and then see what you have.
Good luck, keep us posted.
Without actually seeing the blow-by it’s hard to say. For a quick test I plug both valve cover holes with the palm of my hands (PCV and other) at idle. Then I remove one hand and if there is actually pressure there, then I would say the blow-by is excessive. They used to make gauges for that but I haven’t seen one for a long time.
No pressure, have a nice day.
I apoligize for the late update y’all, ive been havin some family issues to work out. Here is what I’ve done:
1. Advanced the initial timing to 6 degrees before TDC
2. Adjusted the idle mixture screws evenly
3. Raised the idle speed slightlyAfter these adjustments I achieved 19 inches/hg. It seems it was mainly a timing issue since the idle to 2k rpm test with a snap of the throttle allowed me to believe the rings and seals are in good shape even before I started messing with the timing.
Attached is a picture of my setup. Its been cleaned up a little bit since then. Ive added new headers, plugs/wires, air cleaner, breather, etc since the picture was taken. Yes it is a quadrajet 🙂
I always liked those wide valve covers on a Chevy big block. Looks purdy. Thanks for the pic. Does the truck run better now?
It runs alot better. I feel I have quite a bit more power. I further advanced the timing since. I am now at 8 degrees initial timing at idle. And thank you Eric, I love the valve covers too. I should post a current picture on this thread tommorow because I just changed out the master cylinder today so no more rusty cylinder.
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