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Do you have vacuum advance connected?
Have you replaced the stock HEI springs to bring total advance in at a lower rpm?
Cam Shaft 1974 455
- Thread starter Larryd
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Have you replaced the stock HEI springs to bring total advance in at a lower rpm?
Yes I have vacuum advance connected. I have not replaced the stock HEI springs. I know how to replace them but I don't have any experience as to which springs to use to advance at lower RPM. Plug tips looked ok but not tan in color. I would say slightly blackened.
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So if you have original springs how did you see 34 degrees at the rpm numbers you mentioned?
I have an adjustable dial on timing light. Ran engine at rpm and readjusted timing light and it told us the advance.
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At what rpm 2500 to 3000? Stock springs typically they don't achieve full advance till 4k+. Where did you get this distributor?
Humm I bought it several years ago and at the time this engine was carbureted and it worked fine. But since I have moved to a throttle body sniper things haven't been so good. I assume this HEI was originally designated for chevrolet. But it worked fine in carbureted mode. Its a little tight with firewall. Would there be a better distributor that is more adjustable electronically that I might have better/easier time working with?
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Chevrolet and Pontiac distributors rotate in opposite directions. Which side is the vacuum advance Drivers or Passenger?
The vacuum advance is on the drivers side with the vacuum port facing the throttle body
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That's where a Pontiac advance would be located but hard to image how the vacuum advance would be pointing forward as opposed more towards drivers side same as stock distributor.
Still not clear about your timing determination. You set the dial back to 34 degrees and then you increased engine speed and stopped when the mark lined up with zero on the damper but would it advance more at 3,500 rpm?
Still not clear about your timing determination. You set the dial back to 34 degrees and then you increased engine speed and stopped when the mark lined up with zero on the damper but would it advance more at 3,500 rpm?
Well I did not try at 3500. I thought I would look at that tomorrow when you said it should achieve full advance at 4k. I was being easy on engine. If it will still run at 3500 I will do the test. It should go there if I ramp up slowly with no load.
How did you line up the timing marks on the timing chain sprockets? Were they facing each other @ 12 and 6 , hookup a vacuum gage to full vacuum source off manifold or your EFI , is it 17”+ and steady or is it <15” and bouncing? If it’s low and bouncing then you probably have open valves , which earlier you said you backed off nuts and it ran better, then swapped out for polylocks . An 068 is kinda lopey at idle and may shake needle on gauge but not make it really bounce . It’s quite possible you have timing gears off a tooth or a full 180 degrees
Easy way to check tdc, disconnect power to distributor (or pull off cap) poke a rag into #1 spark plug hole and bump engine until it Pops the rag out That’s TDC , realign timing marks to 12tdc and check distributor rotor position is pointing to #1 terminal . Check the simple things first .
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Well about two weeks ago we took off the muffler as we had been detecting a faint whistling from the muffler area of the car. So we fired it up again and sure enough the muffler was restricting air flow and causing engine fluttering or loss of power under a load so no more problem! We also suspect the muffler was designed or built for a standard 67 firebird and the 455 air flow is different or greater in this case. I told the original builder of the stainless steel muffler about this situation and told him I feel it needs to flow at least 850 cfm so he said ok. I am waiting on his new build muffler. It has plenty of pep with no muffler at the moment.
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Wait. What ..? What do you mean “took off The Muffler?” Where’s the Dual Exhaust?
Well there is dual exhaust all the way back to the muffler which is tucked behind the rear axel and both exhaust pipes go into the lower ends of the muffler and 2 other pipes exit from the muffler and end up behind the rear wheels between the leaf spring and the body. I believe that was the original design on 1967 firebird