Detonation stumping me
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Detonation stumping me
I rebuilt a 351W with AllPro heads. Ran fine before. He ran it hot and warped the heads. Bored, cut .015 off heads to straighten, put rest together as came apart with .045 deck clearance. Didn't detonate before at 34 degrees total, 16 initial and vacuum advance. Now at part throttle above 2000 it pings horribly with 30 degrees total and no vacuum advance (unhooked it testing). Car sat for 1 year so I thought maybe it was gas. Added octane boost, ran that tank out and many others driving easy. Plugs look slightly lean but not extreme and it ran jetted like this before. Thinking may have vacuum leak somewhere but haven't found it. Couple thoughts:
1. PCV valve is teed into brake booster line- is this correct? Don't remember if this was the way it was before. Could this cause problem?
2. Could a vacuum leak from intake into lifter valley cause this issue? How do I check for that? The intake was not cut, should it have been with .015 off the heads?
Need to get this thing out of my life, any help would be appreciated.
1. PCV valve is teed into brake booster line- is this correct? Don't remember if this was the way it was before. Could this cause problem?
2. Could a vacuum leak from intake into lifter valley cause this issue? How do I check for that? The intake was not cut, should it have been with .015 off the heads?
Need to get this thing out of my life, any help would be appreciated.
Re: Detonation stumping me
I have never seen a PCV tied in with the power brakes. Is this normal for whatever your working on?
Although I have never checked, I always thought the pcv vacuum was considerably less than full manifold vacuum. Are you sucking oil out of the valve cover? How about removing the pcv from the equation and see if that helps?
Although I have never checked, I always thought the pcv vacuum was considerably less than full manifold vacuum. Are you sucking oil out of the valve cover? How about removing the pcv from the equation and see if that helps?
Re: Detonation stumping me
No the pcv valve needs full manifold vacuum preferably off the base of carb not a manifold runner. The power brakes can run off a single runner.
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Re: Detonation stumping me
Im not sure, it was built originally by someone else. I plan to reroute the hoses to eliminate this but was wondering if it was normal as is?travis wrote: ↑Fri Nov 09, 2018 9:12 am I have never seen a PCV tied in with the power brakes. Is this normal for whatever your working on?
Although I have never checked, I always thought the pcv vacuum was considerably less than full manifold vacuum. Are you sucking oil out of the valve cover? How about removing the pcv from the equation and see if that helps?
Re: Detonation stumping me
It is at base of carb, 750 vac secondary Holley, under vacuum secondary diaphragm. The brakes are teed into this port also.
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Re: Detonation stumping me
Check the booster diaphragm for a leak.
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Re: Detonation stumping me
How much can you choke off the Carb before the motor stalls?
This test will give a clue if you have a vacuum leak or not.
This test will give a clue if you have a vacuum leak or not.
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Re: Detonation stumping me
Oil getting into the chamber?
From warped intake flanges...or cooked rings
From warped intake flanges...or cooked rings
Re: Detonation stumping me
Don't see any oil on plugs, rings are new. Compression check is 180psi +/- 15psi. I forgot to choke it out before pulling plugs, I will try that this weekend.
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Re: Detonation stumping me
Try thicker oil, chased a det problem in a highish mileage engine(kinda same since it was ran hot) and all it needed was to go too 10w40. Can't rem if it was just one oil change or a quick 2nd.
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Re: Detonation stumping me
How many degrees of vacuum only advance is set up in the distributor? You mention 16 degrees initial but you mention that when run at 30 degrees with vacuum advance not connected. I am assuming this means there is 14 degrees of mechanical advance in the distributor. So if there is more than 4 degrees of vacuum advance you are seeing over 34 degrees of advance if I am understanding what you have and are describing.
Most vacuum advances I have seen have more than 4 degrees total advance in the unit.
Something here is not working for me?
Am I understanding your description correctly.
Have you checked and verified the TDC timing mark on the damper to see how it corresponds to the piston TDC?
Most vacuum advances I have seen have more than 4 degrees total advance in the unit.
Something here is not working for me?
Am I understanding your description correctly.
Have you checked and verified the TDC timing mark on the damper to see how it corresponds to the piston TDC?
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Re: Detonation stumping me
Will it ping if you add plenty of vacuum advance, something like 45 degree total timing?
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Re: Detonation stumping me
Can't you just retard the timing until it stops pinging? Sounds like you set the initial timing at 34 degrees. Just set it back to 14.
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Re: Detonation stumping me
Any chance you have a head gasket on backwards and the back of the block is hot?
I'd expect it to overheat, but just tossing ideas around
I'd expect it to overheat, but just tossing ideas around
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70 Mustang, 489 FE, TKO-600, Massflo SEFI, 4.11s
71 F100 SB 4x4, 461 FE, 4 speed, port injected EFI, 3.50s