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Engine rattling under acceleration

Engine rattling under acceleration

Old September 16th, 2018, 04:10 PM
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Engine rattling under acceleration

Does anyone know if there is a way to read a spark plug to confirm detonation? I am unfortunately getting a rattle under acceleration with my new 455

Its pretty loud. I have my vac advance hooked up. 52 degrees all in

9.5:1 with iron heads
228 @ .050 duration
870 Holley carb with vac secondary
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Old September 16th, 2018, 04:19 PM
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What is the timing without the vac advance hooked up ? DO you have it hooked to direct manifold vacuum ?
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Old September 16th, 2018, 04:50 PM
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Originally Posted by VinMichael View Post
Does anyone know if there is a way to read a spark plug to confirm detonation? I am unfortunately getting a rattle under acceleration with my new 455

Its pretty loud. I have my vac advance hooked up. 52 degrees all in

9.5:1 with iron heads
228 @ .050 duration
870 Holley carb with vac secondary
If you pull the plugs you'll get specs on the porcelin. Make sure your running the right heat range, 52 degree's is way much for that combo IMO. What's your total without mech advance and what is your base at?
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Old September 16th, 2018, 05:16 PM
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I am using ported vacuum.

It turns out that I was at 36 mechanical when I was at 52 with vacuum advance.

I turned it back to 31 mechanical and took it for a ride with vacuums advance plugged. The rattle was still there but not as loud.

Then I plugged in the vacuum advance and repeated driving conditions. The rattle is the same as when the vacuum advance was plugged. I just timed it again with the vacuum adavance all in and Iím reading 50 degrees.
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Old September 16th, 2018, 05:19 PM
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I am running ACDELCO 4#45S plugs
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Old September 16th, 2018, 05:22 PM
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What octane fuel are you running? What rpm is your total timing coming in at? What distributor are you using?
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Old September 16th, 2018, 05:39 PM
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Using a stock HEI. Total timing is coming in around 2500. I am using Shell 91 octane. I am in California.

I am on a test drive again with a third adjustment. I set the timing back further.

With the vacuum canister plug Iím getting 13 initial and 28 all in. With this setting Iím getting 42 all in with the canister connected.

I am still hearing some rattle but its almost gone.
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Old September 16th, 2018, 05:42 PM
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At least I think itís pinging. Donít want to rule out something like exhaust vibrating on the body or something.

So I thought reading the plug would tell me if itís in fact pinging. But the sound seems to be going away as I take out timing.

The first time around I had a puff of smoke coming out of the breather accompanied by the sound. I saw this since I have no hood. I really had my foot in it in 3rd gear under load when I saw this.

Last edited by VinMichael; September 16th, 2018 at 05:46 PM.
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Old September 16th, 2018, 05:52 PM
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The octane is not helping your situation. How long ago was it rebuilt/
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Old September 16th, 2018, 06:00 PM
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Rebuilt only 25 miles ago. I think it was in fact pinging . I just got back from a test drive. And the sound is gone.

91 octane is the best I can get here in California.
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Old September 16th, 2018, 06:07 PM
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Did you build it or a shop?.
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Old September 16th, 2018, 06:12 PM
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I assembled the engine and selected all of the parts.

Cam was degreed and all clearances measured.
Trans is a TH350 with a TCI 2600 stall and shift kit.
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Old September 16th, 2018, 06:41 PM
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Shame about the bad gas. If you back off the timing any more, you'll likely cripple it. Have you tried any octane boosters?
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Old September 16th, 2018, 06:54 PM
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Do all your tuning with the vacuum advance unplugged. You might want to put some heavier springs on the weights to delay full advance. Once you have your initial and centrifugal advance dialed in, then work on the vacuum advance. You will most likely have to limit the vacuum advance with some small screws, or ideally get a adjustable vacuum advance canister from Accel or Crane. It includes a small cam that mechanically limits how much advance the canister adds. You need to remember, every time you change the advance limit cam, you need to reset the base timing. The cam changes the base position of the pole piece, that changes intitial timing. There are detailed instructions in the vaccine advance kit that explains all this much better than I can here.

Whatever you do, once you have the timing dialed in with the advance unhooked, donít change the initial timing to get rid of pinging with the advance hooked up. Make sure the advance in connected to manifold vacuum. A little pinging under mild acceleration, but the pinging should go away once you add more throttle and manifold vacuum falls off.
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Old September 16th, 2018, 09:13 PM
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Ive never played with any fuel additives. And I hear the ethanol in Californiaís fuel isnít helping the cause either

I will be ordering an adjustable vacuum canister tonight. Also ordering a wideband sensor and gauge.

Last edited by VinMichael; September 17th, 2018 at 05:11 AM.
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Old September 17th, 2018, 04:55 AM
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Originally Posted by VinMichael View Post
Ive never played with any fuel additives. And I hear the ethanol in California’s fuel isn’t helping the cause either
I will be ordering an adjustable vacuum canister tonight. Also ordering a wideband sensor and gauge.
That will help.
I think you're all forgetting, the vacuum advance is strictly designed to aid in better cruise, and is not in play during full throttle acceleration.
Set you base and total. THEN use an adjustable canister to fine tune your part throttle response.
I've done a handful of 10.0:1 builds for CA and all run fine at 33-34* total with an additional 8-10* at part throttle, and that's on 91 as well.

Last edited by cutlassefi; September 17th, 2018 at 04:59 AM.
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Old September 17th, 2018, 07:24 AM
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Originally Posted by cutlassefi View Post
I think you're all forgetting, the vacuum advance is strictly designed to aid in better cruise, and is not in play during full throttle acceleration.
^^^THIS! Vacuum advance requires, ya know, VACUUM to operate. At W.O.T. there is no vacuum.
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Old September 17th, 2018, 10:54 AM
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Originally Posted by joe_padavano View Post
^^^THIS! Vacuum advance requires, ya know, VACUUM to operate. At W.O.T. there is no vacuum.
I might be lean then. Which explains post number #4. There was just as much rattle with the canister connected at 31 total as there was with the canister disconnected. Since vacuum is zero at WOT, anyway, and I did the test at WOT both ways.

Wideband and adjustable canister are on the way.
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Old September 17th, 2018, 03:00 PM
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If you feel the need for an adjustable cannister, get a kit that comes with the assortment of springs to help you dial in your distributor. Your timing may be coming in too soon. In addition buy a vacuum advance stop/limiter so you can dial it in also.
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