Help! Chevy 454 timing?

A friend has a chevy 454 7.2L engine which is not original to his truck. (So there is no timing specs sticker for this engine.) The book we got said to refer to the sticker on the truck....

Anyone know what the spark timing should be set to?

I found something which said 4 degrees at 3500 rpm with vacuum advance disconnected. Correct?

Reply to
Bill
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That doesn't sound right. If it's got a vacuum advance it must have a mechanical advance so at 3500 rpm that would be at it's full advance of probably around 25 or 28 degrees. So if you set the timing at 4 degrees at

3500 rpm when at idle the timing would be retarded by about 24 degrees. I would say the timing should be around 6 to 8 degrees before TDC at idle with the vacuum advance plugged. Still not knowing what year and all it's just a guess.

nospam

Reply to
NoSpam

I meant 6 to 8 degrees BTDC (Before Top Dead Center) I think much faster than I can type.

nospam

Reply to
NoSpam

Depending on year and application, spec. ranges from 4*-8* BTDC. I'd start at 8* and work my way down if she started pingin'!

Doc

Reply to
"Doc"

He said the 454 engine was from a 76 chevy pick-up truck, but someone told him they did not make 454 engines in 76?

Can I tell from any numbers on the engine block what the spark timing should be? And maybe looking up the number on the internet (where?)somewhere or in a book (which book?)

Or if setting the timing by starting at 8 and working down to 4. How would we know when we hit the correct number? Pinging, then lower the timing until the pinging goes away, then that would be about right?

Reply to
Bill

Generic engine stuff (any brand):

To be absolutely correct in your settings you'd have to know precisely what the camshaft is and the crank is, actual compression ratio, and a buncha other stuff. And beyond that, eventually you have to allow for timing chain stretch.

Every engine has an "ideal" timing, but no engine has a predicted "perfect" timing.

As someone mentioned earlier, your best bet is to advance the timing till you get slight pinging under maximum load, and then back off a little till it stops. For an engine that's not computer run this technique is, IMO, better in every way than the factory numbers so many revere without thinking through what timing is all about.

The factory number for timing is generally safe, but there's not much else going for it.

Reply to
Bill Vajk

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