Owners of P30 454 chassis, what are u setting the timing at?

Mine is setting around 12* before TDC. I had my distributor recurved a couple of years ago, I believe I could get another degree or two more but it runs great and no pinging on 87 grade gas pulling a 5000 lb trailer.
Also with the GM setting you could always go down the highway at 55mph and and hand time it like I used to do with my 66 chevy van:-)

My old 79 454 in a Itasca model P30 called for 7 BTDC. I always set it just before it would cause PING which was about 15 BTDC. Much greater HP that way. replace the 2 Electronic modules in the distributor. Engine heat cause them to 'Start' to fail about every 2 years. U'll know when the RPM's start to become iradic at idle. Install a TACH. Check the exhaust 'Baffle'. Its at the end of the passenger side manifold. Its a vacuum operated door inside the exhaust pipe. They get burned & stick closed. Check for exhaust manifold leaks. 454's are notorious for that. The only fix is to install the best METAL aftermarket exhaust gaskets U can buy. Many 454's came from the factory with NO gaskets. If U'r 454 is equiped with an exhaust gas Air pump system, Remove the pump, install shorter fan belt, plug or pinch off all 8 air tubes to each cyclinder. That air being pumped into exhaust head makes em run RED HOT. ie; cracked manifolds & exhaust leaks.

toolman1 wrote:
Having been a GM Master Tech, all of the above reply's are good, and I would consider checking each one, BUT, there is another possibility. Some of the Mark IV engines had their timing marks below the harmonic balancer @ a 6 o'clock position, if you were to imagine the harmonic balancer as a clock face. If the installed engine is a crate motor, the timing tab may be incorrect for you're application, or the installer may have overlooked swapping the tab to it's proper position.

He did mention crawling underneath to set the timing so I assume the tab is down in the 4 - 5 o'clock position and he's using number 5 cylinder. If he can set the timing at 16 with no ping that would be great. I would switch to mid-grade or premium gas if needed to get the timing up there. The increase in performance and timing will more than offset the increase in gas.

You can get a rebuild kit for the advance mechanism at just about any auto parts store. It should come with 3 sets of springs for the weights, light, medium, heavy. You want to go heavy enough so you have no mechanical advance at idle but not too heavy. You want all the mechanical advance in by 2500 rpm. Install the heavy set of springs so you know you have no mechanical advance at idle. Then drop down to medium, if the timing jumped up then that's too light. If it didn't then drop down to light. You can mix the springs, 1 light and 1 medium or 1 medium and 1 heavy. It takes some trial and error but it's worth it. Use the combination that gives no mechanical advance at idle, full advance by 2500.

Bottom line, 4* is no good. It will run like a dog and run hot.

Pretty sure it's the original engine with just around 50,000 miles. The timing mark tab is almost below the balancer and is bolted to the oil pan.

Having been a GM Master Tech, all of the above reply's are good, and I would consider checking each one, BUT, there is another possibility. Some of the Mark IV engines had their timing marks below the harmonic balancer @ a 6 o'clock position, if you were to imagine the harmonic balancer as a clock face. If the installed engine is a crate motor, the timing tab may be incorrect for you're application, or the installer may have overlooked swapping the tab to it's proper position.

Vacuum to distributor is straight from the manifold.



No emissions gadgets that I can see. Worry about engine knock if I crank it up 16 degrees advance with regular gas. Might meet at the middle at 10 though. It's not the easiest thing to set the timing on these as you have to crawl under it to check it, then go back inside to adjust it.

Gonna throw some old fashioned hot rodder stuff into this...

In the 80's (and 70's) there were a lot of wierd things done in the name of low emissions, that may or may not have affected truck engines....

In an ideal world, a chevy engine will have 16-18 degrees of initial timing, 32 to 36 degrees of total timing (measurements taken with any vacuum advance disconnected and plugged)

Vacuum advance will provide another 12 to 16 degrees, and for best performance it will be on full manifold vacuum. Hot,out of gear advance at idle will be well over 30 degrees, and cruising advance could be 50 degrees or better.

In no cases should there be enough advance to cause pinging.

During the 70's and 80's, they did a buncha wierd stuff with timing. "transmission controlled spark" that prevented full advance until you were in high gear.
Ported vacuum advance that prevented full advance until you had some throttle in it.
And generally lots of stuff like this that did weird things to the engine in the name of keeping cumbustion temps up and minimizing NOX emissions.

So, if it were me...
I'd remove all those wierd gadjets and vacuum lines.
Connect the vacuum advance to full manifold vacuum.
Recurve the mechanical advance to provide 16 degrees at 2200 rpm and zero at 1000 (this is important, most engines in this era had way too much mechanical advance to compensate for having way too little initial and vacuum advance!)

And set the inital timing (vacuum advance disconnected and plugged) to 16 degrees.

Also put a vacuum gauge on it while your are timing along with as stated plug the vacuum advance. I ran mine at 16-32 or more. The higher the better, less for the back off for the ping. At lease with the RV you can get a good running system with the dog house off and set it where it runs the best at hi-way speed and hills.

Take the distributor cap off and check to see if the mechanical advance mechanism is free or if it is stuck.

Yes and plugged it.