Moparts

440 ignition timing

Posted By: Moparmaniacc

440 ignition timing - 10/04/21 01:18 AM

This is a newly rebuilt 440 Challenger with a mild roller cam, 4 seconds flat distributor, headers and 4 speed. I know you guys are going to tell me to use a timing light, but - I like to try and find the best seat of the pants performance just by moving the distributor in small steps around my "sweet spot". I've got a mark on my distributor and on my block.

So this is what what happens. If I keep advancing the timing past my sweet spot - the car will not ping at full throttle, but the idle gets rougher and the car bucks back and forth when I'm trying to cruise around at 30 or 40 mph in 2nd or 3rd. (Is this "surge" like in VCODE's recent Thermoquad post?)

So I'm trying to get my distributor sorted out before I start fooling around with my brand new Holley 750 vacuum secondary. My problem is, the car doesnt feel as strong as it should. Should I go back into the distributor and move the limiter plate to allow more advance? Should I really follow FBO's directions and plug the distributor into a constant vacuum source, which doesn't make sense to me?

thanks in advance! John

Posted By: BSB67

Re: 440 ignition timing - 10/04/21 01:34 AM

Use a timing light.
Posted By: Ramrod39

Re: 440 ignition timing - 10/04/21 01:53 AM

Originally Posted by BSB67
Use a timing light.


haha
Posted By: GODSCOUNTRY340

Re: 440 ignition timing - 10/04/21 02:03 AM

This is how I find my engine's sweet spot. Get the engine at normal operating temp, turn the carb idle screw until the engine is at 2500 RPMs, now start advancing your distributor until the engine just starts to slow down, back it off till it clears up. Sweet spot.
Posted By: fourgearsavoy

Re: 440 ignition timing - 10/04/21 02:45 AM

When you unplug the hose off the advance does it still "surge" at cruise speeds. I really don't get the "don't want to use a timing light thing" It's hard to give guidance when we don't know where your timing is. It's like the guy at the track complaining about his car running slower than expected and you ask him where the timing is set and he says "I've had it everywhere" Not a very intelligent response because timing is more important than ever with the crap fuels we have today.
Set your total at 34* without vacuum and see how it runs twocents

Gus beer
Posted By: Cab_Burge

Re: 440 ignition timing - 10/04/21 02:51 AM

I've race Mopars and won with them at NHRA races in stock and in the heads up 10.90 and 9.90 classes with BB, SB and 426 hemi.
All the BB like between 34 and 36 total timing at the tracks we tested on, I weld up the stock advance slots and make them have around 16 degree mechanical advance so I can set the idle timing between 14 to 18 BTDC to get the total timing where I want it. I also use a set of real light advance springs from Mr. Gasket, part #95B I think.
As far as the butt dyno, yours and mine probably are not calibrated the same shruggy Most butt dyno normally won't feel .030 to .009 ET and or from .3 to 1.5 MPH gain in the 1/4 mile shruggy twocents The time slip will show those changes accurately up scope
Tune it to you like or love it and then read the real results with a good timing light twocents scope
Posted By: TJP

Re: 440 ignition timing - 10/04/21 01:49 PM

The last two responses from Cab and 4 gear are spot on twocents
Your surging is likely the motor telling you it has too much advance whistling

Also, checking for pinging due to excess advance is best done from low RPM and speeds (20 MPH or so) in 3rd or 4th gear while putting the motor under a heavy load like climbing a hill, and then accelerating from both part throttle and again at WOT wink
Posted By: DaveRS23

Re: 440 ignition timing - 10/04/21 02:27 PM

Most of our big blocks like a similar timing set-up. So there is not really any need to experiment with timing schemes that are out of the ordinary. You have some good advice in this thread from guys that have a ton of experience.

Who chose to use a vacuum secondary 750 carb on a cammed 440 with a 4 speed?
Posted By: SomeCarGuy

Re: 440 ignition timing - 10/04/21 02:49 PM

The new engine masters tested mopar heads and timing and 34-36 was the ticket. I’ve had the best luck with smooth running at 34 with 906 heads. I gained .5 mpg by running 38, but the engine didn’t have that smooth feel like fuel injection running that much.
Posted By: Copper Dart

Re: 440 ignition timing - 10/04/21 02:50 PM

Originally Posted by TJP
The last two responses from Cab and 4 gear are spot on twocents
Your surging is likely the motor telling you it has too much advance whistling

Also, checking for pinging due to excess advance is best done from low RPM and speeds (20 MPH or so) in 3rd or 4th gear while putting the motor under a heavy load like climbing a hill, and then accelerating from both part throttle and again at WOT wink


Pinging is taking place long before a human ear is going to hear it especially from the drivers perspective and over the exhaust and road noises. driveIf you can hear it, it has gone from a small hammer tapping on your valvetrain to a sledge hammer. hammer Just sayin'
Copper
Posted By: GY3

Re: 440 ignition timing - 10/04/21 02:53 PM

Originally Posted by BSB67
Use a timing light.


x2.

Anything else is just guessing.

Did a dude with a timing light run off with your girlfriend? (trying to understand the reason for timing light aversion)
Posted By: moparx

Re: 440 ignition timing - 10/04/21 04:12 PM

you can possibly get rid of the cruise [light throttle/high vacuum] bucking by using a 3/32" allen key into the advance can, and turning the can spring to a tad less vacuum advance at your cruise rpm.
e-booger did an article for mopar muscle magazine on tuning the vacuum advance a while ago.
look it up on their site. it's a well written piece, and should be tried before saying the heck with it, and just capping off the advance can.
in some instances, it makes a world of difference on the performance of a vehicle no matter what engine you have under the hood.
it has worked for me many, MANY times, while most just cap the can without even trying to tune it.
i highly recommend reading that article and applying it to your combination ! up
beer
Posted By: Moparmaniacc

Re: 440 ignition timing - 10/04/21 11:48 PM

Yes, I do recall that article and will check it out again. And I will cure my timing light aversion for everyone, thanks !
Posted By: KWF340

Re: 440 ignition timing - 10/05/21 01:28 AM

Here's the link to the article.

Link
Posted By: Mr.Yuck

Re: 440 ignition timing - 10/05/21 01:52 PM

Step one, buy a timing light. 2, unhook the vacuum advance, 3. start the car, 4. turn the idle up to 2300 rpm, 5. set full timing in at 36*, 6, back idle down to normal, 7. turn idle mixtures crews for best vacuum, 8. Go for a run. If you have a delay/bog you will need to mess with the spring in the "pod". You might also have to change the power valve.
Posted By: Cab_Burge

Re: 440 ignition timing - 10/05/21 05:19 PM

I have seen stock distributors have the big spring let the advance work up to over 5000 RPM shock scope
If the advance is all in by 3000 RPM make sure you rev the motor high enough to not have any more advance after that twocents scope wrench
To much advance can and will kill parts down
© 2024 Moparts Forums