amc 401 Total Timing Advance

rixcj

Hi. Does anyone know what the total timing advance is for a 401 ( guessing somewhere between 32-39)? Thanks, Rich.

BREK

Well it's not a 401, but my 390 made the most power on the dyno @ 36

rixcj

Thanks, Brek. But isn't this info in some sort of jeep bible, or FSM. Isn't this info also provided with some new cam kits?

BREK

I'm sure the info is in a tsm, my comp 292h cam kit did not come with any of this info in the box all it came with was a cam card.

ironman_gq

I think 36 is the generally accepted mark for max power

rixcj

Well,it seems that the general consensus is 36, so I'll go with that. Thanks!

donwag

Performance American Style (AMC factory performance guide) recommends 38-40 degrees total advance and all in by 3K rpm. I used this guide on my 401, curved my MSD dizzy accordingly. Runs great.

mike4089

how do you go about setting the timing advance exactly??? i have a 360 that i believe i set the timing at 5 degrees when at idle...but how do you get it to 36-38 degrees above 3000 rpms....also is 5 degrees enough at idle...my motor runs a little warm always around 200-210 and i was told that maybe a change in the timing could cool it down a little

tufcj

I run my 390 at 14 initial and another 24 mechanical for a total of 38 degrees. Mechanical advance is usually adjusted with springs, weights, and a stop, but how its done varies with the manufacturer of your distributor. The factory points style is basically a GM system, so you can use a GM recurve kit. 78-up electronic is Ford, there should be kits made for that. I run a Mallory Unilite, they make a recurve kit and tool to adjust mechanical advance. Bob tufcj

AMX69PHATTY

It's debateable, but there is a write-up floating around out there on the web about attaching the Vacuum Advance to MANIFOLD Vacuum rather than PORTED Vacuum to help an engine run cooler. A lean mixture burns much slower than a rich mixture and idle mixture is adjusted to lean best idle so the addition of the vacuum advance at idle helps it run cooler cleaner and smother. Trick is to get the correct Vacuum Advance canister that will not "hunt" at idle depending on your engine vacuum at idle. Vacuum Canister should give Full Advance at 2 inches lower vacuum than engine manifold vacuum at idle.

Agree with the 36-40 total by 2500-3000 rpms, NOT including the Vacuum Advance.
Total of initial adv, mechanical adv, and vacuum adv, is about 50-54 degrees.
The Initial timing really doesn't "matter", what matters is with full mechanical advance, and NO vacuum advance hooked up, the total should be 36-40 degrees and the initial ends up being whatever it is.

Stock Advance set-ups are very conservitive and set-up with warranty in mind
and far from being what works for the best power and performance.

What Distributor are you running ?

Anyone running a Delco Points Type Distributor that wants to try attaching the Vacuum Advance to Manifold Vacuum,
I have For Sale the illusive apparently discontinued "desireable"
B28 Vacuum Advance Canisters mentioned in that article for the small cap Delco points type Dizzy.
It's compatible if the dizzy has been converted to UniLite or Petronix, etc.

Specs for the B28 Vac Adv Can:
Adv Start @ 3-5 inches of vacuum
Adv Fully @ 6-8 inches of vacuum
Total Adv = 8 deg Dizzy / 16 deg Crank

mike4089

what if your running an HEi unit....how do you go about setting that?? i think i need to look at my timing becuase i think i only set it at about 5 degrees at idle

AMX69PHATTY

Same applies to HEI Dizzy's.
Just the Mechanical Advance Recurve Kits are different part numbers
and the Vacuum Advance Cans are different part numbers.
I prefer the "stock" style off the shelf Vac Cans to the "pricey" Adjustable ones
available from Crane, Accel, MSD, etc.

On HEI's the Total Mechanical Advance is determined by the
Weights, Springs, and the Mech Adv Cam Plate supplied in the Kits.
On Points Type it's determined by a Pin, Slot, and a Bushing
that comes in the Kits and goes on the Pin to limit travel in the slot.

For the HEI, the Vacuum Can to get is:

Desireable "HotRod" Vacuum Advance Canister for GM HEI Distributors

AR15 - Stamped on Flange of ALL Brands

#1973508 - ACDelco
#DV1843 - Wells - AutoZone
#VC1843 - Echlin - Napa
#VC262 - Standard Motor Products - CarQuest
#DR347 - Niehoff - where ?
#V399 - Borg-Warner - Advanced AutoParts

Start Adv @ 3-5 inches of Vacuum
Fully Adv @ 9-11 inches of Vacuum
Total Adv = 7.5 deg Dizzy / 15 deg Crankshaft

"HotRod" Timing Advance Set-Up for HEI Dizzy:

14 deg Intial Advance set with NO Mechanical or Vacuum Adv at idle
24 deg Mechanical Adv all in by 2500-3000 RPM's
38 deg Sub-Total Initial and Full Mechanical Advance
15 deg Vacuum Advance
53 deg Absolute Full Total Potential Advance

... with Vac Adv Can attached to Manifold Vacuum
14 deg initial Advance
15 deg Vacuum Advance with Engine Vacuum at Idle above 11 inches
29 deg Total Advance at Idle with NO Mechanical Adv coming in at Idle

Be careful of Detonation.
Reduce Initial advance, or the rate and/or amount of mechanical if it pings.

A Dial-Back Timing Light is a "must have" to get it set up right.

:idea:

mike4089

what does it mean when the motor has come up to running temperature and you get done driving and when you go to start the motor back up it turns over really slow for a couple of revs then turns over like normal and fires off....mine does this sometimes and i didnt know if it was the timing or what...i have a brand new battery so i know its not that...

tufcj

Your initial timing is probably a bit too far advanced. Try backing it down a couple of degrees. Bob tufcj

AMX69PHATTY

Agree, first guess would be too much initial timing making it difficult to turn over and start-up when up to temp. In Jegs and Summit they offer "Starter Saver" electronic boxes that reduce the spark advance by 10 or 20 degrees when cranking to help prevent this, or back off the initial timing as mentioned. Old school drag racers, and I guess even nowadays, completely locked down the distributor advance internally and sat the timing at 36-40 fixed total and used the "Starter Saver" to back it off so it could be easily started.