timing on 401 and 425

G

gforcecuda

Member
on stock 401's and 425's what do these motors like in total timing (with vacuum disconnected)...how much initial is best. how much timing should the vacuum pull in at cruising speed?
 
timing....

I set mine on 8 deg. because of the catpee gas.... supposed to be 12 deg. basic.....then the vac brings the rest , up to 30 or 31 total....the most important thing to check out is the rubber advance limiter that is under the rotor... it dries out and crumbles all to pieces letting the dist over advance.... a brass one works better... and dont rot....
 
gforcecuda said:
how much timing should the vacuum pull in at cruising speed?
Click to expand...

I'm repeating what I was told by a reputable source. Originally vacuum advance added about 20 degrees but limiting it to around 10 is better for a grand total of 42
My 66 425 also had a rubber bushing (barely left) on the vertical post for the vac advance as well. Note the rubber bushing on this NOS shaft as Doc mentioned and the one from my 66.
 

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Not for cruising down the highway. Total, yes, but when your foot is in it there's little to no vacuum anyway. 32*-34* total centrifugal advance at 2500-2700 RPM's. The trick is 36* until 3800 then back off 4*, without electronics.
 
by 32 to 34 degrees centrifugal I presume you mean with the initial added in? or is that all distributor degrees? meaning 40 to 42 total without vacuum..how are you taking out the 4 degrees at a certain RPM without electronics?
 
12* initial, 20* built into the dist. This is crankshaft *. Dist. * is 1/2 Took me a long time to figure out how to do it. Sorry, my secret. Ruined many a distributor figuring that one out.
 
Hey Tom - you were the reputable source I was referring to :hurray:.

I was studying the timing curves in the shop manual.

According to the chart for an auto trans, the vacuum adds 10 degrees for a grand total of 40 initial, mech, and vacuum. But under the specifications page for the "max advance degrees vacuum" specification it says 14-18 degrees but it doesn't say if thats auto or manual trans.

Back to the chart; the manual transmission on the other hand, adds 18 degrees taking the grand total up to 50 degrees. The manual transmission also shows a difference of 4 degrees more mechanical advance with the total of it being higher at 34.5 vs 30.5 for the auto.

I know the book is only a starting point and experience equals reality but I can see why there is often some confusion on this topic.
 
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hey tom do you recurve points/hei distributors? also need a 7/8th rear swaybar to fit on unboxed rear control arms or panhard rod bar to fit on a 68 buick wildcat?:shield:
 
The timing & advance curves are for all styles of driving. Now remember I'm more toward the performance aspect of all this. I have been playing with this stuff for a long time. My experience & my opinion are just that. It may not agree with what everyone else has done or experienced. Many problems are caused by the "rubber" bushings drying out & falling off to the point if you are not aware of them even being there to begin with you have NO clue. The more initial advance the better it helps to get a heavy car moving. Between a stock & a 2x4 distributor the advance rates aren't that far off. Everyone is looking for the 2x4 distributor. If your willing to experiment a little ANY distributor can be used. A standard dist. uses 2 1/2* initial & has FULL manifold vacuum for the vacuum advance for a better idle & better throttle response with so little initial advance. The dist. has 15* advance built in (30*@ crank)for a total of 32 1/2* at the crank fully advanced. Add about 20* of vacuum at crank, (10* dist.) & now you have over 50* of advance cruising, but who cruises at 4600 or so RPM's??? The 2x4 has 12* initial with 10* built in (20@crank) for a total of 32*. Again, vacuum is about 20* fully advanced, but again, who cruises at 4400RPM's??? The 2x4 full advance comes in at about 2-300RPMs less than the standard dist. ALL the advance rates are pretty similar in ALL applications, give or take a few degrees & RPM's. Confused yet????

Tom T.

P.S. yes I do re-curve distributors & convert to electronics, but only for a completely stock set-up. No MSD, Crane, etc.
 
I just committed to buy a Sun 504 Distributor Machine. Also a Sun 1115 Analyzer. I have a lot of 30's thru 70's cars. hopefully I can recurve these distributors and change springs to get them to function like they need to. My Caballero Wagon has the bored out 401 in it..backed by a 4L60E trans and 9" rear. It was in Rod and Custom a few months back. Runs great but it trembles when you first take off at a light. I have changed the accelerator pump around and it is better with a bigger shot, but it still trembles some. This 10% Menthanol in the gas is really screwing me up on all my lawnmowers, weed eaters, and old fuel pumps and carbs. I drove the Wagon to the Texas Roundup in Austin from my house in Gainesville, Ga. really fun event. Saw lots of nail head powered hot rods there. drove it non stop back on Sunday following the event..over 1,000 miles...old nail cruises at 80 with the cruise control on..with a 355 gear and the overdrive, it is just sluffing along...would cruise at 100 if I wanted a ticket..thanks for sharing your experience..kinda weird, I can't hardly get the old nail to spark knock...I had always just twisted a distributor until the motor got happy...the hold some RPM and twisted it to see if it was happiest at the same spot...Then drive it to see how it did...then advance it a little until it rattled, then back it off until it didn't..This old Buick doesn't want to rattle..I have jacked it up pretty high..no spark knock..
 
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