Timing by Vacuum Reading?

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70DusterBob

70DusterBob

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I have a rather modified engine, high compression, large cam, 408, and I need to know what the best way to time it is because there is no standard measurement for it. I can start with the recommended timing, which is 10-16 Initial, idle in other words, and ramp it up to 34-46 at approx 3000 rpm, but there is a huge difference between 10-16 advanced.

My buddy said that I can use a vac gauge, and set the timing to make the vacuum gauge read its highest vacuum reading. Is the a good way, some sort of starting point, or what?

I have always had pretty stock engines before this 408, I have an MSD 6AL box, w/a MSD Mechanical Advance Dizzy, no vacuum advance on it. I will probably get a million different replies because this is not an exact science, but I need to know.

Thanks
 
That works many times, sometimes you must retard it a bit to keep it from kicking on the starter, but that setting is ONLY good for initial/ idle timing. YOU MUST make sure the "curve" is ok and that you are not over-advancing at the higher end

two ways to determine that:

1....Have a degreed balancer or degree yours, or measure out what 35 or so degrees is by calculating "degrees per inch" on the measured circumference of the balancer, then mark it

2....Get a "dial up" or knob controlled delay timing light which can read out total timing from a dial. BE AWARE these can be problematic with an MSD ignition
 
On stock motors, for initial timing, that works great. Not sure about hotrod stuff.
 
The vacuum gauge is used to adjust the carbs air/fuel mixture. Set the initial timing to whatever the engine will take and still start without lugging the engine down.
Curves and total timing are another thing. As you said a non stock engine has no book specs. If it pings, back off on the timing.
Making a/f and timing adjustments on non stock engines often requires someone who has experience with a similar set-up. Can't really be done on line or over the phone. Look for local help.
 
I would recommend getting the timing where ever it likes to be for your idle/starting and then get your distributor curved for what ever it likes on the top end for most power and no pinging. Dont worry about any factory specs
 
First mistake. Not having vac adv on a big cammed engine like this. The VA unit needs to be adjustable to work with the lower-ed vac of the big cam.

Second mistake. Using a vac gauge to set idle timing & mixture. Might work ok with stock cam, but useless with large cam & gauge needle bouncing around.

Third mistake. Choice of buddies.

Fourth mistake. Buying a useless big bucks MSD dist that [a] has no vac adv & has a magnetic pick up that has less cyl-to-cyl accuracy than a stock Mopar dist.

This is the first thing you need to do, then report back with the result. Five min test:
[1] warm up engine, put into gear if auto.
[2] Engine idling, loosen dist clamp
[3] Slowly turn the dist CCW, starting from about 12* BTDC. Idle rpm will increase & get smoother [ how do I know this? ]
[4] Keep going CCW until you reach the highest idle rpm.
[5] Then toggle dist CW/CCW until you are sure of highest idle rpm.
[6] NOW check the timing. Do not be surprised if it is 30+ degrees. That is a guess on my part because you haven't provided the cam specs.
 
Bewy said:
First mistake. Not having vac adv on a big cammed engine like this. The VA unit needs to be adjustable to work with the lower-ed vac of the big cam.

Second mistake. Using a vac gauge to set idle timing & mixture. Might work ok with stock cam, but useless with large cam & gauge needle bouncing around.

Third mistake. Choice of buddies.

Fourth mistake. Buying a useless big bucks MSD dist that [a] has no vac adv & has a magnetic pick up that has less cyl-to-cyl accuracy than a stock Mopar dist.

This is the first thing you need to do, then report back with the result. Five min test:
[1] warm up engine, put into gear if auto.
[2] Engine idling, loosen dist clamp
[3] Slowly turn the dist CCW, starting from about 12* BTDC. Idle rpm will increase & get smoother [ how do I know this? ]
[4] Keep going CCW until you reach the highest idle rpm.
[5] Then toggle dist CW/CCW until you are sure of highest idle rpm.
[6] NOW check the timing. Do not be surprised if it is 30+ degrees. That is a guess on my part because you haven't provided the cam specs.
Click to expand...

Hey, he's a good buddy. I don't think the vacc timing is a good idea, although the other things may be a mistake, he's not.

Other than that, the engine starts perfectly, I'm running 13.5-14 afr, with slightly higher and lower temporary movements, but it is staying pretty much between 13.5-14 idle, during 2,000 - 2,500 transition and above 2,500. When I am around 2,500 rpm and nail it, AFR drops below 11 and then picks up immediately to 13.5, then climbs to 14. These are good AFR readings from what I have gathered. Timing, well, I haven't dug too deeply into it. It is a Blue Print Engine's 408, I can post the cam specs, if you can tell me exact timing, but my guess is that even with the specs you won't be able to tell me what to put it at. I could be wrong about that, but IDK. If you can tell me where to at least start it at, I will post them.

Right now it is sitting right at about 17 Advanced. and Peaking at 34. I only have so many springs to work with, but the engine doesn't seem to like anything but 16 or 17 initial and 34 total. I cannot for the life of me hear it ping, so that's out. I have an EGT gauge, but it doesn't go above normal temps. If I go with more advance, 18+ she doesn't like to start when hot. 17 Starts Perfectly. I may have it timed right, but what makes me wonder is it is rough under acceleration. Around 2,500-3,000 rpm in 2nd heavy acceleration makes it run kind of rough, not like the car is going to fall apart, but it is rough. I don't know if this is normal or not. I haven't taken it to 3rd 2,500 - 3,000 yet because if it is rough in second I assume it will be worse in third.

You are the first one who has told me to get a vac advance dizzy with this engine. Why do you believe it is necessary? I am using an AFR to set the carb jets, bleeds, acc cams, pump nozzles, power valve, and idle screws on my Holley DP 750. She is running extremely well right now, only thing is this running rough 2,500 to 3,000 or so with heavy acceleration.
 
Here's how I do it without anything. Unplug the vacuum advance and block the hose if it has one "just because". If not, don't worry about it.

Next get it up to operating temp. Now, standing on the passenger's side, loosen the distributor just barely enough you can turn it.

Now, put one hand on the valve cover and get a feel for how the engine vibration feels. Next, start pulling in more (counter clockwise) initial timing. You'll notice the idle increase, that's good. That's the engine telling you it wants more initial timing. When you feel the engine start an extra "rumble" and kinda "beating" through the valve cover, you've gone too far, back it off until it just quits that. Now plug the vacuum can back in (if equipped) and go drive it.

Try to lug the engine in high gear at as low of a speed as possible. If it spark knocks (pings) back off a HAIR, like maybe 2 degrees and test drive it again. If if doesn't spark knock, then leave it alone. Nine times out of ten that procedure will work and be about dead on.

You'll still need to check with a timing light for the total advance and WHEN it is all in. You don't want a total of anymore than about 36 all in by about 2500. So, if you end up with like 40 or more, you're going to have to limit total timing. There are a couple ways to do it.

Don Gould at Four Seconds Flat sells the FBO limiter plate with different length slots that limits the total mechanical advance. OR you can weld the slots up in the distributor governor. I just did that recently to an electronic ignition distributor for my slant 6. I've done both. The limiter plate and welding the slots and I prefer welding the slots. The distributor has to come apart either way, so what the hell?

Lastly, you'll want to tailor the curve with lighter springs. I've done a LOT of them through the years and one light and one medium spring usually gets it RIGHT in the ballpark for most engines.

You can map out the whole curve if you want, but I usually don't mess with all that. For instance, my slant 6 has 23.5 degrees initial timing with a total of 33.5 degrees all in by 2700 RPM. It loves the crap out of it. It has a BIG solid flat tappet and lots of compression and runs like moody's goose. It's all in the tune. That's how I do it and it works for "ME".
 
RustyRatRod said:
Here's how I do it without anything. Unplug the vacuum advance and block the hose if it has one "just because". If not, don't worry about it.

Next get it up to operating temp. Now, standing on the passenger's side, loosen the distributor just barely enough you can turn it.

Now, put one hand on the valve cover and get a feel for how the engine vibration feels. Next, start pulling in more (counter clockwise) initial timing. You'll notice the idle increase, that's good. That's the engine telling you it wants more initial timing. When you feel the engine start an extra "rumble" and kinda "beating" through the valve cover, you've gone too far, back it off until it just quits that. Now plug the vacuum can back in (if equipped) and go drive it.

Try to lug the engine in high gear at as low of a speed as possible. If it spark knocks (pings) back off a HAIR, like maybe 2 degrees and test drive it again. If if doesn't spark knock, then leave it alone. Nine times out of ten that procedure will work and be about dead on.

You'll still need to check with a timing light for the total advance and WHEN it is all in. You don't want a total of anymore than about 36 all in by about 2500. So, if you end up with like 40 or more, you're going to have to limit total timing. There are a couple ways to do it.

Don Gould at Four Seconds Flat sells the FBO limiter plate with different length slots that limits the total mechanical advance. OR you can weld the slots up in the distributor governor. I just did that recently to an electronic ignition distributor for my slant 6. I've done both. The limiter plate and welding the slots and I prefer welding the slots. The distributor has to come apart either way, so what the hell?

Lastly, you'll want to tailor the curve with lighter springs. I've done a LOT of them through the years and one light and one medium spring usually gets it RIGHT in the ballpark for most engines.

You can map out the whole curve if you want, but I usually don't mess with all that. For instance, my slant 6 has 23.5 degrees initial timing with a total of 33.5 degrees all in by 2700 RPM. It loves the crap out of it. It has a BIG solid flat tappet and lots of compression and runs like moody's goose. It's all in the tune. That's how I do it and it works for "ME".
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RRR , that not too quick with todays crappy gas ?? I always thot it might be ok , say for higher octane , asking for a friend , ------------as they say !
may need to bring mine in quicker , all in at 3400 on 93 pump---??/
 
Just a thought. Since Blueprint engines dynos every engine have you thought to contact them about what they recommend since it is one of theirs ?
 
Here is our detailed installation guide that is on our website, and was just updated. section 6 is how we recommend setting timing.
https://cdn.shopify.com/s/files/1/2...llation_Guide_-_Single_Pages.pdf?v=1631108823

IF the engine was purchased as a complete dressed unit, with distributor, we set the timing at the plant, and Chisel mark the distributor/intake so timing can be set, in case it get bumped, within at least a few degrees. i see this is an MSD, and 6AL, which didn't come from us.

Total and initial timing requirements are on the recommendations page online. 34 total is all these need. NOT any more.
Mopar 408CI Stroker Crate Engine | Small Block Chrysler | Fully Dressed | Roller Cam

This should be as simple as verifying total timing at XXXX RPM (wherever it stops advancing). Then idling it down, and verifying initial timing is within 10-16. If it's not, then those pro billets have limiter bushing options to limit total travel. if you want to play with the curve, they also obviously have different strength springs.

NOW, all that being said... i don't see it mentioned if the "roughness" cleans up at any point, or gets worst given different driving conditions. We're alot of information away from just assuming the distributor has the wrong advance springs, but i'm also assuming bob has checked the timing as described in our guide, and it's been verified with a timing light to be correct.

I don't recall if this left with an/or intake and carb on it. But "roughness" could be anything from a blown power valve, to something as minor as jetting or idle mixture adjustments, choke operation, fuel pressure, something disrupting airflow, etc.

I'm not on here all the time, so please feel free to reach out to tech at 308-236-1050. ask for ken or brian, they are the senior guys.

upload_2021-9-29_12-16-2.png
 
bob mCcarty said:
RRR , that not too quick with todays crappy gas ?? I always thot it might be ok , say for higher octane , asking for a friend , ------------as they say !
may need to bring mine in quicker , all in at 3400 on 93 pump---??/
Click to expand...
You never know till you try. It might be. But just do like I said and back off 2 degrees at a time until it stops rattling.
 
from what I recall with a vac guage you turn distributor till highest vacuum then back off 1 inch hg then lock it down. I havent done it this way often as i like a timing light,but I did have a 65 327 once where the timing marks didnt line up for some reason and I had to do it this way...customer was ok with it in the end...
 
Duster Bob,
Let me apologise for post #6. I came across a bit 'too' heavy & I don't know the bold print got in, only meant to 'bold' a few words.
I have been doing this for 40+ years. Back in the 70s, I was mounting solenoids on the sides of dizzys because I couldn't get adj vac adv units HERE to increase idle timing. The sol pulled in the breaker plate to advance the timing once the engine was running. Not a perfect set up, but better than nothing.

Ign timing is a most MISUNDERSTOOD subject, even amongst seasoned mechanics.

No apologies for what I am about to say because some of the comments above are just NONSENSE without knowing the cam specs. Such as initial timing is within 10-16*. You determine initial timing from the procedure in post 6, & that is where you start. Many racers used to & still do, 'lock' their dists. That means if the engine made best HP with 40* of timing, the engine also idled with 40*. My engine has a locked dist, 35*. My adj vac adv unit, which is connected to manifold vacuum, adds 13*. So it idles with 48*. [ Ported vac adv is useless. MVA does everything that PVA does, & more ]
David Vizard. Author of 30+auto books & over 4000 articles. Consultant to F1 teams, major auto companies, cam companies, you name it.

This is what he says about idle timing in his Holley book [ think about why idle timing might be important for setting up a carb ].
"The optimum idle advance is typically about 35-40* for a short cammed street engine & though not commonly realized ] ** ain't that the truth** as much as 50* for a street strip engine".
Elsewhere in the book: 'To get an optimum idle....timing often needs to as much s 45-50*'.
It gets mentioned in a carb book because idle timing is the starting point for tuning the carb's idle circuit. NOT the other way round.
By using an adj vac unit, which works down to about 6-7" of vac, you add the extra timing reqd for best idle quality, highest vac & best off-idle tip in response. The engine makes more HP at idle when it has the correct idle timing, so that it carries the load off idle without a stumble.

More specific to Mother, p. 34 of Mopar Muscle magazine Oct 2015. "Initial timing went from 15 to 26* while adding an inch of vacuum......a dramatic gain in low rpm throttle response was realized. "
 
Another option: subscribe to 318willrun. He covers initial and total timing in videos.
:lol::lol:
 
From Super Chevy, May 2016. Yes, it is a Chebby but believe it or not, the same principles are involved. Only the numbers will change, very slightly.
p. 56 "Plugging your vac adv unit into a direct [ manifold ] source will allow it to engage at idle, which is good for a number of reasons."

p. 58: " Plug the vac adv into a ported source & check idle rpm. Now switch to a direct source & check idle rpm again. We'll bet money the rpm increased. Why? Because the additional ign timing....allowed the engine to more effectively burn the A/F mixture. It therefore produces more power [ even at idle ] and rpm rises as a result".
 
Boxing in timing adjustment only "one" way certainly doesn't work for everything. Just do whatever is easiest and works best for YOU.
 
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At the risk of sounding arrogant, I'm going to make a very blunt statement. Everyone is entitled to their opinion, but the literature posted above in my post, and on the BluePrint Engines website was written and comprised by a company that has produced 370,000 + engines, in 40 years, with many employees being there for the entire run, and having a hand in the published procedures for how we, the engine manufacturer, suggest you tune our engines, to prolong longevity. We are in the business of longevity built engines, and preserving customers warranties. Bob has our contact info, and recommendations. Happy to help any time.
 
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You didn't say if automatic or manual trans or stall.
For automatics;
setting the Idle-timing, on an SBM, by highest idle-vacuum is a terrible idea.
Unless you have a minimum ~3600rpm stall with iron heads, or a minimum ~3200 stall with alloys,
AND,
your PowerTiming is limited simultaneously to whatever it takes to prevent detonation.
Now, why your street engine would have those stalls, is beyond me, especially if a stroker.
But if a manual trans,
setting the Idle-timing, on an SBM, by highest idle-vacuum is beyond a terrible idea.


The exact right way to set the Idle-Timing is;
by adjusting the transfer-port exposure underneath the Primary blades to a lil taller than wide; closing up the secondaries completely, and leaving them alone at those settings;
then
adjusting the timing down to whatever it takes to hit a reasonably slow enough rpm, that the trans does Not bang into gear, AND stays running!, AND the engine takes throttle without hesitation.
If the exhaust burns your eyes, then you will need to add some bypass air, and then reset the IDLE TIMING again, to get the rpm down.

Occasionally, if you can't get rid of an Idle tip-in sag, you might have to increase the transfer slot exposure slightly, then start over again.
I guarantee this will work up to and including the 292/292/108 Mopar cam. Using this method, I tuned this cam in my 367 to idle in Neutral at 700 (manual trans) and idle around the parking lot at 550rpm,
with just 5* of Idle-Advance, and a starter gear of 9.44
and with no tip-in sag on the 750DP carb. So, I know the method works.
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No, my normal Idle-Timing was NOT 5*; I just used that number to avoid bucking and toe-ing the clutch. The normal idle-timing was 12 to 14. To get the 5*, I used an adjustable, dash-mounted, timing-retard module, which had a 15* working range.
My V-can was modified to provide 22* of PT (Part Throttle) advance.
The module was set initially to provide 7* retard/ 8* advance. This allowed up to 20* of idle-Timing which I used after starting the engine cold, and this eliminated the need for a choke.
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Since that time (1999) I have used this same method on many other engines and combos; and for a while in the early 2000s I was the go-to guy in my neighborhood, for doing this kind of work, which I did at home.
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But for best results, there is a long list of "pre-flight" checks to be done.
The toughest one to find was tight ring-gaps. If your ring-gaps and/or skirts are too tight, the engine will be a beotch to make run smoothly.
IMO
the KB street specs for hypers are too tight. I ended up taking my engine apart and loosening it up a lil, then starting over. I now run it at 207*F, all the time. Since that 292/108 cam, this engine has seen two other cams; idle-tuned the same way.
 
Johnny Mac said:
At the risk of sounding arrogant, I'm going to make a very blunt statement. Everyone is entitled to their opinion, but the literature posted above in my post, and on the BluePrint Engines website was written and comprised by a company that has produced 37,000 + engines, in 40 years, with many employees being there for the entire run, and having a hand in the published procedures for how we, the engine manufacturer, suggest you tune our engines, to prolong longevity. We are in the business of longevity built engines, and preserving customers warranties. Bob has our contact info, and recommendations. Happy to help any time.
Click to expand...
Yeah, I kinda lost sight of the fact it was a blueprint engine. My bad. The procedure I outlined was taught to me by a retired Mercedes-Benz mechanic that was on the line from the early 40s to the late 70s. He was our high school auto shop teacher, James Lovett.

I fully agree to follow Blueprint's procedure for their engines for timing. That said, I'd like to see how close the two procedures would come to netting the same results.
 
The engine has no clue who built it. Claiming XX total timing is THE number is just wrong. Timing lights don’t all read the same. 3-4 degrees difference is common. That also means that initial timing can vary that far. The only way to get the initial correct is to test for it. Once that is correct you can work in total timing and thats done by reading the plugs. Once you get the total correct you can work on the curve. Or better yet, start out with a guy who has tuned distributors for awhile like Halifaxhops and let him dial in your distributor on his machine.
 
Rat Bastid said:
The engine has no clue who built it. Claiming XX total timing is THE number is just wrong. Timing lights don’t all read the same. 3-4 degrees difference is common. That also means that initial timing can vary that far. The only way to get the initial correct is to test for it. Once that is correct you can work in total timing and thats done by reading the plugs. Once you get the total correct you can work on the curve. Or better yet, start out with a guy who has tuned distributors for awhile like Halifaxhops and let him dial in your distributor on his machine.
Click to expand...
Right! Two identically built engines can like totally different timing curves. Let the engine and circumstances dictate the timing curve.
 
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