351W Vacuum and Timing Readings

I know I'm on a tractor site but maybe you guys can help. Already asked this on another auto related forum and not getting much response. I have a 1965 Mustang with a mildly built 351W. Cam, heads, etc. Car seems to have gotten a little sluggish on low end so I started some diagnostics. All done with engine at operating temp. Timing mark of 0 has been confirmed to tdc. Distributor does not have vacuum advance.

Vacuum (port on bottom of carb) - bounces between 10.5-11.5 at 750 rpm

Timing
750 rpm - 18 - I get a slight 5 degree jump about every 8 seconds or so
1800 rpm - 30
3000 rpm - 36
3750 rpm - 40 - maxed out here

Vacuum seems ok for a mild build? My understanding is that worked engines can have a lower vacuum.

Should the slight jump in timing be a concern or can that be normal with a car like this?

Do my timing numbers seem a bit high? Would it be ok to keep the vacuum gauge hooked up to the bottom of the carb and dial in the timing that way? My understanding is you can turn the distributor to where it gets the highest vacuum and then back it down 1 psi for the most efficient timing. Then check timing mark to make sure it's in a good range. That sound about right or is there a better way for a novice to know the best timing for the vehicle?

I'd say all bets are off if you don't know what cam is in it. When I bought some edelbrock cams they came with specific instructions for timing settings. IIRC they were way farther advanced to start with than stock settings.

(quoted from post at 07:53:42 07/25/18) I'd say all bets are off if you don't know what cam is in it. When I bought some edelbrock cams they came with specific instructions for timing settings. IIRC they were way farther advanced to start with than stock settings.

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Unfortunately the guy I bought the car from didn't know what cam is in it.

I think your vacuum numbers are low, may have a vacuum leak.
Take a can of carb cleaner and spray the gasket joints at carb
to manifold and manifold to heads hose going to brake booster.
As for timming may need to change weights in distributor to
delay full advance in timing.

(quoted from post at 08:04:36 07/25/18)
Take a can of carb cleaner and spray the gasket joints at carb
to manifold and manifold to heads hose going to brake booster.

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will do

depends... on cam.. if its a "waddle waddle" cam, :roll: vacuum will be very low at idle. And timing will be around 12 degrees advanced.... And low end will suck. The valve springs will have a lot to do with performance as the cam :twisted: will run up till the springs float.

backing off timing might help low end but will take high end. about all you can do is set high idle and run a bit rich.

Again,, assuming its a waddle waddle. 3/4 street grind or better. I ran a 3/4 track grind so low end was a joke.

I think your timing numbers look about right.

I would agree that idle vacuum seems low, I would want to see it up around 15, depending on cam grind.

It is important that your power valve does not open up above idle vacuum.

(quoted from post at 08:21:50 07/25/18) depends... on cam.. if its a "waddle waddle" cam, :roll: vacuum will be very low at idle. And timing will be around 12 degrees advanced.... And low end will suck. The valve springs will have a lot to do with performance as the cam :twisted: will run up till the springs float.

backing off timing might help low end but will take high end. about all you can do is set high idle and run a bit rich.

Again,, assuming its a waddle waddle. 3/4 street grind or better. I ran a 3/4 track grind so low end was a joke.

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I don't get some of your terms, LOL.

waddle waddle - if you mean cam lope, yes I have cam lope.

3/4 street grind?

Total advance for that engine is 35 degrees. { you always need the specs of the cam even if it means replacing it].

Ok i will tell yo what i know of the 351 W and how we use to set them up back in the day . I use to work in a large Ford dealership and we were heavily involved in in the Drag Club i was the so called expert as i was the performance adviser and head wrench . So first off for get the retard as that was the first things that went to the dumpster now as to curb timing this all depending on if it was a automatic or a four gear , on a four gear timing was set a 10 degrees BTDC and a slush box at 5-8 BTDC. total full advance was 38 degrees at 1800 on the four gears and and 36 degrees at 2000 for the auto. ( now keep in mind here first we were working with 10.5 to 1 compression C /Ced heads and most all the 351 W's in the club were now sporting the C9OZ 6250 C cam that was made for the 221-302 and just by swapping firing order you could run that cam. We were running Holley 650 vac secondary with staggered jetting On the four spped cars were were running 298 dual point dist. and signal points on the automatic . Now please don't ask me how i curved the dist. for each as it has been 49 years ago and i made the mistake of letting a friend BORROW my notes and all my tech books as he was working on his 65 Mustang with a 289 271 . and one night out with the GUYS they were involved in a wreck and he died . I neve saw my big thick black binder again and it had a trove of info and part numbers and phone numbers . Now what i do know today is with what is out there for PUMP gas your not going to doing the 10.5 to 1 compression thing and your not going to be hitting them 36=38 degree full advance . Last i talked with OLD friends who were still playen they were having a hard time at 9.5 and 34 degrees with the 93 pump gas even on the street. Ah for the good old days

Your advance is coming in way to fast as the spec.s i gave you are Dist RPM's , This is where my old notes would help . I spent a lot of time tryen different things back then . when you turn up your curb ideal from stock curb ideal you are starting to get into your mechanical advance and stuff starts changing . The art of curving a Dist. is almost dead and gone today . I think i am the only one that still has a dist machine and knows how to use it . Only thing it gets used for now is working on old tractor dist.

Hello nrowles,

Try power tuning the engine. Here is how: with a warm engine set the idle between
1200 to 2000 R.P.M.'S. Loosen the distributor hold down bolt just enough so you
can turn it. Hook up a vacuum gauge to the engine. Slowly rotate the distributor to obtain maximum vacuum. Then, rotate
the distributor the other way so that the vacuum reading drops slightly. Tighten
the distributor, and road test. You should see an improvement in power. If it
pings you can regard the timing a bit, usually no need to do it. This procedure
will give you all the power the engine has with the current set up. If not enough power, then you need to look for
other issues,

Guido.

Darn it Guido, that is how I time my tractors, and get a lot of flack here.

Hello David G,

Me too, get some flack as well. They just don't understand or want to learn. More manifold pressure, { vacuum IS negative pressure} 2" of vacuum = about 1 lb. of pressure, = more power! Wish somebody would try it and tell us how else to do better.....You and I know it works. I could quote a text book reference? May be NOT! Tried that too!,

Guido.

(quoted from post at 11:56:26 07/25/18) Hello David G,

Me too, get some flack as well. They just don't understand or want to learn. More manifold pressure, { vacuum IS negative pressure} 2" of vacuum = about 1 lb. of pressure, = more power! Wish somebody would try it and tell us how else to do better.....You and I know it works. I could quote a text book reference? May be NOT! Tried that too!,

Guido.

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Why do you get flack for it? Doesn't seem hard to do. Is it a risky position to put your distributor/timing?

Some folks just want to go by manual, fuel has changed a lot in 70 years, and I do not crank start.

We did the exact thing on all our cars for years. If I remember correctly the harmonic balancers would slip a little on the rubber and you really couldn't depend on the timing lights, so this is what we had, especially if we had built the engines some (or a lot)' I also used to use the tv in the living room when I had a garage that was attached to the house. It would have lines across it and show every time a cyl, would fire. Boy, we're telling our ages now Guido. LOL

yes.. waddle waddle... cam lope.. bad cam lope...

so no low end, no low end vacum, due to overlap. "waddle waddle" crosses most languages.

back in the 60s... cams were order for either a street grind or a track grind...

street grinds had to limit on overlap so make constant starting in traffic bearable... and you could even get it in a hydraulic lifter setting. Idle speeds below 2000 were doable although hard to drive in traffic or low rpms... No waddle tilll you got to around 3/4 grind.. then lots of waddle waddle...

Track grinds were insane, required a 2000 rpm idle, hugely modified torque converter stall speed and were never made to idle or start off from an idle... all starts were at very high rpms... beyond waddle waddle so more "womp papa womp papa" then to stacatto machine gun as moved up a bit. and extremely low and jumping vacuum all over the gauge. Timing even more advanced that yours. 3800 rpm stall speeds.

(quoted from post at 12:37:47 07/25/18) Hello nrowles,

Try power tuning the engine. Here is how: with a warm engine set the idle between
1200 to 2000 R.P.M.'S. Loosen the distributor hold down bolt just enough so you
can turn it. Hook up a vacuum gauge to the engine. Slowly rotate the distributor to obtain maximum vacuum. Then, rotate
the distributor the other way so that the vacuum reading drops slightly. Tighten
the distributor, and road test. You should see an improvement in power. If it
pings you can regard the timing a bit, usually no need to do it. This procedure
will give you all the power the engine has with the current set up. If not enough power, then you need to look for
other issues,

Guido.

Click to expand...

do it for blind timing,, works fantastic on engines with lower rpms settings and shorter timing curves.

Problem is... you optimized the engine at that rpm and with no load on it.

again works well on simply low rpm engines, not worth a darn on any wide rpm or heavy load changing engine, or especially with overlap on a big cam.. that changes flow [b:a7fc015f34]completely[/b:a7fc015f34] at higher rpms.[i:a7fc015f34][u:a7fc015f34]. Will usually not give correct setting for these engines and cause them to run hot and retarded.

Again,, not bad for lower performance low rpm engines.. Especially good if no timing marks or blind timing. Will always get you into the ball park for these engines. Hopefully you can see where is works well and where is works not so well.

The vacuum gauge was a huge tool up till '65 or so when the emissions started over-riding optimum vacuum settings and vacuum timing. pcv valves started the demise, lean jets pretty much killed it... no timing advance till in high gear in 69 or so was the final nail. Day of 21 to 23?? lbs is a memory. long live the queen.[/u:a7fc015f34][/i:a7fc015f34]

Hello Keith Molden,

Well? I guess is better then the alternative? Like you I have been at it for decades. I wish that those that are growing up would at least challenge the info. I try........ Their loss!

Guido.

Check to make sure vacuum to distributor is ported and not manifold vacuum.

(quoted from post at 12:10:22 07/25/18) The art of curving a Dist. is almost dead and gone today . I think i am the only one that still has a dist machine and knows how to use it . Only thing it gets used for now is working on old tractor dist.

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Where are you located?
Been a while since I hear of someone with a working dist machine.
I have a MSD dist for my Ford 406 FE engine I'd love to curve out.
The bulb burned out in my old Sun dist machine several years ago and I never could find one.
Finally scraped it a few years ago when we where cleaning out the old shop building.
I messed with a few of these MSD's and never have got them to work like I wanted.

Need a little more info to work with.

It's a 351W with aftermarket cam of unknown size.
What carburetor is on it? Brand and size.
Automatic or manual?
If auto, stock convertor or aftermarket with higher stall?
If auto what is the vacuum at idle with the trans in drive?
Does it idle ok and is sluggish taking off or does it not want to idle well.
Is it gassy smelling at idle or about normal.

10-14 inches of vacuum is about normal for a small block with a mild performance cam, I've ran some pretty radical cams that only had 7 inches of vacuum or less at idle.
For a mild cam with a little lope or rumble you shouldn't need more than 12 degrees base timing at 800-1000 engine rpm.
With todays gas and modern cam grinds 34-36 degrees total is max.
I like to have total advance by 2700-3000 engine rpm.
Sound like some lighter springs are needed in the dist.
Also what dist are you running, stock or aftermarket?

(quoted from post at 06:54:58 07/26/18)
Need a little more info to work with.

It's a 351W with aftermarket cam of unknown size.
What carburetor is on it? Brand and size.
Automatic or manual?
If auto, stock convertor or aftermarket with higher stall?
If auto what is the vacuum at idle with the trans in drive?
Does it idle ok and is sluggish taking off or does it not want to idle well.
Is it gassy smelling at idle or about normal.

10-14 inches of vacuum is about normal for a small block with a mild performance cam, I've ran some pretty radical cams that only had 7 inches of vacuum or less at idle.
For a mild cam with a little lope or rumble you shouldn't need more than 12 degrees base timing at 800-1000 engine rpm.
With todays gas and modern cam grinds 34-36 degrees total is max.
I like to have total advance by 2700-3000 engine rpm.
Sound like some lighter springs are needed in the dist.
Also what dist are you running, stock or aftermarket?

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I sprayed some carb cleaner around base of carb and manifold and no change in engine sound/rpm. Seems there is no vacuum leak.

Checked fuel pressure and it was steady at 6 so I'm good there.

Took the car for a rip and it was pinging. Not sure how the timing changed but it did. Backed it down to 14. Got dark. Will run it on Saturday to see if that's helped.

To answer your questions....

10 months old Holley 670 Street Avenger with electric choke. 4 speed toploader. Idles fine but a bit sluggish on take off. This car just stinks of smells all around but I can't say any worse than usual. It is an MSD distributor WITHOUT vacuum advance. From what I've been reading I agree that my total advance should come in at least 800 rpms sooner.

Dropping it back to 14 should help with the pinging but you may need to back up to 12.
Don't know a lot about the newer Holley's but that should be a pretty good carb.
There's tuning instructions on Holley's web site for making sure the carb is set properly.
Is the electric chock wired up, if not it can cause a rich condition.

There's a spring kit you can get for the MSD to help with the timing curve.
On the ones I was working with we were trying to get a quick curve for our app but with the 2 lightest springs the advance weights wouldn't settle down until rpm dropped below 1000, this was causing the timing to hang up while still advanced about 6 degrees interfering with the idle setting.
For you car one light spring and one medium spring should get you full advance around 2700-3000 and still settle down for a good idle.

Probably how I'll set mine whenever I get time to work on my 406 FE engine, been a while since I tuned 3 two barrel carbs but I think I remember how.

Love those Ford Tri Power multiple carb setups.

(quoted from post at 20:06:52 07/26/18)
Dropping it back to 14 should help with the pinging but you may need to back up to 12.
Don't know a lot about the newer Holley's but that should be a pretty good carb.
There's tuning instructions on Holley's web site for making sure the carb is set properly.
Is the electric chock wired up, if not it can cause a rich condition.

There's a spring kit you can get for the MSD to help with the timing curve.
On the ones I was working with we were trying to get a quick curve for our app but with the 2 lightest springs the advance weights wouldn't settle down until rpm dropped below 1000, this was causing the timing to hang up while still advanced about 6 degrees interfering with the idle setting.
For you car one light spring and one medium spring should get you full advance around 2700-3000 and still settle down for a good idle.

Probably how I'll set mine whenever I get time to work on my 406 FE engine, been a while since I tuned 3 two barrel carbs but I think I remember how.

Love those Ford Tri Power multiple carb setups.

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Choke is hooked up. The power wire had come loose already before and the idle ran way high so it's pretty obvious when that's loose.

I do need to look at the carb. I'm gonna have to look at the tuning instructions but I was thinking the bowls should be set at the bottom of the sight screw hole. I cracked both primary and secondary yesterday and there was fuel coming out so the floats may need adjusted.

I was looking at those spring kits online last night. It seems like most of what I've read agrees with what you are saying that my total timing should come in at a lower rpm.