My Combo, Manifold Or Ported VAC Advance, We'll See...

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Mopar Sam

Mopar Sam

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There have been several threads on vac. advance lately, and since I now have my old rusty truck running, I will be wanting to find out what my combo wants. I have a couple of things that may skew the results some, so at least to me, it will be interesting to see what it wants.


First, my combo:

1967 D100 short stepside, lightened a little.
340 based 414 stroker
ProComp heads with the pushrod holes plugged and redrilled for W2 rockers. 210 cc intake ports, 2.08/ 1.6 valves, 50 degree seats.
Solid Roller 251/256 with 640/640 lift on a 106 installed at 105
11.6:1 compression (My chambers ended up being bigger than expected)
KB ICON flat tops .015 above deck
Felpro 1008 gaskets, so, around .025 quench clearance
Holley W2 Strip Dominator ported to match above heads, also some work in the plenum
727 full manual, 8" converter
4.57 gears , 31" tires, on the street

Now, the parts that are maybe a little different from the norm.

First, the only distributor that I have without shot bushings is an old lean burn (factory locked out) unit. I did add a vac pod to it.

Second, and probably the one most won't like, is my 1 barrel carb. (an old 5000 series Predator) I have done a couple of mods to it, the
best being blocking the outermost holes in the spray bar. This cleaned up the idle mixture a bunch. I am also running a 5 percent
leaner fuel cam

Now the kicker, at least for now. My budget is spent. No choice to change distributors or carb. I lost a lot of parts when we moved. I had a tried and true 750 DP that is now MIA. So, I'll be using what I have.

My goal is some decent drag times, hopefully this year. And, to get good enough mpg to afford to drive the thing. To me that is at least 15 mpg.
The Predator may be hungrier than that though.

So, Vacuum advance will have to be a big part of the equation, and I will try both ported and manifold.

Now, I have some work to do, the Predator has no provisions for either ported or manifold, but I will drill the carb for ported, and my spacer for manifold vacuum.
 
Post pictures cause it sounds like a sweet ride. Sorry to hear you are at the end of your budget.
 
ch1ll said:
Post pictures cause it sounds like a sweet ride. Sorry to hear you are at the end of your budget.
Click to expand...
I'll try to get some pics. Budget comes and goes, but hey, that happens. I like a good challenge.
 
I'm always at the end of my budget. LOL

Some here will say if your build wants manifold vacuum, it's a bad or poor build. I don't necessarily share that sentiment. Although it's certainly possible it can be a crutch for a non optimal build, I like to think of it as "just doing it a different way". Both my vehicles for example, ran fine with either ported or manifold vacuum. Both of them "just happen" to run a little better on manifold vacuum. I wouldn't call it night and day, but it's a noticeable difference. Enough that they are staying with manifold vacuum.

The big block Chevelles used manifold vacuum on the distributor all the way to 71 and maybe 72. Were they "bad builds"? 3700 pound cars that could run low 14s and high 13s from the factory? I'd hardly call that "bad".
 
"IF" i run a vacuum advance, I run ported. That's just me, and a sure bet is to do opposite of me :)
 
Pics of my first start with no fuel pump, my son holding a funnel full of gas.

image0 (1).jpeg
 
RustyRatRod said:
I'm always at the end of my budget. LOL
Click to expand...
Yeah, but you still manage to get things done. Some really cool stuff, like your slant 6 build.

Your vacuum advance thread is what got me to thinking about doing this on mine. Thanks.
 
Love the Predator! I've had some experience with those in mud trucks and some on the street.
 
Mopar Sam said:
Yeah, but you still manage to get things done. Some really cool stuff, like your slant 6 build.

Your vacuum advance thread is what got me to thinking about doing this on mine. Thanks.
Click to expand...
Thanks. But man, I tell you what. I've been in the right place at the right time and dealt with a lot of fantastic people. There's no way I'd be where I am without the help of others.
 
RustyRatRod said:
Love the Predator! I've had some experience with those in mud trucks and some on the street.
Click to expand...
I had one in the 80s, but gave up on it too soon. I was just a kid, and listened to everybody telling me it was junk.

I got this one CHEAP, took it apart and cleaned it up and reassembled without needing 1 gasket. I was sure I would need a kit, but it looked like someone had put new gaskets in and then put it on a shelf for 20 years..
 
Mopar Sam said:
I had one in the 80s, but gave up on it too soon. I was just a kid, and listened to everybody telling me it was junk.

I got this one CHEAP, took it apart and cleaned it up and reassembled without needing 1 gasket. I was sure I would need a kit, but it looked like someone had put new gaskets in and then put it on a shelf for 20 years..
Click to expand...
Cool! The biggest mistake people make is getting one without the idle circuit and then throwing it away because it won't idle. lol They are dead simple though.
 
RustyRatRod said:
Cool! The biggest mistake people make is getting one without the idle circuit and then throwing it away because it won't idle. lol They are dead simple though.
Click to expand...
Mine is an early one, no idle circuit, but it was suggested on a FB site to plug the 2 outermost spray bar holes (8 total) ,to clean up the idle. I did with some belzona, and with this roller cam it idles pretty good at 1000, and could probably go lower. This is with timing locked at 34 degrees.

Instead of a bellcrank for the throttle, I used the accelerator pedal and cable from the 2003 Ram that I recently parted out.
 
Newbomb Turk said:
Did you do a video of that work on YouTube??

Seems I watched a video on that or something similar a couple of years ago.
Click to expand...
Yes, a poorly done video. This was before the heads/intake were done, several more hours of work after that.

 
Ok I'm a lil confused;
I'm not being a smartazz when I say;
your 414 with a 251* cam, in a pick-up truck, will be spinning about 3300 at 65 mph:
and you are looking for 15 mpgs with a Predator?
I'll be waiting right here to see how that plays out.
Ok wait, maybe just a lil smartypants crept in there.

I know nothing about the Predator, but I hope she's is a pretty good mixer with the throttles nearly closed, and, you will have to mod the VA out to at least 20/24 degrees, to run close to 56* hiway timing, with that tight .025 squish. I highly recommend you get a dash-mounted, dial-back, electronic timing module so you can change the cruize timing on the fly; this will save you weeks of testing.

Ima thinking that combo will want full-time manifold vacuum to the VA.
But if the PowerTiming is locked at 36* and you add 24 VA at idle; that's 50 stinking degrees!
I don't think the engine will like that..... so now, Ima thinking to get rid of the locked out distributor.
Whatever you do, you are probably gonna be the pioneer so Best of "luck" to you.
 
AJ/FormS said:
Ok I'm a lil confused;
I'm not being a smartazz when I say;
your 414 with a 251* cam, in a pick-up truck, will be spinning about 3300 at 65 mph:
and you are looking for 15 mpgs with a Predator?
I'll be waiting right here to see how that plays out.
Ok wait, maybe just a lil smartypants crept in there.

I know nothing about the Predator, but I hope she's is a pretty good mixer with the throttles nearly closed, and, you will have to mod the VA out to at least 20/24 degrees, to run close to 56* hiway timing, with that tight .025 squish. I highly recommend you get a dash-mounted, dial-back, electronic timing module so you can change the cruize timing on the fly; this will save you weeks of testing.

Ima thinking that combo will want full-time manifold vacuum to the VA.
But if the PowerTiming is locked at 36* and you add 24 VA at idle; that's 50 stinking degrees!
I don't think the engine will like that..... so now, Ima thinking to get rid of the locked out distributor.
Whatever you do, you are probably gonna be the pioneer so Best of "luck" to you.
Click to expand...

With the Predator, 15 mpg may be a dream, but one I'll aim for.

I am going to play with the rate the manifold vac advance comes in, and ported may be the better option.

Yes you are right about the distributor, and I may at some point change it. In fact I would much prefer one I could put a curve in, but for now I'm stuck with this one.

Thanks for the comments.
 
Mopar Sam said:
With the Predator, 15 mpg may be a dream, but one I'll aim for.

I am going to play with the rate the manifold vac advance comes in, and ported may be the better option.

Yes you are right about the distributor, and I may at some point change it. In fact I would much prefer one I could put a curve in, but for now I'm stuck with this one.

Thanks for the comments.
Click to expand...


Just so you know, I just went through a similar thing like MVA today. My friend has a 73 Duster with a 340 I did.

A measured 10.64:1 and a little 280/.480 lift Chrysler circle track cam.

I would rather he had a cam that had LESS seat timing with the same at .050 timing. Or quicker.

Anyway, his cousin is a true bubble gummer. And he reads forums and takes every word as gospel.

So when said cousin was helping him last year, he did a “POWER TIMING” thing…some bull squirt nonsense like that.

I had no idea what he had done.

First he went down a plug range. Then he set the timing “by ear”. And he did by that by doing what I detest.

He set the idle low, then he just turned the distributor until his EAR said it was set. He never hit it with a timing light and didn’t have a clue what the total was.

I fixed the **** I had to and we took it for a drive. I’m thinking this thing idles like straight garbage and it feels like it’s down on power.

I’m trying to figure out WTF happened since the last time I drove it.

I pull a plug and it’s the wrong heat range. And I say who the frick put these plugs in? He says his cousin.

So I put the correct plugs in and it’s a bit better but the idle is crap on a cracker.

So I take out the timing light. I’m STUNNED when it says 30 initial at 900 RPM. And 40 total. Unreal.

Now I’m doing the Daffy Duck, loosing my mind. I’m thinking the distributor came loose so I try and tighten it up. But it’s tighter than (add in whatever you want here) so I asked just what went down after the last time I drove it.

That’s when the story comes out. So I said WTF is he doing. The upshot is he’s an idiot.

So I reset the timing at 24 initial and 36 total at 6k. Right where it should be.

And guess what? It now idles nicely at 1k and when it drops into gear it goes to 900 rpm.

It didn’t want all that initial. Why? Because the cam matches the compression ratio.

I’d bet everything I have that if I picked a different cam it would take even less initial timing and maybe a bit less at rpm. To really sort it out it shoud be on the dyno.

Like I say, MVA is a bandaid for a build with two much cam, not enough compression or both.

Too bad his bone headed cousin doesn’t have the common sense God gave a hammer. He’d be better off if he was as smart as a hammer.

A ball peen hammer, not a carpenters hammer. Those hammers are pretty dumb. No offense to carpenters here.

Edit: I forgot to point out that that 6 degrees of initial pissed it off at idle. My friend is a car guy but not a tuner. Even he could tell as soon as it fired up it was idling better than it was before.
 
Last edited:
Newbomb Turk said:
Just so you know, I just went through a similar thing like MVA today. My friend has a 73 Duster with a 340 I did.

A measured 10.64:1 and a little 280/.480 lift Chrysler circle track cam.

I would rather he had a cam that had LESS seat timing with the same at .050 timing. Or quicker.

Anyway, his cousin is a true bubble gummer. And he reads forums and takes every word as gospel.

So when said cousin was helping him last year, he did a “POWER TIMING” thing…some bull squirt nonsense like that.

I had no idea what he had done.

First he went down a plug range. Then he set the timing “by ear”. And he did by that by doing what I detest.

He set the idle low, then he just turned the distributor until his EAR said it was set. He never hit it with a timing light and didn’t have a clue what the total was.

I fixed the **** I had to and we took it for a drive. I’m thinking this thing idles like straight garbage and it feels like it’s down on power.

I’m trying to figure out WTF happened since the last time I drove it.

I pull a plug and it’s the wrong heat range. And I say who the frick put these plugs in? He says his cousin.

So I put the correct plugs in and it’s a bit better but the idle is crap on a cracker.

So I take out the timing light. I’m STUNNED when it says 30 initial at 900 RPM. And 40 total. Unreal.

Now I’m doing the Daffy Duck, loosing my mind. I’m thinking the distributor came loose so I try and tighten it up. But it’s tighter than (add in whatever you want here) so I asked just what went down after the last time I drove it.

That’s when the story comes out. So I said WTF is he doing. The upshot is he’s an idiot.

So I reset the timing at 24 initial and 36 total at 6k. Right where it should be.

And guess what? It now idles nicely at 1k and when it drops into gear it goes to 900 rpm.

It didn’t want all that initial. Why? Because the cam matches the compression ratio.

I’d bet everything I have that if I picked a different cam it would take even less initial timing and maybe a bit less at rpm. To really sort it out it shoud be on the dyno.

Like I say, MVA is a bandaid for a build with two much cam, not enough compression or both.

Too bad his bone headed cousin doesn’t have the common sense God gave a hammer. He’d be better off if he was as smart as a hammer.

A ball peen hammer, not a carpenters hammer. Those hammers are pretty dumb. No offense to carpenters here.

Edit: I forgot to point out that that 6 degrees of initial pissed it off at idle. My friend is a car guy but not a tuner. Even he could tell as soon as it fired up it was idling better than it was before.
Click to expand...

Thanks, that is exactly what this thread is about, giving the motor what it wants, not what I think it wants. If that is ported, great. If manifold great. Either way, with the weight of the truck, even with an 8" converter, I think the curves should not be too quick to come in. But then again, I intend to find out. One thing about this '67 truck, with my long arms the distributor is easy to reach.


I did find an old points distributor this afternoon, that has barely any bushing wear. That may be an option for a dist. that I can put a curve in. I am using an old 80s MSD 6, the one without a rev limiter.

First will be figuring out what the thing needs, and that will take some seat time, and some "testing" for plug reading purposes.
 
Forgot to mention, me tuning by ear would be like having a blind man pick out paint colors.

I am always telling my wife to use her outside voice.
 
Sam,
If mileage is the goal, then there will be little difference between PVA & MVA. MVA will give a smoother idle, more vacuum, run cooler at idle & have better tip-in response [ this is based on comparing idle timing after adding MVA...with the stock ign timing ].
And I can tell you from years of experience, your engine will want AT LEAST 30* [ probably more ] for best idle. MVA is one way of providing that. Beware of the bullshit in another post.

img307.jpg
 
Bewy said:
Sam,
If mileage is the goal, then there will be little difference between PVA & MVA. MVA will give a smoother idle, more vacuum, run cooler at idle & have better tip-in response [ this is based on comparing idle timing after adding MVA...with the stock ign timing ].
And I can tell you from years of experience, your engine will want AT LEAST 30* [ probably more ] for best idle. MVA is one way of providing that. Beware of the bullshit in another post.

View attachment 1716282368
Click to expand...


Thanks, I'll be testing later this week to see what it likes.
 
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