HEI missing vacuum line?? - Team Camaro Tech
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post #1 of 12 (permalink) Old Mar 30th, 13, 08:07 AM Thread Starter
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HEI missing vacuum line??

I'm an old guy who got back into cars after 35 years. I'm not up to date on HEI ignition. I had some work done on the 350, cam and alum heads. When I got it back there is no vacuum line on the distributor. The car seems to run good at all rpms. So heres my questions.
1. Can someone explain how this works?
2. Would I be better off with the line back on?
3. If it doesn't matter should I plug the holes?
I'm not a guru, but I've rebuilt more than 10 engines in the past. I just remember the point system better.
Thanks in advance........................................... .................
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post #2 of 12 (permalink) Old Mar 30th, 13, 09:48 AM
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Re: HEI missing vacuum line????

Hey Joe, I'm no pro with HEI myself but does your HEI have a vacuum advance? Some HEI do not have vacuum advance. I'm assuming you do since you're asking about plugging it. Have you read the sticky in the Performance section? Here it is .... https://www.camaros.net/forums/showthread.php?t=150344
Great thread about VA and running full manifold vacuum and such. Give it a read.

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post #3 of 12 (permalink) Old Mar 30th, 13, 09:57 AM
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Re: HEI missing vacuum line????

Yes, give the sticky a good read as Robert suggests then try some options.
Make noted as to the action taken, then compare results.
Not a bad idea to have a vacuum line connected to it, full manifold vacuum.
The action may make it a better running engine.
Plug gap I found best for an HEI is 0.045".
Again, note the action and compare results later.

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post #4 of 12 (permalink) Old Mar 30th, 13, 03:06 PM
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Re: HEI missing vacuum line??

Quote:
1. Can someone explain how this works?
Basically the same as a pionts system... has a module (the electronic pionts) that 'open and close' triggered by a magnetically induced current by the sharp ring in the bottom of the dizzy... the only real difference... with GM modules... is if u leave the ign on, the module will automatically turn the current off so u dont burn out the coil over night.

Quote:
2. Would I be better off with the line back on?
Any street driven car should have VA....if a non pollution /EGR pre early 70s type engie set up it must have VA on manifold vacuum to operate corectly, AND the VA and cent curves should be modified to suit...this effects starting, idle and cruise .

Quote:
3. If it doesn't matter should I plug the holes?
The hole at the VA end, no need it is only a diapham and spring inside... the hole at the manfold end hell yeah, thats a big inlet manfold leak screwing up your mixtuires right thru the operating and engine load range.

Quote:
but I've rebuilt more than 10 engines in the past. I just remember the point system better.
Dialing in the timing ... ie amount of cent advance by changing the tails shape of the counterweights is the same, as is changing springs for rate of cent advance and start finish, of VA and spring weight inside the VA... only diffence is dont need to set pionts dwell.

My Spelling is not incorrect...it is creative

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post #5 of 12 (permalink) Old Mar 30th, 13, 04:39 PM Thread Starter
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Re: HEI missing vacuum line??

Thanks guys, I'll start with the sticky and go from there. Steps, the motor is a 71 but I don't think that's much different from a 69 model so I'll work with your ideas too.
Thanks again. Might be awhile before I can let you guys know how I made out. I drive the car around alot, it seems to run pretty good even when I get into it.
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post #6 of 12 (permalink) Old Mar 30th, 13, 05:06 PM
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Re: HEI missing vacuum line??

Timing could be locked out or it has a large cam with little to no vacuum which would not advance anyway.
My old 406 was like this, and ran perfectly fine.

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post #7 of 12 (permalink) Old Mar 30th, 13, 09:34 PM Thread Starter
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Re: HEI missing vacuum line??

OK, great sticky.... I understand what John is saying. With that said I do alot of around town driving and I'm in agreement, I need the vacuum. First though let me thank Doug for his input but I don't race it enough and could use the milage.
My next concern is when I hook it up the car is not going to run right. So here's the set up if anyone can give me ideas on timing etc.
It's a 350 with a Comp hyd roller cam. Numbers on the cam box are 12-423-8 then cs xr276hr-10.
Specs Int. 276 Exh. 282
[email protected] .050: 224 230 Lobe step 110
Valve lift .502 .510
No addtional bore on block and a 650 Holley.
I havn't looked but asume theres a vacuum port somewhere below the throtle plates on the Holley.
So where do I go from here?
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post #8 of 12 (permalink) Old Mar 31st, 13, 05:51 AM
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Re: HEI missing vacuum line??

OK, there should be 2 ports on the right side, on the base plate, and near the front bowl. One is ported and the other is full vacuum.
Connect a line between the HEI and either port. Some like ported and some like full....see what one you/your car likes and dial it in.
Now with the vac. advance hooked up, you'll need to check your timing, and watch for spark knock.
Good luck and we're here if you need help

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post #9 of 12 (permalink) Old Mar 31st, 13, 02:51 PM
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Re: HEI missing vacuum line??

Quote:
Steps, the motor is a 71 but I don't think that's much different from a 69 model so I'll work with your ideas too.
It doesnt matter if it is a1908 or 1990, its about having or not having the EGR and mid 70s pollution stuff hooked in.
basically Pollution stuff has a low cent degrees and very high VA degrees on ported vaccuum, and non polltion has over 20/ 22 degrees in the cent and around 7 to 10 degrees in the VA on manifold vaccuum
Ball park u are looking at around 8 to 12 degrees of intial...easy fire up low loading of the starter armiture.
Engine fires and the VA is all in giving a stable idle around the 16/ 18 degrees... over 20 for big cams... the VA should be all in at intial advance manifold vaccuum (no more than 1" above) with mixture screws adjusted to best idle temporially...generally VA starts about 5 to 7" and finishes around the 12 to 13 " ...
Total,(intial+cent) on modern fuels, engine designes, cams etc, will be in the 32 to 36 degree range around the 3000/ 3200 rpm range
The amount of degrees in the VA should not exceed 42 degrees (intial+cent+ VA) unless dialing in timing with knock sensor.

Filling / rounding off the counter weight tail wher contacts the anvail increases the degrees in the cent...about .5 to 1.5 mm...
Changing springs changes the rpms the cent (total) degrees.
Filling out the slots, or using stops mounted under the VA mounting screws, top or bottom end as required changes the VA deg range and start / finish pionts.
'adjustable' VAs change the tension and the amount the diapham moves at the same time, and are not always adjustable enough to have enough vacuum and number of degrees at the same time.
Dialing in a Dizzie is locking the counter weights, no VA ....
then establishing
the best idle advance and using the intial and what is in the VA to achieve this 'tuning piont'
The best total (power curve) is established.. starting around 36/ 37 degrees the runing power runs and retardd till u feel the power drop off suddenly, then ad 2 or 3 degrees..

Then adjust the cent, VA , springs to work at those esblished tuning points.

To dial in for best results the carb idle, powe circuit and cruise circuits need to be in ball park 1st...
idle and cruise around the mid 15s AFR and power mid 11s to mid 12 afr.

Timing/dizzie is a hi precision instument...to have a given engine max cylinder pressure, explosion at a given point (not in the range) somewhere between 12 and 18 deg ATDC...change compression, rpms, bore stroke ratio , mixture, fuel type or octane, and the timing requirements change.

My Spelling is not incorrect...it is creative

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post #10 of 12 (permalink) Old Mar 31st, 13, 04:06 PM Thread Starter
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Re: HEI missing vacuum line??

WOW, now it's getting deep. Thanks Steps, I'll have to read this several times before I make a move. I would never have put this much thought into a vacuum line. I may even have to take it to a pro. I'll get the old timing light out and go at it next weekend. Thanks again
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post #11 of 12 (permalink) Old Apr 1st, 13, 03:05 PM
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Re: HEI missing vacuum line??

Quote:
WOW, now it's getting deep.
No not really... think about it.. we spend a lot of time and money getting panels perfectly blocked down and lined up... we measure bearing piston to wall tollerances down to thou of an inch, we spend time dialing in cams...
Then when the car is all finished, throw any old curved dizzy in and runs, and with ANY LUCK it is close enough to run without issues, yet a couple degrees either way can make huge differences in how long the engine lasts/ wears, economy and power.
And then go and do the same with a carb out of the box...
We will replace a oil pump re building an engine but not bother with pulling header tanks on the radiator and clean out the cooling system.

I do not understand this logic.

My Spelling is not incorrect...it is creative

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post #12 of 12 (permalink) Old Apr 9th, 13, 10:34 AM Thread Starter
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Re: HEI missing vacuum line??

If anyone is still following this I just wanted to thank everyone again for all the great information. I hooked up to the manifold vacuum, cranked her up, made no other changes and she's running like a champ and much cooler. I don't get it but I love it.
Thanks again, I'll hold onto this info in case it's a fluke that it's running so good.
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