I have a 67 396 375 I pulled the old distributor and installed a GM HEI. It came with 14 degrees mechanical and 10 degrees of vacuum for a total of 24 degrees at 2200 rpm.
I set the inital timing with the vacuum blocked off at 10 degrees advance. This is the original setting of the old one. It starts and idles fine but when you drive it it seems retarted and doesn't rev as quick as before. What am I doing wrong?

I run more timming than 24 total @ 3000RPM, I run 36-38 @ 3000 in my street car with 92 or 87 octane and don't have a ping.

More timing will wake it up at idel with vac hock up i am at 18 degs my total @3000 tho is 38 with no pinging you my wont to play with advance springs i have one light one one heavey one. From a dead stop i can fry my tires with no bog or hesatation.

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Don Pell 66 396 Beaumont.
Once bitten twice shy.
Don Pell 66 396Beaumont.
Once bitten twice shy

When you hooked the power wire up, did you hook the original wire up? Or run a new wire from the fuse box for a full 12 volts to the coil? The original wire is a resistor, supplying only 9 volts. This might cause that sluggish feeling, if you did, set your spark plug gap at at least .045 to take advantage of the hotter spark. If you did all of this, the team is right, the total timing is not enough or too much. Just a suggestion.

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My70ChevelleSS (http://albums.photopoint.com/j/AlbumIndex?u=1551080&a=11764957)

Thanks for the info. When I ordered the dist. I never told them what advance I wanted. How do you change the mech advance?

There's a kit available from any performance supplier for around $5 which comes complete with instructions for re-curving your distributor. It comes with new weights, bushings, and springs for the mechanical advance.

If your distributor is completely new or rebuilt, you can re-curve it by just changing the springs in the advance mechanism. The lightest springs give total advance early, and the heavier ones bring it on later. You can mix and match to get what you need.

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My Elky Page (http://www.geocities.com/chadjlandry/index.html) (updated 3-31-01)
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Chad Landry
TC Member #643
'68 El Camino

I was told that changing the springs would only change at what rpm the advance comes in.
Is that true?

Yes light springs and the advance comes on early heavey springs comes on laiter like menchend time to test and tune.

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Don Pell 66 396 Beaumont.
Once bitten twice shy.
Don Pell 66 396Beaumont.
Once bitten twice shy

Eddie,

that is true about the spring's. all so I am a bit confused as the HEI distributor has between 20* and 24* of mechanical advance. I have never seen one with that low of a mechanical advance.

if you are using manifold vacuum you want a vacuum can that will give you between 10* and 18* of advance at the crank. if you are using ported or timed vacuum you probably want about 20* at the crank.

with ported vacuum you have to use a lazy mechanical advance curve, one the will all come in by around 4500RPM and start at about 2000RPM. with manifold vacuum you want it all in by 3000RPM and to start at about 800 or 1000RPM.

a manifold vacuum set use's vacuum advance as an enhancement to the curve for idle quality and cruse eficiency. in a ported set up the vacuum advance is part of the timing curve and a supplement to it when you have a load on the motor.

I like the crane advance kit. it will cost you about $20.00, it has an adjustable advance can and spring's for the mechanical with great instructions'. it also has a vacuum advance limiter plate.

I bought the Dist from Sumitt. I told them I had a stock 375hp and that's what they sent. I'm taking the vacuum from the carb.
Thank's
ED

Eddie,

that is where the manifold and timed vacuum port's are for the distr.

do you have vacuum at the port at idle? if you do that is called manifold vacuum.

most cam's used in a street BB or SB like about 10* to 14* of base timing and total time of between 30* and 38* at about 2800RPM to 4000RPM, this is with out the vacuum advance hooked up. with it hooked up ad about 10* to 20*, what ever the vacuum advance give's you, this is called adjusted totale timing of betweeen 40* and 58*. this is an old subject do a search on the site for it. you will find a bunch of post's by a man named I-man, Ignition man, he give's the skinny on using manifold vacuum very well.

I prefer manifold my self. other people like ported. you need to decide what will work best for you. on a street motor a vacuum advance is a must in my mind. as a cam and timing profile that will not need it or be helped by it is too aggressive for a street motor. this is the type of cam used on a drag or race only motor. they only make about 2" to 5" of vacuum at idle.

vacuum advance is to help keep plug's clean and to give you a good burn at cruse.

[This message has been edited by ilbl8 (edited 04-13-2001).]

[This message has been edited by ilbl8 (edited 04-13-2001).]

Yes I do have vacuum at idle. I have a 780 holley and it is taken of the front right hand side of the carb. At idle the timing is at 10 degrees with the vacuum disconnected an the rpm at 900. You hook the vacuum back up and the timing goes off the tab and the idle to 1500 you try and idle it back down and you can't get it below 1100. Man I'am confused. With the old dist it would idle at 900 at 10 degrees with no problem. I don't no the specs on the old dist.

<BLOCKQUOTE>quote:</font><HR>Originally posted by ilbl8:
Eddie,

that is true about the spring's. all so I am a bit confused as the HEI distributor has between 20* and 24* of mechanical advance. I have never seen one with that low of a mechanical advance.

if you are using manifold vacuum you want a vacuum can that will give you between 10* and 18* of advance at the crank. if you are using ported or timed vacuum you probably want about 20* at the crank.

with ported vacuum you have to use a lazy mechanical advance curve, one the will all come in by around 4500RPM and start at about 2000RPM. with manifold vacuum you want it all in by 3000RPM and to start at about 800 or 1000RPM.

a manifold vacuum set use's vacuum advance as an enhancement to the curve for idle quality and cruse eficiency. in a ported set up the vacuum advance is part of the timing curve and a supplement to it when you have a load on the motor.

I like the crane advance kit. it will cost you about $20.00, it has an adjustable advance can and spring's for the mechanical with great instructions'. it also has a vacuum advance limiter plate.<HR></BLOCKQUOTE>

Distributors are rated in distributor degrees, and one distributor degree equals two crank degrees. Your 14° distributor will give you 28° at the crank. Setting your initial timing to 8° will give you 36° total. Vacuum advance should be 8-10° at the distributor, 16-20 on the crank.
Ported vacuum is the same as manifold vacuum, it is tapped from a hole that is covered by the throttle blade at an idle. Anything above an idle uncovers the hole and provides full manifold vacuum to the advance mechanism. Engines with poor idle quality will benefit from full manifold vacuum applied to the vacuum advance. Here's a link to a treatise on ignition timing for modified engines. http://members.aol.com/DVAndrews/timing.htm

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67 Nova 385" daily driver - 12.1 @ 112
64 Chevelle Road Racer in the works
67 Nova Wagon under construction

to get your idle down some I bet you need to open the secondary butter fly's some. there is a screw on the bottom of the carb on the left/passenger side to do this with. be careful you need about .020" to .030" of the transfer slot showing or you will have an off idle stumble or bog.

At 900 rpm the new dist may have the mechanical adv kicking in making adjustments impossible at that rpm.You need to get the idle below 900. What do you mean by can not get idle below 1100? The screw backs away from the stop or the engine dies?If the screw is off the stop and it is still high the idle bleed screws may be opened too much or the fast idle screw is not released or is set too high.

Rene
66_Malibu

[This message has been edited by shooter (edited 04-14-2001).]

Eddie, not for nothing, but if is a 375hp/67 car why the heck did you stick a Summitt HEI in there. It aint going to make it go faster. And it will make it look FUGLY. Well, you done did it, but if you could turn back the hands of time you might have considered a Pertronix ( carries my hi comp mill to 7000) or an HEI conversion by Dave Ray ( slightly better than the Pertronix IMO).

Now, why this budget part is causing some problems I dont exactly know. If your mill is anything like mine it will like about 38-40 total with closed chamber heads. Total DOES NOT include vacuum advance. Set it at 8, as mentioned, and without the vacuum on, it should show 36 total at full advance ( 8+28 ((or 2X14 - remember the crank spins twice for every full rev of the distributor)).

I would argue that is IS NOT the best setup for most hi compression big blocks. MOST ( not all) perfer a short curve of maybe 20 crank degrees with another 15-16 inital degrees. And if your compression is still 11:1 ( as mine is) you dont want that much vacuum, maybe 8-12 is all.

Honestly, I'd can the HEI. If your old distributor is still tight put an OLD STYLE Pertronix on it. You can use your stock coil, or their Flamerthrowe which wants a full 12V. Or if its loose, send it to Dave in cali and have him put an HEI trigger in it.

Again, a 375hp 67 is a very rare bird. I would encourage you to keep that engine as close to stock as possible. Me, I wouldn't put any Summit or Moroso crap in there at all. Oh and BTW, most of it dont make you go any faster as you have just experienced.

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Gene Chaas
Gold Member 62/ACES 3112
67 SS 427 (http://www.chevelles.com/feature/october2000.html)
"Be big. Be a builder."

[This message has been edited by 427L88 (edited 04-14-2001).]

I had the GM HEI in the box laying around that I had bought sometime ago so I put it in so I wouldn't have to deal with the single point (non original,tired) that someone had put in the car. As soon as I can find a correct original I'll put it back in. This is the first time I've been involved with TC tech, You guys are great!!

What you need to do it make a limiter to stop the vac advance from giving to much advance at idel i did this with my hei with help from dave Ray i have 12 int and 8 with vac can to full time port.

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Don Pell 66 396 Beaumont.
Once bitten twice shy.
Don Pell 66 396Beaumont.
Once bitten twice shy