I was into the dist in my BB Chevelle after recurving the one in my Camaro. How much would I stand to gain ET and MPH in the 1320 based on the following. I had run a best of a 12.98 @ 108 with the dist base at 15* and 10* mech. With a ported vac. source The vac adv began at 10 inches and offered 10*. I now set it at 8 degrees base 38* total in by 2600 and a manifold vac source for the same cannister. I had 60' times in the 2.0-2.1 range. Can this new discovery put me in the low 12s Hi 11s?

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67 prostreet BB Camaro The Combat Rat
80 z28 Camaro 355ci
71 BB SS Chevelle (clone)
2002 35th anniv SS Z28 conv.

The vacuum advance will have no effect on a quarter mile run. It provides no advance at WOT.

It is difficult to predict what you will gain from re-curving. I can not tell from what you have said if you have modified your centrifugal advance. The "total" is the initial plus the centrifugal and ignoring the vacuum can. If you have 8* initial and 30* centrifugal, you have 38* total. The vacuum can adds to that only at cruise or idle if it is set up that way.

-Mark.

30* mechanical is A LOT. I personally like around 20* mechanical. Like Stingr69 said its hard to tell, but I think it could be worth a tenth or two if you really set it up right.

I would try to get away from using vacuum advance to help it idle. Instead of having base at 8* and adding 10* more vacuum, why not reduce the available mechanical advance from 30* down to 22*, then set base timing at 14* or 16* without the can? Then you would have 16* at idle (using ported advance), still have 38* at 2600-2800 RPM, AND the vacuum advance can now do what it's supposed to do - add timing at cruise RPM.

Just my opinion.

The combustion chamber shape/size has a huge effect in determining the total needed for the total advance to work right.

Big blocks by nature tend to respond well to total timing in the 38-42* range.

If this were my call, with the vac adv disabled, i`d set the initial at 18-20* with 18* in the distributor. This will give 36-38* total. Use whatever springs needed to have it all in by say, 2400-2800 rpm.

With an adjustable can, set it up to where the motor will cruise with no bobbles.
Total adv can be 50* at this point and as long as it`s out of detonation there will be no problems.

To help answer your question, IMO asking for nearly 1 full second with only a timing adjustment is (barring a totally trashed dist set up) will NOT happen, no way. Your ET vs MPH shows room for improvement but not a miracle




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78 Camaro hyd cam 406
TH350-3.23 gear
11.86 ET
116.7 MPH

Milan; If you are having traction problems like your 60ft looks like you don't want to increase the low end with a quicker curve. The next time you go to the track bring some heavier dist springs and give them a try it might really help and is an easy change.

I guess I was just hoping for a miracle. Thanks Eric, I guess I belong to the manifold vac crowd. It was laboring to crank once in a while at 15* thats the reason I chose a base number around 8-10 degrees. I guess I dont understand what is the downside of a curve that starts at 8 and works up to 38 supplemented with vac advance that goes away below 10 inches. I was thinking I had it nailed but a lot of members have other suggestions. What am I missing? I will do the oger. I am pretty sure it was a slight bog that was slowing my 60' times I didnt feel like it was spinning(I could be wrong) I just figured with drag radials and how the engine sounded (labored) I figured there was a tuning problem. I appreciate all the dist input!! Here were my thoughts for doing what I did please chime in if my logic is flawed. I figured that a low base would allow for easy cranking,a graduall mechanical coming in at 1500 and fully in by 2600-2800 and use vac to provide a nice Idle and a clean burn while cruising. I had hooked up a vac guage to the "velle and drove it for a couple of years watching what happens at under varying loads with the old curve. BUT I am green and learing a hell of a lot when it comes to performance. There is a huge diff between fixing cars for a living (up till a few years ago) and trying to be a HP tuner. So I am learing to be humble. I guess I just want to understand why things happen. so please keep it coming, and thanks

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67 prostreet BB Camaro The Combat Rat
80 z28 Camaro 355ci
71 BB SS Chevelle (clone)
2002 35th anniv SS Z28 conv.

Milan if it is a bog that is killing your 60ft times and not wheel spin than you need to increase the advance at low speed not slow it down. What carb do you have?

a Holley 780 vac secondary

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67 prostreet BB Camaro The Combat Rat
80 z28 Camaro 355ci
71 BB SS Chevelle (clone)
2002 35th anniv SS Z28 conv.

Oger What I was figuring was happening is that at the line as I would brake torque.I would only see about 15-20 degrees advance with the old curve and the max was 25. now my max is 38-40. I would brake and leave at about 1500 I have about 28 there and the rest 10-12 degrees is in 2600 rpm. What ya think?

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67 prostreet BB Camaro The Combat Rat
80 z28 Camaro 355ci
71 BB SS Chevelle (clone)
2002 35th anniv SS Z28 conv.