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I'm not trying to hijack but want to ask about my similar timing concerns. I think this is exactly in line with what has been discussed here for several pages. Ya'll may have even answered this and I missed it. I'm running 17 initial timing without vacuum advance, 33 at idle with vacuum advance all in, then 34 total by 3,000 rpm. So, yes, I've got the dreaded 16 degrees of vacuum advance. However, I'm not hearing any pinging and I don't see any shiny specks on my plugs. What benefits am I missing by not using the Lars VAC? I already have one but have postponed installing it for all the reasons listed above. Plus, I wonder if I might idle hotter in the summer with my vacuum advance limited to just 10.
 

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Youre not alone. I have a VERY similar situation... I feel like my performance is down a bit, but my timing is set high, in all areas, and I have no ping. Seriously makes me wonder if the balancer slipped.
 

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Youre not alone. I have a VERY similar situation... I feel like my performance is down a bit, but my timing is set high, in all areas, and I have no ping. Seriously makes me wonder if the balancer slipped.
I've not been to the drag strip yet, but I feel like mine is running strong. This is a fairly fresh build with a new balancer so I think my numbers are correct. Now, on top of that, I found this old post from Lars in 2007 that still said up to 16 vacuum advance was OK. GTO Tuning and Setup Tips Maybe fuel has changed enough since then to make 10 from vacuum advance the best number today. I think what I may do is keep my current setup with the Pertronix distributor as is, then put the VAC limiter in my original distributor (much simpler to do apparently) then check them back to back. That is IF I can find a free Friday afternoon/evening and it's not raining, and the drag strip is open for test and tune...
And again, not to hijack, but for full information. This is a recently built 467 stroker with 6X heads and the XE 274 cam, so not stock internals at all.
 

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Yes Lars has revised that number, based on research with the new gasoline. That is why he developed the corrector. 10 is perfect on vac advance for idle and cruise. 8 to 12, ok.

17 is really too much. Maybe you are not pinging on acceleration, but dropping out real fast from WOT adds 17 degrees to timing real fast as well. Better to have it at 10 degrees.

l have set up lot’s with 18 base + 18 Centrifigal + 10 vacumn.......28 idle vac and 46 at light throttle cruise. If you have a stout cam it can take 28 at idle. Most don’t need that much to run cool. Low to Mid 20’s I usually shoot for......unless the cam is real hot then high

Like 24 Centrifigal, 12 base and 10 vac.....that’s 36 total and 22 idle with full manifold vac.

3000 RPM all in is a good number. Corvettes go lower. The problem getting lower is not allowing the springs to bring in Centrifugal timing at idle.

lighter springs do that.

You have done a great job on your timing, I would stick with it and finish it just perfect with that vacumn corrector. You have a transition point on acceleration where your vac timing is still in and your Centrifigal is adding timing.....that could get pretty high with your current numbers, and it really is not giving you better performance or cooling.
 

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Remember that timing can be both too far advanced for optimal running or too retarded for optimal running. This is some swag and each engine combo is different. The guys like Bear, Pontiac Jim and Big D, LA Tech, 052, Pontic, blkjudge stay tuned in to their engines. And get a feel for what what is right as well.

if you can get a good feel and the numbers are right then you are spot on, and have perfect timing. Not saying that can’t run like you are you are just pushing the edges of the sweet spot.

if tuning yours I would up that Centrifigal to 22 and set your base at 14 with then 10 vac for 24 Idle timing and stay with all in @3000 RPM. But that would allow a setting of 36 total where yours is 34......

upping to 36 now would push your idle timing to 35, really not needed and could cause kickback and pinging on acceleration.

Remember you guys are in a good spot, we are fine tuning here. Gonna do a 63 split window corvette and a 61 corvette next week,...bet they will have 50 to 60 degrees of timing when all totaled up, and all at the wrong times and places!
 

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Yes Lars has revised that number, based on research with the new gasoline. That is why he developed the corrector. 10 is perfect on vac advance for idle and cruise. 8 to 12, ok.

17 is really too much. Maybe you are not pinging on acceleration, but dropping out real fast from WOT adds 17 degrees to timing real fast as well. Better to have it at 10 degrees.

l have set up lot’s with 18 base + 18 Centrifigal + 10 vacumn.......28 idle vac and 46 at light throttle cruise. If you have a stout cam it can take 28 at idle. Most don’t need that much to run cool. Low to Mid 20’s I usually shoot for......unless the cam is real hot then high

Like 24 Centrifigal, 12 base and 10 vac.....that’s 36 total and 22 idle with full manifold vac.

3000 RPM all in is a good number. Corvettes go lower. The problem getting lower is not allowing the springs to bring in Centrifugal timing at idle.

lighter springs do that.

You have done a great job on your timing, I would stick with it and finish it just perfect with that vacumn corrector. You have a transition point on acceleration where your vac timing is still in and your Centrifigal is adding timing.....that could get pretty high with your current numbers, and it really is not giving you better performance or cooling.
Thank you. That is what I was needing to learn.
 

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Discussion Starter · #187 ·
Ok got the MSD vacuum advance limiter installed in about 5 minutes, set it in the middle so the advance plate moves about half of what it can move...it was 85° in the garage at 8pm with a fan and I had had enough heat for the day so I'll time it up another night.
143377
143378
 

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Good work! And have to salute MSD engineers for going the extra mile and engineering this stop.

All the Holley Companies have contributed so much to motor sports historically, MSD, Accel, Quick Fuel, Mr. Gasket, B&M, Earl’s fittings, Flowmaster, Hooker, Hurst, Mallory and Tremec and many more!

So great job MSD engineers. Now go the extra mile and make vacumn cans for both diameter distributors. Points and HEI that as manufactured only pulls 10 at the crank, with no stops needed and has adjustability for RATE of vacumn.....and will fit original and MSD distributors. ......maybe someday.

If anyone can do it it is MSD.
 
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