I took the Beau out for its first real drive tonight after all the changes done this winter. New 3.73, posi, UD cam, vortec heads,, edelebrock rpm int, 650 speed demon and electric fan. I have been playing(struggling) with the carb for 2 weeks to get it to idle properly and think I am darn close now. I have my initial timing at 14 and with vacuum adv. disconnected I get a total of 34 btdc at about 3100 rpm, which from my research should be perty close.This is with an aftermarket HEI. With my vacuum connected at 3100 I am close to 50*. Now I have read every post on this subject and thought I had it all figured out but now I am not sure. The car ran good and was very peppy :D
I think my Beau finally has some bite. Does the timing at 50 sound about right or should I be limiting my vacuum advance ? I know there is an article somewhere by a fellow named Lars?? but I can't find the link
Any help out there

Jerry

You want your total timing between 32 and 38. 50 is to high.

Get an adjustable vacuum canister or one that has about 10 degrees total. If you ever run at the track, I would bump the initial to 18 if it will crank and unplug the vacuum advance.

My Opinion FWIW 50* total including vacuum advance is not too far off for old style SB's but since you have Vortec heads they don't need that much timing ......regardless of heads you have too much advance in your vacuun can sounds like you using the typical low perf GM can 16* @20hg ....most perf vacuum advance cans work best around 10-12* at 12hg ... buy an adjustable one of braze up the slot in yours ...... what vacuum does your motor make at idle ? Any pinging at part throttle?

Initial at 14* or 28* at crank is not too bad but i would try 16* or 32 at crank and add 6* btdc for a total of 38 all in at 3100rpm your vortec head motor might even like 4*btdc 36total better..... at idle or up to 12hg the vacuum can will add 10* for atotal of 48 but that vacuum advance of 10* goes away fast as the vacuum drops

Again my opinion only every motor is different....also assuming your tdc mark is accurrate Bil

Your vacuum advance is never computed into your total advance. Once you go full throttle your engine pulls no vacuum therefore you get no vacuum advance ....Vacuum advance is a part-throttle only thing.

Vortec heads have very efficent combustion chambers and work best with about 32-34* of total timing. I've never seen a vortec motor benefit from anything higher.

Gary At GMPP says no more than 32 degrees total timing in by 3000 rpms with the Vortec heads.

Several guys on the Camaro board have tested it and confirm that their best E.T. did in fact come with 32 degrees total timing.


Dwayne

BTW,
Check your mail. I sent you the article written by Lars

broke, if he makes a trip down the highway, the timing will be at full advance, 50 degrees. My truck with 2.73 gears is a 2500 rpm at 70 mph.

Thanks guys. I can achieve the 32* total by 3000 rpm by changing weights and having my initial at 12*. The engine definately likes more timing at idle but I assume this is achieved by the vacuum advance. I guess the answer then is to change weights and initial then maybe limit my vacuum advance. I have one of Cranes advance limiting cams on the dist now but have not set it.By the way I have my vacuum run from manifold vacuum right now. If I was to run it with ported I wouldn't get any more vacuum advance at idle, only when the rpm goes up. Correct?

More Vortec timing disscussion in another thread (http://www.nastyz28.com/ubb/Forum8/HTML/007870.html)

Just some more info
Dwayne

Thanks a lot Dwayne, great read. It sort of sums it all up. I am going to try it this weekend

Double whammy

blumount: what are your cam specs?

UD276H10 276/276, 221/221 @.050, 454/454 lift, 110 lsa installed on 104 icl.

Jerry,
I will respectfully disagree with everyone. 50 deg is not out of range with no load on the engine. If it was not pinging or showing any signs of detonation, it should be fine. As soon as you get a load on it, the vacuum advance will lower the timing and it will be fine. The Vortec heads supposedly run better with a bit less timing, but ... the engine is the true test. If it likes that much timing then let it have it. You could try reducing it some and see if performance improves, but it sounds like it is running pretty good... why mess with it ????
Just my opinion,

Well Bill, I wasn't going to jump to change things. It never pinged but then again it wasn't a real long road test like lugging the engine or opening it right up.It idles nice now where the timing is set. I read the post where vortecs like a max. of 32* total timing.To do this I would have to set initial at 12* with the 20* of mech. advance I have. I had a deuce of a time getting the demon carb to idle and I am wondering now if changing initial timing(lower) might affect it. I will try that this weekend and see how it responds. I am not going to make any big changes until the girl gets some real driving time in.
Bill, I appreciate your input as I respect your opinion along with everyone elses. Thats why this site is here is think.
Thank you

I apologize for posting something not directly related, but I have a quick question for you blumont. I will be running the same cam in my 333, and I was just wondering how you like your's?
Thanks smile.gif

71Chevy. So far so good with the cam. I wasn't looking for anything real radical as I don't plan on racing it, just a nice fairly quick driver. I have not got enough driving time on it yet to say what it is like. I know my baby definately has more power but I have not really opened it up.It seems to idle nice with a very little bit of a lope. I am still really in the tuning stage but getting closer. I am going to take it for another road test this weekend and maybe open it up a bit. I will keep you informed.
Back to the timing issue. I tried setting initial at 12* with a total timing of 32*. I have a feeling it still likes more timing at idle, like around 14-16, at least with this demon carb it does.If i did this I would have to limit my mech advance to to keep total around 32* I will have to do some research on how to do this.

Well I tried it out with the timing at 12 initial and total of 32*. I went for a nice long cruise. Off idle it had a flat spot and not quite as responsive but at wide open throttle she really cooked. A great feeling. I came home and set initial to 15* which gives me a total of about 35*. I took her out again and from idle up it is very responsive with no flat spots. At wide open it was still good but not quite as good as before. Of course this is only using my uncalibrated seat of my jeans dyno. I think my old girl has some real potential. From this I am slowly coming to the conclusion that I might need to limit my mechanical advance to 16-17*.
Pegleg, I think you will be very pleased with your cam. I know I have a smile :D from ear to ear.