I installed a 99 350 vortec in a duece coop put intake and carb on it now I having timing issue with the hei unit. Is it possible for the hei to have to much total advance. I have about 32 degrees total out of the dizzy so when i set initial timing at 8 degrees this gives me 40 which makes for nasty knock above 2400 rpm.
Due to the high swirl design of Vortecs they only like 31-33 degrees total. Any more and you hurt power.
We have somthing happening here that probably has not happened since the beginning of the HAMB. A question asked by a person with 1 post is answered by a person with 1 post What are the odds??? I almost forgot, retard your timing Gary
we set up one in my buddy el camino, we limited it to 28 degrees and i think like 10 at idle, thats the set up that worked best for us, it also pobably had a larger cam. jeff
If you modify the distributor so it has less mech advance, then you can have the 32 degrees total timing that most vortec headed motors like and a more reasonable initial timing setting.some guys just weld up a little of the advaNCE SLOT BUT i THINK YOU CAN BUY BUSHINGS TO LIMIT THE TRAvel too. (SORRY BOUT THE CAPS i BUMPED THE KEY HEH. DOUG
99 out of 100 stock GM distributors are pre set at the factory with 12 degrees distributor advance..thats 24 engine degrees . Set the timing at 10 degrees and you have almost a perfect setting of 34 degrees. In this case less is actually more , meaning it will more than likely love 30-32 degrees with todays gas etc. Many of the aftermarket HEI units are way over this setting. Some (over there) bored the limit hole way over size !!! I can curve ya up something if needed...
Alright thats a lot of good info. Ive i think this dizzy has to much advance in it. PLAN B limit the advance. I cant find any kit/part # for this so I will attempt the method of limiting travel on the advance slots in a day or two. Any Ideas are welcomed. This will be strictly a cost cutting decision. Otherwise known as a challenge. Plan C just go buy one.
I Figured it out on my own ..... The vaccum advance can be swapped for one with less travel on it. I used a washer on th v advance to shorten its travel wich brought up the base timing. and dialed it write in on the first try. 9 degres at idle and 32 all in. the vaccum advance has a #24 stamped on it if I do the math it advanced time 24 degres. Can you get a v advance can with 18 or 20 degres in it. I know somebody already new this ,it was to easy. Bottom line is I still have to test drive it. I will report back
There are a huge variety of vac adv cans. Back when I was recurving dist's I had a favorite Napa pn that I used but I no longer have that info. I selected the can based on it's vacuum requirement and always had to make a stop to limit the travel to 10 degrees. You need to set the timing with the vac line disconnected. The other problem with Hei dist's is that some of them keep advancing up to 5000 or 6000 crank rpm. I always welded up the limit slot and cut the weights down to increase their leverage. This allowed me to use stiffer springs than is typically used in a recurve. This way the adv weights move in a very positive fashion, both opening and closing.
Crane cams makes a vacuum advance limiter that goes on the screw in the back. It is cam shaped and is adjustable. If you have an hei distributor you will notice TWO extra screw holes where the rotor mounts. I put two small allen screws in these two holes with lock nuts and this setup limits the total advance. Just make sure the rotor sits flat when you reinstall it. 93 pump gas and Vortec heads 28 to 30 degrees total and maybe 10 to 15 vacuum total. The advance setup in an hei will over advance at high rpm. Try forcing the weights with your fingers and you will see what I mean.
I was trying to remember the pn of the vac can I used so I did a google and came up with a great thread: http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html
The huge vac travel is because all or nearly all HEI cars had EGR...cans with about half that travel for non-EGR use came on big trucks with HEI, my usual source, or order one for the biggest truck application in the book. Both GM and NAPA cans have degrees marked on the shank. Moroso makes a good kit with weights shaped to limit advance and a bucket of spring choices (lighter better, imho). I don't think you'll find a limiter slot on a stock HEI...those were on the previous distribs, HEI limit is a hook on heel of weights. Stock curve usually too slow and too long.
OK more to learn, timng the motor with no load and timing light in hand is one thing but under a load is total different. The lesson is it gets really close to proper timing with the light. the rest is done with seat time. Most important item was the ported vaccum for the advance unit the motor finally came to life after hooking it up to direct intake vaccumm.
when you hooked it to direct vacuum you took some travel out of the vacuum advance, basicall shortening the travel of the vacuum advance. accel sells an adjustable vacuum advance also. jeff
The Jalopy Journal
