I recently put a HEI in my 68 skylark it has a 400 w/mild cam does anyone knows where do set the igtion timing
I would suggest starting at about 12* initial. That's a guess, my street/strip HEI is set to 13* initial. Well, OK, more like 14* probably, darn thing always moves a hair when I tighten the clamp
You need to set the total timing at 30-34*, depending on what your engine likes. No one can tell you where your initial timing should be. That depends entirely on the curve in that HEI. The downside of using an HEI from a 75 era Buick is that they often had more mechanical advance than desireable. This means you may need to run less initial than you want in order to keep the total on target. Set your total advance(without vacuum advance) to what your engine likes, then see what your initial ends up. If it is too low, you need to have the HEI recurved. Generally, Buicks like 12* or more initial.
Timing Larry, my engine likes to run at 35 total. I have an hei with an MSD 6. I have aloud part throttle ping. I set my total at 35 degrees at 2,500 and my initail is then at 22-24. that is ok but when I plug in my vacuum advance my timing at idle goes to about 48-50. I have a crane adjustable vacuum advance however turning the allen screw in or out does not change it. Included in the kit is a vacuum advance limiter. Have you used this? What is the best way to set it up to keep my vacuum advance to a 10-15 dregree aditional advance at idle. The instructions show it backwards. Thanks Tim
ported vacuum ?? Are you using the ported vaccum from the carb ? or are you just straight from the manifold ? you should have it plugged to a ported so that your not using any vaccum advance at idle....the whole thing is to get the advance at part throttle and then none at full when you are at operating rpm when the mechanical picks up the diff.......then you can adjust the pot on the dist to adjust the speed and amount of part throttle advance till it gets to total.. Mark
I am using the vacuum port off of the left front side of the carb. It has vacuum at idle and really pulls the vacuum advance up. Where else can I plug into? Tim
???? I will have to look at one of the old ones we used as we now use a holley dominator....and it is on the passenger side....if you can wait till this evening I will look...but seems to me it was on the passenger side too. is this the same port you have been using all along ? Mark
off idle adjustment ?? Almost sounds to me like you have the carb open too much off the idle....that way you would have vaccum at the port....where is your initial / may be your off idle thus allowing vaccum into the ported ??? Mark
This was originally a two barrel engine. I am using a stock four barrel intake with a stock quad. The engine runs rough at idle so I need to have the idle in nutral at about 1,200rpm's or it will kill when I put it into gear at low stall on my switch pitch trans. It needs to idle at 900-1,000 in gear. I am running Postens GS112 cam so it has quite a lobe to it. My initial timing needs to be set at about 22-24 to get my 35 total in at 2,500 rpm's. I am currently running without my vacuum advance hooked up. It seems fine. What should my timing be at idle with the vacuum advance on??? Please check my post in small block tech under " Idle speed with Postens GS112" Thanks Tim
compression ratio ..... What compression ratio do you have with this cam ? thats alot of cam for the street .....you may have not enough idle vac to run the carb in the idle mode...thus running into an open throttle. This could be your prob...if so...you really may want to rid yourself of the vaccum advane all together and just run the mechanical....as you are not really developing any real power till your up in the rpm range where your carb is well off vaccum advance use anyways.... Mark
My comression ration is 10.20. I have power brakes and they work fine. I am going to use Cranes vacumm advance limiter and see if that will work.I think I will try and limit the vacuum advance to about eight degrees so that I run about 41-43 at idle. What do you think? Tim
43 degrees ??? Tim...thats an awful lot of advance at idle !! does the motor dtonate alot ? With that cam I think you would be best off just trashing the vaccum advance dist and using only mechanical.....really should look for about 12-14 degrees with that cam at idle....then you can shoot it up to the 34-38 mark at your power band which is in the 3500 rpm range plus....... Mark Did you dgreethis cam when you put it in ?? where is it at ??
The motor does not seem to detonate without the vacuum advance off, when I use vacuum I get an awful ping at light throttle. JW put my engine together and he did degree the cam, I don't recall where he has it, but I can find out. I do not have a dial timing light so I had the dyno shop make am rk for me on the balancer to signal 35 dgrees. I line that mark up at about 2,800 rpm's without vacuum. I then check my initail and it is at about 22-24. How can I get my 35 total without cranking the initail way down??
well..... Tim... You should really try to have the initial at about 12-14.....then with your vaccum advance at part throttle ( and thats why we have the adjustable type ) we then shoot to get our advance up the curve till the mecanical can take over when the vaccum disappers at full throttle and rpm gain.... Try putting the initial at that 12-14 range and then adjust the carb to get the idle proper......then you can use the adjustable advance pot to get the " ping ' under control as the mechanical kicks in....( you look like you have 11-12 dgrees mechanical ) at 2500....so....with the 12 - 14 at idle and the 12 or so mechanical you could use another 10 or so in the vaccum advance...you shoukld also have a bit more mechanical advance left in the dist....maybe 18 toatal or so ..that way at 3000 or more you at wot with no vaccum should have that 32-34 total were all looking for.... make any sense ?? ????? Mark
Yes, however what will happen at WOT when my vacuum advance goes away? Then my total advance will be about 26-28. . Tim
total advance.. Hi Tim... Yes you are right...and thats why I was saying you should have a bit more mechanical left in yout dist....if not you need to have it recurved...to get that advance to the 34 0r so we are talking about...thats why you plug the dist and get all your rpms and mechanical in to see what your total is...the vaccuum advance is realy only there to give you better throttle respons at lower rpms as thats really whre most street cars need it... truthfully the steps are as we talked about earlier.....initial...mechanical....total advance and then play with the vacuum to get the advance in quicker at low rpms ( the adjustable to control the ping ) thus the proper ignition curve. Now remember we are now days using only 91 or so gas so that really puts the damper on speeding up the ignition curve ou: The whole reason we need the advance anyways is to allow the combustion of the fuel air mixture to keep up with the engine..piston speed. :3gears: Hope your getting this all worked out as timing is so very sensitive..... Mark
That sound good Mark. I will let you know how it goes! By the way I have local gas station with 100 octane that I use but it is $3.75 a gallon...ouch! Tim
100 octane ...! gee Tim !! that would be a dream come ture for me !!! sure wish we had that here....non the less we all have to work with what we got. Sure hope that works for you and let me know how all turns out...nothing better than being able to throttle it all the way and know its ALL there !!! Took my sons gs apart today....sure wish i were his age again and knew what i know now.....how fun that would be !!! Mark
