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It is 9 to 1 with a 214/214 .472/.472 on a 110 LSA. The car runs great, thanks Mark the cam is great. I have had nothing but issues with Mallory distributor so it is going for sale with my 88. I currently have a HEI that is typical would come in around 3000 rpm total, in the car now. I also have a HEI out of the 260 with a much faster curve, all in by 2500 rpm. Also is there any bushings or otherwise that limit the extra timing that every factory HEI puts out above 4000 rpm? I know welding or brazing is done by some.
Here is a picture from the Gbody forum of placing a 1/4 in screw in one of the holes on the distributor arm and grinding it down to limit the arm movement to the total advance you want. I'm assuming it was you that asked the question here:
welding, brazing, JB weld, all work. There are bushings in some of the aftermarket timing kits too but they don't get you too far.
I have found that to bring advance all the way in by 2500 rpm often requires light enough springs that one tends to be in the mechanical advance curve at idle, especially in cammed situations idling 700rpm and above.
I prefer all in by 3000 for that reason alone.
With your cam and 9:1 I would try to set up for about 20 degrees mechanical in by 3000.
Figure your engine will like 32-35 total at WOT so your initial timing would be set 12-15.
I wouldn't add more than 10 vacuum advance to that.
It seems to like this slow curve. I have 22 initial and would guess close to 40 dgrees total plus a ton of vacuum advance. I find 36 total quickest at the track. I find no matter what springs are used, most HEI's have a slow curve. The 260 distributor is the exception, advance at 500 rpm. The 78 800 cfm custom Qjet you built me Ken is a perfect match for this 350. I almost forgot about that set screw method. I tried it but must have installed it on the wrong side, timing wouldn't go below 40 degrees. I will switch sides and try it again. I will actually do it to both these distributors if it works on one.
It is impossible for you to definitively know that every HEI in existence exhibits this issue.
Just an educated guess. Of course I tested two HEI distrbutors with very different curves. Others have found similar so it doesn't mean everyone. I thought you were FOS on some HEI's having quick advance curves, this 260 is definitely aggressive.
Of course I tested two HEI distrbutors with very different curves.
Yes, there are MANY different weight and center bars for the HEI, and each gives a different curve. I remember reading some old posts by IgnitionMan where he said there were about 420 different curve combinations with the factory weights /center bars.
Last edited by Fun71; June 13th, 2017 at 05:37 PM.
A lot of distributors will give an additional 2-3 degrees at 4-5k rpm. That's why I always recommend checking the upper rpm levels.
I definitely agree with this. I have seen the same in lots of cases on the Sun504machine.
Most of the mechanical timing comes in relatively quickly, and the last few degrees come in more slowly as rpms get up there. changing springs doesnt have too much effect on this characteristic of the curve. I believe its the interaction of the weights and the profile of the top "cam" on the distributor shaft.
22 degrees seems like a lot of initial to me on a true 9:1 motor. If it were a low compression 7.5:1 or 8:1 deal then yes Id expect it to like 21 or 22 initial, and I would limit the mechanical to 14 or 15, shooting for the low-mid 30s total. In fact I did this with great results on my Trans Ams 403cid
you should set it where the engine is the happiest so long as it doesn't ping.
I believe its the interaction of the weights and the profile of the top "cam" on the distributor shaft.
That is definitely the case with the HEI distributor. The interface between the weights and center bar is what limits the total amount of advance - there isn't a bushing for a hard stop like what is used in the points distributor.
Yeah it may be a degree or two too many, no pinging just a little bucking under load. I can add the adjustable vacuu advance as well. I think I will leave the curve alone, just add the positive stop on the right side and use 38 total on the street and 36 at the track.
OK so I installed the Crane adjustable vacuum advance and added my positive stop on the right side this time. I think with the 30 degree vacuum advance can I had on there was too much advance. The Crane is a 20 degree can, should be plenty and get rid of the slight bucking. I am pretty sure even with light springs, this distributor won't come all in before 3000 rpm. I left the springs as is. I will check the curve before the track. Even if I have to run 25 base to hit 36 total, I have no problem with that.
A 20 degree vacuum advance can is too much. You will probably get some surging at cruise. If so limit it to 15 with a stop. You can get your curve to come in sooner with a crane spring kit. I don't understand the even if I have to run 25 base statement. With a 25 base your starter will not be happy.
It is probably sitting at 40 degrees plus or was at idle with vacuum advance. The stop I added is limiting the mechanical advance, I will need to see exactly how much. That his why I said it may need 25 initial or some grinding on the stop. I find the Olds V8 loves a lot of part throttle timing.
Last edited by olds 307 and 403; June 17th, 2017 at 11:37 AM.
I have limited the travel of a 20 degree vacuum advance unit by JB welded a small washer or coin in the area where the rod travels stopping it about half way worked good just sand the metal rough a little . I like manifold vacuum on the advance but yeah with total mechanical set in race mode coming in early its too much to have a full 20
I was able to limit the travel of an original 24º vacuum canister to 16º by slipping a bushing over the part of the rod that moves in the slot. Below is a picture I snagged off thw web showing a similar setup:
I later made a small plate that screwed onto the arm. I used slotted holes so it was adjustable and now have it at 10º (similar to the one below):
I was able to limit the travel of an original 24º vacuum canister to 16º by slipping a bushing over the part of the rod that moves in the slot. Below is a picture I snagged off thw web showing a similar setup:
I later made a small plate that screwed onto the arm. I used slotted holes so it was adjustable and now have it at 10º (similar to the one below):
I find the 20 isn't too much, the 30 degree can was, it is going back on the 260. I am using manifold vacuum and personally think a 25 degree can would actually be perfect but this 20 degree can will work fine. Also this canister is adjustable, I think it is set on full advance.
June 13th, 2017, 06:36 AM
. I will remove the stop and test drive.
