Vacuum source

[kully 560]

hi stephen sorry to get back to you a day or 2 late ,as I had long work days. I am not sure if you knew but the 260 setup is replaced with a l28 /f54 block stock with n47 head , 1971 4 bolt su carbs ,e46 intake , jet hot headers,new 1979 e12/80 dissy .I tried the manafold vaccum and the motor seems to idle higher than ported vaccum .I still have the carbon canister in the car and had a bad smell all the time when I hooked the canister up to the manifold vaccum. my 1974 service manual showed the front carb/ ported vaccum hooked up to the carbon canister and with a tee inline to the dissy vaccum advance.so I tried it and the smell is just about gone at idle, and my orignal takeoff had a hestation which is gone all together now . you are right about my hybrid alot of different stuff but the car seems to run its best now . also my timming is set at 15btdc and it seems to idle very smooth now . not quite sure about the vaccum delay if it will work better but if you think so I would sure be willing to give it a try .kurt

Edited March 27, 2009 by kully 560

[sblake01]

I was just saying that I was not sure that you're setup would be the same as the rest of the cars in this thread. Each year of E12-80 dist. seem to be a bit different. I discovered that a few years back and Carl and Bruce's statements early give more credence to that. The 79 dist. seems to work best with the vacuum source being the manifold pulling though a vacuum delay valve. That has been my experience. Now that may or may not apply to carbureated cars but Arne stated that the advance came on too quick when it's from the manifold rather that the ported vacuum. Placing a delay valve in that line puts the advance right in spec and still pulls enough at idle to be smooth. I don't know how or if that would differ with carbs since my experience is with EFI but I would think that the effect would be the same.

[kully 560]

stephen I do not know if the vaccum delay would come on to hard or very gradual I have never used one . but I should hook up a vaccum gauge to my ported vaccum just to see what it is pulling at let say 2500 rpms.also check my timming advance also at that rpms to see how much it advances.maybe the is something to gain with the vaccum delay I will put that one on my list of fun things to play with. thanks kurt

[beandip]

hi stephen sorry to get back to you a day or 2 late ,as I had long work days. I am not sure if you knew but the 260 setup is replaced with a l28 /f54 block stock with n47 head , 1971 4 bolt su carbs ,e46 intake , jet hot headers,new 1979 e12/80 dissy .I tried the manafold vaccum and the motor seems to idle higher than ported vaccum .I still have the carbon canister in the car and had a bad smell all the time when I hooked the canister up to the manifold vaccum. my 1974 service manual showed the front carb/ ported vaccum hooked up to the carbon canister and with a tee inline to the dissy vaccum advance.so I tried it and the smell is just about gone at idle, and my orignal takeoff had a hestation which is gone all together now . you are right about my hybrid alot of different stuff but the car seems to run its best now . also my timming is set at 15btdc and it seems to idle very smooth now . not quite sure about the vaccum delay if it will work better but if you think so I would sure be willing to give it a try .kurt

Kurt, I am running about the same set up as you now. I have a Dist from a manual tranny Z. I have a F-54 with a P-79 now and with SUs . I have never had any issues with detonation so far and I have about 40K on the engine. the compression is 9.5 since the head is milled. and am running at 15btdc also. When I had my L-24 in the Z, I had the same dist and never a problem at 10 and 12* advance. I am wondering if the shape of the combustion chamber maybe the reason for the early engines like Arne's detonating, that and his has higher compression. My L-24 was bone stock and a '73. Both engines I connected the same way with the ported vacuum supplying the advance pot. Gary

[Arne]

There are too many variables to say with any kind of certainty what the root cause of my detonation was. Obviously the advance curve of the particular distributor I used was one possibility. And Gary is right, the later P79/90 heads as he is using have the most ping-resistant chamber design of any of the L-series heads. My '71 does have a factory compression ratio that is among the highest of the L-series. And considering the low mileage on my car, it is definitely possible that my car could have significant carbon build-up in the chambers as well.

Would a vacuum delay valve have helped my problem? Too late to say now, but it sounds quite possible.