Vacuum on my 2.7 DIST w/cams webers

[kens_74_911s]

My 74 911s is what I'm working on to get it prepped into a daily driver. I did some crazy stuff to it ( my 5th early car so was keeping some stuff for the impact B/Car) Running the stock 2.7 but we cut the CIS pistons a bit to clear the early 911s 02 cams I picked up long time ago. Also dumped all the CIS and am running 40 DIA's choked to 34mm. Basically jetted close to Bruce Andersons spec's in his book.
I am running a custom pipe similar to some of the early S dual outlet pipes I have run. Its a design that runs two internal perforated cones in a vessel similar to a stock pipe with fixed divider on center. Anyway I went through some challenges early on with points and dumped that a few years ago. Running an MSD 6 blaster Ign. and pointless rotor set so think I'm all good there now. Seems I am getting some pre ignition knock I thought it was exhaust but moved timing back and it made a difference. The early S cammed Webers had an extra circuit so hope I’m not a tad lean as well but could play with emulsions tubes since I don’t have the additional enrichment like the S camed Webers ran.
Main Question :
I do not have the Dist Vacuum port hooked up I am looking at drilling some holes in my manifolds one per side and Tee connection running to Dist to see what it does for me. I need to look closer at it to determine if its a vacuum retard or advance unit. I am thinking it is vacuum retard so under lower RMP and vacuum like accelerating it pulls IGN timing back some then when spooled up Centrifugal adv. overpowers that as open carb. also lowers vacuum. Am I on track with these thoughts? I think my pipe is to restrictive and may open it up and let it breathe more. Past experience with these 911 engines running Webers and a cam is less restriction on exhaust is best . I was trying to tone it down some but may have a bit to much back pressure also for a motor with big holes. Let me know your thoughts ! Ken

[Flat6pac]

The 2.7 and earlier pods are retard units to meet emissions. They work off the area below the butterfly and vacuum between 7 to 15 degrees for ignition after TDC, depending on the pod.

[kens_74_911s]

So May be wasting my time porting it off my manifolds It seems. I may have a lean ign. ping and restricted pipe . ( I if I drive like a normal driver its all great- something about that push you back in the seat and all those rev sounds is addictive to me -OH yea just rolled to 50 so someting in my blood I guess... ) That MSD seems tricky to get a good timing indication with my Snap on digital light, but I need to look at it again. I bumped it by hand to retard yesterday and she still seems happy. seemed a littLe softer on my accell curve that is crazy anyway when she is spooled up . Making me think if I freed up the pipe I could clean up my low/midrange curve.

Its a off base setup to take a low/mid comp 2.7 and cut then pistons for those hot cams, I realize that I was on a budget when I built it. Probably a great motor to drop a turbo on. But I am willing to work with it Have a local with a chassis dyno, probably worth a session there to better understand what I am delaing with. Thanks for message

[Flat6pac]

Find the time for 2.8, about 9.5 compression with JE pistons. The 2.7 S pistons, if they are S and not regular 2.7 of 1974, cutting recesses in the face just gleens you compression low enough to turbo charge..nowhere for any bang for the buck..
Bruce

[kens_74_911s]

Yea like I said working with what I had trying to save some $ was building machinery then , had machinist running parts on my machines we just did it. It's very driveable and the 2nd car I have had with those early vintage S cams, and can't say more. I wonder how a turbo or two would play out on it but. I do like the simplicity and sounds of those webers singing to me...