WASyL

i did some search but found nothing that would help me.
my setup is 383HSR with 165cc heads (http://www.summitracing.com/parts/EDL-60859/) cam: CS XR276HR-12 with 1.51 rockers. What would be the best base timing for me?? I was running 6 BTDC but was wondering if i should move to 8 or 10 BTDC ?
any suggestions?

best regards

vetteoz

iTrader: (13)

Generally best for perf to run as much advance as your engine can take without getting knock or pinging
Can you datalog to see if you are getting knock counts with more advance?

Americanmouse

iTrader: (7)

I'm running 383 modified TPI, and my base timing is 20º. My compression is 10:75:1. Engine temp gets as high as 190-195º. I usually run a mix of premium fuel with racing fuel. The car seem to really like it there, with no pining/knocking either.

WASyL

maybey i havn't made my self clear, im not asking about spark map in ECM but how to set base timing with distributor orientation.
20deg ? how to set this high where timing pointer is only up to 10-12 deg ?
also can you share with me your spark advance map ??

best regards

Orr89RocZ

iTrader: (20)

I dont think it really matters what your base timing is since overall timing in the bin is what will control the motor. As long as the bin has the base timing constant set to match your actual base timing, you are good to go.

Set the base timing to the lowest timing the motor will still idle at. For my old 383, it would start to stumble and run poorly with 8 deg so I ran 10 deg base timing. In the bin total timing came out to be around 28 at idle.

WASyL

well now it is 6 and idle is not as good as it should be but i'm not sure if it is not fault of the cam. my vacuum is at about 45-50 kPa where i would like to se about 70-80 kPa below 0. i know that all depends on spark advance controled by ECM (MSII in my setup) but getting good vacuum can be done this way
can i see your bin with spark advance map?

best regards

Orr89RocZ

iTrader: (20)

If you dial in the fuel right, and play with the timing, you can develop more vacuum but I think your looking for alot of vacuum, more so than a stock motor. Is 70kpa like 20 inches of Hg? 15 would be good on a 383 with a decent cam.

What cam do you have and what compression?

With the EST wire disconnected, set your base timing where it idles on its own, possibly rather choppy but stable. When EST is connected back the timing should be over 20. If you have a decent sized cam, you may want to go as high as 30. Play with it and see what gives you the most vacuum at idle. Higher timing you go, the higher the idle speed will move so you have to also play with that to keep it lower if you want to. Abit more idle speed also helps bump vacuum.

I know another car with a big cam that idles smoothly at 750ish rpm with 30 deg timing at idle. Seems to like alot more timing at idle and still has decent vacuum for brakes.

Playing with my own car, I've noticed I can gain around 2" of Hg just by advancing timing from around 16 to around 30 at idle. Car seems to idle the same no matter what timing I have but it likes the higher timing for vacuum.

So play with overall timing as controlled by the main spark table in your MSII. Set the base to w/e you want, as it really shouldnt matter. Overall timing is what matters.

WASyL

my cam is: CS XR276HR-12
Duration at 050 inch Lift 224 int./230 exh.
Valve Lift with Factory Rocker Arm Ratio 0.503 int./0.510 exh. lift but have 1.51 rockers
i havn't counted CR by my self but as i can recall what my friend did it would be at around 10,5 i think

thanks for all suggestions

best regards

Orr89RocZ

iTrader: (20)

Thats not a huge cam for a 383 so you should beable to hit more vacuum. Could try 8 deg base timing and tune it between 24-30 deg at idle and see what it likes best. I would think 15-17" of Hg is possible but more than thought I would doubt it. My 401 uses a mild 233/233 cam and I can get 15" of Hg so far with near 29 deg timing or so. Still playing with it.

Get a vacuum gauge to a port on the intake or T into the brake booster line. watch the gauge and try different settings to see where it wants to be.

WASyL

i do have vacuum gauge with MSII so i'll try to do that

best regards