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Please help with vacuum pressure test
Hi Guys,
My motor is running fine as far as I can tell, but I want to make sure that I have it tuned properly. I running a Ford Crate ( specs below ) that has 4k on it. No changes have been made by me. Timing set at 10 deg. Carb is a holley 770 cfm street avenger. No changes from factory settings. spec sheet https://picasaweb.google.com/1120929...61519566160738 test video https://www.youtube.com/watch?v=UUNM...ature=youtu.be From my limited knowledge it seems that the timing may need to be advanced a few degrees. What do y'all think. thanks, Roger |
Your vacuum looks fantastic. Adjust idle air mix screws to get max vacuum, I never hear of adjusting timing for vacuum. As far as timing what oem say as far as total at xxx rpm. Then adjust base not to exceed.
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There are a couple of ways to adjust base timing. One of them is with a vacuum gauge. Set the timing where the vacuum is the highest at your desired idle rpm. Make sure the engine is good and warm.
Remember, that only sets your base timing. You still need to check and (maybe) adjust your advance curve. |
The carbed SBF/Windsor Ford likes quite alot of base timing.
Since you have a vacuum dist, you might set timing at 10 w/ the vacum haouse OFF the dist. OK. If you put on the vacuum hose what timing do you have now? It should idle at around 16 degrees. If now you have the timing correct, adjust idle speed with idle screw on carb. Check timing again. Still at 14- 18 degrees? (Might be even better at 20, all comes down to cam and combo) OK. If not, you might adjust timing w/ vacuum hose on as well.... Then check total timing. I'll guess it should be around 36 (34- 40) at maximum and come in at around 3000. Some talk alot about vacuum. I've never cared as long as the engine runs good & the power brakes work.... RS |
OOPS!
I set the timing to 10 degrees with the vacuum advance connected. Okay, now I go back and set the timing to 10 degree with the vac advance OFF and then see what reading I get when I reconnect it. Is this correct? thanks for the help, Roger |
Roger, most of us ignore the curb idle number and just check the total advance amount. Plug the vacuum advance, put a nice bright mark at 35 degrees and then rev the engine up to 3500 RPM, put your timing light on your mark and see how close you are to that bright line -- don't worry about the numbers. Then, through trial and error, try adjusting your timing in small increments (and not when the engine is revving at 3500, btw) to find the sweet spot that is before, on top of, or after that line -- and you do that by driving the car. Don't forget to hook your advance back up each time.
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Hi Guys,
Thanks for the replies. I was just looking at the spec sheet that came with the engine. It says that the timing should be 36 degrees at 5000 rpm. So I guess I put a mark on 36 degrees and rev the engine up with the advance connected. |
Sure, put the line at 36, disconnect the vacuum advance, rev it up to 3500rpm and see how close you are to that line. Drive it, then adjust the timing so you're a little past the line, drive it, then adjust the timing so you're a little before the line, drive it, and after a while you'll find the exact spot that your car likes the most. Always have your head/eye in the same spot when you're pointing the gun. You know you can sometimes make 34 degrees "look like" 36 degrees by just angling your head and eye a different way. If you get to the point where you can say "my car runs best when the timing is just a hair past that red line on the balancer" then that's what you're shooting for. It doesn't matter what the actual number turns out to be, it's how your car drives.
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And always disconnect and plug your vacuum advance when you are checking/setting your timing. Hook it back up for driving.
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The engine is "idling" at 1150 rpm and yet pulls 15-16 inches of vacuum.
I would be slowing the engine down to 800-850, the vacuum will drop to 8-12, then check the base timing. You should have around 18-20 at idle, vacuum hose disconnected and plugged, 35 at 3000rpm. |
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