timing (again)
Thread Starter
Racer
Joined: Sep 2002
Posts: 392
Likes: 0
From: Iowa
timing (again)
After running on the new cam and manifold for a few hours I checked timing again and this is what I have.
Intitial @ 700 - 1000 RPM = 12 deg.
Reved up above 1000 RPM with vac adv removed = 38 deg.
reved up with vac adv hooked up = 48 deg.
The guy that helped me with the engine work is telling me to just leave the vac advance disconnected. What do you guys think. :confused:
Intitial @ 700 - 1000 RPM = 12 deg.
Reved up above 1000 RPM with vac adv removed = 38 deg.
reved up with vac adv hooked up = 48 deg.
The guy that helped me with the engine work is telling me to just leave the vac advance disconnected. What do you guys think. :confused:
Melting Slicks
Joined: Mar 2001
Posts: 3,365
Likes: 5
From: Lake Villa IL
Cruise-In IV Veteran
Cruise-In V Veteran
St. Jude Contributor
Re: timing (jetech)
That's way too high. Is it pinging? It sounds as though you have the distributor in wrong. 34 to 36 degrees is the maximum amount of advance most sb Chevy's will stand.
Instructor
Joined: Nov 2002
Posts: 228
Likes: 0
Re: timing (jetech)
I would check the mech advance springs under the rotor button ,sounds like they are broke or weak. I would get a recurve kit and start with the middle springs. set the int. timing with vac. advance disconnected at 8degs and connect the advance and check total at 3000rpm should be 36-38 degs if not adjust to 36-38 and check int with advance disconnected . You may have to change springs to get timing right but by no means leave the vac. advance disconnected they put it there for a reason. (Driveability and better fuel mileage)
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: timing (Perfomer)
38 without the vacuum connected is just right. Be aware that vacuum advance is negligable at full throttle since thers practically no vacuum available at full throttle. Disconnecting the vacuum advance will not effect your full throttle performance. It will however effect your part throttle response. If you have no pinging youll get better mileage and throttle response with it connected. Your #'s sound right to me. One question. Do you have the vacuum line connected to a full vacuum source or a ported vacuum source? In my opinion the ported source will work better overall, but there is always debate on the subject.
Thread Starter
Racer
Joined: Sep 2002
Posts: 392
Likes: 0
From: Iowa
Re: timing (Jvette73)
I have the vac adv hooked to the port where it was hooked up to before (front upper left) on the carb. I am sure the distributor is in correct and the springs and weights are ok. Could it be because the only smog stuff left on the engine now is the cat and vapor canister so now the original vac adv is the wrong set up and the engine is no longer so de-tuned?
Racer
Joined: Jul 2002
Posts: 275
Likes: 13
From: South Bend, Indiana
Re: timing (jetech)
After running on the new cam and manifold for a few hours I checked timing again and this is what I have.
Intitial @ 700 - 1000 RPM = 12 deg.
Reved up above 1000 RPM with vac adv removed = 38 deg.
reved up with vac adv hooked up = 48 deg.
The guy that helped me with the engine work is telling me to just leave the vac advance disconnected. What do you guys think. :confused:
Intitial @ 700 - 1000 RPM = 12 deg.
Reved up above 1000 RPM with vac adv removed = 38 deg.
reved up with vac adv hooked up = 48 deg.
The guy that helped me with the engine work is telling me to just leave the vac advance disconnected. What do you guys think. :confused:
38 deg. isn't a problem. When I had an L48 with Comp Cam 368, it was happiest with 40.
Point 2. If you haven't degreed you dampener, your timing is apprximate. Chevy dampeners are notorious for the outer ring slipping and rotating with age.
1976 406 12to1 CR, TH400 3000 swich pitch, 4.11, nitrous
Safety Car
Joined: Feb 1999
Posts: 3,630
Likes: 14
From: Fountain Hills AZ
Re: timing (jetech)
And the problem is? I don't see any problem with those specs but I am suprised that your vacuum advance is only adding 10º. Are you sure that the 48º reading was taken with it revved high enough for all mechanical advance to be in? Like Jim posted, max advance on some stock distributors doesn't arrive until around 4,500 rpm.
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Thread Starter
Racer
Joined: Sep 2002
Posts: 392
Likes: 0
From: Iowa
Re: timing (Vetterodder)
Next weekend when I get a chance I will get some more accurate numbers. I guess the one thing that I really don't like is the 48 with vac. I am pretty sure I had the rpm's up there but I will make sure. Thanks to all of you for your input. :cheers: :flag
Pro
Joined: May 2001
Posts: 596
Likes: 0
From: Yardley PA
Re: timing (jetech)
Don't worry about the 48 deg with vac. With vac -not at full throttle!- I get 54 degrees and she is not pinging. That is just to lower emmissions and boost fuel economy. The only worry is when she pings.
Read Lars' tech paper on the subject of timing and you will sleep much better with 48 degrees and more... http://www.corvettefaq.com/c3/HowToSetTiming.doc
Enjoy driving it!
Stefan :seeya
Read Lars' tech paper on the subject of timing and you will sleep much better with 48 degrees and more... http://www.corvettefaq.com/c3/HowToSetTiming.doc
Enjoy driving it!
Stefan :seeya
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Re: timing (Jvette73)
:iagree: Sounds like Jvette73 nailed your problem jetech. The only job the vacuum advance has (that Iv'e heard of) is at low RPM/ low load but high manifold vacuum to roadblock predetonation. Correct me if I'm wrong but vacuum advance allows enough advance at idle/low RPM and falls off as RPM increases (manifold vacuum decreases) - then the distributor wieghts & springs do thier thing.
If your hooked to a ported vacuum it would explain the higher advance at high RPM with vacuum connected and normal (?) advance at high RPM while disconnected.
The Forum use to have a tech section with common question & answers. You may find some carb pix with vacuum hose routing with a search. I have one on the hard drive for a 350 Qjet and if I knew how to post it I surely would. :rolleyes:
If your hooked to a ported vacuum it would explain the higher advance at high RPM with vacuum connected and normal (?) advance at high RPM while disconnected.
The Forum use to have a tech section with common question & answers. You may find some carb pix with vacuum hose routing with a search. I have one on the hard drive for a 350 Qjet and if I knew how to post it I surely would. :rolleyes: