timing question
Thread Starter
Intermediate
Joined: Oct 2014
Posts: 38
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timing question
I am working on getting my freshly build 383 Stroker to time perfectly. I went through the HEI to ensure that nothing was sticking, reinstalled existing weights and springs (delco). Timed all in to 36* at 3K, Timing goes all in at around 2,400. Do I need stronger springs to push it from 2,400 to 3,000? or is 2400 good?
I hooked up vac advance and readjusted idle and at idle it pushes advance to almost 38* at idle. Im thinking can is shot.
Because of new cam, Vac is around 14" at idle. Timing chain is set straight up, Cam is .465 intake .488 Ex.
At WFO it pings very noticeably at low RPM (during gear shifts with vac advance connected)
I hooked up vac advance and readjusted idle and at idle it pushes advance to almost 38* at idle. Im thinking can is shot.
Because of new cam, Vac is around 14" at idle. Timing chain is set straight up, Cam is .465 intake .488 Ex.
At WFO it pings very noticeably at low RPM (during gear shifts with vac advance connected)
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
If it pings and all else is as it should be, then you have too much advance or too much too early. Stronger springs will delay the advance until later rpm and may solve your problem.
Does the ping go away at a certain rpm?
Keep in mind that the springs do not have to be the same. one can be stronger than the other to achieve your desired advance at the desired rpm.
38* at idle would not be unusual with lots of initial timing. I run 36* with the vac can plugged in but I'm at a high altitude and can get away with that easier than if I were at sea level.
If the ping persists through out the rpm range then you need to back off total timing to get rid of it. Easiest way is to reduce initial timing.
Does the ping go away at a certain rpm?
Keep in mind that the springs do not have to be the same. one can be stronger than the other to achieve your desired advance at the desired rpm.
38* at idle would not be unusual with lots of initial timing. I run 36* with the vac can plugged in but I'm at a high altitude and can get away with that easier than if I were at sea level.
If the ping persists through out the rpm range then you need to back off total timing to get rid of it. Easiest way is to reduce initial timing.
Melting Slicks
Joined: Jun 2011
Posts: 3,114
Likes: 597
I am working on getting my freshly build 383 Stroker to time perfectly. I went through the HEI to ensure that nothing was sticking, reinstalled existing weights and springs (delco). Timed all in to 36* at 3K, Timing goes all in at around 2,400. Do I need stronger springs to push it from 2,400 to 3,000? or is 2400 good?
I hooked up vac advance and readjusted idle and at idle it pushes advance to almost 38* at idle. Im thinking can is shot.
Because of new cam, Vac is around 14" at idle. Timing chain is set straight up, Cam is .465 intake .488 Ex.
At WFO it pings very noticeably at low RPM (during gear shifts with vac advance connected)
I hooked up vac advance and readjusted idle and at idle it pushes advance to almost 38* at idle. Im thinking can is shot.
Because of new cam, Vac is around 14" at idle. Timing chain is set straight up, Cam is .465 intake .488 Ex.
At WFO it pings very noticeably at low RPM (during gear shifts with vac advance connected)
As far as the vacuum advance unit goes during acceleration there should be 0 additional advance and only centrifugal advance. I think you need to change to heavy springs to get the max advance closer to 4000 rpm and max out at 32. You may not require vacuum advance unless highway and light cruising is a big part of the driving.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
My opinion, I'm an old fart......have been redoing distributor advance curves since back in the 1970's when Mr Gasket sold USA made recurve kits....not the Chinese sourced CRAP they sell now ( wouldn't use any of those kits! ) I like advance quick by 2500RPMs for an auto transmission car but, in a manual transmission car....I stretch it out a little to 2800-3000 RPMs to keep tuning gremlins away at the point of clutch engagement. I also believe if you have really light quick springs in the advance, that they wont properly control the weights at higher RPMS as the weights can slam into the stops and because the spring is so light, the weights will bounce back off the stops.
If your getting pinging with the vacuum can hooked up...time to retard the timing a little or eliminate the vacuum advance entirley, yes cruise mileage might suffer a little but, not much else. Is there an adjustment on your vacuum can....did it come with a limiter stop like the old Crane Cams set ups used....you can limit the travel of the vacuum can rod by making a stop for the linkage rod.
If your getting pinging with the vacuum can hooked up...time to retard the timing a little or eliminate the vacuum advance entirley, yes cruise mileage might suffer a little but, not much else. Is there an adjustment on your vacuum can....did it come with a limiter stop like the old Crane Cams set ups used....you can limit the travel of the vacuum can rod by making a stop for the linkage rod.
Last edited by Solid LT1; Nov 20, 2014 at 10:29 PM.
Drifting
Joined: Sep 2010
Posts: 1,412
Likes: 50
From: Laguna Niguel California
You haven't stated info about heads or compression. That makes a big difference. Like others have said, you could disconnect vacuum altogether or try ported vacuum. Modified engines can behave differently. I have fairly high compression (10.5:1) with fast burn heads and use no vacuum. Timing adjustment is something you kind of have to do by Braille.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
Likes: 6,364
From: At my Bar drinking and wrenching in Lafayette Colorado
1. Your centrifugal curve is too quick.
2. Your vacuum advance is too long.
You need to correct it as follows:
1. Install springs to make your full centrifugal advance come in at about 3,000 rpm.
2. Modify your vacuum advance and limit it to no more than 12 degrees of advance.
This assumes that your centrifugal curve is not too short (you didn't state what your initial timing ended up being after setting total to 36), and that initial timing is in the mid-teen range with the 36 total.
Lars
Last edited by lars; Nov 21, 2014 at 04:47 PM.
Thread Starter
Intermediate
Joined: Oct 2014
Posts: 38
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9.5:1 comp ratio, stockish heads. And initial after all in at 36 is around 17*. I blocked off vac and drove it today, seemed to run fine. I bought Mr gasket kit to rob springs per Lars paper, we shall see how that might affect it. The mr g weights and such look to be complete junk. So ill post an update following.
Thanks all for the replys,
Thanks all for the replys,
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