Timing for 383 Stroker - Team Camaro Tech
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  #1  
Old Nov 29th, 10, 08:37 AM
jkkrs310 jkkrs310 is offline
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Default Timing for 383 Stroker

I just had a 383 recently built and when I got it back the timing was so far advanced it couldn't be read on the marker. I knew something wasn't right since the car just have the power it should and it bogged/hesitate/ from a standing start and pinged on heavy load. I adjusted the timing to about 17* at idle and it made a world of difference.

My questions:
1.) What is a good idle timing starting point based on my specs below?

2.) Can you walk me through how to set timing (process)?

3.) I have an HEI dist so is it necesary to also set the timing at 3k rpm as well or will the dist automatically set the advance based on the idle timing?

4.) By retarding the timing do I basically lose performace at some point......so I'm guessing that I need to find the optimal point by trial and error?


Here's what my 383 engine has: New GM 4 bolt main, Major internals are all Probe Industries Pistons, Crank and rods. Bearings (rod and main) are Clevite perfect circle (P-Bearings), Roller Rockers are Scorpion Performance, Hydralic Roller Camshaft custom made and custom ground cam from Isky (Duration 282 / Cam Lift 353 / Valve Lift 530......duration at .050 is 234) I took this from my ISKY cam sheet, Manley Pushrods, Gear Drive Set Cloyes, Heads are Alluminum Patriot Performance 185cc Intake and 64 cc combustion chamber (2.02"/1.60"), Compression 9.86:1 - 9.90:1, 2400 Holeshot torque convertor, 4.10 posi rear end, Headers, Edelbrock Performer 600 Carb 1505, Victor Jr Manifold, March Mid Mount Pulley System, Electric Fan.

Thanks in advance
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  #2  
Old Nov 29th, 10, 09:18 AM
BPOS BPOS is offline
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Default Re: Timing for 383 Stroker

I would disconnect and plug the vacuum advance. Set the timing @ 36* BTDC at 3,000 RPM (or the point at which it no longer advances). This is your "total timing" Let the engine come back down to idle, and note where the timing is at idle. This is now your base point for tuning.

If you want to advance or retard the timing from this point, you don't have to stick your head under the hood with a screaming engine - just go off of the idle figure, with vac advance disconnected. Whatever you add or subtract from the idle timing will be added or subtracted from the total timing.

hook your vac advance back up when you're done.
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  #3  
Old Nov 29th, 10, 10:50 AM
hhott71 hhott71 is offline
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Default Re: Timing for 383 Stroker

Drag strip times and plug reading should guide you to your ultimate best total timing.
It can be anywhere from 32 to 44 on a SBC
You then work back to limit your Centrifugal advance so you can have a 8-16 initial advance.
If it is street driven, you can add ported?timed advance so you get maximum fuel economy, an adjustable advance can so you don't over/under advance is helpful.

Vacuum advance does not work at WOT, and shouldn't be an idle crutch.
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  #4  
Old Nov 29th, 10, 11:52 AM
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Default Re: Timing for 383 Stroker

Quote:
Originally Posted by jkkrs310 View Post
my questions:
1.) what is a good idle timing starting point based on my specs below?

2.) can you walk me through how to set timing (process)?

3.) i have an hei dist so is it necesary to also set the timing at 3k rpm as well or will the dist automatically set the advance based on the idle timing?

4.) by retarding the timing do i basically lose performace at some point......so i'm guessing that i need to find the optimal point by trial and error?
1. More important at this point is total timing (somewhere around 2800 - 3200 rpm).

2. Keep reading...

3. Disconnect and plug the vacuum advance when checking/setting the timing (as Al suggests). Rev the engine to about 3000 rpm and watch the timing light to see where the total is. Do the same and set the total timing to 34 degs. (you won't see too many sbc strokers that like more than 34 degs total.) Now check the idle and adjust it to where you want it then check the idle timing. (vacuum advance still disconnected) Ideal would be about 14 degs showing you have 20 degrees of mechanical in the distributor. Now hook the vacuum adv back up to a manifold source (vacuum at idle) and check the idle advance again. subtract the first idle reading from this one to know what your vacuum can adds to this... 10 degs of vacuum advance would be ideal.

Write down your readings. Once you can tell us what the readings are, we can help you dial them in better...

4. More is not always better and less does not always reduce performance. Every combo is a bit different and requires it's own specific settings. Timing is critical in best performance, total timing is all about WOT, idle timing is critical to keep the engine from building too much heat and for off idle response and vacuum advance is a bonus adjustable advance that is mainly for part throttle cruising but also can be used to help idle quality...

Provide your current settings;
TOTAL =
IDLE =
VACUUM =
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  #5  
Old Nov 29th, 10, 12:46 PM
Steptoe Steptoe is offline
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Default Re: Timing for 383 Stroker

Quote:
Do the same and set the total timing to 34 degs. (you won't see too many sbc strokers that like more than 34 degs total.)
Because of the stroke/bore ratio the max cyclinder pressure will be closer to 15 ADC than the 22 deg.

Tend to set the the total a little over advanced, plot the curve at 1500 rpms 2000, 2500 3000 etc...use springs/weight that give a nice round curve starting around the 45 deg then curves nicely off just underneath....that will get you close in the ball park, enough that dyno will make insignificant changes.
Start retarding the curve till you feel power drops off,(Do this with the rpms near where the curver is all in and above) it will drop off withing a couple degrees....advance it back up about 2 deg above this piont...any further makes the car sound stronger, but the power drops off very slowly as you get higher.

Once the all in is esptablished, its a matter of establishing your idle advance.
Still with VA disconected...play around...so you find say 16 deg is stable.
Return the dizzy to where you established the power...
If the cent is already at or very close to this, fine....use a VA that starts and comes in above idle vac but all in cruising up a slop vac
If the intial is too low, use a VA that is all in or no more than 1" above the idle vac with this curve and has the number of degrees in it to take the intial cent +vac upto what you want once the engine is fired...modern HEI dizies usually require more degrees to be put in the curve to run manifold vac.
A low intial cent (minus the VA) has far less load on the starter moter, easier firing, less load on batteries etc.
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  #6  
Old Nov 29th, 10, 05:24 PM
jkkrs310 jkkrs310 is offline
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Default Re: Timing for 383 Stroker

I've never done this hence the questions but on the timing marker it doesn't go above 16* so how do you set total timing at 34*? My timing gun is only a strobe light type.

I think I understand the process but what is ideal idle rpm?
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  #7  
Old Nov 29th, 10, 06:28 PM
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Default Re: Timing for 383 Stroker

See if the local parts counter will lend or rent you a "dial-back" timing light... With it you set the dial to the degs you want, rev the engine and adjust the timing so the pointer and mark on the balancer line up at zero.
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  #8  
Old Nov 30th, 10, 04:13 PM
jkkrs310 jkkrs310 is offline
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Default Re: Timing for 383 Stroker

Thanks. How can I do it with the timing light I have? Is it possible to do everything stated in the posts?
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  #9  
Old Nov 30th, 10, 04:44 PM
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Default Re: Timing for 383 Stroker

Quote:
Originally Posted by jkkrs310 View Post
Thanks. How can I do it with the timing light I have? Is it possible to do everything stated in the posts?
You can get timing tape and install it on your balancer so you can read total timing with your light.
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  #10  
Old Nov 30th, 10, 06:07 PM
JohnZ JohnZ is offline
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Default Re: Timing for 383 Stroker

Quote:
Originally Posted by jkkrs310 View Post
Thanks. How can I do it with the timing light I have? Is it possible to do everything stated in the posts?
Measure the circumference of the balancer and divide by ten; cut a piece of masking tape that long (which is 36*) and place it on the balancer, clockwise with the end butted against the timing index line. When the bottom (most clockwise) end of the tape aligns with the "0" mark on the timing tab, you're at 36* BTDC.

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  #11  
Old Nov 30th, 10, 06:27 PM
Steptoe Steptoe is offline
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Default Re: Timing for 383 Stroker

I do like John says...use the wifes dress making tape...measure the circumferance. mm is the easest units to work in.
divide by 36 that gives 10 degs.
This part is easest to do from under the car.
measure with the tape each 10 deg then 2x mark with a punch out to 45 to 50 deg.
Always measure with the dressmaking tape and always measure from TDC.
using dividers and or from 1 10 deg to the next adds errors as u go higher.

I then mark the 5 deg inbetween.
Wipe down with a bit of thinners on a rag...then wipe white paint over the area....let tack off well, then gently wipe down with a clean rag with thinners.
The surface wipes off leaving the double and single punch marks easy read with the timing light....
To make things even better, punch each 10 deg with 1 2 3 etc...its sometimes easy to get lost where u are when the rpms are high..

OR head up the parts store...know what size balancer you have and but a ready made stick on tape...I have never used one so cant comment on how accrute or how well they last up.
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  #12  
Old Dec 1st, 10, 01:11 PM
jkkrs310 jkkrs310 is offline
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Default Re: Timing for 383 Stroker

"When the bottom (most clockwise) end of the tape aligns with the "0" mark on the timing tab, you're at 36* BTDC."

Ok I think I undertand this part but what do I do from there? Sorry first time.
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  #13  
Old Dec 1st, 10, 01:18 PM
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Default Re: Timing for 383 Stroker

The reason I suggested buying timing tape as opposed to making your own is it's already got the degrees marked out on it. Use the pointer and read off the tape to determine your advance...

If you use a piece of tape representing 36 degs then just divide it into 36 equal parts and your good to go up to 36 degs BTDC reading the same way...
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  #14  
Old Dec 1st, 10, 02:06 PM
reelknots reelknots is online now
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Default Re: Timing for 383 Stroker

See if this helps you..
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  #15  
Old Dec 2nd, 10, 08:02 AM
jkkrs310 jkkrs310 is offline
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Default Re: Timing for 383 Stroker

This is awesome. Thank you.
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