hey guys,
I have a 1988 383 modified TPI with a modified 700r4, and I'm using a Big end 3000 stall converter. I also have a custom chip burned from Ed Wright at Fast Chip. My cam is a Comp cam duration at .050 is 230/244 1.6:1 lift at 544/576 lob separation is 112 degrees. The car has been been running well as it is, but I'm looking to squeeze extra hp out of it. I've been running my base timing at 16 degrees, and it seems ok. But I've been able to bump it up to about 20 degrees and I'm not getting any detonation. Anyways I don't have access to a dyno so its been pretty much by feel as to what to set it at. Also I called Comp. cams they told me I should set my base at 8-12 degrees. I tried that and was not that impressed. ED Wright said I should set the base timing at 6 degrees btdc. I was not impressed at all of how it felt so I brought it back up to 16 degrees which has more power and pull by feel of course.
So what do you guys think it should be at?

 

6 BTDC is the stock base timing. Most SBC's like 34-36 degrees of total advance. Most well designed SBC builds like around 6-12 degrees of initial advance. I'd stick at 16 degrees, how's your cold starting? How's the idle?

 

Mine is a 388, or 6.4L and it likes 10°, but it's a bit milder than yours.
Are you disabling the ECM timing control before setting the baseline?

 

Cold starting is fine, and idle is at 900-1000 rpms which is also good. I also am disconnecting the ecm timing control. As far as base timing goes at 16 degrees, you don't think I should try and run at 20 degrees or so?

 

I'd never recommend 20 degrees of initial on a SBC :x
I think 12 should be plenty. Are you sure your getting a timing curve at all? Could be why more initial feels better for you.

 

I have a MSD HEI distributor part no. 8366 that I can't change the timing curves like you can with others, were you can adjust/change the springs. The only thing I can do is rotate clockwise/counterclockwise once it goes into closed loop of course. If I try to lower the timing and bring up the rpms it starts to stall/hesitate backfire.

 

I'm running a 355 with a solid roller similar in size to yours. Mines a Comp 236 @ .050" .550 lift 110 LSA. Like you I have never been to a dyno but mine seems to run pretty good right now with my initial at 15 degrees, 20 degrees mechanical and 15 degrees vacuum hooked up to manifold vacuum. I show 30 degrees at idle because of the vacuum. My car will idle nicely at 700 and has 15 inches of vacuum.

Edit: forgot that I did change the initial and mechanical around yesterday. I now run 20 initial and 15 mechanical.

 

What's the specs of this motor? Heads/Cam more specifically?

 

What is mechanical?

 

Mechanical advance is the amount of advance that the distributor brings in as the RPM's increase. If your running a computer controlled stock distributor, it would be the equivalent of how much the computer advances the timing as the RPM's increase. How fast the advance comes in is called your timing curve.

 

Thanks!

 

As initial timing is increased the starter requires more torque (current) to turn the engine, increases coolant heat load, and possibly pinging/detonation so as long as you don't have a problem with that then I say give it what it likes.
FYI
Copper looses its ability to conduct electrons as its temperature rises, this means that the copper wire now literally has a higher resistance which, dramatically reduced current flow and energy. For a street car this is not a good thing.
At the track it's a moot point, you can always get a boost, or a push start.

 

I used to have starting issues when the engine would get hot from driving around. I ended up getting a remote solenoid like they use on Fords which pretty much eliminated the problem. I also use a Start/retard box too which helps alot.

 

While this is true, the opposite can also be true. When I first started my motor up, I had a cam bigger than this one. I had my initial timing at 8 degrees with no vacuum advance. The car would take forever to get started and the headers would glow within 5 minutes of having the motor on at idle. Reason being, my big cam was bleeding off so much cylinder pressure that 8 degrees advance barely created enough pressure to keep the motor going and the combustion process was continuing into the exhasut. I have a Powermaster mini starter, but I have no problems at all starting my motor up with 20 initial. I also have no problems at all with hot starts and that is now with temps being 95 plus right now in orlando.

 

Ed Wright will be tuning the timing tables and will have to set the base timing value in the chip to match whatever you put the base at on the motor.

It doesnt matter what you end up with. Shouldnt need more than 10-12 deg initial with EST disconnected. If the car feels sluggish then it needs tuned more. Actual timing will be controlled in the chip.

Now if you had the chip made with 12 deg and then you bumped the actual base to 16 while leaving the chip at 12, then you just added 4 deg to the entire spark table. If it runs better like that, then the chip needs tuned more to add 4 deg spark and leave base timing as a set value that matches the motor, whether it be 12 or 16 or whatever.

I left my 383 at 10-11 deg since it would not idle well on its own with less timing than that. So base was 10 deg and my total timing seen at idle was 28.

 

Are you checking your timing with the by-pass connector disconnected? On my L98 I saw 20-22* at idle, but only 6* advance BTDC with it DIS-CONNECTED.

Jake

 

Ofcourse. The EST must be disconnected when setting base timing. With it connected you will see whatever is in the chip which for a stock L98 is around 20-22 deg.

 

[QUOTE=Orr89RocZ;4657763]Ofcourse. The EST must be disconnected when setting base timing. With it connected you will see whatever is in the chip which for a stock L98 is around 20-22 deg.[/QUOTE]

That's what I was seeing on the 415 I had in my 86 Vette with the base timing set at 6 degrees BTDC.

Guys on another Forum were claiming their engine didn't have a by-pass connector. Turned out they just couldn't find it.

I was just wondering if OP was setting his timing without disconnecting it.

Jake

 

I found some old notes that I took from talking to Ed Wright in the past, and my first note said 6 degrees btdc. In a second note from talking to him he said that 16 degrees is OK as long as no detonation.
Tonight I bumped my timing up to 20 degrees and idle to 900-1000 rpms. Temp. was about 160 degrees. I then raised the rpms up to 3000 and held it there and it seemed OK no detonation or backfire. Also seemed to have a good throttle response. I'm going to try and raise it up a little more tomorrow and see how it runs.

 

One more thing I keep forgetting to mention. I'm using a cam offset bushing, which if I recall is 3 degrees. Would that change my base timing at all?

 

I'd be very careful with advancing the timing that much. You may not see anything happen with free reving, but soon as you get into loaded conditions you may have problems. I'd leave it at 6-10 or so, and have him give a more aggressive curve in his chip.

 

I have my initial that high and idle even higher becuase of vacuum advance and because I can set my total advance to still be a normal 35 degrees or so. With you though, the amount of advance that comes in with your curve is set by the computer. The computer doesnt know that your advancing the timing 10 degrees so its still adding a bunch of advance as you rev it up. If your going to put that much more initial into it, you need to have the chip reburned to lessen the amount of advance you get.

 

Just an update.
I talked to Ed and he said there must be a mechanical issue, more than likely how I installed my cam. So I'll look at that over the winter, since I need to re-seal my timing cover anyway since its leaking there. He did say he could change my curve advance which I may consider. But for now summer is drawing to a close so I'm going to enjoy whats left of it. He also said if it likes that much advance go for it, just be carful of any dentination/pinging issues. I did raise it back up, and now its at 20 from 15 degrees. I then did some free reving and held it for a bit. Also some road tests hole shots etc. I must say it really likes it alot. I even took my wife for a spin, and she said the car has never pulled as hard as it does now. I also checked the timing again once I reconnected the EST. It's saying at 8-900rpms at idle the total timing is 34-35 degrees.

 

If you adjusted your initial timing - the timing you put in using your timing light and by turning the distributor - to 20 degrees and your engine "likes" it, you've done something else wrong.

20 degrees of initial is much too much if everything else is correct. Could be your cam phasing, your TDC/timing tab indicators, something. If your engine REALLY has 20 degrees of initial advance, your starter should be laboring big-time. Especially when the engine is hot, and you crank the engine trying to start it.

I fear this is going to bite you at some point.

Jake

 

From memory I recall the 2 dots one the cam and the other on the crank are lined up to each other(6 & 12). But I won't know for sure til I pull the cover off this winter. I'm not sure what you mean by cam phasing. I have considered that my timing tab could be the problem. It is aftermarket with a adjustable slider that I have set at zero. I've always had trouble with my mini high torque starter when the engine gets hot. My compression is 10:75:1 so that don't help, and I have Hooker long tube Headers next to the starter. I have done a couple things though recently that have fixed the issue. One I have a MSD Start/Retard box, and the other is a remote solenoid. Since I've added those 2 items I haven't had any starting issues.

 

Something else I just thought of. When the crank damper is at TDC to the timing tab and I'm at number #1 piston. Should the rotor be exactly at number #1 to the distributor cap? I currently have the distributor setup that way, but should it be one tooth before or after per meshing with the cam gear so as to get the right firing?

 

Cam phasing is basically a term used to indicate the position of the camshaft in relation to the #1 piston. When a camshaft is degreed-in and found to need to be moved - advanced or retarded - because the numbers obtained during the degreeing process don't match the cam card OR the installer has some special position he wants the cam to be installed at what he's doing is phasing (or re-phasing) the cam. Phasing is just the technical term for how the cam is positioned.

When the dots are not correctly aligned the camshaft will be out of "phase". That condition is also what guys mean when they use the term "one tooth off". If that's done (one tooth off) the characteristics of the cam are dramatically altered. The engine may or may not even run but if it does run it'll run dramatically different from the way it was designed to run.

Most manuals you see that have diagrams show the dot to dot method. This is to make it easier to see that both dots are in alignment. However with the dots in that dot to dot configuration the #1 piston is on the EXHAUST stroke AND the #6 piston is on the COMPRESSION stroke. So when installing the distributor either the cam dot has to be positioned at the 12 o'clock position OR the distributor rotor pointed at the #6 distributor cap terminal. Otherwise the distributor will be 180 degrees out resulting in back-fires and a no start condition.

In order to verify the accuracy of the timing tab and TDC on the balancer there are a couple of ways guys go about it - Using a Dial Indicator method or using the Positive Stop method.

I prefer the Positive Stop method since it eliminates the #1 piston dwell time at Top Dead Center. The time the piston remains still/unmoving but while the crank can still be turned/moved is what we refer to as "dwell time".. The Positive Stop method requires using a degree wheel and a way to Stop the movement of the #1 piston. Either a STOP/tool screwed into the #1 spark plug hole (used when the heads are installed) or a metal strap bolted across the #1 cylinder bore (used when the heads are NOT installed) are what's used. Either way will allow you to set or verify the accuracy of TDC shown by your timing tab and balancer TDC mark.

I believe most guys don't verify the accuracy of TDC when building an engine but it's very important in order to have accurate ignition timing.

Hope this helps.

Jake

 

Since your engine starts and runs then your ignition timing setting is close. Probably not ideal/perfect, but close. The best way to determine which initial advance or timing curve is ideal would be to do back to back testing and let the engine's performance tell you what it likes best.

So, in reference to the highlighted area in your question, there's no cause for concern. If your current setting was dramatically wrong, the engine would let you know by not starting/labored cranking, not running or would backfire. Since it starts and runs you're into the "fine tuning" area of initial timing advance. Where your rotor is pointing, etc., is no longer anything to be concerned about since your engine starts and runs.

In order for our engine's to start and run they need some amount of initial ignition timing advance; it's the AMOUNT of that timing advance that the testing will show to be ideal.

What many don't realize is that excessive initial timing advance will "feel" to be best, but the engine's power will actually fall off once the RPMs climb. They engine power does, what we call, 'fall off'. So that which feels GREAT down low actually hurts power up top.

The best way I've found to get in the ball park on initial timing is to set the #1 piston at 4/6/8/10 degrees BTDC (Before Top Dead Center) on COMPESSION stroke by using the timing tab on the timing chain cover and the TDC mark on the balancer. Then set the rotor tip to point EXACTLY at the #1 distributor cap terminal. With the setup that way the engine will fire and run (assuming all else is correct). Now this depends on the timing tab and TDC mark on the balancer being accurate. However, since your engine starts and runs, you're beyond all that.

Once the engine is idling, the AMOUNT of initial timing advance then becomes a fine-tuning task. The timing curve - how much and how quickly the timing advances - becomes a fine-tuning task too.

Based on what you've posted, I now suspect you're timing tab - on the Timing Chain Cover - and/or the TDC mark on your balancer aren't positioned correctly. You'll need to check and adjust the tab if you plan tp rely on it for your ignition timing adjustments. I could type up a Step-By-Step procedure on how to do that (LOTS of typing though) but I'm hoping you can find the procedure on the web to save me all that work, LOL

Hope this helps.

Jake

 

Wow!
sounds like you've been doing your homework. As far as checking the timing tab, any suggestions as far as what to search the web for? Also I'm guessing a piston stop would just determine my timing mark on the damper in relation to number one piston. In regards to the timing mark tab, I figured as long as it shows the correct increments that even the cheap ones will work. Or is there actual precision in those, and you get what you pay for.

 

There are basically two ways to go about this:

Many timing tabs have to be selected based on the diameter of the balancer. Otherwise the distance between the degree marks/ZERO location on the timing tab won't be accurate.

Then there's the adjustable version, the benefit of which (an adjustable Timing Tab) is that it's a "one size fits many" tab that can be adjusted to work with different diameter balancers. I prefer the adjustable versions.

"Also I'm guessing a piston stop would just determine my timing mark on the damper in relation to number one piston." Finding Absolute Top Dead Center is the MOST critical part of the entire process. If that's incorrect, everything that follows will also be incorrect. It's the key to accurate ignition timng.

Just use a Search engine and type in something like "Adjustable Timing Tab" or "Timing Tape", something along those lines.

Naw, no homework on this. It's basic stuff taken from memory that I've known for decades.
Jake

 

Awesome!
I didn't know different size dampers would change the the timing marks. (Is there much of a difference?) This is my second damper on the engine. The first one ended up being junk, and the one I have now is a really good one recommended by a local speed shop. I bought a piston stop a few years ago, but it didn't work so well as it would only thread a couple of turns into the spark plug hole. If I would use a wrench to tighten it up more it would strip the threads in the spark plug hole. I compared the threads to one of my spark plugs and they appear the same. So it just got tossed into the junk box.

 

Nice to see someone else getting it right. I read so often on here that they have the rotor facing number 1 plug and it still wont start. The distributor doesnt care which way the rotor is facing or which cylinder is firing. The rotor can be wherever, so long as its pointed at number 1 on the cap when initially lining everything up.

 

Update!
I had a old piston stop that's some kind of generic brand, and it was striping out the spark plug threads. So Saturday I picked a Comp. Cam piston stop, and tried it out Sunday night. Well it turns out my timing marks were off in relation to the damper marks. Without touching my current timing of what I thought was 20 degrees, and resetting my adjustable timing tab to true TDC per the new piston stop. I started and let my engine warm up for a few minutes. Then I shut it off, and disconnected the EST. Hooked up my timing light, and started it back up. At about 900rpms the timing now says its at 10 degrees.

Thanks a lot for everyones help/input!!!

 

Now that's more like it. Glad it worked out for you.

Jake