The engine runs much better at 15* static timing. When I lower it to 6*, the engine slows down a bunch and stalls.

Should I burn a chip with more timing in the timing table and attempt to set the static timing back to 6 to 8*?

 

Check the balancer.

 

I'd also like to add if the engine has an aftermarket timing tab pointer and it was not set to zero with the engine at TDC (set by a degree wheel),, there's no telling where the actual timing is. I use to see this a lot with people bringing me an engine pingging terribly with the timing at "6" just to find out the timing tab was the wrong one,,, or bent,,, and actual timing was more like 18 degrees.

 

Well, supposively, the pro engine shop would have gotten the pointer correct. They said that they installed the cam straight up. But, if the engine likes 15*, then I will assume that the pointer is wrong. I will keep on working on this issue.

 

What kind of timing does the PROM give the engine at idle? It may be too low in the main spark advance table....

A more aggressive cam will want/need more timing at idle than a stock one....

I have 8* base and 26* delivered at idle and mine is pretty happy.... I also used a Fluidampr which means no more worrying about how accurate the balancer is....

 

Doc, cam timing could be perfect and your timing tab pointer may be fine as for as that goes.

I agree with what Matt said.

There are a number of reasons that will allow one to argue these statements,,, but GENERALLY speaking,,,, stock cams with a LTR TPIs,,, as a COMPROMISE with the stock chip,,,, seem to like 8-10 degrees, typical street cams with say 4 degrees advancement seem to like 10 – 12 degrees (if you can hook it). My modified TPI/SLP intake system with TFS G1 heads on a flat-top 355 liked 10 degrees with the stock chip,, but I couldn’t hook it. As an FYI, I “degreed” in my timing tab (so I know mine was right),, and my combination after the StealthRam swap (short runner intake) liked 14* with the stock chip. It needed that much down low to get the car moving (and to “ET”) with the gears and converter I’m running,, but had too much timing up high. Based on your combination in your sig,, and my experiences,,, 15* seems a little high as a compromise with the stock chip,, although it’s very possible it would like that kind of timing at idle and part throttle.

I don't know the spark tables,,, but I can tell you IF the pointer is correct,,, that once you jack the timing over 12 degrees,,, the stock chip usually puts more total timing in most engines than they need / like at the upper RPM. Using my StealthRam combination,, set at 14* with the stock chip as an example,,, a custom chip adding more timing at lower rpms than stock (and running less initial timing),, or taking out timing at higher rpms (and running the same initial timing) would have fixed my “problem” and picked up a little ET to boot. So you definitely need to look into burning a custom chip,, give the engine what it wants and don’t be so hung up on a number,, especially if you don’t know 100%, positively, for sure, it’s “right”.

 

I don't remember for sure, but I think the stock PROM table has 20* in the idle ranges of the stock spark advance table. This is assuming a 6* base which is also the stock setting for the initial timing setting (with bypass disconnected). So when upping the timing through base adjustments only you are moving the entire timing map up by whatever you move it - unless of course it begins to sense knock in which case the ECM will back timing off and re-apply it as it is able to without inducing more knock. The best way to tune your timing is to burn a PROM with a stock or close to stock base timing setting (the lower base helps with starting routines) and adjusting the actual main spark advance table as that is what the engine is actually seeing once the bypass is plugged in and the engine is running.

If some of you already know this stuff, sorry. Just thought I would put it out there to possibly help the discussion .

I tried everything from the stock 20* to 29* at idle but it seemed to like the 26* setting as it idled nice and smooth but didn't tend to hang higher in the RPM before settling back down to idle when coming down from above idle operation like the higher timing settings did.

 

Very interesting stuff, thanks to all of you.

I'm "burning" my own Eproms. The lowest timing value in the top left corner of the table is 20. This area in the timing table would be the idle RPM region and engine load. So I am thinking that making the 20s all 25s might help.

Also, I could not do the minimum air/IAC precedure this morning. The engine will not idle without the IAC out to 160 steps. ( I think that is full out, allowing the max air flow thru to the engine.

The LS1 guys (me being one of them) when installing a big cam must drill a hole in the TB plate to get the engine enough air at idle so as not to have the IAC full open. What do you guys think?

 

Well the idle timing value won't be the ones in the far upper left corner by default.... To figure out where you are idling on the timing table you need to know what rpm it idles at and what MAP signal the engine produces at that rpm. Then you can use the table to figure out your idle timing setting(s). You will want to change a range of the values to get it to sustain the change you make as the engine will most likely not stay in that one single cell timing value-wise at any one time and thus will do some math and split the values in the corresponding tables with what is in the one it most often uses at idle and feed that advance to the engine or just jump around in a few of the cells.

I would just play around with the timing a little at a time and see how it drives. Always keep a close eye on knock counts when messing with the timing - and even the AFR if you have a WBO2, or at least the BLMs and see what they are doing. Timing can alter your air fuel ratio.... Start by adding a little bit of timing to the table and putting the base back down to a more reasonable level like 6 or 8* and be sure to set that in the initial base timing setting in the constants table for the PROM as well....

As for the minimum air, you shouldn't have a problem getting enough air without drilling a hole in the TB plate. I have gotten my 383 to idle through the TB (both the 52 and the 58) without drilling holes. I usually just start opening the throttle blades until I see an IAC value of about 20 counts and leave it at that assuming I don't have any vacuum leaks of course....

Have you jacked the minimum air setting all the way open and it still won't idle, or?

 

Matt,

The top left corner of the timing table is populated with many 20s, like from 400 RPM to 1000 RPM and engine loads from 0 to 64.

I have started a new bin file whereby a I changed the 20s to 25s.

BTW: I just drilled both TB plates with an 1/8" hole. The engine does not stall out on me anymore. Now maybe I can complete the minimum idle air and IAC procedure. And reset the timing.

 

Well it certainly doesn't hurt it to have a couple of holes in the TB at all so that is cool that you have that solved. Seems odd that it would need that to idle alright though....

It sounds like you have a good handle on the timing table. I just meant that the actual idle cell may be more towards the middle of the table in the lower RPM and not all the way over to the left. Mine idles around 70kpa and 800 RPM so it is pretty far to the right of the table.... Or at least it is farther to the right (higher kpa and less vacuum) than a stock combo or a less aggressive camshaft equipped combo would have. I left any of the values below where mine idles stock to aid in starting but a small jump shouldn't affect it much. Too much timing will make the engine harder for the starter to spin on extended cranking. Of course, if everything is working properly it shouldn't need to crank excessively anyways....

Good luck - although it sounds like you are all dialed in on your own anyways .

 

Thanks for all the help above.

Matt, the engine load at idle is about 53 and MAF at 15 gr/sec and at 1000RPM.

I guess that with 45 more cubes and a bigger cam than I have ever run, I need some different logic but still need to work via the 165 ECM and the $6E definition file.

Drilling the TB plates comes from the LS1 guys with very big cams. Otherwise they would get an error code related to the IAC count.

Also, maybe from what was said above, I may need more timing than I have used is the past. So I have alot of digging and tuning to do here.

BTW: I ported out the SuperRam runners & top plenum, and match ported to the intake. I ported the runners out to allow a golf ball to drop thru. So from the intake side of things, the engine should be breathing pretty good.