Hi,

I have read few threads that I could find, but havent got straight answers. So I decided to make new thread, I hope I don't ask anything stupid

I understand how to tune fueling parameters and it's pretty straightforward. Datalogging and corrections loop. But I haven't found much information about timing corrections.

At the moment, I could get car idling so-so after moving initial timing from distributor about 10 degrees. But the timing on different RPM-s is way off (quite normal after cam swap, I guess). Car is not driveable. I used slightly ported stock swirl-port heads and smaller B-body LT1 cam with 1.6 ratio rockers. As I have understood from one topic, the simplest way to get timing mostly correct would be using corretions from similar LT1 car? If so, then what car would be good candidate? Or are there any other methods to get basic ignition timing correct?

My own common sense tells that I should get timing mostly right even before driving and datalogging and then I should deal fueling and timing fine tuning. I think more fatal is wrong ignition timing than slightly off fueling and my car runs pretty rich anyway at the moment, so I think fueling corrections are not the first priority to deal with.

I would appreciate any hints to adjust basic timing corrections so I can run and drive the car and make more adjustments after datalogging.

Oh, and how can I change base timing back to zero degrees? I know that I should change base timing angle and then make corrections to timing tables, but I looked to BIN and there is base timing angle value "84.38 degrees". I could not exactly understand how it relates to zero mark?

Edit: that 84.38 degrees was actually from broken xdf definition, I downloaded latest one and it fixed it. Now I see 0.00 degrees

 

Tuning timing I believe is done most accurately on a dyno. a lot is written about it on this forum. A sticky above may shed some light.

Iron Head LT1 in cop car might be a good choice. May timing is like 29d plus the PE adder. I think it is AKXY is for 1987 MY cop car and may be more conservative.

I would search Fast355 posts as he poseted a lot of SA tables.

 

I would double check that the valve adjustment has been done correctly.

RBob.

 

Valves are adjusted properly, I double checked it already.

I used SA table I found from free tune topic (similar cam and heads) and the engine got working better - it does not backfire anymore under moderate load, don't hesitate but acceleration is slowish. Datalogging showed some detonation under moderate load and MAP votage rised to about 1.6V at idle. I think that timing table could be good starting point, but needs plenty of work.

It seems that for some reason these engines love pretty high advance at idle. If I remember right then stock advance was 22 degrees or slightly more. In the bin I copied SA table, it was even 27 degrees. I understand it depends on head design?

 

Well have been pretty busy lately, but tried some modifications last weekend.

Seemed that best combo I got was stock ANTT bin with SA main table from LT1 cop car bin. I needed to modify VE table in low to moderate RPM areas, got BLMs around 126-128 mostly, and the car runs better. It's kind of slow, but it does not hesitate until 2500 rpms no more and relying to datalogs, there's only few ocassional knocks in mid-to high load regions.

I found that there is knock count around 10 that is registered when I start the engine - seemed kind of high - before cam change it was 4-5. WinALDL shows about 10 knocks on the moment when I stop the engine too - it seems somhow normal, as my unmodified truck does it too.

Now question about SA tables. As the car has slowish acceleration and AFR seems to be fine, I guess, it's too retarded timing. I tried to offset whole main table advanced 2 degrees and got more knocks under load. I compared stock SA table and LT1 table and they are not too different. After comparision seemed the correction tables not too different too. LT1 table seems to have few degrees advanced at mid to high load regions, but it really is 2-4 degrees only. And I have seen pretty wild tables working with SP heads here, so I don't get it at the moment. I attach the main SA table that is in the bin now, maybe somebody could comment it?

 

This may seem like a dumb question, but are you sure the valve lash is set correctly, 5&7 wires in the right order and you unplugged the est connctor when you timed the car. Something seems wrong. I ran a hotter LT4 cam in a 305 tbi truck on the stock tune and it ran great.

 

Everything I have touched with swirl ports liked 26-30° of advance by 3,600 rpm at 100 kpa. I think some get too caught up with knock counts and run too little timing. 1.6:1 roller rocker arms make alot of noise that the ecm sees as knock. A stock TBI 305 van ran 22-24° advance in 93-95 and made 185 hp during those years.

 

I set valve lash as usual - set crank to TDC first cylinder valves closed, removed pushrod play and turned nut another half turn. I then set valve lashes according to table I used many times before, turned crank 360 degrees and set the lash of another valves. This method has worked before, so I don't see, how it could not work this time.

I have checked wires and yes, EST connector was open, when I set the base timing.