Mastiff

I read the configuration out of the EPROM from my 7747 and was comparing to a standard 350 bin file I got on DIY-EFI. I'm new at this, but the spark table looks kind of off. Can this be right? Notice the huge jump in spark going from 800 to 1000 RPM. The stock table was smooth and gradual all around. Is there some reason it shoud be like this, or is possibly just in error?

Mastiff

Here's the factory spark table I'm comparing against. It looks smooth in comparison.

Grumpy

Looks like one of the add spark until it knocks and back down 1d type of tuning, IMO.

You'd do better, IMO, with starting with a stock table and then adding just enough timing to get peak performance.

There's a huge difference between those two sentences.

Mastiff

Funny thing is, I have no knock sensor and I didn't get any knock, even with this table. At least I didn't notice if I was...

Thanks for the help.

Grumpy

Reguardless, that's alot of timing.
Lean mixtures, as well as too rich of mixtures will like alot of timing.

There is a train of thought about tuning that generates a tune with alot of fuel at WOT, and timing. There's so much fuel, that detonation does happen, but takes alot of timing to get the charge burning. So the car feels peepy, but knocks the corners off of the pistons.

Mastiff

Interesting. So how can you be confident that you have a good tune? It sounds like you could have too much gas and too much timing, then get good BLM's and no knock? All I really have to go off of is knock and BLM's to get the right VE and spark. It'd be tough if I there are multiple spark/VE combinations that give good data with some of them being harmful to the motor.

3.8TransAM

Im gonna paraphrase Bruce here :-)

U want the best performance possible with the least amount of timing, means your gooing to have to do alot of spark table work

Find the least amount that gives u the best results :-)

Fuleing is easier if you have a wideband whether it be the diy wb02 or an Innovate, lets u see whats actually going on

later
Jeremy

Grumpy

Notes, and when your done taking notes, take some more.
For the new guy, there is no better training aid then notes.
With good note taking the trends will become apparent.

As you get familiar with your comb., it gets alot easier.

But, you gotta take notes, and look to see what makes the engine happy.

And if you have any doubts, then you need to practice your plug reading.

funstick

im with grumpy on this. read plugs alot. as for timming. theres so many variables to that questions. heads,cam comperssion , dynamic and static. cylinder filling manifolding headers etc etc etc.

the best thing to do is like grumpy siad. least amount of spark consistant with performance. also notes are important. lots of notes. best thing to do at first is log log log. get familair with your engine. make note of how it runs. collect base line and data to compare baselines to after you do make changes.

As for spark tables them selves start with the very basics. use a mild distributor style curve. i usualy start with a base time of 20 btdc at idle then bring it to around 29-32 by 2800-3000 rpm. usually itll base line most pump gas SBC engines well enough to get them runnign well. i also have lots of experience tunning alot of different engines. so i take into account all the things that make up the engine.

anyways start simple work your way up keep note keep base lines and note when things stat going backwaards.

Mastiff

I replaced the weird table with the factory one and the car idled terribly. It was surging in and out quite noticeably. There is a 4 degree timing difference at idle, maybe the retarded timing dropped the idle and the ECM was running around trying to keep the target idle RPM?

One thing I'm not sure of: I thought the factory setting was to set the distributor to zero degrees mechanically and the ECM took it from there? But then on some other thread, I thought someone was telling me to use more like 6 degrees as the base timing. Which one is it?

Thanks for all the help.

Grumpy

Did you try adjusting the fuel?.

Personally on a SBC I like using 6-8d. Varies by engine.

Mastiff

I left everything alone and just changed the spark to start. So I'm pretty close to the factory tune except that the PROM has the knock and EGR stuff removed. I didn't really expect to see much difference, but there is the 4 deg difference at idle...

Does it matter whether I change my distributor as opposed to just adding timing across the board to the spark table? I was considering adding 4 degrees to the factory table to see what that did.