I've rebuilt the motor (mild cam, ported intake, siamese ports, injectors, rings etc) and finally got the software to read the computer. We got the fuel curve right and now I was wondering what timing is recommended for a TPI. I have 6 deg base timing and the timing download (WOT) looks like this:
rpm degs
1600 24.6
2000 26.4
2400 28.5
2800 29.9
3200 29.9
3600 29.9
4000 29.9
4400 30.6
4800 32.3

My '77 had about 35 deg total advance all in by 3-3500rpm.

Do these computer vettes like advance? I was thinking of changing it to 35 deg all in by 3500.

Any advice??

 

Start by advancing the base timing to 8* and see what that gets ya.

 

Should be 6 base timing,above that ping ping.

 

you will not always get detonation with + *6 timing. Thats what the knock sensor is for. I'de go for 8* or possibly 10* and see what happens.

 

Just remember that your software is reading the chip. It doesn't "see" the base timing. Advance the base to 10* and reread. It will be the same. From what you've posted, you already have 36* at 2800 rpms. You can experiment with different base timings and use your 1/4 mile mph (not ET) as to what is best.

RACE ON!!!

 

The standard on mine is 1 degree 1 mph plus or minus.
Its your motor.
Race gas 106 unleaded will help but on an L98 not like you expect it to help.
I have to watch it mine on is on a 150 shot of juice.

 

I've had no problems running 10 degrees on regular unleaded (87 octane) fuel. If you're having detonation, there is probably another issue....ie knock sensor, spark plug issue, etc.

10 degrees will wake it up on the bottom end.

 

I run 14* base timing on 85 octane gasoline with the knock sensor disconnected. No knock.

RACE ON!!!

 

"Just remember that your software is reading the chip. It doesn't "see" the base timing. Advance the base to 10* and reread. It will be the same. From what you've posted, you already have 36* at 2800 rpms."

Ah, so you should add the base timing to whatever shows on the computer?

I should have mentioned my base is set at 6 deg.

 

For years when the car was 'semi stock' it liked 8* Advanced, and that was with a PErf. Resources Chip (modified time table too). I always run the highest octane though, never anything below 91 in the vette..

On another note, whenever I have run race gas (103or higher octane) it slowed the car down by a crap load..

 

some computers will show total timing differently. i have a 91 l98 730 ecm $8d . in the chip it has a intial base spark setting. it is at 6* . it tells your computer what your base is at. if your base is higher the computer doesnt know it.. so basiclly the computer will subtract the initial base in the chip thinking your mechanical base is at 6*. they will offset each other. so your actual timing is shown in the sa tables.

example.. 10* base - 6* initial base setting + sa tables = total timing.
i didnt include and other advancements like egr or pe, those will factor in also..

so on my car i have 6* base - 6* initial base +31.99* at 100 kpa at 4500 rpm's with no pe advancement or egr. so i will have 31.99* total timing at that kpa and rpm..

here is and example of my lower sa table.. 4600 rpms being top left and 100 kpa being right

39.73 42.89 42.89 40.78 36.56 33.40 35.86 34.80 34.80 31.99 31.99 31.99
39.73 42.89 42.89 40.78 36.91 34.45 35.86 34.80 34.80 31.99 31.99 31.99
39.73 42.89 42.89 40.78 37.27 34.45 35.86 34.80 34.80 33.75 33.75 33.75
39.73 42.89 42.89 40.78 37.27 35.16 35.86 34.80 34.80 34.80 34.80 34.80
39.73 42.89 42.89 40.78 37.97 35.16 35.86 34.80 34.80 34.80 34.80 34.80
39.73 42.89 42.89 40.78 37.97 35.86 35.86 34.80 34.80 34.80 34.80 34.80
39.73 42.89 42.89 40.78 38.67 36.21 35.86 34.80 34.80 34.80 34.80 34.80
39.73 42.89 42.89 40.78 38.67 36.56 35.86 34.80 34.80 34.80 34.80 34.80
39.73 42.89 42.89 40.78 38.67 36.21 35.86 34.80 34.80 34.80 34.80 34.80
39.73 42.54 42.19 40.43 38.67 35.51 35.86 34.80 34.80 34.80 34.80 34.80
37.97 40.78 40.78 39.73 38.32 34.80 35.86 34.80 34.80 34.80 34.80 34.80
35.16 38.67 38.67 38.32 36.56 34.10 35.86 34.80 34.80 34.80 34.80 34.80
33.05 35.51 36.21 36.21 34.45 32.70 35.86 34.80 34.80 34.80 34.80 34.80
32.34 33.75 34.45 34.45 33.40 32.70 35.86 34.80 34.80 34.80 34.80 34.80
31.99 31.99 32.70 33.05 32.34 31.99 35.86 34.80 34.80 34.80 34.80 34.80
31.99 31.99 31.99 31.99 31.99 31.99 35.86 34.80 34.80 34.80 34.80 34.80
31.99 31.99 31.99 31.99 31.99 31.99 35.86 34.80 34.80 34.80 34.80 34.80

 

keep in mind that im not familliar with how your computer read total timing..

also i have a miniram and a large cam and it likes extra timing in a lower rpms.. i have 34* of timing in right off of idle.. for a tpi you will not need that much...

 

That is why I added 6* to your 30* (29.9*) at 2800 rpms to conclude that you WERE running 36* at 2800 rpms. Also, I ASSUMED (a bad thing to do) that your concern was with the WOT (as in an analog centrifugal) timing curve. Unfortunately none of this can be verified with a timing light because you can't duplicate WOT conditions in your driveway.

RACE ON!!!

 

cfi.. his base timing is included in his sa table.. if you take his value at 4800 rpms of 32.3 and you added in a 6* base and you add in whatever his pe advance is you would be way over 40* that is not true. his value of 32.3* is including his base of 6* then you add your pe. that is assuming his base is at 6*. if he moves his base to 10* that will move his entire curve up 4* then he will have a total timing of 36.3* at 4800 + his pe advance.

 

I get 32.3 + 6 = 38.3. Well below 40 degrees, not "be way over 40*" However, I concede the possibility that may it be correct that the spec of 6* may be a part of what he is reading. I admit I don't truly know that. But especially without the 6* base added back in, those numbers are impossibly low. The are even incredibly, way low, if they are steady state numbers and not PE numbers. Cruising down the highway at 2500 rpms the spark should occur at 48* to 52* BTDC. To me, these look like PE (WOT) numbers, and to be "reasonable" they should be PLUS the base and not include it. Again, I am going by what "looks reasonable" and not by what I know. Even if I'm wrong, do you see my reasoning?

RACE ON!!!

 

I get 32.3 + 6 = 38.3. Well below 40 degrees, not "be way over 40*



you need to factor in pe advance.. whatever his is at.. and i know they are at least 2* so it will be over 40* and that is way to high for a sb chevy..

if it is true what you are saying.. then when my base was set at 12* and my wot timing in sa table is 32* that is 44* total.. with no knock ..no way.. you need to sutract the initial base int he chip.mine is 6* that will give me a total of 36*..

most new chevy crate engines are calling for 32* total at 3500 rpms and above..

 

Once again, I am ASSUMING, that when you say "pe" you are referring to Power Enhancement mode. That would be the same as WOT. The PE timing would be the same thing as the centrifugal advance with an analog distributor. That advance curve wouldn't be subject to addition advance at WOT. It WOULD receive additional advance in a cruise mode to simulate the added advance of a vacuum advance, analog.


[QUOTE=mos90]if it is true what you are saying.. then when my base was set at 12* and my wot timing in sa table is 32* that is 44* total.. with no knock ..no way.. you need to sutract the initial base int he chip.mine is 6* that will give me a total of 36*..]/QUOTE]I am not sure of myself on that point, as I said, so I won't try to argue it. It seems logical that Chevy would give the engine more than 30* advance at WOT. And I have a hard time believing that PE ADDS timing.


Yes, but these are newer technology engines with faster burn, more efficient, heads. Chris O' has an old tech, 1985, with 76 cc iron heads. My engine is stock and has the same heads. I run 14* base, on 85 octane gas, with the knock sensor disconnected, and *I* get no knock.

RACE ON!!!

 

That's what I thought! Admittedly I am not the one downloading the info (friend with the laptop) and these figures are the ones told to me. The pe figures are zeroed out.

And sorry, I forgot to mention the run was a WOT run checking the AF ratio. I always run 98 octane.

Thanks all for your help thus far.

 

I run my stock 350 enigine in the race car on premium fuel with 40* timing at 2000 RPM and don't have a bit of problem. And the motor is a bone stock sbc with mismatched pistons and 150,000 miles on it.

 

That is correct. Your table +the base. That is where people get into trouble with setting the base above 6* and the chip still saying 6*. There is a "maximum" advance limit in the chips, so even if you max out the table + 6* base the PE advance will stop once the hard limit in the chip is reached.

I learned the above from listening to others, doing as much reading on PROM tuning as I could and from 3+ years experiance playing with PROM tuning myself.
Of course I could be wrong..but that's how I've seen it working.