What total timing @2000, 3000, 4000, 5000 RPM do you see ? What total timing is optimum? My C5 likes 26-28 at wot, trying to set up 1989 C4 for this weekend. Thanks in advance Ron B.

 

At the hit of the throttle spark advance jumps from around 26-27deg BTDC to 31-33deg BTDC and stays there through the 1-2 upshift at 5,200rpm, where I get out of it on the street.

My base timing is 8deg BTDC.

If your '89 has an adjustable TPS (slotted mounting holes) youi can also tweak timing and enrichment a little by bumping the base idle value from the stock .54Vdc to the more agressive .65Vdc. This will give a crisper throttle response.

 

Base timing at 8 degrees gave 31-33 total timing. Are you using the stock prom? Thanks for your replys. Ron B.

 

When you talk of "total timing" and "WOT" are you speaking of revving it in neutral, or accelerating down the drag strip? 26*-28* doesn't sound like near enough "total timing", for full power. I don't know much about the LTx engines, but that won't cut it for the L98. You cannot measure "total timing" in a computer controlled car without putting it under load.

RACE ON!!!

 

I'm running the stock EPROM and yes that was data from a pass down the 1/4 mile using my Auto Xray in Monitor Mode.

 

That is a surprisingly low total. Have you been able to determine at what rpms the 31*-33* was first attained? I'll bet there is room for a lot more performance in the timing curve. Mine has to be worse.

RACE ON!!!

 

65ZO1, Thanks for the info . I think 33 degrees total at wot might be near the limit with 91 octane here in SD. I will try 8 degrees for initial timing and try to borrow a tech 1 to check my total. Have a great weekend! Ron B.

 

OK, here's some scan data from a street run:
TPS----RPM----Speed----ADV----Ret
0.86----775------8-------27-----0
4.58---2,600-----9-------34-----1
4.72---3,523----28-------31-----2
4.70---4,488----35-------34-----1
4.72---5,200----45-------36-----0
4.72---3,750----55-------32-----0
4.72---3,710----61-------32-----1
4.72---4,370----66-------34-----3
4.72---4,550----72-------34-----5
2.56---4,870----77-------34-----4
1.09---2,680----78-------48-----2
0.78---2,730----76-------48-----1

First off it looks like it wants to start at 34deg BTDC and run about 36deg BTDC by 5k RPM but knock retard is holding it back.

CFI-EFI, you may be right about some more power in there. It looks as though I may need a new ESC module again.

BTW, I'm running 93 octane fuel, a 160 deg F T-stat and fan switch. This pass was taken in the evening with about 160deg F of coolant temp.

 

That is a very interesting and informative chart. My first inclination, would be to try to duplicate the conditions and repeat the run with the knock sensor disconnected. The timing is more than enough (too much?) at 2600 in first gear, but *I* would think you'd like to see the same advance from 4488 and 5200 come in at about 3000.

Is "ADV" the total spark advance? Or is it the electronic advance that gets added to the base timing? Also, "Ret" is the numbers of degrees of timing pulled out by the ESC? I find the "Ret" numbers, in the last three entries, after you backed off the throttle, intriguing. Can you be getting "false" counts? I wouldn't expect true knock with cool evening air, your water temp, and gasoline. That is why I suggested a repeat with no knock sensor. Do you still have the stock compression ratio? This is all VERY interesting.

RACE ON!!!

 

Well my AutoXray manual says that ADV is amount of spark advance from the ignition module, Since that module likely doesn't know how much I've rotated the dist, I guess that data does not include the base timing offset of 8deg BTDC.

Yep it's stock CR; it still has stock cam & heads and not been opened up.

That's a good idea to make a run w/o the knock sensor connected.

A few years ago I was plagued by false knock counts and Gordon suggested the upgrade ESC module, which cured the problem. Since I don't know the failure mode of that module, I guess it's possible it needs to be replaced. I haven't made any mechanical changes to the engine that would account for mechanically induced false knock.

 

That's what I suspected. In which case it seems that LESS overall timing would be desirable, but coming in quicker. At first, I was taking it as a "true" total. Based on the "plus 8", I'm more inclined to think is IS real detonation. It is worse under the higher load of 2nd gear, as true knock would be. Where you are showing 34*, we both know that's 42*, then up, from there.

Next question. At 4370 rpm you show 34* of advance, (really 42) and 3* of retard. Does that mean the advance WOULD be 37* (actually 45*), if the ESC hadn't pulled out the 3*? Or is it 34* from the ECM, minus the 3* (31) pulled out by the ECS?

The reason I asked about the CR and the combustion chambers, is that a well built modified engine will require less advance to make max power. With the stock combustion chambers and squish area, 38-42 MAY be desirable.

If this were a mechanical advance distributor, I'd say shorten up the centrifugal advance and leave the 8* base, or maybe a little more and get it to be "all in" at 3000-3400 rpms.

I guess I'm better off not knowing what mine is doing. I've got 14* of base timing. Now you've got ME worried.

RACE ON!!!